Event handling (#5)

- Refactor `event` handling (heavily inspired by [crates-tui](https://github.com/ratatui/crates-tui/) via [Tui with Terminal and EventHandler](https://ratatui.rs/recipes/apps/terminal-and-event-handler/))
- Refactor widget structure
- Disable `nixos-unstable` temporarily
- Add `.rustfmt.toml`

src/events.rs

@@ -0,0 +1,76 @@
+use crossterm::event::{Event as CrosstermEvent, EventStream, KeyEvent, KeyEventKind};
+use futures::{Stream, StreamExt};
+use std::{pin::Pin, time::Duration};
+use tokio::time::interval;
+use tokio_stream::{wrappers::IntervalStream, StreamMap};
+
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
+enum StreamKey {
+    Ticks,
+    Render,
+    Crossterm,
+}
+#[derive(Clone, Debug)]
+pub enum Event {
+    Init,
+    Quit,
+    Error,
+    Tick,
+    Render,
+    Key(KeyEvent),
+    Resize(u16, u16),
+}
+
+pub struct Events {
+    streams: StreamMap<StreamKey, Pin<Box<dyn Stream<Item = Event>>>>,
+}
+
+impl Default for Events {
+    fn default() -> Self {
+        Self {
+            streams: StreamMap::from_iter([
+                (StreamKey::Ticks, tick_stream()),
+                (StreamKey::Render, render_stream()),
+                (StreamKey::Crossterm, crossterm_stream()),
+            ]),
+        }
+    }
+}
+
+impl Events {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub async fn next(&mut self) -> Option<Event> {
+        self.streams.next().await.map(|(_, event)| event)
+    }
+}
+
+fn tick_stream() -> Pin<Box<dyn Stream<Item = Event>>> {
+    let tick_interval = interval(Duration::from_secs_f64(1.0 / 10.0));
+    Box::pin(IntervalStream::new(tick_interval).map(|_| Event::Tick))
+}
+
+fn render_stream() -> Pin<Box<dyn Stream<Item = Event>>> {
+    let render_interval = interval(Duration::from_secs_f64(1.0 / 60.0)); // 60 FPS
+    Box::pin(IntervalStream::new(render_interval).map(|_| Event::Render))
+}
+
+fn crossterm_stream() -> Pin<Box<dyn Stream<Item = Event>>> {
+    Box::pin(
+        EventStream::new()
+            .fuse()
+            // we are not interested in all events
+            .filter_map(|event| async move {
+                match event {
+                    Ok(CrosstermEvent::Key(key)) if key.kind == KeyEventKind::Press => {
+                        Some(Event::Key(key))
+                    }
+                    Ok(CrosstermEvent::Resize(x, y)) => Some(Event::Resize(x, y)),
+                    Err(_) => Some(Event::Error),
+                    _ => None,
+                }
+            }),
+    )
+}