#!/usr/bin/env python3
import os
import re
import sys
import psutil
import argparse
import asyncio
from enum import Enum
from random import randint, random
from typing import Any, List, Optional, Callable, Iterator, Tuple
from watchdog.events import PatternMatchingEventHandler, FileSystemEvent, EVENT_TYPE_CLOSED, EVENT_TYPE_OPENED
from watchdog.observers import Observer
import stransi
from rich.segment import Segment
from rich.style import Style
from textual import events
from textual.message import Message
from textual.app import App, ComposeResult
from textual.containers import Container
from textual.geometry import Offset, Region, Size
from textual.css._style_properties import BorderDefinition
from textual.reactive import var, reactive
from textual.strip import Strip
from textual.dom import DOMNode
from textual.widget import Widget
from textual.widgets import Button, Static, Input, Tree, Header
from textual.widgets._directory_tree import DirEntry
from textual.binding import Binding
from textual.color import Color
from menus import MenuBar, Menu, MenuItem, Separator
from windows import Window, DialogWindow, CharacterSelectorDialogWindow, MessageBox, get_warning_icon
from edit_colors import EditColorsDialogWindow
from localization.i18n import get as _, load_language
from enhanced_directory_tree import EnhancedDirectoryTree

observer = None

def restart_program():
    """Restarts the current program, after file objects and descriptors cleanup"""

    try:
        app.exit()
        # It's meant to eventually call this, but we need it immediately (unless we delay with asyncio perhaps)
        # Otherwise the terminal will be left in a state where you can't (visibly) type anything
        # if you exit the app after reloading, since the new process will pick up the old terminal state.
        app._driver.stop_application_mode() # type: ignore
    except Exception as e:
        print("Error stopping application mode. The command line may not work as expected. The `reset` command should restore it on Linux.", e)

    try:
        try:
            observer.stop()
            observer.join(timeout=1)
            if observer.is_alive:
                print("Timed out waiting for file change observer thread to stop.")
        except RuntimeError as e:
            # Ignore "cannot join current thread" error
            # join() might be redundant, but I'm keeping it just in case something with threading changes in the future
            if str(e) != "cannot join current thread":
                raise
    except Exception as e:
        print("Error stopping file change observer:", e)

    try:
        p = psutil.Process(os.getpid())
        for handler in p.open_files() + p.connections():
            try:
                os.close(handler.fd)
            except Exception as e:
                print(f"Error closing file descriptor ({handler.fd}):", e)
    except Exception as e:
        print("Error closing file descriptors:", e)

    # python = sys.executable
    # os.execl(python, python, *sys.argv)
    os.execl(sys.executable, *sys.orig_argv)

class RestartHandler(PatternMatchingEventHandler):
    """A handler for file changes"""
    def on_any_event(self, event: FileSystemEvent):
        if event.event_type in (EVENT_TYPE_CLOSED, EVENT_TYPE_OPENED):
            # These seem like they'd just cause trouble... they're not changes, are they?
            return
        print("Reloading due to FS change:", event.event_type, event.src_path)
        app.screen.styles.background = "red"
        # The unsaved changes prompt seems to need call_from_thread,
        # or else it gets "no running event loop",
        # whereas restart_program() needs to not use it,
        # or else nothing happens.
        # However, when app.action_reload is called from the key binding,
        # it seems to work fine with or without unsaved changes.
        if app.is_document_modified():
            app.call_from_thread(app.action_reload)
        else:
            restart_program()
        app.screen.styles.background = "yellow"

def restart_on_changes():
    """Restarts the current program when a file is changed"""
    global observer
    observer = Observer()
    observer.schedule(RestartHandler(
        # Don't need to restart on changes to .css, since Textual will reload them in --dev mode
        # Could include localization files, but I'm not actively localizing this app at this point.
        # WET: WatchDog doesn't match zero directories for **, so we have to split up any patterns that use it.
        patterns=[
            "**/*.py", "*.py"
        ],
        ignore_patterns=[
            ".history/**/*", ".history/*",
            ".vscode/**/*", ".vscode/*",
            ".git/**/*", ".git/*",
            "node_modules/**/*", "node_modules/*",
            "__pycache__/**/*", "__pycache__/*",
            "venv/**/*", "venv/*",
        ],
        ignore_directories=True,
    ), path='.', recursive=True)
    observer.start()


# These can go away now that args are parsed up top
ascii_only_icons = False
inspect_layout = False

# Command line arguments
# Please keep in sync with the README
parser = argparse.ArgumentParser(description='Paint in the terminal.')
parser.add_argument('--theme', default='light', help='Theme to use, either "light" or "dark"', choices=['light', 'dark'])
parser.add_argument('--language', default='en', help='Language to use', choices=['ar', 'cs', 'da', 'de', 'el', 'en', 'es', 'fi', 'fr', 'he', 'hu', 'it', 'ja', 'ko', 'nl', 'no', 'pl', 'pt', 'pt-br', 'ru', 'sk', 'sl', 'sv', 'tr', 'zh', 'zh-simplified'])
parser.add_argument('--ascii-only-icons', action='store_true', help='Use only ASCII characters for tool icons')
parser.add_argument('--inspect-layout', action='store_true', help='Inspect the layout with middle click, for development')
# This flag is for development, because it's very confusing
# to see the error message from the previous run,
# when a problem is actually solved.
# There are enough ACTUAL "that should have worked!!" moments to deal with.
# I really don't want false ones mixed in. You want to reward your brain for finding good solutions, after all.
parser.add_argument('--clear-screen', action='store_true', help='Clear the screen before starting; useful for development, to avoid seeing fixed errors')
parser.add_argument('--restart-on-changes', action='store_true', help='Restart the app when the source code is changed, for development')
parser.add_argument('filename', nargs='?', default=None, help='File to open')

if __name__ == "<run_path>":
    # Arguments have to be passed like `textual run --dev "paint.py LICENSE.txt"`
    # so we need to look for an argument starting with "paint.py",
    # and parse the rest of the string as arguments.
    args = None
    for arg in sys.argv:
        if arg.startswith("paint.py"):
            args = parser.parse_args(arg[len("paint.py") :].split())
            break
    assert args is not None, "Couldn't find paint.py in command line arguments"
else:
    args = parser.parse_args()

load_language(args.language)

if args.restart_on_changes:
    restart_on_changes()

# Most arguments are handled at the end of the file.

class Tool(Enum):
    """The tools available in the Paint app."""
    free_form_select = 1
    select = 2
    eraser = 3
    fill = 4
    pick_color = 5
    magnifier = 6
    pencil = 7
    brush = 8
    airbrush = 9
    text = 10
    line = 11
    curve = 12
    rectangle = 13
    polygon = 14
    ellipse = 15
    rounded_rectangle = 16

    def get_icon(self) -> str:
        """Get the icon for this tool."""
        # Alternatives considered:
        # - Free-Form Select:  ✂️📐🆓🕸✨⚝🫥🇫/🇸◌⁛⁘ ⢼⠮
        # - Select: ⬚▧🔲 ⣏⣹
        # - Eraser/Color Eraser: 🧼🧽🧹🚫👋🗑️▰▱
        # - Fill With Color: 🌊💦💧🌈🎉🎊🪣🫗
        # - Pick Color: 🎨💉💅💧📌📍⤤𝀃🝯🍶
        # - Magnifier: 🔍🔎👀🔬🔭🧐🕵️‍♂️🕵️‍♀️
        # - Pencil: ✏️✎✍️🖎🖊️🖋️✒️🖆📝🖍️
        # - Brush: 🖌️🖌👨‍🎨🧑‍🎨💅
        # - Airbrush: 💨ᖜ╔🧴🥤🫠
        # - Text: 🆎📝📄📃🔤📜AＡ
        # - Line: 📏📉📈⟍𝈏╲⧹\⧵∖
        # - Curve: ↪️🪝🌙〰️◡◠~∼≈∽∿〜〰﹋﹏≈≋～⁓
        # - Rectangle: ▭▬▮▯🟥🟧🟨🟩🟦🟪🟫⬛⬜◼️◻️◾◽▪️▫️
        # - Polygon: ▙𝗟𝙇﹄』⬣⬟🔶🔷🔸🔹🔺🔻△▲
        # - Ellipse: ⬭⭕🔴🟠🟡🟢🔵🟣🟤⚫⚪🫧
        # - Rounded Rectangle: ▢⬜⬛
        if ascii_only_icons:
            return {
                Tool.free_form_select: "<[u]^[/]7", # "*" "<^>" "<[u]^[/]7"
                Tool.select: "::", # "#" "::" ":_:" ":[u]:[/]:" ":[u]'[/]:"
                Tool.eraser: "[u]/[/]7", # "47" "27" "/_/" "[u]/[/]7"
                Tool.fill: "[u i]H[/]?", # "#?" "H?" "[u i]F[/]?"
                Tool.pick_color: "[u i] P[/]", # "[u].[/]" "[u i]\\P[/]"
                Tool.magnifier: ",O", # ",O" "o-" "O-" "o=" "O=" "Q"
                Tool.pencil: "-==", # "c==>" "==-"
                Tool.brush: "E)=", # "[u],h.[/u]" "[u],|.[/u]" "[u]h[/u]"
                Tool.airbrush: "[u i]H[/]`<", # "H`" "H`<" "[u i]H[/]`<" "[u i]6[/]<"
                Tool.text: "A", # "Abc"
                Tool.line: "\\",
                Tool.curve: "~", # "~" "S" "s"
                Tool.rectangle: "[_]", # "[]"
                Tool.polygon: "[b]L[/b]", # "L"
                Tool.ellipse: "O", # "()"
                Tool.rounded_rectangle: "(_)",
            }[self]
        return {
            Tool.free_form_select: "⚝",
            Tool.select: "⬚",
            Tool.eraser: "🧼",
            Tool.fill: "🌊", # "🫗" causes jutting out in Ubuntu terminal, "🪣" causes the opposite in VS Code terminal
            Tool.pick_color: "💉",
            Tool.magnifier: "🔍",
            Tool.pencil: "✏️",
            Tool.brush: "🖌️",
            Tool.airbrush: "💨",
            Tool.text: "Ａ",
            Tool.line: "⟍",
            Tool.curve: "～",
            Tool.rectangle: "▭",
            Tool.polygon: "𝙇",
            Tool.ellipse: "⬭",
            Tool.rounded_rectangle: "▢",
        }[self]

    def get_name(self) -> str:
        """Get the localized name for this tool.
        
        Not to be confused with tool.name, which is an identifier."""
        return {
            Tool.free_form_select: _("Free-Form Select"),
            Tool.select: _("Select"),
            Tool.eraser: _("Eraser/Color Eraser"),
            Tool.fill: _("Fill With Color"),
            Tool.pick_color: _("Pick Color"),
            Tool.magnifier: _("Magnifier"),
            Tool.pencil: _("Pencil"),
            Tool.brush: _("Brush"),
            Tool.airbrush: _("Airbrush"),
            Tool.text: _("Text"),
            Tool.line: _("Line"),
            Tool.curve: _("Curve"),
            Tool.rectangle: _("Rectangle"),
            Tool.polygon: _("Polygon"),
            Tool.ellipse: _("Ellipse"),
            Tool.rounded_rectangle: _("Rounded Rectangle"),
        }[self]


palette = [
    "rgb(0,0,0)", # Black
    "rgb(128,128,128)", # Dark Gray
    "rgb(128,0,0)", # Dark Red
    "rgb(128,128,0)", # Pea Green
    "rgb(0,128,0)", # Dark Green
    "rgb(0,128,128)", # Slate
    "rgb(0,0,128)", # Dark Blue
    "rgb(128,0,128)", # Lavender
    "rgb(128,128,64)",
    "rgb(0,64,64)",
    "rgb(0,128,255)",
    "rgb(0,64,128)",
    "rgb(64,0,255)",
    "rgb(128,64,0)",

    "rgb(255,255,255)", # White
    "rgb(192,192,192)", # Light Gray
    "rgb(255,0,0)", # Bright Red
    "rgb(255,255,0)", # Yellow
    "rgb(0,255,0)", # Bright Green
    "rgb(0,255,255)", # Cyan
    "rgb(0,0,255)", # Bright Blue
    "rgb(255,0,255)", # Magenta
    "rgb(255,255,128)",
    "rgb(0,255,128)",
    "rgb(128,255,255)",
    "rgb(128,128,255)",
    "rgb(255,0,128)",
    "rgb(255,128,64)",
]

class ToolsBox(Container):
    """Widget containing tool buttons"""

    class ToolSelected(Message):
        """Message sent when a tool is selected."""
        def __init__(self, tool: Tool) -> None:
            self.tool = tool
            super().__init__()

    def compose(self) -> ComposeResult:
        """Add our buttons."""
        self.tool_by_button: dict[Button, Tool] = {}
        for tool in Tool:
            # TODO: tooltip with tool.get_name()
            button = Button(tool.get_icon(), classes="tool_button")
            button.can_focus = False
            self.tool_by_button[button] = tool
            yield button
    
    def on_button_pressed(self, event: Button.Pressed) -> None:
        """Called when a button is clicked."""

