Implement recursive directory searching and directory monitoring

src/Services/LibraryManager.vala

@@ -1,44 +1,127 @@
 public class Music.LibraryManager : Object {
     public ListStore songs { get; construct; }
 
+    private List<FileMonitor> directory_monitors;
+    private Queue<File> unchecked_directories;
+    private HashTable<string, uint> position_by_uri;
+    private bool is_scanning = false;
+
     private static GLib.Once<LibraryManager> instance;
     public static unowned LibraryManager get_instance () {
         return instance.once (() => { return new LibraryManager (); });
     }
 
     construct {
         songs = new ListStore (typeof (AudioObject));
+        directory_monitors = new List<FileMonitor> ();
+        unchecked_directories = new Queue<File> ();
+        unchecked_directories.push_tail (File.new_for_path (Environment.get_user_special_dir (UserDirectory.MUSIC)));
+        position_by_uri = new HashTable<string, uint> (str_hash, str_equal);
+
         detect_audio_files.begin ();
     }
 
-    public async void detect_audio_files () throws Error {
-        File directory = File.new_for_path (Environment.get_user_special_dir (UserDirectory.MUSIC));
-        var enumerator = directory.enumerate_children (
-            "standard::*",
-            FileQueryInfoFlags.NOFOLLOW_SYMLINKS,
-            null
-        );
-
-        FileInfo info = null;
-        while ((info = enumerator.next_file (null)) != null) {
-            var file = directory.resolve_relative_path (info.get_name ());
-            if (info.get_file_type () == FileType.DIRECTORY) {
-                continue;
-            } else {
-                if (file.query_exists () && "audio" in ContentType.guess (file.get_uri (), null, null)) {
-                    var audio_object = new AudioObject (file.get_uri ());
-
-                    string? basename = file.get_basename ();
-
-                    if (basename != null) {
-                        audio_object.title = basename;
+    private void on_directory_change (File file, File? other_file, FileMonitorEvent event_type) {
+        uint position = Gtk.INVALID_LIST_POSITION;
+        if (file.get_uri () in position_by_uri) {
+            position = position_by_uri[file.get_uri ()];
+        }
+
+        switch (event_type) {
+            case DELETED:
+                if (position != Gtk.INVALID_LIST_POSITION) {
+                    songs.remove (position);
+                }
+                break;
+
+            case CHANGES_DONE_HINT:
+                if (position != Gtk.INVALID_LIST_POSITION) {
+                    songs.remove (position);
+                }
+
+                FileInfo file_info;
+                try {
+                    file_info = file.query_info ("standard::*", NONE);
+                } catch (Error e) {
+                    warning (e.message);
+                    return;
+                }
+
+                if (file_info.get_file_type () == FileType.DIRECTORY) {
+                    unchecked_directories.push_tail (file);
+                    detect_audio_files.begin ();
+                } else if (is_file_valid (file)) {
+                    songs.append (create_audio_object (file));
+                }
+
+                break;
+
+            default:
+                break;
+        }
+    }
+
+    public async void detect_audio_files () {
+        if (is_scanning) {
+            return;
+        }
+
+        is_scanning = true;
+
+        while (!unchecked_directories.is_empty ()) {
+            var directory = unchecked_directories.pop_head ();
+
+            try {
+                var directory_monitor = directory.monitor (NONE);
+                directory_monitor.changed.connect (on_directory_change);
+                directory_monitors.append (directory_monitor);
+            } catch (Error e) {
+                warning ("Failed to monitor directory %s: %s", directory.get_path (), e.message);
+            }
+
+            try {
+                var enumerator = directory.enumerate_children (
+                    "standard::*",
+                    FileQueryInfoFlags.NOFOLLOW_SYMLINKS,
+                    null
+                );
+
+                FileInfo info = null;
+                while ((info = enumerator.next_file (null)) != null) {
+                    var file = directory.resolve_relative_path (info.get_name ());
+                    if (info.get_file_type () == FileType.DIRECTORY) {
+                        unchecked_directories.push_tail (file);
+                        continue;
                     } else {
-                        audio_object.title = audio_object.uri;
+                        if (is_file_valid (file)) {
+                            songs.append (create_audio_object (file));
+                            position_by_uri[file.get_uri ()] = songs.get_n_items () - 1;
+                        }
                     }
-
-                    songs.append (audio_object);
                 }
+            } catch (Error e) {
+                warning ("Failed to get children of directory %s: %s", directory.get_path (), e.message);
             }
         }
+
+        is_scanning = false;
+    }
+
+    private bool is_file_valid (File file) {
+        return file.query_exists () && "audio" in ContentType.guess (file.get_uri (), null, null);
+    }
+
+    private AudioObject create_audio_object (File file) {
+        var audio_object = new AudioObject (file.get_uri ());
+
+        string? basename = file.get_basename ();
+
+        if (basename != null) {
+            audio_object.title = basename;
+        } else {
+            audio_object.title = audio_object.uri;
+        }
+
+        return audio_object;
     }
 }