Add cursor to TextInputComponent for better commit message support (#117)

see #46

src/components/textinput.rs

@@ -8,12 +8,11 @@ use crate::{
 };
 use anyhow::Result;
 use crossterm::event::{Event, KeyCode, KeyModifiers};
-use std::borrow::Cow;
 use strings::commands;
 use tui::{
     backend::Backend,
     layout::Rect,
-    style::Style,
+    style::{Modifier, Style},
     widgets::{Clear, Text},
     Frame,
 };
@@ -25,6 +24,7 @@ pub struct TextInputComponent {
     msg: String,
     visible: bool,
     theme: Theme,
+    cursor_position: usize,
 }
 
 impl TextInputComponent {
@@ -40,19 +40,56 @@ impl TextInputComponent {
             theme: *theme,
             title: title.to_string(),
             default_msg: default_msg.to_string(),
+            cursor_position: 0,
         }
     }
 
-    ///
+    /// Clear the `msg`.
     pub fn clear(&mut self) {
         self.msg.clear();
     }
 
-    ///
+    /// Get the `msg`.
     pub const fn get_text(&self) -> &String {
         &self.msg
     }
 
+    /// Move the cursor right one char.
+    fn incr_cursor(&mut self) {
+        if let Some(pos) = self.next_char_position() {
+            self.cursor_position = pos;
+        }
+    }
+
+    /// Move the cursor left one char.
+    fn decr_cursor(&mut self) {
+        let mut new_pos: usize = 0;
+        for (bytes, _) in self.msg.char_indices() {
+            if bytes >= self.cursor_position {
+                break;
+            }
+            new_pos = bytes;
+        }
+        self.cursor_position = new_pos;
+    }
+
+    /// Get the position of the next char, or, if the cursor points
+    /// to the last char, the `msg.len()`.
+    /// Returns None when the cursor is already at `msg.len()`.
+    fn next_char_position(&self) -> Option<usize> {
+        let mut char_indices =
+            self.msg[self.cursor_position..].char_indices();
+        if char_indices.next().is_some() {
+            if let Some((bytes, _)) = char_indices.next() {
+                Some(self.cursor_position + bytes)
+            } else {
+                Some(self.msg.len())
+            }
+        } else {
+            None
+        }
+    }
+  
     ///
     pub fn set_text(&mut self, msg: String) {
         self.msg = msg;
@@ -71,16 +108,43 @@ impl DrawableComponent for TextInputComponent {
         _rect: Rect,
     ) -> Result<()> {
         if self.visible {
-            let txt = if self.msg.is_empty() {
-                [Text::Styled(
-                    Cow::from(self.default_msg.as_str()),
+            let mut txt: Vec<tui::widgets::Text> = Vec::new();
+            if self.msg.is_empty() {
+                txt.push(Text::styled(
+                    self.default_msg.as_str(),
                     self.theme.text(false, false),
-                )]
+                ));
             } else {
-                [Text::Styled(
-                    Cow::from(self.msg.clone()),
-                    Style::default(),
-                )]
+                // the portion of the text before the cursor is added
+                // if the cursor is not at the first character
+                if self.cursor_position > 0 {
+                    txt.push(Text::styled(
+                        &self.msg[..self.cursor_position],
+                        Style::default(),
+                    ));
+                }
+
+                txt.push(Text::styled(
+                    if let Some(pos) = self.next_char_position() {
+                        &self.msg[self.cursor_position..pos]
+                    } else {
+                        // if the cursor is at the end of the msg
+                        // a whitespace is used to underline
+                        " "
+                    },
+                    Style::default().modifier(Modifier::UNDERLINED),
+                ));
+
+                // the final portion of the text is added if there is
+                // still remaining characters
+                if let Some(pos) = self.next_char_position() {
+                    if pos < self.msg.len() {
+                        txt.push(Text::styled(
+                            &self.msg[pos..],
+                            Style::default(),
+                        ));
+                    }
+                }
             };
 
             let area = ui::centered_rect(60, 20, f.size());
@@ -128,11 +192,39 @@ impl Component for TextInputComponent {
                         return Ok(true);
                     }
                     KeyCode::Char(c) if !is_ctrl => {
-                        self.msg.push(c);
+                        self.msg.insert(self.cursor_position, c);
+                        self.incr_cursor();
+                        return Ok(true);
+                    }
+                    KeyCode::Delete => {
+                        if self.cursor_position < self.msg.len() {
+                            self.msg.remove(self.cursor_position);
+                        }
                         return Ok(true);
                     }
                     KeyCode::Backspace => {
-                        self.msg.pop();
+                        if self.cursor_position > 0 {
+                            self.decr_cursor();
+                            if self.cursor_position < self.msg.len() {
+                            }
+                            self.msg.remove(self.cursor_position);
+                        }
+                        return Ok(true);
+                    }
+                    KeyCode::Left => {
+                        self.decr_cursor();
+                        return Ok(true);
+                    }
+                    KeyCode::Right => {
+                        self.incr_cursor();
+                        return Ok(true);
+                    }
+                    KeyCode::Home => {
+                        self.cursor_position = 0;
+                        return Ok(true);
+                    }
+                    KeyCode::End => {
+                        self.cursor_position = self.msg.len();
                         return Ok(true);
                     }
                     _ => (),