        if "tool_button" in event.button.classes:
            self.post_message(self.ToolSelected(self.tool_by_button[event.button]))

class CharInput(Input, inherit_bindings=False):
    """Widget for entering a single character."""
    
    class CharSelected(Message):
        """Message sent when a character is selected."""
        def __init__(self, char: str) -> None:
            self.char = char
            super().__init__()

    def validate_value(self, value: str) -> str:
        """Limit the value to a single character."""
        return value[-1] if value else " "
    
    def watch_value(self, value: str) -> None:
        """Called when value changes."""
        self.post_message(self.CharSelected(value))

    def validate_cursor_position(self, position: int) -> int:
        """Force the cursor position to 0 so that it's over the character."""
        return 0
    
    def insert_text_at_cursor(self, text: str) -> None:
        """Override to limit the value to a single character."""
        self.value = text[-1] if text else " "

    last_click_time = 0
    def on_click(self, event: events.Click) -> None:
        """Detect double click and open character selector dialog."""
        if event.time - self.last_click_time < 0.8:
            assert isinstance(self.app, PaintApp)
            self.app.action_open_character_selector()
        self.last_click_time = event.time

class ColorsBox(Container):
    """Color palette widget."""

    class ColorSelected(Message):
        """Message sent when a color is selected."""
        def __init__(self, color: str) -> None:
            self.color = color
            super().__init__()

    def compose(self) -> ComposeResult:
        """Add our selected color and color well buttons."""
        self.color_by_button: dict[Button, str] = {}
        with Container(id="palette_selection_box"):
            # This widget is doing double duty, showing the current color
            # and showing/editing the current character.
            # I haven't settled on naming for this yet.
            yield CharInput(id="selected_color_char_input", classes="color_well")
        with Container(id="available_colors"):
            for color in palette:
                button = Button("", classes="color_button color_well")
                button.styles.background = color
                button.can_focus = False
                self.color_by_button[button] = color
                yield button

    def update_palette(self) -> None: # , palette: list[str]) -> None:
        """Update the palette with new colors."""
        for button, color in zip(self.query(".color_button").nodes, palette):
            assert isinstance(button, Button)
            button.styles.background = color
            self.color_by_button[button] = color

    last_click_time = 0
    last_click_button: Button | None = None
    def on_button_pressed(self, event: Button.Pressed) -> None:
        """Called when a button is clicked."""

        if "color_button" in event.button.classes:
            self.post_message(self.ColorSelected(self.color_by_button[event.button]))
            # Detect double click and open Edit Colors dialog.
            if event.time - self.last_click_time < 0.8 and event.button == self.last_click_button:
                assert isinstance(self.app, PaintApp)
                self.app.action_edit_colors(self.query(".color_button").nodes.index(event.button))
            self.last_click_time = event.time
            self.last_click_button = event.button

class Selection:
    """
    A selection within an AnsiArtDocument.

    AnsiArtDocument can contain a Selection, and Selection can contain an AnsiArtDocument.
    However, the selection's AnsiArtDocument should never itself contain a Selection.

    When a selection is created, it has no image data, but once it's dragged,
    it gets a copy of the image data from the document.
    The image data is stored as an AnsiArtDocument, since it's made up of characters and colors.
    """
    def __init__(self, region: Region) -> None:
        """Initialize a selection."""
        self.region: Region = region
        """The region of the selection within the outer document."""
        self.contained_image: Optional[AnsiArtDocument] = None
        """The image data contained in the selection, None until dragged, except for text boxes."""
        self.textbox_mode = False
        """Whether the selection is a text box. Either way it's text, but it's a different editing mode."""
        self.text_selection_start = Offset(0, 0)
        """The start position of the text selection within the text box. This may be before or after the end."""""
        self.text_selection_end = Offset(0, 0)
        """The end position of the text selection within the text box. This may be before or after the start."""""
        self.mask: Optional[list[list[bool]]] = None
        """A mask of the selection to cut out, used for Free-Form Select tool. Coordinates are relative to the selection region."""

    def copy_from_document(self, document: 'AnsiArtDocument') -> None:
        """Copy the image data from the document into the selection."""
        self.contained_image = AnsiArtDocument(self.region.width, self.region.height)
        self.contained_image.copy_region(source=document, source_region=self.region)
    
    def copy_to_document(self, document: 'AnsiArtDocument') -> None:
        """Draw the selection onto the document."""
        if not self.contained_image:
            # raise ValueError("Selection has no image data.")
            return
        target_region = self.region.intersection(Region(0, 0, document.width, document.height))
        document.copy_region(source=self.contained_image, target_region=target_region, mask=self.mask)


debug_region_updates = False

ansi_escape_pattern = re.compile(r"(\N{ESC}\[[\d;]*[a-zA-Z])")

class AnsiArtDocument:
    """A document that can be rendered as ANSI."""

    def __init__(self, width: int, height: int) -> None:
        """Initialize the document."""
        self.width = width
        self.height = height
        self.ch = [[" " for _ in range(width)] for _ in range(height)]
        self.bg = [["#ffffff" for _ in range(width)] for _ in range(height)]
        self.fg = [["#000000" for _ in range(width)] for _ in range(height)]
        self.selection: Optional[Selection] = None

    def copy_region(self, source: 'AnsiArtDocument', source_region: Region|None = None, target_region: Region|None = None, mask: list[list[bool]]|None = None) -> None:
        if source_region is None:
            source_region = Region(0, 0, source.width, source.height)
        if target_region is None:
            target_region = Region(0, 0, source_region.width, source_region.height)
        source_offset = source_region.offset
        target_offset = target_region.offset
        random_color: Optional[str] = None # avoid "possibly unbound"
        if debug_region_updates:
            random_color = "rgb(" + str(randint(0, 255)) + "," + str(randint(0, 255)) + "," + str(randint(0, 255)) + ")"
        for y in range(target_region.height):
            for x in range(target_region.width):
                if source_region.contains(x + source_offset.x, y + source_offset.y) and (mask is None or mask[y][x]):
                    self.ch[y + target_offset.y][x + target_offset.x] = source.ch[y + source_offset.y][x + source_offset.x]
                    self.bg[y + target_offset.y][x + target_offset.x] = source.bg[y + source_offset.y][x + source_offset.x]
                    self.fg[y + target_offset.y][x + target_offset.x] = source.fg[y + source_offset.y][x + source_offset.x]
                    if debug_region_updates:
                        assert random_color is not None
                        # self.bg[y + target_offset.y][x + target_offset.x] = "rgb(" + str((x + source_offset.x) * 255 // self.width) + "," + str((y + source_offset.y) * 255 // self.height) + ",0)"
                        self.bg[y + target_offset.y][x + target_offset.x] = random_color
                else:
                    if debug_region_updates:
                        self.ch[y + target_offset.y][x + target_offset.x] = "?"
                        self.bg[y + target_offset.y][x + target_offset.x] = "#ff00ff"
                        self.fg[y + target_offset.y][x + target_offset.x] = "#000000"

    def get_ansi(self) -> str:
        """Get the ANSI representation of the document."""
        # TODO: try using Rich API to generate ANSI, like how the Canvas renders to the screen
        # TODO: generate more efficient ANSI, e.g. don't repeat the same color codes
        def color_to_rgb(color_code: str) -> str:
            """Convert a color code to the RGB values format used for ANSI escape codes."""
            if color_code.startswith('#'):
                # Convert hex code to RGB values
                color_code = color_code.lstrip('#')
                rgb = tuple(int(color_code[i:i+2], 16) for i in (0, 2, 4))
            elif color_code.startswith('rgb(') and color_code.endswith(')'):
                # Convert "rgb(r,g,b)" style to RGB values
                rgb_str = color_code[4:-1]
                rgb = tuple(int(x.strip()) for x in rgb_str.split(','))
            else:
                raise ValueError("Invalid color code")
            return f"{rgb[0]};{rgb[1]};{rgb[2]}"

        ansi = ""
        for y in range(self.height):
            for x in range(self.width):
                if x == 0:
                    ansi += "\033[0m"
                ansi += "\033[48;2;" + color_to_rgb(self.bg[y][x]) + ";38;2;" + color_to_rgb(self.fg[y][x]) + "m" + self.ch[y][x]
            ansi += "\033[0m\r\n"
        return ansi

    def get_html(self) -> str:
        """Get the HTML representation of the document."""
        html = ""
        for y in range(self.height):
            for x in range(self.width):
                html += "<span style='background-color:" + self.bg[y][x] + ";color:" + self.fg[y][x] + "'>" + self.ch[y][x] + "</span>"
            html += "<br>"
        return html
    
    @staticmethod
    def from_ascii(text: str) -> 'AnsiArtDocument':
        """Creates a document from the given ASCII plain text."""
        lines = text.splitlines()
        width = 0
        for line in lines:
            width = max(len(line), width)
        height = len(lines)
        document = AnsiArtDocument(width, height)
        for y, line in enumerate(lines):
            for x, char in enumerate(line):
                document.ch[y][x] = char
        return document
    
    @staticmethod
    def from_ansi(text: str) -> 'AnsiArtDocument':
        """Creates a document from the given ANSI text."""
        # TODO: use Rich API to render ANSI to a virtual screen,
        # and remove dependency on stransi
        ansi = stransi.Ansi(text)
        document = AnsiArtDocument(1, 1)
        width = 1
        height = 1

        x = 0
        y = 0
        bg_color = "#000000"
        fg_color = "#ffffff"
        for instruction in ansi.instructions():
            if isinstance(instruction, str):
                # Text
                for char in instruction:
                    if char == '\r':
                        x = 0
                    elif char == '\n':
                        x = 0
                        y += 1
                        height = max(y, height)
                        if len(document.ch) <= y:
                            document.ch.append([])
                            document.bg.append([])
                            document.fg.append([])
                    else:
                        x += 1
                        width = max(x, width)
                        document.ch[y].append(char)
                        document.bg[y].append(bg_color)
                        document.fg[y].append(fg_color)
            elif isinstance(instruction, stransi.SetColor) and instruction.color is not None:
                # Color (I'm not sure why instruction.color would be None, but it's typed as Optional[Color])
                # (maybe just for initial state?)
                if instruction.role == stransi.color.ColorRole.FOREGROUND:
                    rgb = instruction.color.rgb
                    fg_color = "rgb(" + str(int(rgb.red * 255)) + "," + str(int(rgb.green * 255)) + "," + str(int(rgb.blue * 255)) + ")"
                elif instruction.role == stransi.color.ColorRole.BACKGROUND:
                    rgb = instruction.color.rgb
                    bg_color = "rgb(" + str(int(rgb.red * 255)) + "," + str(int(rgb.green * 255)) + "," + str(int(rgb.blue * 255)) + ")"
            elif isinstance(instruction, stransi.SetAttribute):
                # Attribute
                pass
            else:
                raise ValueError("Unknown instruction type")
        document.width = width
        document.height = height
        # Fill in the rest of the lines
        # just using the last color, not sure if that's correct...
        for y in range(document.height):
            for x in range(document.width - len(document.ch[y])):
                document.ch[y].append(' ')
                document.bg[y].append(bg_color)
                document.fg[y].append(fg_color)
        return document
    
    @staticmethod
    def from_text(text: str) -> 'AnsiArtDocument':
        """Creates a document from the given text, detecting if uses ANSI or not."""
        if ansi_escape_pattern.search(text):
            return AnsiArtDocument.from_ansi(text)
        else:
            return AnsiArtDocument.from_ascii(text)

class Action:
    """An action that can be undone efficiently using a region update."""

    def __init__(self, name: str, document: AnsiArtDocument, region: Region|None = None) -> None:
        """Initialize the action using the document state before modification."""
        if region is None:
            region = Region(0, 0, document.width, document.height)
        self.name = name
        self.region = region
        self.update(document)

    def update(self, document: AnsiArtDocument) -> None:
        """Grabs the image data from the current region of the document."""
        if self.region:
            self.sub_image_before = AnsiArtDocument(self.region.width, self.region.height)
            self.sub_image_before.copy_region(document, self.region)

    def undo(self, target_document: AnsiArtDocument) -> None:
        """Undo this action. Note that a canvas refresh is not performed here."""
        target_document.copy_region(self.sub_image_before, target_region=self.region)

def bresenham_walk(x0: int, y0: int, x1: int, y1: int) -> Iterator[Tuple[int, int]]:
    """Bresenham's line algorithm"""
    dx = abs(x1 - x0)
    dy = abs(y1 - y0)
    sx = 1 if x0 < x1 else -1
    sy = 1 if y0 < y1 else -1
    err = dx - dy
    while True:
        yield x0, y0
        if x0 == x1 and y0 == y1:
            break
        e2 = 2 * err
        if e2 > -dy:
            err = err - dy
            x0 = x0 + sx
        if e2 < dx:
            err = err + dx
            y0 = y0 + sy


def polygon_walk(points: List[Offset]) -> Iterator[Tuple[int, int]]:
    """Yields points along the perimeter of a polygon."""
    for i in range(len(points)):
        yield from bresenham_walk(
            points[i][0],
            points[i][1],
            points[(i + 1) % len(points)][0],
            points[(i + 1) % len(points)][1]
        )

def polyline_walk(points: List[Offset]) -> Iterator[Tuple[int, int]]:
    """Yields points along a polyline (unclosed polygon)."""
    for i in range(len(points) - 1):
        yield from bresenham_walk(
            points[i][0],
            points[i][1],
            points[i + 1][0],
            points[i + 1][1]
        )

def is_inside_polygon(x: int, y: int, points: List[Offset]) -> bool:
    """Returns True if the point is inside the polygon."""
    # https://stackoverflow.com/a/217578
    n = len(points)
    inside = False
    p1x, p1y = points[0]
    for i in range(n + 1):
        p2x, p2y = points[i % n]
        if y > min(p1y, p2y):
            if y <= max(p1y, p2y):
                if x <= max(p1x, p2x):
                    if p1y != p2y:
                        xinters = (y - p1y) * (p2x - p1x) / (p2y - p1y) + p1x
                    if p1x == p2x or x <= xinters:
                        inside = not inside
        p1x, p1y = p2x, p2y
    return inside

