From d4fa61e4358bdc83173c346121c992836f1b7152 Mon Sep 17 00:00:00 2001
From: mo8it <mo8it@proton.me>
Date: Thu, 26 Sep 2024 12:26:24 +0200
Subject: [PATCH] Debounce file change events

---
 src/watch.rs              |  8 ++--
 src/watch/notify_event.rs | 91 +++++++++++++++++++++++++++++++++------
 2 files changed, 82 insertions(+), 17 deletions(-)

diff --git a/src/watch.rs b/src/watch.rs
index fd89b29..11450b4 100644
--- a/src/watch.rs
+++ b/src/watch.rs
@@ -69,11 +69,11 @@ fn run_watch(
     // Prevent dropping the guard until the end of the function.
     // Otherwise, the file watcher exits.
     let _watcher_guard = if let Some(exercise_names) = notify_exercise_names {
+        let notify_event_handler =
+            NotifyEventHandler::build(watch_event_sender.clone(), exercise_names)?;
+
         let mut watcher = RecommendedWatcher::new(
-            NotifyEventHandler {
-                sender: watch_event_sender.clone(),
-                exercise_names,
-            },
+            notify_event_handler,
             Config::default().with_poll_interval(Duration::from_secs(1)),
         )
         .inspect_err(|_| eprintln!("{NOTIFY_ERR}"))?;
diff --git a/src/watch/notify_event.rs b/src/watch/notify_event.rs
index 5ed8fd1..2051e54 100644
--- a/src/watch/notify_event.rs
+++ b/src/watch/notify_event.rs
@@ -1,15 +1,71 @@
+use anyhow::{Context, Result};
 use notify::{
-    event::{MetadataKind, ModifyKind},
+    event::{AccessKind, AccessMode, MetadataKind, ModifyKind, RenameMode},
     Event, EventKind,
 };
-use std::sync::{atomic::Ordering::Relaxed, mpsc::Sender};
+use std::{
+    sync::{
+        atomic::Ordering::Relaxed,
+        mpsc::{sync_channel, RecvTimeoutError, Sender, SyncSender},
+    },
+    thread,
+    time::Duration,
+};
 
 use super::{WatchEvent, EXERCISE_RUNNING};
 
+const DEBOUNCE_DURATION: Duration = Duration::from_millis(200);
+
 pub struct NotifyEventHandler {
-    pub sender: Sender<WatchEvent>,
-    /// Used to report which exercise was modified.
-    pub exercise_names: &'static [&'static [u8]],
+    error_sender: Sender<WatchEvent>,
+    // Sends the index of the updated exercise.
+    update_sender: SyncSender<usize>,
+    // Used to report which exercise was modified.
+    exercise_names: &'static [&'static [u8]],
+}
+
+impl NotifyEventHandler {
+    pub fn build(
+        watch_event_sender: Sender<WatchEvent>,
+        exercise_names: &'static [&'static [u8]],
+    ) -> Result<Self> {
+        let (update_sender, update_receiver) = sync_channel(0);
+        let error_sender = watch_event_sender.clone();
+
+        // Debouncer
+        thread::Builder::new()
+            .spawn(move || {
+                let mut exercise_updated = vec![false; exercise_names.len()];
+
+                loop {
+                    match update_receiver.recv_timeout(DEBOUNCE_DURATION) {
+                        Ok(exercise_ind) => exercise_updated[exercise_ind] = true,
+                        Err(RecvTimeoutError::Timeout) => {
+                            for (exercise_ind, updated) in exercise_updated.iter_mut().enumerate() {
+                                if *updated {
+                                    if watch_event_sender
+                                        .send(WatchEvent::FileChange { exercise_ind })
+                                        .is_err()
+                                    {
+                                        break;
+                                    }
+
+                                    *updated = false;
+                                }
+                            }
+                        }
+                        Err(RecvTimeoutError::Disconnected) => break,
+                    }
+                }
+            })
+            .context("Failed to spawn a thread to debounce file changes")?;
+
+        Ok(Self {
+            error_sender,
+            update_sender,
+            exercise_names,
+        })
+    }
 }
 
 impl notify::EventHandler for NotifyEventHandler {
@@ -22,8 +78,8 @@ impl notify::EventHandler for NotifyEventHandler {
             Ok(v) => v,
             Err(e) => {
                 // An error occurs when the receiver is dropped.
-                // After dropping the receiver, the debouncer guard should also be dropped.
-                let _ = self.sender.send(WatchEvent::NotifyErr(e));
+                // After dropping the receiver, the watcher guard should also be dropped.
+                let _ = self.error_sender.send(WatchEvent::NotifyErr(e));
                 return;
             }
         };
@@ -32,6 +88,10 @@ impl notify::EventHandler for NotifyEventHandler {
             EventKind::Any => (),
             EventKind::Modify(modify_kind) => match modify_kind {
                 ModifyKind::Any | ModifyKind::Data(_) => (),
+                ModifyKind::Name(rename_mode) => match rename_mode {
+                    RenameMode::Any | RenameMode::To => (),
+                    RenameMode::From | RenameMode::Both | RenameMode::Other => return,
+                },
                 ModifyKind::Metadata(metadata_kind) => match metadata_kind {
                     MetadataKind::Any | MetadataKind::WriteTime => (),
                     MetadataKind::AccessTime
@@ -40,12 +100,17 @@ impl notify::EventHandler for NotifyEventHandler {
                     | MetadataKind::Extended
                     | MetadataKind::Other => return,
                 },
-                ModifyKind::Name(_) | ModifyKind::Other => return,
+                ModifyKind::Other => return,
             },
-            EventKind::Access(_)
-            | EventKind::Create(_)
-            | EventKind::Remove(_)
-            | EventKind::Other => return,
+            EventKind::Access(access_kind) => match access_kind {
+                AccessKind::Any => (),
+                AccessKind::Close(access_mode) => match access_mode {
+                    AccessMode::Any | AccessMode::Write => (),
+                    AccessMode::Execute | AccessMode::Read | AccessMode::Other => return,
+                },
+                AccessKind::Read | AccessKind::Open(_) | AccessKind::Other => return,
+            },
+            EventKind::Create(_) | EventKind::Remove(_) | EventKind::Other => return,
         }
 
         let _ = input_event
@@ -62,6 +127,6 @@ impl notify::EventHandler for NotifyEventHandler {
                     .iter()
                     .position(|exercise_name| *exercise_name == file_name_without_ext)
             })
-            .try_for_each(|exercise_ind| self.sender.send(WatchEvent::FileChange { exercise_ind }));
+            .try_for_each(|exercise_ind| self.update_sender.send(exercise_ind));
     }
 }