Merge 006da34ada into sapling-pr-archive-bolinfest

codex-rs/tui/src/scroll_event_helper.rs

@@ -0,0 +1,71 @@
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::AtomicI32;
+use std::sync::atomic::Ordering;
+use std::sync::mpsc::Sender;
+use std::sync::Arc;
+use std::thread;
+use std::time::Duration;
+
+use crate::app_event::AppEvent;
+
+pub(crate) struct ScrollEventHelper {
+    app_event_tx: Sender<AppEvent>,
+    scroll_delta: Arc<AtomicI32>,
+    timer_scheduled: Arc<AtomicBool>,
+}
+
+/// How long to wait after the first scroll event before sending the
+/// accumulated scroll delta to the main thread.
+const DEBOUNCE_WINDOW: Duration = Duration::from_millis(100);
+
+/// Utility to debounce scroll events so we can determine estimate the
+/// "magnitude" of the scroll event by accumulating them over a short window.
+impl ScrollEventHelper {
+    pub(crate) fn new(app_event_tx: Sender<AppEvent>) -> Self {
+        Self {
+            app_event_tx,
+            scroll_delta: Arc::new(AtomicI32::new(0)),
+            timer_scheduled: Arc::new(AtomicBool::new(false)),
+        }
+    }
+
+    pub(crate) fn scroll_up(&self) {
+        self.scroll_delta.fetch_sub(1, Ordering::Relaxed);
+        self.schedule_notification();
+    }
+
+    pub(crate) fn scroll_down(&self) {
+        self.scroll_delta.fetch_add(1, Ordering::Relaxed);
+        self.schedule_notification();
+    }
+
+    /// Starts a one-shot timer **only once** per burst of wheel events.
+    fn schedule_notification(&self) {
+        // If the timer is already scheduled, do nothing.
+        if self
+            .timer_scheduled
+            .compare_exchange(false, true, Ordering::SeqCst, Ordering::SeqCst)
+            .is_err()
+        {
+            return;
+        }
+
+        // Otherwise, schedule a new timer.
+        let tx = self.app_event_tx.clone();
+        let delta = Arc::clone(&self.scroll_delta);
+        let timer_flag = Arc::clone(&self.timer_scheduled);
+
+        thread::spawn(move || {
+            thread::sleep(DEBOUNCE_WINDOW);
+
+            let accumulated = delta.swap(0, Ordering::SeqCst);
+            // Only emit if something really happened.
+            if accumulated != 0 {
+                let _ = tx.send(AppEvent::Scroll(accumulated));
+            }
+
+            // Allow a new timer to be started on the next wheel event.
+            timer_flag.store(false, Ordering::SeqCst);
+        });
+    }
+}