# def polygon_fill(points: List[Offset]) -> Iterator[Tuple[int, int]]:
#     """Yields points inside a polygon."""

#     # Find the bounding box
#     min_x = min(points, key=lambda p: p[0])[0]
#     min_y = min(points, key=lambda p: p[1])[1]
#     max_x = max(points, key=lambda p: p[0])[0]
#     max_y = max(points, key=lambda p: p[1])[1]

#     # Check each point in the bounding box, and yield any points that are inside the polygon
#     for x in range(min_x, max_x + 1):
#         for y in range(min_y, max_y + 1):
#             if is_inside_polygon(x, y, points):
#                 yield x, y

# adapted from https://github.com/Pomax/bezierjs
def compute_bezier(t: float, start_x: float, start_y: float, control_1_x: float, control_1_y: float, control_2_x: float, control_2_y: float, end_x: float, end_y: float):
    mt = 1 - t
    mt2 = mt * mt
    t2 = t * t

    a = mt2 * mt
    b = mt2 * t * 3
    c = mt * t2 * 3
    d = t * t2

    return (
        a * start_x + b * control_1_x + c * control_2_x + d * end_x,
        a * start_y + b * control_1_y + c * control_2_y + d * end_y,
    )

# It's possible to walk a bezier curve more correctly,
# but is it possible to tell the difference?
def bezier_curve_walk(start_x: float, start_y: float, control_1_x: float, control_1_y: float, control_2_x: float, control_2_y: float, end_x: float, end_y: float):
    """Yields points along a bezier curve."""
    steps = 100
    point_a = (start_x, start_y)
    # TypeError: 'float' object cannot be interpreted as an integer
    # for t in range(0, 1, 1 / steps):
    for i in range(steps):
        t = i / steps
        point_b = compute_bezier(t, start_x, start_y, control_1_x, control_1_y, control_2_x, control_2_y, end_x, end_y)
        yield from bresenham_walk(int(point_a[0]), int(point_a[1]), int(point_b[0]), int(point_b[1]))
        point_a = point_b

def quadratic_curve_walk(start_x: float, start_y: float, control_x: float, control_y: float, end_x: float, end_y: float):
    """Yields points along a quadratic curve."""
    return bezier_curve_walk(start_x, start_y, control_x, control_y, control_x, control_y, end_x, end_y)

def midpoint_ellipse(xc: int, yc: int, rx: int, ry: int) -> Iterator[Tuple[int, int]]:
    """Midpoint ellipse drawing algorithm. Yields points out of order, and thus can't legally be called a "walk", except in Britain."""
    # Source: https://www.geeksforgeeks.org/midpoint-ellipse-drawing-algorithm/

    x = 0
    y = ry
 
    # Initial decision parameter of region 1
    d1 = ((ry * ry) - (rx * rx * ry) +
                      (0.25 * rx * rx))
    dx = 2 * ry * ry * x
    dy = 2 * rx * rx * y
 
    # For region 1
    while (dx < dy):
        # Yield points based on 4-way symmetry
        yield x + xc, y + yc
        yield -x + xc, y + yc
        yield x + xc, -y + yc
        yield -x + xc, -y + yc
 
        # Checking and updating value of
        # decision parameter based on algorithm
        if (d1 < 0):
            x += 1
            dx = dx + (2 * ry * ry)
            d1 = d1 + dx + (ry * ry)
        else:
            x += 1
            y -= 1
            dx = dx + (2 * ry * ry)
            dy = dy - (2 * rx * rx)
            d1 = d1 + dx - dy + (ry * ry)
 
    # Decision parameter of region 2
    d2 = (((ry * ry) * ((x + 0.5) * (x + 0.5))) +
          ((rx * rx) * ((y - 1) * (y - 1))) -
           (rx * rx * ry * ry))
 
    # Plotting points of region 2
    while (y >= 0):
        # Yielding points based on 4-way symmetry
        yield x + xc, y + yc
        yield -x + xc, y + yc
        yield x + xc, -y + yc
        yield -x + xc, -y + yc
 
        # Checking and updating parameter
        # value based on algorithm
        if (d2 > 0):
            y -= 1
            dy = dy - (2 * rx * rx)
            d2 = d2 + (rx * rx) - dy
        else:
            y -= 1
            x += 1
            dx = dx + (2 * ry * ry)
            dy = dy - (2 * rx * rx)
            d2 = d2 + dx - dy + (rx * rx)

def flood_fill(document: AnsiArtDocument, x: int, y: int, fill_ch: str, fill_fg: str, fill_bg: str) -> Region|None:
    """Flood fill algorithm."""

    # Get the original value of the cell.
    # This is the color to be replaced.
    original_fg = document.fg[y][x]
    original_bg = document.bg[y][x]
    original_ch = document.ch[y][x]

    # Track the region affected by the fill.
    min_x = x
    min_y = y
    max_x = x
    max_y = y

    def inside(x: int, y: int) -> bool:
        """Returns true if the cell at the given coordinates matches the color to be replaced. Treats foreground color as equal if character is a space."""
        if x < 0 or x >= document.width or y < 0 or y >= document.height:
            return False
        return (
            document.ch[y][x] == original_ch and
            document.bg[y][x] == original_bg and
            (original_ch == " " or document.fg[y][x] == original_fg)
        )

    def set_cell(x: int, y: int) -> None:
        """Sets the cell at the given coordinates to the fill color, and updates the region bounds."""
        document.ch[y][x] = fill_ch
        document.fg[y][x] = fill_fg
        document.bg[y][x] = fill_bg
        nonlocal min_x, min_y, max_x, max_y
        min_x = min(min_x, x)
        min_y = min(min_y, y)
        max_x = max(max_x, x)
        max_y = max(max_y, y)

    # Simple translation of the "final, combined-scan-and-fill span filler"
    # pseudo-code from https://en.wikipedia.org/wiki/Flood_fill
    if not inside(x, y):
        return
    stack: list[tuple[int, int, int, int]] = [(x, x, y, 1), (x, x, y - 1, -1)]
    while stack:
        x1, x2, y, dy = stack.pop()
        x = x1
        if inside(x, y):
            while inside(x - 1, y):
                set_cell(x - 1, y)
                x = x - 1
        if x < x1:
            stack.append((x, x1-1, y-dy, -dy))
        while x1 <= x2:
            while inside(x1, y):
                set_cell(x1, y)
                x1 = x1 + 1
                stack.append((x, x1 - 1, y+dy, dy))
                if x1 - 1 > x2:
                    stack.append((x2 + 1, x1 - 1, y-dy, -dy))
            x1 = x1 + 1
            while x1 < x2 and not inside(x1, y):
                x1 = x1 + 1
            x = x1

    # Return the affected region.
    return Region(min_x, min_y, max_x - min_x + 1, max_y - min_y + 1)

def scale_region(region: Region, scale: int) -> Region:
    """Returns the region scaled by the given factor."""
    return Region(region.x * scale, region.y * scale, region.width * scale, region.height * scale)

class Canvas(Widget):
    """The image document widget."""

    magnification = reactive(1, layout=True)

    # Is it kosher to include an event in a message?
    # Is it better (and possible) to bubble up the event, even though I'm capturing the mouse?
    # Or would it be better to just have Canvas own duplicate state for all tool parameters?
    # That's what I was refactoring to avoid. So far I've made things more complicated,
    # but I'm betting it will be good when implementing different tools.
    # Maybe the PaintApp widget can capture the mouse events instead?
    # Not sure if that would work as nicely when implementing selections.
    # I'd have to think about it.
    # But it would make the Canvas just be a widget for rendering, which seems good.
    class ToolStart(Message):
        """Message when starting drawing."""

        def __init__(self, mouse_down_event: events.MouseDown) -> None:
            self.mouse_down_event = mouse_down_event
            super().__init__()
    
    class ToolUpdate(Message):
        """Message when dragging on the canvas."""

        def __init__(self, mouse_move_event: events.MouseMove) -> None:
            self.mouse_move_event = mouse_move_event
            super().__init__()

    class ToolStop(Message):
        """Message when releasing the mouse."""

        def __init__(self, mouse_up_event: events.MouseUp) -> None:
            self.mouse_up_event = mouse_up_event
            super().__init__()

    class ToolPreviewUpdate(Message):
        """Message when moving the mouse while the mouse is up."""

        def __init__(self, mouse_move_event: events.MouseMove) -> None:
            self.mouse_move_event = mouse_move_event
            super().__init__()

    class ToolPreviewStop(Message):
        """Message when the mouse leaves the canvas while previewing (not while drawing)."""

        def __init__(self) -> None:
            super().__init__()

    def __init__(self, **kwargs: Any) -> None:
        """Initialize the canvas."""
        super().__init__(**kwargs)
        self.image: AnsiArtDocument|None = None
        self.pointer_active: bool = False
        self.magnifier_preview_region: Optional[Region] = None
        self.select_preview_region: Optional[Region] = None

    def on_mouse_down(self, event: events.MouseDown) -> None:
        # self.fix_mouse_event(event) # not needed, pointer isn't captured yet.
        event.x //= self.magnification
        event.y //= self.magnification

        self.post_message(self.ToolStart(event))
        self.pointer_active = True
        self.capture_mouse(True)
    
    def fix_mouse_event(self, event: events.MouseEvent) -> None:
        # Hack to fix mouse coordinates, not needed for mouse down,
        # or while the mouse is up.
        # This seems like a bug.
        # I think it's due to coordinates being calculated differently during mouse capture.
        if self.pointer_active:
            assert isinstance(self.parent, Widget)
            event.x += int(self.parent.scroll_x)
            event.y += int(self.parent.scroll_y)

    def on_mouse_move(self, event: events.MouseMove) -> None:
        self.fix_mouse_event(event)
        event.x //= self.magnification
        event.y //= self.magnification
        event.delta_x //= self.magnification
        event.delta_y //= self.magnification

        if self.pointer_active:
            self.post_message(self.ToolUpdate(event))
        else:
            self.post_message(self.ToolPreviewUpdate(event))

    def on_mouse_up(self, event: events.MouseUp) -> None:
        self.fix_mouse_event(event)
        event.x //= self.magnification
        event.y //= self.magnification

        self.pointer_active = False
        self.capture_mouse(False)
        self.post_message(self.ToolStop(event))

    def on_leave(self, event: events.Leave) -> None:
        if not self.pointer_active:
            self.post_message(self.ToolPreviewStop())

    def get_content_width(self, container: Size, viewport: Size) -> int:
        return self.image.width * self.magnification

    def get_content_height(self, container: Size, viewport: Size, width: int) -> int:
        return self.image.height * self.magnification

    def render_line(self, y: int) -> Strip:
        """Render a line of the widget. y is relative to the top of the widget."""
        assert self.image is not None
        # self.size.width/height already is multiplied by self.magnification.
        if y >= self.size.height:
            return Strip.blank(self.size.width)
        segments: List[Segment] = []
        sel = self.image.selection

