gui/playlist: Support drag and drop for adding tracks to playlists

Dragging onto a sidebar row without a valid playlist will prompt the
user to create a new playlist.  I could probably add a "New Playlist"
row at some point, but this is easier for now :)

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

gui/playlist.c

@@ -207,6 +207,31 @@ void __gui_playlist_row_expanded(GtkTreeView *treeview, GtkTreeIter *iter,
 	gui_sidebar_filter_row_expanded(iter, true);
 }
 
+void __gui_playlist_drag_data_received(GtkTreeView *treeview, GdkDragContext *context,
+				       gint x, gint y, GtkSelectionData *data,
+				       guint info, guint time, gpointer user_data)
+{
+	struct playlist *playlist;
+	GtkTreeIter iter;
+
+	if (gui_sidebar_iter_from_xy(x, y, &iter))
+		playlist = gui_sidebar_iter_playlist(&iter);
+	if (!playlist)
+		playlist = gui_pl_user_add_dialog();
+	if (!playlist)
+		goto out;
+
+	if (playlist == playlist_lookup(PL_SYSTEM, "Collection") &&
+	    gui_model_get_playlist() == playlist_lookup(PL_SYSTEM, "Hidden"))
+		__gui_playlist_delete(NULL, NULL);
+	else if (playlist != playlist_lookup(PL_SYSTEM, "History"))
+		__gui_playlist_add_selected_to(playlist);
+
+out:
+	g_signal_stop_emission_by_name(treeview, "drag_data_received");
+	gtk_drag_finish(context, true, true, time);
+}
+
 bool __gui_playlist_init_idle()
 {
 	struct playlist *playlist = playlist_current();

gui/sidebar.c

@@ -256,6 +256,10 @@ void gui_sidebar_init()
 	GtkTreeSelection *selection;
 	GtkTreeIter iter;
 
+	gtk_tree_view_enable_model_drag_dest(gui_sidebar_treeview(),
+					gui_model_drag_targets, gui_model_n_targets,
+					GDK_ACTION_MOVE);
+
 	if (!gui_sidebar_iter_first(&iter)) {
 		__gui_sidebar_add_header(&iter, "Playlists", "emblem-documents");
 		__gui_sidebar_add_header(&iter, "Dynamic",   "emblem-generic");

share/ocarina/ocarina.ui

@@ -768,6 +768,8 @@ audio-volume-medium</property>
                         <property name="search_column">1</property>
                         <property name="enable_tree_lines">True</property>
                         <signal name="button-press-event" handler="__gui_sidebar_button_press" swapped="no"/>
+                        <signal name="drag-data-received" handler="__gui_playlist_drag_data_received" swapped="no"/>
+                        <signal name="drag-drop" handler="__gui_treeview_drag_drop" swapped="no"/>
                         <signal name="key-press-event" handler="__gui_sidebar_keypress" swapped="no"/>
                         <signal name="row-activated" handler="__gui_playlist_row_activated" swapped="no"/>
                         <signal name="row-collapsed" handler="__gui_playlist_row_collapsed" swapped="no"/>