From c2c696872b99432b2e148bdb2e16e6a0002674bd Mon Sep 17 00:00:00 2001
From: Kevin Hoerr <kjhoerr@submelon.dev>
Date: Tue, 24 Feb 2026 22:20:37 +0000
Subject: main.rs: Counter tutorial

---
 src/main/rust/main.rs | 142 ++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 133 insertions(+), 9 deletions(-)

(limited to 'src/main')

diff --git a/src/main/rust/main.rs b/src/main/rust/main.rs
index 77ab480..4796c46 100644
--- a/src/main/rust/main.rs
+++ b/src/main/rust/main.rs
@@ -1,19 +1,143 @@
-use ratatui::{DefaultTerminal, Frame};
+use crossterm::event::{self, Event, KeyCode, KeyEvent, KeyEventKind};
+use ratatui::{
+    DefaultTerminal, Frame,
+    buffer::Buffer,
+    layout::Rect,
+    style::Stylize,
+    symbols::border,
+    text::{Line, Text},
+    widgets::{Block, Paragraph, Widget},
+};
 use std::io::Result;
 
+#[derive(Debug, Default)]
+pub struct App {
+    counter: u8,
+    exit: bool,
+}
+
 fn main() -> Result<()> {
-    ratatui::run(app)
+    ratatui::run(|term| App::default().run(term))
 }
 
-fn app(terminal: &mut DefaultTerminal) -> Result<()> {
-    loop {
-        terminal.draw(render)?;
-        if crossterm::event::read()?.is_key_press() {
-            break Ok(());
+impl App {
+    /// runs the application's main loop until the user quits
+    pub fn run(&mut self, terminal: &mut DefaultTerminal) -> Result<()> {
+        while !self.exit {
+            terminal.draw(|frame| self.draw(frame))?;
+            self.handle_events()?;
         }
+        Ok(())
+    }
+
+    fn draw(&self, frame: &mut Frame) {
+        frame.render_widget(self, frame.area());
+    }
+
+    fn handle_events(&mut self) -> Result<()> {
+        match event::read()? {
+            // it's important to check that the event is a key press event as
+            // crossterm also emits key release and repeat events on Windows.
+            Event::Key(key_event) if key_event.kind == KeyEventKind::Press => {
+                self.handle_key_event(key_event)
+            }
+            _ => {}
+        };
+        Ok(())
+    }
+
+    fn handle_key_event(&mut self, key_event: KeyEvent) {
+        match key_event.code {
+            KeyCode::Char('q') => self.exit(),
+            KeyCode::Left => self.decrement_counter(),
+            KeyCode::Right => self.increment_counter(),
+            _ => {}
+        }
+    }
+
+    fn exit(&mut self) {
+        self.exit = true;
+    }
+
+    fn decrement_counter(&mut self) {
+        self.counter -= 1;
+    }
+
+    fn increment_counter(&mut self) {
+        self.counter += 1;
     }
 }
 
-fn render(frame: &mut Frame) {
-    frame.render_widget("hello world", frame.area());
+impl Widget for &App {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        let title = Line::from(" Counter App Tutorial ".bold());
+        let instructions = Line::from(vec![
+            " Decrement ".into(),
+            "<Left>".blue().bold(),
+            " Increment ".into(),
+            "<Right>".blue().bold(),
+            " Quit ".into(),
+            "<Q> ".blue().bold(),
+        ]);
+        let block = Block::bordered()
+            .title(title.centered())
+            .title_bottom(instructions.centered())
+            .border_set(border::THICK);
+
+        let counter_text = Text::from(vec![Line::from(vec![
+            "Value: ".into(),
+            self.counter.to_string().yellow(),
+        ])]);
+
+        Paragraph::new(counter_text)
+            .centered()
+            .block(block)
+            .render(area, buf);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ratatui::style::Style;
+
+    #[test]
+    fn render() {
+        let app = App::default();
+        let mut buf = Buffer::empty(Rect::new(0, 0, 50, 4));
+
+        app.render(buf.area, &mut buf);
+
+        let mut expected = Buffer::with_lines(vec![
+            "┏━━━━━━━━━━━━━ Counter App Tutorial ━━━━━━━━━━━━━┓",
+            "┃                    Value: 0                    ┃",
+            "┃                                                ┃",
+            "┗━ Decrement <Left> Increment <Right> Quit <Q> ━━┛",
+        ]);
+        let title_style = Style::new().bold();
+        let counter_style = Style::new().yellow();
+        let key_style = Style::new().blue().bold();
+
+        expected.set_style(Rect::new(14, 0, 22, 1), title_style);
+        expected.set_style(Rect::new(28, 1, 1, 1), counter_style);
+        expected.set_style(Rect::new(13, 3, 6, 1), key_style);
+        expected.set_style(Rect::new(30, 3, 7, 1), key_style);
+        expected.set_style(Rect::new(43, 3, 4, 1), key_style);
+
+        assert_eq!(buf, expected);
+    }
+
+    #[test]
+    fn handle_key_event() {
+        let mut app = App::default();
+        app.handle_key_event(KeyCode::Right.into());
+        assert_eq!(app.counter, 1);
+
+        app.handle_key_event(KeyCode::Left.into());
+        assert_eq!(app.counter, 0);
+
+        let mut app = App::default();
+        app.handle_key_event(KeyCode::Char('q').into());
+        assert!(app.exit);
+    }
 }
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