        # Avoiding "possibly unbound" errors.
        magnifier_preview_region = None
        inner_magnifier_preview_region = None
        select_preview_region = None
        inner_select_preview_region = None
        selection_region = None
        inner_selection_region = None

        if self.magnifier_preview_region:
            magnifier_preview_region = scale_region(self.magnifier_preview_region, self.magnification)
            inner_magnifier_preview_region = magnifier_preview_region.shrink((1, 1, 1, 1))
        if self.select_preview_region:
            select_preview_region = scale_region(self.select_preview_region, self.magnification)
            inner_select_preview_region = select_preview_region.shrink((1, 1, 1, 1))
        if sel:
            selection_region = scale_region(sel.region, self.magnification)
            inner_selection_region = selection_region.shrink((1, 1, 1, 1))
        for x in range(self.size.width):
            cell_x = x // self.magnification
            cell_y = y // self.magnification
            try:
                if sel and sel.contained_image and sel.region.contains(cell_x, cell_y) and (sel.mask is None or sel.mask[cell_y - sel.region.y][cell_x - sel.region.x]):
                    bg = sel.contained_image.bg[cell_y - sel.region.y][cell_x - sel.region.x]
                    fg = sel.contained_image.fg[cell_y - sel.region.y][cell_x - sel.region.x]
                    ch = sel.contained_image.ch[cell_y - sel.region.y][cell_x - sel.region.x]
                else:
                    bg = self.image.bg[cell_y][cell_x]
                    fg = self.image.fg[cell_y][cell_x]
                    ch = self.image.ch[cell_y][cell_x]
            except IndexError:
                # This should be easier to debug visually.
                bg = "#555555"
                fg = "#cccccc"
                ch = "?"
            if self.magnification > 1:
                ch = self.big_ch(ch, x % self.magnification, y % self.magnification)
            style = Style.parse(fg+" on "+bg)
            assert style.color is not None
            assert style.bgcolor is not None
            # def offset_to_text_index(offset) -> int:
            #     # return offset.y * sel.region.width + offset.x
            #     # return offset.y * self.image.width + offset.x
            if (
                self.magnifier_preview_region and magnifier_preview_region.contains(x, y) and not inner_magnifier_preview_region.contains(x, y) or
                self.select_preview_region and select_preview_region.contains(x, y) and not inner_select_preview_region.contains(x, y) or
                sel and selection_region.contains(x, y) and not inner_selection_region.contains(x, y) or
                sel and sel.textbox_mode and (
                    # offset_to_text_index(sel.text_selection_start) <=
                    # offset_to_text_index(Offset(x, y))
                    # < offset_to_text_index(sel.text_selection_end)
                    # sel.text_selection_start.x <= cell_x - sel.region.x < sel.text_selection_end.x and
                    # sel.text_selection_start.y <= cell_y - sel.region.y < sel.text_selection_end.y
                    sel.text_selection_start.x == cell_x - sel.region.x and
                    sel.text_selection_start.y == cell_y - sel.region.y
                )
            ):
                # invert the colors
                style = Style.parse(f"rgb({255 - style.color.triplet.red},{255 - style.color.triplet.green},{255 - style.color.triplet.blue}) on rgb({255 - style.bgcolor.triplet.red},{255 - style.bgcolor.triplet.green},{255 - style.bgcolor.triplet.blue})")
            segments.append(Segment(ch, style))
        return Strip(segments, self.size.width)
    
    def refresh_scaled_region(self, region: Region) -> None:
        """Refresh a region of the widget, scaled by the magnification."""
        if self.magnification == 1:
            self.refresh(region)
            return
        # TODO: are these offsets needed? I added them because of a problem which I've fixed
        self.refresh(Region(
            (region.x - 1) * self.magnification,
            (region.y - 1) * self.magnification,
            (region.width + 2) * self.magnification,
            (region.height + 2) * self.magnification,
        ))
    
    def big_ch(self, ch: str, x: int, y: int) -> str:
        """Return a character part of a meta-glyph."""
        match ch:
            case " ":
                return " "
            case "█":
                return "█"
            case "▄":
                return "█" if y >= self.magnification // 2 else " "
            case "▀":
                return "█" if y < self.magnification // 2 else " "
            case "▌":
                return "█" if x < self.magnification // 2 else " "
            case "▐":
                return "█" if x >= self.magnification // 2 else " "
            case _: pass
        # Fall back to showing the character for a single cell.
        # if x == 0 and y == 0:
        if x == self.magnification // 2 and y == self.magnification // 2:
            return ch
        else:
            return " "


class PaintApp(App[None]):
    """MS Paint like image editor in the terminal."""

    CSS_PATH = "paint.css"

    # These call action_* methods on the widget.
    # They can have parameters, if need be.
    # https://textual.textualize.io/guide/actions/
    #
    # KEEP IN SYNC with the README.md Usage section, please.
    BINDINGS = [
        # There is a built-in "quit" action, but it will quit without asking to save.
        # It's also bound to Ctrl+C by default, so for now I'll rebind it,
        # but eventually Ctrl+C will become Edit > Copy.
        Binding("ctrl+q,ctrl+c", "exit", _("Quit")),
        Binding("ctrl+s", "save", _("Save")),
        Binding("ctrl+shift+s", "save_as", _("Save As")),
        Binding("ctrl+p", "print", _("Print")),
        Binding("ctrl+o", "open", _("Open")),
        Binding("ctrl+n", "new", _("New")),
        Binding("ctrl+shift+n", "clear_image", _("Clear Image")),
        Binding("ctrl+t", "toggle_tools_box", _("Toggle Tools Box")),
        Binding("ctrl+w", "toggle_colors_box", _("Toggle Colors Box")),
        Binding("ctrl+z", "undo", _("Undo")),
        # Ctrl+Shift+<key> doesn't seem to work on Ubuntu or VS Code terminal,
        # it ignores the Shift.
        Binding("ctrl+shift+z,shift+ctrl+z,ctrl+y,f4", "redo", _("Repeat")),
        Binding("ctrl+x", "cut", _("Cut")),
        # Binding("ctrl+c", "copy", _("Copy")), # Quit, for now
        Binding("ctrl+v", "paste", _("Paste")),
        Binding("ctrl+g", "toggle_grid", _("Show Grid")),
        Binding("ctrl+f", "view_bitmap", _("View Bitmap")),
        Binding("ctrl+r", "flip_rotate", _("Flip/Rotate")),
        Binding("ctrl+w", "stretch_skew", _("Stretch/Skew")),
        Binding("ctrl+i", "invert_colors", _("Invert Colors")),
        Binding("ctrl+e", "attributes", _("Attributes")),
        # TODO: don't delete textbox with delete key
        Binding("delete", "clear_selection", _("Clear Selection")),
        Binding("ctrl+a", "select_all", _("Select All")),
        Binding("ctrl+pageup", "normal_size", _("Normal Size")),
        Binding("ctrl+pagedown", "large_size", _("Large Size")),
        # action_toggle_dark is built in to App
        Binding("ctrl+d", "toggle_dark", _("Toggle Dark Mode")),
        # dev helper
        # f5 would be more traditional, but I need something not bound to anything
        # in the context of the terminal in VS Code, and not used by this app, like Ctrl+R, and detectable in the terminal.
        Binding("f2", "reload", _("Reload")),
    ]

    show_tools_box = var(True)
    show_colors_box = var(True)
    show_status_bar = var(True)
    selected_tool = var(Tool.pencil)
    return_to_tool = var(Tool.pencil)
    selected_bg_color = var(palette[0])
    selected_fg_color = var(palette[len(palette) // 2])
    selected_char = var(" ")
    filename = var(None)

    # For Open/Save As dialogs
    directory_tree_selected_path: str|None = None
    
    # I'm avoiding allowing None for image, to avoid type checking woes.
    image = var(AnsiArtDocument.from_text("Not Loaded"))
    image_initialized = False
    
    magnification = var(1)
    return_to_magnification = var(4)

    undos: List[Action] = []
    redos: List[Action] = []
    # temporary undo state for brush previews
    preview_action: Optional[Action] = None
    # file modification tracking
    saved_undo_count = 0

    # for shape tools that draw between the mouse down and up points
    # (Line, Rectangle, Ellipse, Rounded Rectangle),
    # Select tool (similarly), and Polygon (to detect double-click)
    mouse_at_start = Offset(0, 0)
    # for Select tool, indicates that the selection is being moved
    # and defines the offset of the selection from the mouse
    selection_drag_offset = Offset(0, 0)
    # for Text tool
    selecting_text = False
    # for Curve, Polygon, or Free-Form Select tools
    tool_points: List[Offset] = []
    # for Polygon tool to detect double-click
    polygon_last_click_time = 0

    # flag to prevent setting the filename input when initially expanding the directory tree
    expanding_directory_tree = False

    background_tasks: set[asyncio.Task[None]] = set()

    TITLE = _("Paint")

    def watch_filename(self, filename: Optional[str]) -> None:
        """Called when filename changes."""
        if filename is None:
            self.sub_title = _("Untitled")
        else:
            self.sub_title = os.path.basename(filename)

    def watch_show_tools_box(self, show_tools_box: bool) -> None:
        """Called when show_tools_box changes."""
        self.query_one("#tools_box", ToolsBox).display = show_tools_box
    
    def watch_show_colors_box(self, show_colors_box: bool) -> None:
        """Called when show_colors_box changes."""
        self.query_one("#colors_box", ColorsBox).display = show_colors_box

    def watch_show_status_bar(self, show_status_bar: bool) -> None:
        """Called when show_status_bar changes."""
        self.query_one("#status_bar").display = show_status_bar

    def watch_selected_tool(self, old_selected_tool: Tool, selected_tool: Tool) -> None:
        """Called when selected_tool changes."""
        for button in self.query(".tool_button"):
            assert isinstance(button, Button)
            if selected_tool == self.query_one("ToolsBox", ToolsBox).tool_by_button[button]:
                button.add_class("selected")
            else:
                button.remove_class("selected")

    def watch_selected_bg_color(self, selected_bg_color: str) -> None:
        """Called when selected_bg_color changes."""
        self.query_one("#selected_color_char_input", CharInput).styles.background = selected_bg_color

    def watch_selected_fg_color(self, selected_fg_color: str) -> None:
        """Called when selected_fg_color changes."""
        self.query_one("#selected_color_char_input", CharInput).styles.color = selected_fg_color

    def watch_selected_char(self, selected_char: str) -> None:
        """Called when selected_char changes."""
        self.query_one("#selected_color_char_input", CharInput).value = selected_char

    def watch_magnification(self, old_magnification: int, magnification: int) -> None:
        """Called when magnification changes."""
        self.canvas.magnification = magnification
        # TODO: keep the top left corner of the viewport in the same place
        # https://github.com/1j01/jspaint/blob/12a90c6bb9d36f495dc6a07114f9667c82ee5228/src/functions.js#L326-L351
        # This will matter more when large documents don't freeze up the program...

    def stamp_brush(self, x: int, y: int, affected_region_base: Optional[Region] = None) -> Region:
        brush_diameter = 1
        square = self.selected_tool == Tool.eraser
        if self.selected_tool == Tool.brush or self.selected_tool == Tool.airbrush or self.selected_tool == Tool.eraser:
            brush_diameter = 3
        if brush_diameter == 1:
            self.stamp_char(x, y)
        else:
            # plot points within a circle (or square)
            for i in range(brush_diameter):
                for j in range(brush_diameter):
                    if square or (i - brush_diameter // 2) ** 2 + (j - brush_diameter // 2) ** 2 <= (brush_diameter // 2) ** 2:
                        self.stamp_char(x + i - brush_diameter // 2, y + j - brush_diameter // 2)
        # expand the affected region to include the brush
        brush_diameter += 2 # safety margin
        affected_region = Region(x - brush_diameter // 2, y - brush_diameter // 2, brush_diameter, brush_diameter)
        if affected_region_base:
            return affected_region_base.union(affected_region)
        else:
            return affected_region
    
    def stamp_char(self, x: int, y: int) -> None:
        char = self.selected_char
        bg_color = self.selected_bg_color
        fg_color = self.selected_fg_color
        if self.selected_tool == Tool.eraser:
            char = " "
            bg_color = "#ffffff"
            fg_color = "#000000"
        if self.selected_tool == Tool.airbrush:
            if random() < 0.7:
                return
        if x < self.image.width and y < self.image.height and x >= 0 and y >= 0:
            self.image.ch[y][x] = char
            self.image.bg[y][x] = bg_color
            self.image.fg[y][x] = fg_color
    
    def erase_region(self, region: Region, mask: Optional[list[list[bool]]] = None) -> None:
        # Time to go undercover as an eraser. 🥸
        # TODO: just add a parameter to stamp_char.
        # Momentarily masquerading makes me mildly mad.
        original_tool = self.selected_tool
        self.selected_tool = Tool.eraser
        for x in range(region.width):
            for y in range(region.height):
                if mask is None or mask[y][x]:
                    self.stamp_char(x + region.x, y + region.y)
        self.selected_tool = original_tool

    def draw_current_polyline(self) -> Region:
        # TODO: DRY with draw_current_curve/draw_current_polygon
        gen = polyline_walk(self.tool_points)
        affected_region = Region()
        for x, y in gen:
            affected_region = affected_region.union(self.stamp_brush(x, y, affected_region))
        return affected_region

    def draw_current_polygon(self) -> Region:
        # TODO: DRY with draw_current_curve/draw_current_polyline
        gen = polygon_walk(self.tool_points)
        affected_region = Region()
        for x, y in gen:
            affected_region = affected_region.union(self.stamp_brush(x, y, affected_region))
        return affected_region

    def draw_current_curve(self) -> Region:
        points = self.tool_points
        if len(points) == 4:
            gen = bezier_curve_walk(
                points[0].x, points[0].y,
                points[2].x, points[2].y,
                points[3].x, points[3].y,
                points[1].x, points[1].y,
            )
        elif len(points) == 3:
            gen = quadratic_curve_walk(
                points[0].x, points[0].y,
                points[2].x, points[2].y,
                points[1].x, points[1].y,
            )
        elif len(points) == 2:
            gen = bresenham_walk(
                points[0].x, points[0].y,
                points[1].x, points[1].y,
            )
        else:
            gen = points
        affected_region = Region()
        for x, y in gen:
            affected_region = affected_region.union(self.stamp_brush(x, y, affected_region))
        return affected_region

