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//! Crossterm event reader with scroll debouncing.
use std::time::{Duration, Instant};
use crossterm::event::{
Event as CrosstermEvent, KeyCode, KeyEvent, KeyEventKind, KeyModifiers, MouseButton,
MouseEventKind,
};
use tokio::sync::mpsc;
use super::AppEvent;
/// Handles crossterm event reading and dispatches [`AppEvent`]s.
pub struct EventHandler {
/// Channel sender for emitting events.
tx: mpsc::UnboundedSender<AppEvent>,
/// Channel receiver for consuming events.
rx: mpsc::UnboundedReceiver<AppEvent>,
/// Tick rate for periodic updates.
tick_rate: Duration,
}
impl EventHandler {
/// Create a new event handler with the given tick rate.
pub fn new(tick_rate: Duration) -> Self {
let (tx, rx) = mpsc::unbounded_channel();
Self { tx, rx, tick_rate }
}
/// Get a clone of the sender for external event producers (agent, tools).
pub fn sender(&self) -> mpsc::UnboundedSender<AppEvent> {
self.tx.clone()
}
/// Start the crossterm event reader loop.
///
/// Uses crossterm's async `EventStream` for zero-latency event delivery.
///
/// Includes a debounce state machine that distinguishes touchpad/mouse scroll
/// (rapid-fire Up/Down arrows via xterm alternate scroll mode `\x1b[?1007h`)
/// from keyboard arrow presses. Touchpad scroll generates arrows every 8-16ms
/// in bursts; keyboard presses are single events with ~300ms before repeat.
/// A 25ms debounce window cleanly separates these two input sources.
///
/// Also handles mouse events (click/drag/up for selection, scroll for terminals
/// that support mouse reporting) and FocusGained for triggering redraws.
pub fn start(&self) {
use futures::StreamExt;
let tx = self.tx.clone();
let tick_rate = self.tick_rate;
tokio::spawn(async move {
let mut reader = crossterm::event::EventStream::new();
let mut tick_interval = tokio::time::interval(tick_rate);
// Debounce state for distinguishing mouse scroll from keyboard arrows
let debounce_window = Duration::from_millis(25);
let scroll_burst_timeout = Duration::from_millis(100);
let mut pending_arrow: Option<(KeyEvent, Instant)> = None;
let mut scroll_burst = false;
let mut last_arrow_time: Option<Instant> = None;
loop {
// Compute debounce deadline if we have a pending arrow
let debounce_deadline = pending_arrow
.as_ref()
.map(|(_, t)| tokio::time::Instant::from_std(*t + debounce_window));
tokio::select! {
biased;
// Debounce timer fires — pending arrow was a keyboard press
_ = async {
match debounce_deadline {
Some(deadline) => tokio::time::sleep_until(deadline).await,
None => std::future::pending().await,
}
} => {
if let Some((key, _)) = pending_arrow.take() {
scroll_burst = false;
if tx.send(AppEvent::Key(key)).is_err() {
break;
}
}
}
maybe_event = reader.next() => {
match maybe_event {
Some(Ok(CrosstermEvent::Key(key))) => {
let is_unmodified_arrow = matches!(
key.code,
KeyCode::Up | KeyCode::Down
) && key.modifiers == KeyModifiers::NONE
&& key.kind == KeyEventKind::Press;
if is_unmodified_arrow {
let now = Instant::now();
// Check if we're in a scroll burst
let in_burst = scroll_burst
&& last_arrow_time.is_some_and(|t| {
now.duration_since(t) < scroll_burst_timeout
});
if let Some((prev_key, _)) = pending_arrow.take() {
// Second arrow arrived within debounce window → mouse scroll
scroll_burst = true;
last_arrow_time = Some(now);
let ev1 = if prev_key.code == KeyCode::Up {
AppEvent::ScrollUp
} else {
AppEvent::ScrollDown
};
let ev2 = if key.code == KeyCode::Up {
AppEvent::ScrollUp
} else {
AppEvent::ScrollDown
};
if tx.send(ev1).is_err() || tx.send(ev2).is_err() {
break;
}
} else if in_burst {
// Continuing a scroll burst
last_arrow_time = Some(now);
let ev = if key.code == KeyCode::Up {
AppEvent::ScrollUp
} else {
AppEvent::ScrollDown
};
if tx.send(ev).is_err() {
break;
}
} else {
// First arrow — buffer it, wait for debounce
pending_arrow = Some((key, now));
}
} else {
// Non-arrow key or arrow with modifiers/repeat:
// flush any pending arrow as keyboard first
if let Some((prev_key, _)) = pending_arrow.take() {
scroll_burst = false;
if tx.send(AppEvent::Key(prev_key)).is_err() {
break;
}
}
// Only forward press and repeat events
if matches!(key.kind, KeyEventKind::Press | KeyEventKind::Repeat)
&& tx.send(AppEvent::Key(key)).is_err()
{
break;
}
}
}
Some(Ok(CrosstermEvent::Mouse(mouse))) => {
let ev = match mouse.kind {
MouseEventKind::ScrollUp => Some(AppEvent::ScrollUp),
MouseEventKind::ScrollDown => Some(AppEvent::ScrollDown),
MouseEventKind::Down(MouseButton::Left) => {
Some(AppEvent::MouseDown { col: mouse.column, row: mouse.row })
}
MouseEventKind::Drag(MouseButton::Left) => {
Some(AppEvent::MouseDrag { col: mouse.column, row: mouse.row })
}
MouseEventKind::Up(MouseButton::Left) => {
Some(AppEvent::MouseUp { col: mouse.column, row: mouse.row })
}
_ => None,
};
if let Some(e) = ev {
// Flush pending arrow before mouse events
if let Some((prev_key, _)) = pending_arrow.take() {
scroll_burst = false;
if tx.send(AppEvent::Key(prev_key)).is_err() {
break;
}
}
if tx.send(e).is_err() {
break;
}
}
}
Some(Ok(CrosstermEvent::Resize(w, h))) => {
// Flush pending arrow before resize
if let Some((prev_key, _)) = pending_arrow.take() {
scroll_burst = false;
if tx.send(AppEvent::Key(prev_key)).is_err() {
break;
}
}
if tx.send(AppEvent::Resize(w, h)).is_err() {
break;
}
}
Some(Ok(CrosstermEvent::FocusGained)) => {
// Flush pending arrow before focus events
if let Some((prev_key, _)) = pending_arrow.take() {
scroll_burst = false;
if tx.send(AppEvent::Key(prev_key)).is_err() {
break;
}
}
if tx.send(AppEvent::FocusGained).is_err() {
break;
}
}
Some(Ok(other)) => {
// Flush pending arrow before other events
if let Some((prev_key, _)) = pending_arrow.take() {
scroll_burst = false;
if tx.send(AppEvent::Key(prev_key)).is_err() {
break;
}
}
if tx.send(AppEvent::Terminal(other)).is_err() {
break;
}
}
Some(Err(_)) => continue,
None => break,
}
}
_ = tick_interval.tick() => {
// Don't flush pending arrow on tick — let debounce timer handle it
if tx.send(AppEvent::Tick).is_err() {
break;
}
}
}
}
});
}
/// Receive the next event.
pub async fn next(&mut self) -> Option<AppEvent> {
self.rx.recv().await
}
/// Try to receive an event without blocking.
/// Returns `None` immediately if no event is queued.
pub fn try_next(&mut self) -> Option<AppEvent> {
self.rx.try_recv().ok()
}
}