Added support for inversion of scrolling (#270)

default-config.toml

@@ -53,3 +53,5 @@ theme = "dark"
 username_highlight = true
 # The shape of the cursor, block (default), underscore, or line.
 cursor_shape = "block"
+# If the scrolling should be inverted.
+inverted_scrolling = false

src/handlers/app.rs

@@ -61,7 +61,44 @@ impl ToString for State {
     }
 }
 
-#[derive(Debug)]
+pub struct Scrolling {
+    /// Offset of scroll
+    offset: usize,
+    /// If the scrolling is currently inverted
+    inverted: bool,
+}
+
+impl Scrolling {
+    pub const fn new(inverted: bool) -> Self {
+        Self {
+            offset: 0,
+            inverted,
+        }
+    }
+
+    /// Scrolling upwards, towards the start of the chat
+    pub fn up(&mut self) {
+        self.offset += 1;
+    }
+
+    /// Scrolling downwards, towards the most recent message(s)
+    pub fn down(&mut self) {
+        self.offset = self.offset.saturating_sub(1);
+    }
+
+    pub const fn inverted(&self) -> bool {
+        self.inverted
+    }
+
+    pub fn jump_to(&mut self, index: usize) {
+        self.offset = index;
+    }
+
+    pub const fn get_offset(&self) -> usize {
+        self.offset
+    }
+}
+
 pub struct App {
     /// History of recorded messages (time, username, message, etc.)
     pub messages: VecDeque<Data>,
@@ -75,8 +112,8 @@ pub struct App {
     pub input_buffer: LineBuffer,
     /// The current suggestion, if any
     pub buffer_suggestion: Option<String>,
-    /// Scrolling offset for the main window
-    pub scroll_offset: usize,
+    /// Interactions with scrolling of the application
+    pub scrolling: Scrolling,
     /// The theme selected by the user
     pub theme_style: Style,
 }
@@ -90,11 +127,11 @@ impl App {
             state: config.terminal.start_state.clone(),
             input_buffer: LineBuffer::with_capacity(INPUT_BUFFER_LIMIT),
             buffer_suggestion: None,
-            scroll_offset: 0,
             theme_style: match config.frontend.theme {
                 Theme::Light => BORDER_NAME_LIGHT,
                 _ => BORDER_NAME_DARK,
             },
+            scrolling: Scrolling::new(config.frontend.inverted_scrolling),
         }
     }
 
@@ -105,6 +142,25 @@ impl App {
     pub fn clear_messages(&mut self) {
         self.messages.clear();
 
-        self.scroll_offset = 0;
+        self.scrolling.jump_to(0);
+    }
+
+    #[allow(dead_code)]
+    pub fn rotate_theme(&mut self) {
+        todo!("Rotate through different themes")
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_no_scroll_overflow_not_inverted() {
+        let mut scroll = Scrolling::new(false);
+        assert_eq!(scroll.get_offset(), 0);
+
+        scroll.down();
+        assert_eq!(scroll.get_offset(), 0);
     }
 }

src/handlers/config.rs

@@ -107,6 +107,8 @@ pub struct FrontendConfig {
     pub state_tabs: bool,
     /// The shape of the cursor in insert boxes.
     pub cursor_shape: CursorType,
+    /// If the scrolling should be inverted
+    pub inverted_scrolling: bool,
 }
 
 impl Default for TwitchConfig {
@@ -147,6 +149,7 @@ impl Default for FrontendConfig {
             username_highlight: true,
             state_tabs: false,
             cursor_shape: CursorType::default(),
+            inverted_scrolling: false,
         }
     }
 }

src/handlers/user_input/input.rs

@@ -188,19 +188,29 @@ async fn handle_insert_type_movements(action: &mut UserActionAttributes<'_, '_>)
 
 fn handle_user_scroll(app: &mut App, key: Key) {
     match app.state {
-        State::Insert | State::MessageSearch | State::Normal => match key {
-            Key::ScrollUp => {
-                if app.scroll_offset < app.messages.len() {
-                    app.scroll_offset += 1;
+        State::Insert | State::MessageSearch | State::Normal => {
+            let limit = app.scrolling.get_offset() < app.messages.len();
+
+            match key {
+                Key::ScrollUp => {
+                    if limit {
+                        app.scrolling.up();
+                    } else if app.scrolling.inverted() {
+                        app.scrolling.down();
+                    }
                 }
-            }
-            Key::ScrollDown => {
-                if app.scroll_offset > 0 {
-                    app.scroll_offset -= 1;
+                Key::ScrollDown => {
+                    if app.scrolling.inverted() {
+                        if limit {
+                            app.scrolling.up();
+                        }
+                    } else {
+                        app.scrolling.down();
+                    }
                 }
+                _ => {}
             }
-            _ => {}
-        },
+        }
         _ => {}
     }
 }
@@ -251,7 +261,8 @@ pub async fn handle_stateful_user_input(
                     return Some(TerminalAction::Quitting);
                 }
                 Key::Esc => {
-                    app.scroll_offset = 0;
+                    app.scrolling.jump_to(0);
+
                     app.state = State::Normal;
                 }
                 _ => {}

src/terminal.rs

@@ -119,8 +119,8 @@ pub async fn ui_driver(
             app.messages.push_front(info);
 
             // If scrolling is enabled, pad for more messages.
-            if app.scroll_offset > 0 {
-                app.scroll_offset += 1;
+            if app.scrolling.get_offset() > 0 {
+                app.scrolling.up();
             }
         }
 

src/ui/mod.rs

@@ -139,7 +139,7 @@ pub fn draw_ui<T: Backend>(frame: &mut Frame<T>, app: &mut App, config: &Complet
     let mut total_row_height: usize = 0;
     let mut display_rows = VecDeque::new();
 
-    let mut scroll_offset = app.scroll_offset;
+    let mut scroll_offset = app.scrolling.get_offset();
 
     let mut total_num_search_results = 0;
     'outer: for data in &app.messages {