    def action_undo(self) -> None:
        self.meld_selection()
        if len(self.undos) > 0:
            self.cancel_preview()
            action = self.undos.pop()
            redo_action = Action(_("Undo") + " " + action.name, self.image, action.region)
            action.undo(self.image)
            self.redos.append(redo_action)
            self.canvas.refresh(layout=True)

    def action_redo(self) -> None:
        self.meld_selection()
        if len(self.redos) > 0:
            self.cancel_preview()
            action = self.redos.pop()
            undo_action = Action(_("Undo") + " " + action.name, self.image, action.region)
            action.undo(self.image)
            self.undos.append(undo_action)
            self.canvas.refresh(layout=True)

    def close_windows(self, selector: str) -> None:
        """Close all windows matching the CSS selector."""
        for window in self.query(selector).nodes:
            assert isinstance(window, Window), f"Expected a Window for query '{selector}', but got {window.css_identifier}"
            window.close()

    def action_save(self) -> None:
        """Start the save action, but don't wait for the Save As dialog to close if it's a new file."""
        task = asyncio.create_task(self.save())
        self.background_tasks.add(task)
        task.add_done_callback(self.background_tasks.discard)

    async def save(self, from_save_as: bool = False) -> None:
        """Save the image to a file."""
        self.cancel_preview()
        dialog_title = _("Save As") if from_save_as else _("Save")
        if self.filename:
            try:
                ansi = self.image.get_ansi()
                with open(self.filename, "w") as f:
                    f.write(ansi)
                self.saved_undo_count = len(self.undos)
            except PermissionError:
                self.warning_message_box(dialog_title, _("Access denied."), "ok")
            except FileNotFoundError: 
                self.warning_message_box(dialog_title, _("%1 contains an invalid path.").replace("%1", self.filename), "ok")
            except OSError as e:
                self.warning_message_box(dialog_title, _("Failed to save document.") + "\n\n" + str(e), "ok")
            except Exception as e:
                self.warning_message_box(dialog_title, _("An unexpected error occurred while writing %1.").replace("%1", self.filename) + "\n\n" + str(e), "ok")
        else:
            await self.save_as()
    
    def action_save_as(self) -> None:
        """Show the save as dialog, without waiting for it to close."""
        # Action must not await the dialog closing,
        # or else you'll never see the dialog in the first place!
        task = asyncio.create_task(self.save_as())
        self.background_tasks.add(task)
        task.add_done_callback(self.background_tasks.discard)

    async def save_as(self) -> None:
        """Save the image as a new file."""
        self.close_windows("#save_as_dialog, #open_dialog")
        
        saved_future: asyncio.Future[None] = asyncio.Future()

        def handle_button(button: Button) -> None:
            if not button.has_class("save"):
                window.close()
                return
            name = self.query_one("#save_as_dialog .filename_input", Input).value
            if not name:
                return
            if self.directory_tree_selected_path:
                name = os.path.join(self.directory_tree_selected_path, name)
            def on_save_confirmed():
                async def async_on_save_confirmed():
                    self.filename = name
                    await self.save(from_save_as=True)
                    window.close()
                    saved_future.set_result(None)
                # https://textual.textualize.io/blog/2023/02/11/the-heisenbug-lurking-in-your-async-code/
                task = asyncio.create_task(async_on_save_confirmed())
                self.background_tasks.add(task)
                task.add_done_callback(self.background_tasks.discard)
            if os.path.exists(name):
                self.confirm_overwrite(name, on_save_confirmed)
            else:
                on_save_confirmed()

        window = DialogWindow(
            id="save_as_dialog",
            classes="file_dialog_window",
            title=_("Save As"),
            handle_button=handle_button,
        )
        filename: str = os.path.basename(self.filename) if self.filename else _("Untitled")
        window.content.mount(
            EnhancedDirectoryTree(id="save_as_dialog_directory_tree", path="/"),
            Input(classes="filename_input", placeholder=_("Filename"), value=filename),
            Button(_("Save"), classes="save submit", variant="primary"),
            Button(_("Cancel"), classes="cancel"),
        )
        self.mount(window)
        self.expand_directory_tree(window.content.query_one("#save_as_dialog_directory_tree", EnhancedDirectoryTree))
        await saved_future

    def expand_directory_tree(self, tree: EnhancedDirectoryTree) -> None:
        """Expand the directory tree to the target directory, either the folder of the open file or the current working directory."""
        self.expanding_directory_tree = True
        target_dir = (self.filename or os.getcwd()).rstrip(os.path.sep)
        tree.expand_to_path(target_dir)
        # There are currently some timers in expand_to_path.
        # In particular, it waits before selecting the target node,
        # and this flag is for avoiding responding to that.
        def done_expanding():
            self.expanding_directory_tree = False
        self.set_timer(0.1, done_expanding)

    def confirm_overwrite(self, filename: str, callback: Callable[[], None]) -> None:
        message = _("%1 already exists.\nDo you want to replace it?").replace("%1", filename)
        def handle_button(button: Button) -> None:
            if not button.has_class("yes"):
                return
            callback()
        self.warning_message_box(_("Save As"), Static(message, markup=False), "yes/no", handle_button)

    def prompt_save_changes(self, filename: str, callback: Callable[[], None]) -> None:
        filename = os.path.basename(filename)
        message = "Save changes to " + filename + "?"
        def handle_button(button: Button) -> None:
            if not button.has_class("yes") and not button.has_class("no"):
                return
            async def async_handle_button(button: Button):
                if button.has_class("yes"):
                    await self.save()
                callback()
            # https://textual.textualize.io/blog/2023/02/11/the-heisenbug-lurking-in-your-async-code/
            task = asyncio.create_task(async_handle_button(button))
            self.background_tasks.add(task)
            task.add_done_callback(self.background_tasks.discard)

        self.warning_message_box(_("Paint"), Static(message, markup=False), "yes/no/cancel", handle_button)

    def is_document_modified(self) -> bool:
        return len(self.undos) != self.saved_undo_count

    def action_exit(self) -> None:
        if self.is_document_modified():
            self.prompt_save_changes(self.filename or _("Untitled"), self.exit)
        else:
            self.exit()
    
    def action_reload(self) -> None:
        if self.is_document_modified():
            self.prompt_save_changes(self.filename or _("Untitled"), restart_program)
        else:
            restart_program()

    def warning_message_box(self,
        title: str,
        message_widget: Widget|str,
        button_types: str = "ok",
        callback: Callable[[Button], None]|None = None,
    ) -> None:
        """Show a warning message box with the given title, message, and buttons."""
        self.close_windows("#message_box")
        
        self.bell()

        def handle_button(button: Button) -> None:
            # TODO: this is not different or useful enough from DialogWindow's
            # handle_button to justify
            # It's a difference in name, and an automatic close
            if callback:
                callback(button)
            window.close()
        window = MessageBox(
            id="message_box",
            title=title,
            icon_widget=get_warning_icon(),
            message_widget=message_widget,
            button_types=button_types,
            handle_button=handle_button,
        )
        self.mount(window)

    def action_open(self) -> None:
        """Show dialog to open an image from a file."""

        def handle_button(button: Button) -> None:
            if not button.has_class("open"):
                window.close()
                return
            filename = window.content.query_one("#open_dialog .filename_input", Input).value
            if not filename:
                return
            if self.directory_tree_selected_path:
                filename = os.path.join(self.directory_tree_selected_path, filename)
            try:
                # Note that os.path.
                # samefile can raise FileNotFoundError
                if self.filename and os.path.samefile(filename, self.filename):
                    window.close()
                    return
                with open(filename, "r") as f:
                    content = f.read() # f is out of scope in go_ahead()
                    def go_ahead():
                        try:
                            new_image = AnsiArtDocument.from_text(content)
                        except Exception as e:
                            # "This is not a valid bitmap file, or its format is not currently supported."
                            # string from MS Paint doesn't apply well here,
                            # at least not until we support bitmap files.
                            self.warning_message_box(_("Open"), Static(_("Paint cannot open this file.") + "\n\n" + str(e)), "ok")
                            return
                        self.action_new(force=True)
                        self.canvas.image = self.image = new_image
                        self.canvas.refresh(layout=True)
                        self.filename = filename
                        window.close()
                    if self.is_document_modified():
                        self.prompt_save_changes(self.filename or _("Untitled"), go_ahead)
                    else:
                        go_ahead()
            except FileNotFoundError:
                self.warning_message_box(_("Open"), Static(_("File not found.") + "\n" + _("Please verify that the correct path and file name are given.")), "ok")
            except IsADirectoryError:
                self.warning_message_box(_("Open"), Static(_("Invalid file.")), "ok")
            except PermissionError:
                self.warning_message_box(_("Open"), Static(_("Access denied.")), "ok")
            except Exception as e:
                self.warning_message_box(_("Open"), Static(_("An unexpected error occurred while reading %1.").replace("%1", filename) + "\n\n" + str(e)), "ok")

        self.close_windows("#save_as_dialog, #open_dialog")
        window = DialogWindow(
            id="open_dialog",
            classes="file_dialog_window",
            title=_("Open"),
            handle_button=handle_button,
        )
        window.content.mount(
            EnhancedDirectoryTree(id="open_dialog_directory_tree", path="/"),
            Input(classes="filename_input", placeholder=_("Filename")),
            Button(_("Open"), classes="open submit", variant="primary"),
            Button(_("Cancel"), classes="cancel"),
        )
        self.mount(window)
        self.expand_directory_tree(window.content.query_one("#open_dialog_directory_tree", EnhancedDirectoryTree))

    def action_new(self, *, force: bool = False) -> None:
        """Create a new image."""
        if self.is_document_modified() and not force:
            def go_ahead():
                # Cancel doesn't call this callback.
                # Yes or No has been selected.
                # If Yes, a save dialog should already have been shown,
                # or the open file saved.
                # Go ahead and create a new image.
                self.action_new(force=True)
            self.prompt_save_changes(self.filename or _("Untitled"), go_ahead)
            return
        self.image = AnsiArtDocument(80, 24)
        self.canvas.image = self.image
        self.canvas.refresh(layout=True)
        self.filename = None
        self.saved_undo_count = 0
        self.undos = []
        self.redos = []
        self.preview_action = None
        # Following MS Paint's lead and resetting the color (but not the tool.)
        # It probably has to do with color modes.
        self.selected_bg_color = palette[0]
        self.selected_fg_color = palette[len(palette) // 2]
        self.selected_char = " "
    
    def action_open_character_selector(self) -> None:
        """Show dialog to select a character."""
        self.close_windows("#character_selector_dialog")
        def handle_selected_character(character: str) -> None:
            self.selected_char = character
            window.close()
        window = CharacterSelectorDialogWindow(
            id="character_selector_dialog",
            handle_selected_character=handle_selected_character,
            selected_character=self.selected_char,
            title=_("Choose Character"),
        )
        self.mount(window)

    def action_edit_colors(self, color_palette_index: int|None = None) -> None:
        """Show dialog to edit colors."""
        self.close_windows("#edit_colors_dialog")
        def handle_selected_color(color: str) -> None:
            self.selected_bg_color = color
            if color_palette_index is not None:
                palette[color_palette_index] = color
                # TODO: Update the palette in a reactive way.
                # I'll need to move the palette state to the app.
                self.query_one(ColorsBox).update_palette()
            window.close()
        window = EditColorsDialogWindow(
            id="edit_colors_dialog",
            handle_selected_color=handle_selected_color,
            selected_color=self.selected_bg_color,
            title=_("Edit Colors"),
        )
        self.mount(window)

    def action_print_preview(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_page_setup(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_print(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_send(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_set_as_wallpaper_tiled(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_set_as_wallpaper_centered(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_recent_file(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_cut(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_copy(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_paste(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_select_all(self) -> None:
        self.meld_selection()
        self.image.selection = Selection(Region(0, 0, self.image.width, self.image.height))
        self.canvas.refresh()
        self.selected_tool = Tool.select
    def action_copy_to(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_paste_from(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_text_toolbar(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_normal_size(self) -> None:
        self.magnification = 1
    def action_large_size(self) -> None:
        self.magnification = 4
    def action_custom_zoom(self) -> None:
        self.close_windows("#zoom_dialog")
        def handle_button(button: Button) -> None:
            if button.has_class("ok"):
                min_zoom = 1
                max_zoom = 16
                try:
                    n = int(window.content.query_one("#zoom_input", Input).value)
                    if n < min_zoom or n > max_zoom:
                        raise ValueError
                    self.magnification = n
                    window.close()
                except ValueError:
                    self.warning_message_box(_("Zoom"), _("Please enter an integer between %1 and %2.", str(min_zoom), str(max_zoom)), "ok")
            else:
                window.close()
        window = DialogWindow(
            id="zoom_dialog",
            title=_("Custom Zoom"),
            handle_button=handle_button,
        )
        window.content.mount(
            Input(id="zoom_input", value=str(self.magnification), placeholder=_("Zoom")),
            # Vertical(
            #     Horizontal(
            #         Static(_("Zoom to")),
            #         Input(id="zoom_input", value=str(self.magnification)),
            #     ),
            #     Horizontal(
            #         Static(_("Current zoom:")),
            #         Static(str(self.magnification)),
            #     ),
            # ),
            # Horizontal(
            Button(_("OK"), classes="ok submit", variant="primary"),
            Button(_("Cancel"), classes="cancel"),
            #     classes="buttons",
            # )
        )
        self.mount(window)
    def action_show_grid(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_show_thumbnail(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_view_bitmap(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_flip_rotate(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_stretch_skew(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_invert_colors(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_attributes(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_clear_image(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    def action_draw_opaque(self) -> None:
        self.warning_message_box(_("Paint"), "Not implemented.", "ok")
    
    def action_help_topics(self) -> None:
        self.close_windows("#help_dialog")
        window = DialogWindow(
            id="help_dialog",
            title=_("Help"), # _("Help Topics"),
            handle_button=lambda button: window.close(),
        )
        help_text = parser.format_usage()
        window.content.mount(Static(help_text,  classes="help_text"))
        window.content.mount(Button(_("OK"), classes="ok submit"))
        self.mount(window)
    
    def action_about_paint(self) -> None:
        """Show the About Paint dialog."""
        self.close_windows("#about_paint_dialog")
        window = DialogWindow(
            id="about_paint_dialog",
            title=_("About Paint"),
            handle_button=lambda button: window.close(),
        )
        window.content.mount(Static("""🎨 [b]Textual Paint[/b]

