gtauri: enable fast mtime-diff filesystem watcher on Android (adds & deletes reflected in ~1s)

harnesses/gtauri/src/lib.rs

@@ -1141,6 +1141,47 @@ fn spawn_fs_watcher(tx: mpsc::Sender<WEvent>) {
     });
 }
 
+fn collect_watched_dirs(roots: &[PathBuf]) -> HashSet<PathBuf> {
+    let mut dirs = HashSet::new();
+    for r in roots {
+        if r.is_dir() {
+            dirs.insert(r.clone());
+            if let Ok(rd) = std::fs::read_dir(r) {
+                for ent in rd.flatten() {
+                    if let Ok(ft) = ent.file_type() {
+                        if ft.is_dir() {
+                            let p = ent.path();
+                            if !p.file_name().map_or(false, |n| n.to_string_lossy().starts_with('.')) {
+                                dirs.insert(p);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+    if let Ok(mut conn) = db::open(&db::db_path()) {
+        if let Ok(entries) = db::list_entries(&mut conn) {
+            for e in entries {
+                if let Some(parent) = std::path::Path::new(&e.path).parent() {
+                    dirs.insert(parent.to_path_buf());
+                }
+            }
+        }
+    }
+    dirs
+}
+
+fn fast_dir_sig(dirs: &HashSet<PathBuf>) -> HashMap<PathBuf, i64> {
+    let mut out = HashMap::new();
+    for d in dirs {
+        if let Ok(m) = std::fs::metadata(d) {
+            out.insert(d.clone(), mtime_ns(&m));
+        }
+    }
+    out
+}
+
 /// Diff two dir-mtime signatures: dirs added, removed, or changed.
 fn changed_dirs(
     old: &HashMap<PathBuf, i64>,
@@ -1181,15 +1222,13 @@ fn watch_files(app: tauri::AppHandle) {
     });
     #[cfg(not(target_os = "android"))]
     spawn_fs_watcher(tx);
-    // Desktop only: the mtime-diff machinery. On Android the MediaStore
-    // URI payloads ARE the change signal (exact paths, no scanning),
-    // and diffing would cost a 10k-entry readdir every second on the
-    // phone — pure overhead for what the payloads already deliver.
-    #[cfg(not(target_os = "android"))]
-    let mut sig: HashMap<PathBuf, i64> = HashMap::new();
-    #[cfg(not(target_os = "android"))]
+
+    let mut watched_dirs = collect_watched_dirs(&scan::roots());
+    let mut sig = fast_dir_sig(&watched_dirs);
     let mut baseline = true;
+    let mut last_dir_refresh = std::time::Instant::now();
     let mut last_full = std::time::Instant::now();
+
     loop {
         let woke = match rx.recv_timeout(std::time::Duration::from_secs(1)) {
             Ok(e) => Some(e),
@@ -1198,7 +1237,6 @@ fn watch_files(app: tauri::AppHandle) {
         };
         let do_full = matches!(woke, Some(WEvent::Full));
         if let Some(WEvent::Fs) = woke {
-            // Coalesce the burst, let the write settle, coalesce again.
             while rx.try_recv().is_ok() {}
             std::thread::sleep(std::time::Duration::from_millis(600));
             while rx.try_recv().is_ok() {}
@@ -1206,40 +1244,30 @@ fn watch_files(app: tauri::AppHandle) {
         if do_full {
             tr("watch: full rescan (5min)");
             rescan(&app);
+            watched_dirs = collect_watched_dirs(&scan::roots());
+            sig = fast_dir_sig(&watched_dirs);
             last_full = std::time::Instant::now();
             continue;
         }
+
+        // Refresh watched dirs periodically (every 30s) to pick up new subdirs
+        if last_dir_refresh.elapsed() >= std::time::Duration::from_secs(30) {
+            watched_dirs = collect_watched_dirs(&scan::roots());
+            last_dir_refresh = std::time::Instant::now();
+        }
+
         // MediaStore event path (Android): MainActivity drops a one-line
         // payload per changed URI and wakes us via nativeFsChange.
-        // Consume on EVERY tick (single read_dir of our own app dir —
-        // no-op when empty, so a lost JNI wake self-heals within the 1 s
-        // backstop) — but NOT while a full rescan is mid-walk: those
-        // payloads wait as files and apply after the walk's apply, so
-        // mid-walk deletions win over the walk's stale snapshot.
-        let applied_ms = if RESCANNING.load(std::sync::atomic::Ordering::Relaxed) {
+        let _applied_ms = if RESCANNING.load(std::sync::atomic::Ordering::Relaxed) {
             false
         } else {
             apply_mediasotre_payload(&app)
         };
-        // Android fallback: the OS said "media changed" but no payload
-        // arrived (permission missing, scanner gap, or the payload was
-        // parked behind a rescan). Full rescan, throttled — the
-        // degraded path, not the common one. Parking behind a rescan
-        // also counts as "not applied": the rescan's next 1 s tick
-        // re-evaluates and either drains the payload or rescans.
-        #[cfg(target_os = "android")]
-        if matches!(woke, Some(WEvent::Fs)) && !applied_ms
-            && last_full.elapsed() >= std::time::Duration::from_secs(30)
-        {
-            tr("watch: full rescan (event, no payload)");
-            rescan(&app);
-            last_full = std::time::Instant::now();
-            continue;
-        }
-        // Desktop: diff the dir-mtime signature, rescan changed subtrees.
-        #[cfg(not(target_os = "android"))]
-        {
-            let next = dir_sig(&scan::roots());
+
+        // Fast directory mtime-diff watch (Android and desktop): catches
+        // out-of-band filesystem adds/removes within ~1 second without
+        // scanning 10k files.
+        let next = fast_dir_sig(&watched_dirs);
         let changed = if baseline {
             baseline = false;
             Vec::new()
@@ -1247,11 +1275,12 @@ fn watch_files(app: tauri::AppHandle) {
             changed_dirs(&sig, &next)
         };
         sig = next;
-            if changed.is_empty() {
-                continue;
-            }
+
+        if !changed.is_empty() {
             tr(&format!("watch: {} changed dir(s)", changed.len()));
             rescan_subtrees(&app, &changed);
+            watched_dirs = collect_watched_dirs(&scan::roots());
+            sig = fast_dir_sig(&watched_dirs);
         }
     }
 }