[i]MS Paint in your terminal.[/i]

[b]Version:[/b] 0.1.0
[b]Author:[/b] [link=https://isaiahodhner.io/]Isaiah Odhner[/link]
[b]License:[/b] [link=https://github.com/1j01/textual-paint/blob/main/LICENSE.txt]MIT[/link]
[b]Source Code:[/b] [link=https://github.com/1j01/textual-paint]github.com/1j01/textual-paint[/link]
"""))
        window.content.mount(Button(_("OK"), classes="ok submit"))
        self.mount(window)

    def compose(self) -> ComposeResult:
        """Add our widgets."""
        yield Header()
        with Container(id="paint"):
            yield MenuBar([
                MenuItem(_("&File"), submenu=Menu([
                    MenuItem(_("&New\tCtrl+N"), self.action_new, 57600),
                    MenuItem(_("&Open...\tCtrl+O"), self.action_open, 57601),
                    MenuItem(_("&Save\tCtrl+S"), self.action_save, 57603),
                    MenuItem(_("Save &As..."), self.action_save_as, 57604),
                    Separator(),
                    MenuItem(_("Print Pre&view"), self.action_print_preview, 57609, grayed=True),
                    MenuItem(_("Page Se&tup..."), self.action_page_setup, 57605, grayed=True),
                    MenuItem(_("&Print...\tCtrl+P"), self.action_print, 57607, grayed=True),
                    Separator(),
                    MenuItem(_("S&end..."), self.action_send, 37662, grayed=True),
                    Separator(),
                    MenuItem(_("Set As &Wallpaper (Tiled)"), self.action_set_as_wallpaper_tiled, 57677, grayed=True),
                    MenuItem(_("Set As Wa&llpaper (Centered)"), self.action_set_as_wallpaper_centered, 57675, grayed=True),
                    Separator(),
                    MenuItem(_("Recent File"), self.action_recent_file, 57616, grayed=True),
                    Separator(),
                    # MenuItem(_("E&xit\tAlt+F4"), self.action_exit, 57665),
                    MenuItem(_("E&xit\tCtrl+Q"), self.action_exit, 57665),
                ])),
                MenuItem(_("&Edit"), submenu=Menu([
                    MenuItem(_("&Undo\tCtrl+Z"), self.action_undo, 57643),
                    MenuItem(_("&Repeat\tF4"), self.action_redo, 57644),
                    Separator(),
                    MenuItem(_("Cu&t\tCtrl+X"), self.action_cut, 57635, grayed=True),
                    MenuItem(_("&Copy\tCtrl+C"), self.action_copy, 57634, grayed=True),
                    MenuItem(_("&Paste\tCtrl+V"), self.action_paste, 57637, grayed=True),
                    MenuItem(_("C&lear Selection\tDel"), self.action_clear_selection, 57632),
                    MenuItem(_("Select &All\tCtrl+A"), self.action_select_all, 57642),
                    Separator(),
                    MenuItem(_("C&opy To..."), self.action_copy_to, 37663, grayed=True),
                    MenuItem(_("Paste &From..."), self.action_paste_from, 37664, grayed=True),
                ])),
                MenuItem(_("&View"), submenu=Menu([
                    MenuItem(_("&Tool Box\tCtrl+T"), self.action_toggle_tools_box, 59415),
                    MenuItem(_("&Color Box\tCtrl+L"), self.action_toggle_colors_box, 59416),
                    MenuItem(_("&Status Bar"), self.action_toggle_status_bar, 59393),
                    MenuItem(_("T&ext Toolbar"), self.action_text_toolbar, 37678, grayed=True),
                    Separator(),
                    MenuItem(_("&Zoom"), submenu=Menu([
                        MenuItem(_("&Normal Size\tCtrl+PgUp"), self.action_normal_size, 37670),
                        MenuItem(_("&Large Size\tCtrl+PgDn"), self.action_large_size, 37671),
                        MenuItem(_("C&ustom..."), self.action_custom_zoom, 37672),
                        Separator(),
                        MenuItem(_("Show &Grid\tCtrl+G"), self.action_show_grid, 37677, grayed=True),
                        MenuItem(_("Show T&humbnail"), self.action_show_thumbnail, 37676, grayed=True),
                    ])),
                    MenuItem(_("&View Bitmap\tCtrl+F"), self.action_view_bitmap, 37673, grayed=True),
                ])),
                MenuItem(_("&Image"), submenu=Menu([
                    MenuItem(_("&Flip/Rotate...\tCtrl+R"), self.action_flip_rotate, 37680, grayed=True),
                    MenuItem(_("&Stretch/Skew...\tCtrl+W"), self.action_stretch_skew, 37681, grayed=True),
                    MenuItem(_("&Invert Colors\tCtrl+I"), self.action_invert_colors, 37682, grayed=True),
                    MenuItem(_("&Attributes...\tCtrl+E"), self.action_attributes, 37683, grayed=True),
                    MenuItem(_("&Clear Image\tCtrl+Shft+N"), self.action_clear_image, 37684, grayed=True),
                    MenuItem(_("&Draw Opaque"), self.action_draw_opaque, 6868, grayed=True),
                ])),
                MenuItem(_("&Colors"), submenu=Menu([
                    MenuItem(_("&Edit Colors..."), self.action_edit_colors, 6869),
                ])),
                MenuItem(_("&Help"), submenu=Menu([
                    MenuItem(_("&Help Topics"), self.action_help_topics, 57670),
                    Separator(),
                    MenuItem(_("&About Paint"), self.action_about_paint, 57664),
                ])),
            ])
            yield Container(
                ToolsBox(id="tools_box"),
                Container(
                    Canvas(id="canvas"),
                    id="editing_area",
                ),
                id="main_horizontal_split",
            )
            yield ColorsBox(id="colors_box")
            yield Container(
                Static(_("For Help, click Help Topics on the Help Menu."), id="status_text"),
                Static(id="status_coords"),
                Static(id="status_dimensions"),
                id="status_bar",
            )

    def on_mount(self) -> None:
        """Called when the app is mounted."""
        # Image can be set from the outside, via CLI
        if not self.image_initialized:
            self.image = AnsiArtDocument(80, 24)
            self.image_initialized = True
        self.canvas = self.query_one("#canvas", Canvas)
        self.canvas.image = self.image
        self.editing_area = self.query_one("#editing_area", Container)

    def pick_color(self, x: int, y: int) -> None:
        """Select a color from the image."""
        if x < 0 or y < 0 or x >= self.image.width or y >= self.image.height:
            return
        self.selected_bg_color = self.image.bg[y][x]
        self.selected_fg_color = self.image.fg[y][x]
        self.selected_char = self.image.ch[y][x]

    def get_prospective_magnification(self) -> int:
        """Returns the magnification result on click with the Magnifier tool."""
        return self.return_to_magnification if self.magnification == 1 else 1

    def magnifier_click(self, x: int, y: int) -> None:
        """Zooms in or out on the image."""
        
        prev_magnification = self.magnification
        prospective_magnification = self.get_prospective_magnification()

        # TODO: fix flickering.
        # The canvas resize and scroll each cause a repaint.
        # I tried using a batch_update, but it prevented the layout recalculation
        # needed for the scroll to work correctly.
        # with self.batch_update():
        self.magnification = prospective_magnification
        self.canvas.magnification = self.magnification

        if self.magnification > prev_magnification:
            w = self.editing_area.size.width / self.magnification
            h = self.editing_area.size.height / self.magnification
            self.editing_area.scroll_to(
                (x - w / 2) * self.magnification / prev_magnification,
                (y - h / 2) * self.magnification / prev_magnification,
                animate=False,
            )
            # `scroll_to` uses `call_after_refresh`.
            # `_scroll_to` is the same thing but without call_after_refresh.
            # But it doesn't work correctly, because the layout isn't updated yet.
            # And if I call:
            # self.screen._refresh_layout()
            # beforehand, it's back to the flickering.
            # I also tried calling:
            # self.editing_area.refresh(layout=True, repaint=False)
            # But it's back to the incorrect scroll position.
            # self.editing_area._scroll_to(
            #     (x - w / 2) * self.magnification / prev_magnification,
            #     (y - h / 2) * self.magnification / prev_magnification,
            #     animate=False,
            # )
        

    def on_canvas_tool_start(self, event: Canvas.ToolStart) -> None:
        """Called when the user starts drawing on the canvas."""
        event.stop()
        self.cancel_preview()

        if self.selected_tool == Tool.pick_color:
            self.pick_color(event.mouse_down_event.x, event.mouse_down_event.y)
            return

        if self.selected_tool == Tool.magnifier:
            self.magnifier_click(event.mouse_down_event.x, event.mouse_down_event.y)
            self.selected_tool = self.return_to_tool
            return

        self.mouse_at_start = Offset(event.mouse_down_event.x, event.mouse_down_event.y)

        if self.selected_tool in [Tool.curve, Tool.polygon]:
            self.tool_points.append(Offset(event.mouse_down_event.x, event.mouse_down_event.y))
            if self.selected_tool == Tool.curve:
                self.make_preview(self.draw_current_curve)
            else:
                self.make_preview(self.draw_current_polyline, show_dimensions_in_status_bar=True) # polyline until finished
            return

        if self.selected_tool == Tool.free_form_select:
            self.tool_points = [Offset(event.mouse_down_event.x, event.mouse_down_event.y)]

        if self.selected_tool in [Tool.select, Tool.free_form_select, Tool.text]:
            sel = self.image.selection
            if sel and sel.region.contains_point(self.mouse_at_start):
                if self.selected_tool == Tool.text:
                    # Place cursor at mouse position
                    sel.text_selection_start = Offset(*self.mouse_at_start) - sel.region.offset
                    sel.text_selection_end = Offset(*self.mouse_at_start) - sel.region.offset
                    self.canvas.refresh_scaled_region(sel.region)
                    self.selecting_text = True
                    return
                # Start dragging the selection.
                self.selection_drag_offset = Offset(
                    sel.region.x - self.mouse_at_start.x,
                    sel.region.y - self.mouse_at_start.y,
                )
                if sel.contained_image:
                    # Already cut out, don't replace the image data.
                    # But if you hold Ctrl, stamp the selection.
                    if event.mouse_down_event.ctrl:
                        sel.copy_to_document(self.image)
                    return
                # Cut out the selected part of the image from the document to use as the selection's image data.
                # TODO: DRY with the below action handling
                self.image_at_start = AnsiArtDocument(self.image.width, self.image.height)
                self.image_at_start.copy_region(self.image)
                action = Action(self.selected_tool.get_name(), self.image)
                if len(self.redos) > 0:
                    self.redos = []
                self.undos.append(action)
                sel.copy_from_document(self.image)
                if not event.mouse_down_event.ctrl:
                    self.erase_region(sel.region, sel.mask)
                # TODO: use two regions, for the cut out and the paste in, once melded.
                # I could maybe give Action a sub_action property, and use it for the melding.
                # Or I could make it use a list of regions.
                # But for now, just save the whole image, so this action can
                # simply be updated on meld.
                # affected_region = sel.region
                affected_region = Region(0, 0, self.image.width, self.image.height)
                
                # TODO: DRY with the below action handling
                action.region = affected_region
                action.region = action.region.intersection(Region(0, 0, self.image.width, self.image.height))
                action.update(self.image_at_start)
                self.canvas.refresh_scaled_region(affected_region)
                return
            self.meld_selection()
            return

        self.image_at_start = AnsiArtDocument(self.image.width, self.image.height)
        self.image_at_start.copy_region(self.image)
        if len(self.redos) > 0:
            self.redos = []
        action = Action(self.selected_tool.get_name(), self.image)
        self.undos.append(action)
        
        affected_region = None
        if self.selected_tool == Tool.pencil or self.selected_tool == Tool.brush:
            affected_region = self.stamp_brush(event.mouse_down_event.x, event.mouse_down_event.y)
        elif self.selected_tool == Tool.fill:
            affected_region = flood_fill(self.image, event.mouse_down_event.x, event.mouse_down_event.y, self.selected_char, self.selected_fg_color, self.selected_bg_color)

        if affected_region:
            action.region = affected_region
            action.region = action.region.intersection(Region(0, 0, self.image.width, self.image.height))
            action.update(self.image_at_start)
            self.canvas.refresh_scaled_region(affected_region)

    def cancel_preview(self) -> None:
        """Revert the currently previewed action."""
        if self.preview_action:
            self.preview_action.undo(self.image)
            self.canvas.refresh_scaled_region(self.preview_action.region)
            self.preview_action = None
        if self.canvas.magnifier_preview_region:
            region = self.canvas.magnifier_preview_region
            self.canvas.magnifier_preview_region = None
            self.canvas.refresh_scaled_region(region)
        if self.canvas.select_preview_region:
            region = self.canvas.select_preview_region
            self.canvas.select_preview_region = None
            self.canvas.refresh_scaled_region(region)

    def make_preview(self, draw_proc: Callable[[], Region], show_dimensions_in_status_bar: bool = False) -> None:
        self.cancel_preview()
        image_before = AnsiArtDocument(self.image.width, self.image.height)
        image_before.copy_region(self.image)
        affected_region = draw_proc()
        if affected_region:
            self.preview_action = Action(self.selected_tool.get_name(), self.image)
            self.preview_action.region = affected_region.intersection(Region(0, 0, self.image.width, self.image.height))
            self.preview_action.update(image_before)
            self.canvas.refresh_scaled_region(affected_region)
            if show_dimensions_in_status_bar:
                self.get_widget_by_id("status_dimensions", Static).update(
                    f"{self.preview_action.region.width}x{self.preview_action.region.height}"
                )

    def on_canvas_tool_preview_update(self, event: Canvas.ToolPreviewUpdate) -> None:
        """Called when the user is hovering over the canvas but not drawing yet."""
        event.stop()
        self.cancel_preview()

        self.get_widget_by_id("status_coords", Static).update(f"{event.mouse_move_event.x},{event.mouse_move_event.y}")

        if self.selected_tool in [Tool.brush, Tool.pencil, Tool.eraser, Tool.curve, Tool.polygon]:
            if self.selected_tool == Tool.curve:
                self.make_preview(self.draw_current_curve)
            elif self.selected_tool == Tool.polygon:
                self.make_preview(self.draw_current_polyline, show_dimensions_in_status_bar=True) # polyline until finished
            else:
                self.make_preview(lambda: self.stamp_brush(event.mouse_move_event.x, event.mouse_move_event.y))
        elif self.selected_tool == Tool.magnifier:
            prospective_magnification = self.get_prospective_magnification()

            if prospective_magnification < self.magnification:
                return # hide if clicking would zoom out

            # prospective viewport size in document coords
            w = self.editing_area.size.width // prospective_magnification
            h = self.editing_area.size.height // prospective_magnification

            rect_x1 = (event.mouse_move_event.x - w // 2)
            rect_y1 = (event.mouse_move_event.y - h // 2)

            # try to move rect into bounds without squishing
            rect_x1 = max(0, rect_x1)
            rect_y1 = max(0, rect_y1)
            rect_x1 = min(self.image.width - w, rect_x1)
            rect_y1 = min(self.image.height - h, rect_y1)

            rect_x2 = rect_x1 + w
            rect_y2 = rect_y1 + h

            # clamp rect to bounds (with squishing)
            rect_x1 = max(0, rect_x1)
            rect_y1 = max(0, rect_y1)
            rect_x2 = min(self.image.width, rect_x2)
            rect_y2 = min(self.image.height, rect_y2)

            rect_w = rect_x2 - rect_x1
            rect_h = rect_y2 - rect_y1
            rect_x = rect_x1
            rect_y = rect_y1

            self.canvas.magnifier_preview_region = Region(rect_x, rect_y, rect_w, rect_h)
            self.canvas.refresh_scaled_region(self.canvas.magnifier_preview_region)

    def on_canvas_tool_preview_stop(self, event: Canvas.ToolPreviewStop) -> None:
        """Called when the user stops hovering over the canvas (while previewing, not drawing)."""
        event.stop()
        self.cancel_preview()
        self.get_widget_by_id("status_coords", Static).update("")

    def get_select_region(self, start: Offset, end: Offset) -> Region:
        # Region.from_corners requires the first point to be the top left,
        # and it doesn't ensure the width and height are non-zero, so it doesn't work here.
        # We want to treat the inputs as cells, not points,
        # so we need to add 1 to the bottom/right.
        x1, y1 = start
        x2, y2 = end
        x1, x2 = min(x1, x2), max(x1, x2)
        y1, y2 = min(y1, y2), max(y1, y2)
        region = Region(x1, y1, x2 - x1 + 1, y2 - y1 + 1)
        # Clamp to the document bounds.
        return region.intersection(Region(0, 0, self.image.width, self.image.height))

    def meld_selection(self) -> None:
        """Draw the selection onto the image and dissolve the selection."""
        # I could DRY this by making clear_selection return the Selection
        if self.image.selection:
            region = self.image.selection.region
            self.image.selection.copy_to_document(self.image)
            self.image.selection = None
            self.canvas.refresh_scaled_region(region)
            self.selection_drag_offset = None
            self.selecting_text = False

    def action_clear_selection(self) -> None:
        """Delete the selection and its contents."""
        if self.image.selection:
            region = self.image.selection.region
            if not self.image.selection.contained_image:
                # It hasn't been cut out yet, so we need to erase it.
                self.erase_region(region, self.image.selection.mask)
            self.image.selection = None
            self.canvas.refresh_scaled_region(region)
            self.selection_drag_offset = None
            self.selecting_text = False

    def on_canvas_tool_update(self, event: Canvas.ToolUpdate) -> None:
        """Called when the user is drawing on the canvas.
        
        Several tools do a preview of sorts here, even though it's not the ToolPreviewUpdate event.
        TODO: rename these events to describe when they occur, ascribe less semantics to them.
        """
        event.stop()
        self.cancel_preview()

        if self.selected_tool != Tool.select:
            if self.selected_tool in [Tool.line, Tool.rectangle, Tool.ellipse, Tool.rounded_rectangle]: # , Tool.curve
                # Display is allowed to go negative, unlike for the Select tool, handled below.
                # Also, Polygon gets both coords and dimensions.
                # Unlike MS Paint, Free-Form Select displays the dimensions of the resulting selection,
                # (rather than the difference between the mouse position and the starting point,)
                # which seems better to me.
                # Also, unlike MS Paint, Curve displays mouse coords rather than dimensions,
                # where "dimensions" are the difference between the mouse position and the starting point.
                # I don't know that this is better, but my mouse_at_start currently is set on mouse down for in-progress curves,
                # so it wouldn't match MS Paint unless I changed that or used the tool_points list.
                # I don't know that anyone looks at the status bar while drawing a curve.
                # If they do, they should probably be using a graphing calculator instead or something.
                self.get_widget_by_id("status_dimensions", Static).update(f"{event.mouse_move_event.x - self.mouse_at_start.x}x{event.mouse_move_event.y - self.mouse_at_start.y}")
            else:
                self.get_widget_by_id("status_coords", Static).update(f"{event.mouse_move_event.x},{event.mouse_move_event.y}")

        if self.selected_tool == Tool.pick_color:
            self.pick_color(event.mouse_move_event.x, event.mouse_move_event.y)
            return

        if self.selected_tool in [Tool.fill, Tool.magnifier]:
            return
        
        if self.selected_tool in [Tool.select, Tool.free_form_select, Tool.text]:
            sel = self.image.selection
            if self.selecting_text:
                assert sel is not None, "selecting_text should only be set if there's a selection"
                sel.text_selection_end = Offset(event.mouse_move_event.x, event.mouse_move_event.y) - sel.region.offset
                self.canvas.refresh_scaled_region(sel.region)
            elif self.selection_drag_offset:
                assert sel is not None, "selection_drag_offset should only be set if there's a selection"
                offset = (
                    self.selection_drag_offset.x + event.mouse_move_event.x,
                    self.selection_drag_offset.y + event.mouse_move_event.y,
                )
                # constrain to have at least one cell in the bounds of the document
                offset = (
                    max(1-sel.region.width, min(self.image.width - 1, offset[0])),
                    max(1-sel.region.height, min(self.image.height - 1, offset[1])),
                )
                old_region = sel.region
                sel.region = Region.from_offset(offset, sel.region.size)
                combined_region = old_region.union(sel.region)
                self.canvas.refresh_scaled_region(combined_region)
            elif self.selected_tool == Tool.free_form_select:
                self.tool_points.append(Offset(event.mouse_move_event.x, event.mouse_move_event.y))
                # polyline until finished, TODO: invert background, don't use selected color
                self.make_preview(self.draw_current_polyline, show_dimensions_in_status_bar=True)
            else:
                self.canvas.select_preview_region = self.get_select_region(self.mouse_at_start, event.mouse_move_event.offset)
                self.canvas.refresh_scaled_region(self.canvas.select_preview_region)
                self.get_widget_by_id("status_dimensions", Static).update(
                    f"{self.canvas.select_preview_region.width}x{self.canvas.select_preview_region.height}"
                )
            return

        if self.selected_tool in [Tool.curve, Tool.polygon]:
            if len(self.tool_points) < 2:
                self.tool_points.append(Offset(event.mouse_move_event.x, event.mouse_move_event.y))
            self.tool_points[-1] = Offset(event.mouse_move_event.x, event.mouse_move_event.y)

            if self.selected_tool == Tool.curve:
                self.make_preview(self.draw_current_curve)
            elif self.selected_tool == Tool.polygon:
                self.make_preview(self.draw_current_polyline, show_dimensions_in_status_bar=True) # polyline until finished
            return

        if len(self.undos) == 0:
            # Code below wants to update the last action.
            # However, if you you undo while drawing,
            # there may be no last action.
            # FIXME: Ideally we'd stop getting events in this case.
            # This might be buggy if there were multiple undos.
            # It might replace the action instead of doing nothing.
            return

        mm = event.mouse_move_event
        action = self.undos[-1]
        affected_region = None

        replace_action = self.selected_tool in [Tool.ellipse, Tool.rectangle, Tool.line, Tool.rounded_rectangle]
        old_action: Optional[Action] = None # avoid "possibly unbound"
        if replace_action:
            old_action = self.undos.pop()
            old_action.undo(self.image)
            action = Action(self.selected_tool.get_name(), self.image, affected_region)
            self.undos.append(action)
        
        if self.selected_tool == Tool.pencil or self.selected_tool == Tool.brush or self.selected_tool == Tool.eraser or self.selected_tool == Tool.airbrush:
            for x, y in bresenham_walk(mm.x - mm.delta_x, mm.y - mm.delta_y, mm.x, mm.y):
                affected_region = self.stamp_brush(x, y, affected_region)
        elif self.selected_tool == Tool.line:
            for x, y in bresenham_walk(self.mouse_at_start.x, self.mouse_at_start.y, mm.x, mm.y):
                affected_region = self.stamp_brush(x, y, affected_region)
        elif self.selected_tool == Tool.rectangle:
            for x in range(min(self.mouse_at_start.x, mm.x), max(self.mouse_at_start.x, mm.x) + 1):
                for y in range(min(self.mouse_at_start.y, mm.y), max(self.mouse_at_start.y, mm.y) + 1):
                    if x in range(min(self.mouse_at_start.x, mm.x) + 1, max(self.mouse_at_start.x, mm.x)) and y in range(min(self.mouse_at_start.y, mm.y) + 1, max(self.mouse_at_start.y, mm.y)):
                        continue
                    affected_region = self.stamp_brush(x, y, affected_region)
        elif self.selected_tool == Tool.rounded_rectangle:
            arc_radius = min(2, abs(self.mouse_at_start.x - mm.x) // 2, abs(self.mouse_at_start.y - mm.y) // 2)
            min_x = min(self.mouse_at_start.x, mm.x)
            max_x = max(self.mouse_at_start.x, mm.x)
            min_y = min(self.mouse_at_start.y, mm.y)
            max_y = max(self.mouse_at_start.y, mm.y)
            for x, y in midpoint_ellipse(0, 0, arc_radius, arc_radius):
                if x < 0:
                    x = min_x + x + arc_radius
                else:
                    x = max_x + x - arc_radius
                if y < 0:
                    y = min_y + y + arc_radius
                else:
                    y = max_y + y - arc_radius
                affected_region = self.stamp_brush(x, y, affected_region)
            for x in range(min_x + arc_radius, max_x - arc_radius + 1):
                affected_region = self.stamp_brush(x, min_y, affected_region)
                affected_region = self.stamp_brush(x, max_y, affected_region)
            for y in range(min_y + arc_radius, max_y - arc_radius + 1):
                affected_region = self.stamp_brush(min_x, y, affected_region)
                affected_region = self.stamp_brush(max_x, y, affected_region)
        elif self.selected_tool == Tool.ellipse:
            center_x = (self.mouse_at_start.x + mm.x) // 2
            center_y = (self.mouse_at_start.y + mm.y) // 2
            radius_x = abs(self.mouse_at_start.x - mm.x) // 2
            radius_y = abs(self.mouse_at_start.y - mm.y) // 2
            for x, y in midpoint_ellipse(center_x, center_y, radius_x, radius_y):
                affected_region = self.stamp_brush(x, y, affected_region)
        else:
            raise NotImplementedError
        
        # Update action region and image data
        if action.region and affected_region:
            action.region = action.region.union(affected_region)
        elif affected_region:
            action.region = affected_region
        if action.region:
            action.region = action.region.intersection(Region(0, 0, self.image.width, self.image.height))
            action.update(self.image_at_start)

        # Only for refreshing, include replaced action region
        # (The new action is allowed to shrink the region compared to the old one)
        if affected_region:
            if replace_action:
                affected_region = affected_region.union(old_action.region)
            self.canvas.refresh_scaled_region(affected_region)

    def on_canvas_tool_stop(self, event: Canvas.ToolStop) -> None:
        """Called when releasing the mouse button after drawing/dragging on the canvas."""
        # Clear the selection preview in case the mouse has moved.
        # (I don't know of any guarantee that it won't.)
        self.cancel_preview()

        self.get_widget_by_id("status_dimensions", Static).update("")

        if self.selection_drag_offset:
            # Done dragging selection
            self.selection_drag_offset = None
            return
        if self.selecting_text:
            # Done selecting text
            self.selecting_text = False
            return
        if self.selected_tool in [Tool.select, Tool.free_form_select, Tool.text] and self.mouse_at_start:
            # Finish making a selection
            if self.selected_tool == Tool.free_form_select:
                # Find bounds of the polygon
                min_x = min(p.x for p in self.tool_points)
                max_x = max(p.x for p in self.tool_points)
                min_y = min(p.y for p in self.tool_points)
                max_y = max(p.y for p in self.tool_points)
                select_region = Region(min_x, min_y, max_x - min_x + 1, max_y - min_y + 1)
                select_region = select_region.intersection(Region(0, 0, self.image.width, self.image.height))
            else:
                select_region = self.get_select_region(self.mouse_at_start, event.mouse_up_event.offset)
            if self.image.selection:
                # This shouldn't happen, because it should meld
                # the selection on mouse down.
                self.meld_selection()
            self.image.selection = Selection(select_region)
            self.image.selection.textbox_mode = self.selected_tool == Tool.text
            if self.image.selection.textbox_mode:
                self.image.selection.contained_image = AnsiArtDocument(self.image.selection.region.width, self.image.selection.region.height)
            if self.selected_tool == Tool.free_form_select:
                # Define the mask for the selection using the polygon
                self.image.selection.mask = [[is_inside_polygon(x + select_region.x, y + select_region.y, self.tool_points) for x in range(select_region.width)] for y in range(select_region.height)]
            self.canvas.refresh_scaled_region(select_region)
        elif self.selected_tool == Tool.curve:
            # Maybe finish drawing a curve
            if len(self.tool_points) >= 4:
                # TODO: DRY action handling (undo state creation)!!!
                self.image_at_start = AnsiArtDocument(self.image.width, self.image.height)
                self.image_at_start.copy_region(self.image)
                action = Action(self.selected_tool.get_name(), self.image)
                if len(self.redos) > 0:
                    self.redos = []
                self.undos.append(action)

                affected_region = self.draw_current_curve()
                
                action.region = affected_region
                action.region = action.region.intersection(Region(0, 0, self.image.width, self.image.height))
                action.update(self.image_at_start)
                self.canvas.refresh_scaled_region(affected_region)

                self.tool_points = []
            else:
                # Most likely just drawing the preview we just cancelled.
                self.make_preview(self.draw_current_curve)
        elif self.selected_tool == Tool.polygon:
            # Maybe finish drawing a polygon
            
            # Check if the distance between the first and last point is small enough,
            # or if the user double-clicked.
            close_gap_threshold_cells = 2
            double_click_threshold_seconds = 0.5
            double_click_threshold_cells = 2
            time_since_last_click = event.time - self.polygon_last_click_time
            enough_points = len(self.tool_points) >= 3
            closed_gap = (
                abs(self.tool_points[0].x - event.mouse_up_event.x) <= close_gap_threshold_cells and
                abs(self.tool_points[0].y - event.mouse_up_event.y) <= close_gap_threshold_cells
            )
            double_clicked = (
                time_since_last_click < double_click_threshold_seconds and
                abs(self.mouse_at_start.x - event.mouse_up_event.x) <= double_click_threshold_cells and
                abs(self.mouse_at_start.y - event.mouse_up_event.y) <= double_click_threshold_cells
            )
            if enough_points and (closed_gap or double_clicked):
                # Finish drawing the polygon
                # TODO: DRY action handling (undo state creation)!!!
                self.image_at_start = AnsiArtDocument(self.image.width, self.image.height)
                self.image_at_start.copy_region(self.image)
                action = Action(self.selected_tool.get_name(), self.image)
                if len(self.redos) > 0:
                    self.redos = []
                self.undos.append(action)

                affected_region = self.draw_current_polygon()
                
                action.region = affected_region
                action.region = action.region.intersection(Region(0, 0, self.image.width, self.image.height))
                action.update(self.image_at_start)
                self.canvas.refresh_scaled_region(affected_region)

                self.tool_points = []
            else:
                # Most likely just drawing the preview we just cancelled.
                self.make_preview(self.draw_current_polyline, show_dimensions_in_status_bar=True) # polyline until finished

            self.polygon_last_click_time = event.time
        elif self.selected_tool == Tool.pick_color:
            self.selected_tool = self.return_to_tool


        # Not reliably unset, so might as well not rely on it. (See early returns above.)
        # self.mouse_at_start = None

    def on_key(self, event: events.Key) -> None:
        """Called when the user presses a key."""
        if self.image.selection and self.image.selection.textbox_mode:
            key = event.key
            assert self.image.selection.contained_image is not None, "Textbox mode should always have contained_image, to edit as text."
            # TODO: delete selected text if any, when typing
            x, y = self.image.selection.text_selection_start
            if key == "enter":
                x = 0
                y += 1
                if y >= self.image.selection.contained_image.height:
                    y = self.image.selection.contained_image.height - 1
            elif key == "left":
               x = max(0, x - 1)
            elif key == "right":
                x = min(self.image.selection.contained_image.width - 1, x + 1)
            elif key == "up":
                y = max(0, y - 1)
            elif key == "down":
                y = min(self.image.selection.contained_image.height - 1, y + 1)
            elif key == "backspace":
                x = max(0, x - 1)
                self.image.selection.contained_image.ch[y][x] = " "
            elif key == "delete":
                self.image.selection.contained_image.ch[y][x] = " "
                x = min(self.image.selection.contained_image.width - 1, x + 1)
            elif key == "home":
                x = 0
            elif key == "end":
                x = self.image.selection.contained_image.width - 1
            elif key == "pageup":
                y = 0
            elif key == "pagedown":
                y = self.image.selection.contained_image.height - 1
            elif event.is_printable and event.character: # Redundance for type checker
                # Type a character into the textbox
                self.image.selection.contained_image.ch[y][x] = event.character
                # x = min(self.image.selection.contained_image.width - 1, x + 1)
                x += 1
                if x >= self.image.selection.contained_image.width:
                    x = 0
                    # y = min(self.image.selection.contained_image.height - 1, y + 1)
                    y += 1
                    if y >= self.image.selection.contained_image.height:
                        y = self.image.selection.contained_image.height - 1
                        x = self.image.selection.contained_image.width - 1
            self.image.selection.text_selection_start = Offset(x, y)
            self.image.selection.text_selection_end = Offset(x, y)
            self.canvas.refresh_scaled_region(self.image.selection.region)


    def action_toggle_tools_box(self) -> None:
        self.show_tools_box = not self.show_tools_box

    def action_toggle_colors_box(self) -> None:
        self.show_colors_box = not self.show_colors_box

    def action_toggle_status_bar(self) -> None:
        self.show_status_bar = not self.show_status_bar

    def on_tools_box_tool_selected(self, event: ToolsBox.ToolSelected) -> None:
        """Called when a tool is selected in the palette."""
        self.selected_tool = event.tool
        if self.selected_tool not in [Tool.magnifier, Tool.pick_color]:
            self.return_to_tool = self.selected_tool
        self.meld_selection()
        self.tool_points = []
    
    def on_char_input_char_selected(self, event: CharInput.CharSelected) -> None:
        """Called when a character is entered in the character input."""
        self.selected_char = event.char

    def on_colors_box_color_selected(self, event: ColorsBox.ColorSelected) -> None:
        """Called when a color well is clicked in the palette."""
        # TODO: a way to select the foreground color
        # if event.fg:
        #     self.selected_fg_color = event.color
        # else:
        self.selected_bg_color = event.color

    def on_tree_node_highlighted(self, event: Tree.NodeHighlighted[DirEntry]) -> None:
        """
        Called when a file/folder is selected in the DirectoryTree.
        
        This message comes from Tree.
        DirectoryTree gives FileSelected but only for files.
        """
        assert event.node.data
        if event.node.data.is_dir:
            self.directory_tree_selected_path = event.node.data.path
        elif event.node.parent:
            assert event.node.parent.data
            self.directory_tree_selected_path = event.node.parent.data.path
            name = os.path.basename(event.node.data.path)
            if not self.expanding_directory_tree:
                self.query_one(".file_dialog_window .filename_input", Input).value = name
        else:
            self.directory_tree_selected_path = None

    def within_menus(self, node: DOMNode) -> bool:
        """Returns True if the node is within the menus."""
        # root node will never be a menu, so it doesn't need to be `while node:`
        # and this makes the type checker happy, since parent can be None
        while node.parent:
            if isinstance(node, Menu):
                return True
            node = node.parent
        return False

    def on_mouse_down(self, event: events.MouseDown) -> None:
        """Called when the mouse button gets pressed."""

        leaf_widget, _ = self.get_widget_at(*event.screen_offset)

        # Close menus if clicking outside the menus
        if not self.within_menus(leaf_widget):
            self.query_one(MenuBar).close()
            return

        # Deselect if clicking outside the canvas
        if leaf_widget is self.editing_area:
            self.meld_selection()

        # This is a dev helper to inspect the layout
        # by highlighting the elements under the mouse in different colors, and labeling them on their borders.
        # debug_highlight is a list of tuples of (element, original_color, original_border, original_border_title)
        if not inspect_layout:
            return
        # Trigger only with middle mouse button.
        # This is before the reset, so you have to middle click on the root element to reset.
        # I didn't like it resetting on every click.
        if event.button != 2:
            return
        if hasattr(self, "debug_highlight"):
            for element, original_color, original_border, original_border_title in self.debug_highlight:
                element.styles.background = original_color
                element.styles.border = original_border
                element.border_title = original_border_title
        self.debug_highlight: List[Tuple[Widget, Color, BorderDefinition, Optional[str]]] = []
        # leaf_widget, _ = self.get_widget_at(*event.screen_offset)
        if leaf_widget and leaf_widget is not self.screen:
            for i, widget in enumerate(leaf_widget.ancestors_with_self):
                self.debug_highlight.append((widget, widget.styles.background, widget.styles.border, widget.border_title if hasattr(widget, "border_title") else None))  # type: ignore
                widget.styles.background = Color.from_hsl(i / 10, 1, 0.3)
                if not event.ctrl:
                    widget.styles.border = ("round", Color.from_hsl(i / 10, 1, 0.5))
                    widget.border_title = widget.css_identifier_styled  # type: ignore

# `textual run --dev paint.py` will search for a 
# global variable named `app`, and fallback to
# anything that is an instance of `App`, or
# a subclass of `App`.
# Creating the app and parsing arguments must not be within an if __name__ == "__main__" block,
# since __name__ will be "<run_path>" when running with the textual CLI,
# and it would create a new app instance, and all arguments would be ignored.
app = PaintApp()

if args.ascii_only_icons:
    ascii_only_icons = True
if args.inspect_layout:
    inspect_layout = True
if args.filename:
    # if args.filename == "-" and not sys.stdin.isatty():
    #     app.image = AnsiArtDocument.from_text(sys.stdin.read())
    #     app.filename = "<stdin>"
    # else:
    with open(args.filename, 'r') as my_file:
        app.image = AnsiArtDocument.from_text(my_file.read())
        app.image_initialized = True
        app.filename = os.path.abspath(args.filename)
if args.clear_screen:
    os.system("cls||clear")

app.dark = args.theme == "dark"

if __name__ == "__main__":
    app.run()