fix(application): fix file loop and use of GTK object after lifecycle

Swappy tried to access Gtk data after the end of the mainloop and the
file save routine had infinite recursion

src/application.c

@@ -179,6 +179,13 @@ static void save_state_to_file_or_folder(struct swappy_state *state,
   g_object_unref(pixbuf);
 }
 
+void on_destroy(GtkApplication *application, gpointer data) {
+  struct swappy_state *state = (struct swappy_state *)data;
+  if (state->output_file != NULL) {
+    save_state_to_file_or_folder(state, state->output_file);
+  }
+}
+
 void brush_clicked_handler(GtkWidget *widget, struct swappy_state *state) {
   switch_mode_to_brush(state);
 }
@@ -200,9 +207,6 @@ void arrow_clicked_handler(GtkWidget *widget, struct swappy_state *state) {
 }
 
 void application_finish(struct swappy_state *state) {
-  if (state->output_file != NULL) {
-    save_state_to_file_or_folder(state, state->output_file);
-  }
   paint_free_all(state);
   buffer_free_all(state);
   cairo_surface_destroy(state->cairo_surface);
@@ -519,6 +523,8 @@ static bool load_layout(struct swappy_state *state) {
   GtkWindow *window =
       GTK_WINDOW(gtk_builder_get_object(builder, "paint-window"));
 
+  g_signal_connect(window, "destroy", G_CALLBACK(on_destroy), state);
+
   state->ui->undo = GTK_BUTTON(gtk_builder_get_object(builder, "undo-button"));
   state->ui->redo = GTK_BUTTON(gtk_builder_get_object(builder, "redo-button"));
 

src/pixbuf.c

@@ -13,18 +13,8 @@ GdkPixbuf *pixbuf_get_from_state(struct swappy_state *state) {
   return pixbuf;
 }
 
-void pixbuf_save_state_to_folder(GdkPixbuf *pixbuf, char *folder) {
+static void write_file(GdkPixbuf *pixbuf, char *path) {
   GError *error = NULL;
-
-  time_t current_time;
-  char *c_time_string;
-
-  time(&current_time);
-
-  c_time_string = ctime(&current_time);
-  c_time_string[strlen(c_time_string) - 1] = '\0';
-  char path[MAX_PATH];
-  snprintf(path, MAX_PATH, "%s/%s %s.png", folder, "Swappshot", c_time_string);
   gdk_pixbuf_savev(pixbuf, path, "png", NULL, NULL, &error);
 
   if (error != NULL) {
@@ -40,6 +30,19 @@ void pixbuf_save_state_to_folder(GdkPixbuf *pixbuf, char *folder) {
   g_free(message);
 }
 
+void pixbuf_save_state_to_folder(GdkPixbuf *pixbuf, char *folder) {
+  time_t current_time;
+  char *c_time_string;
+
+  time(&current_time);
+
+  c_time_string = ctime(&current_time);
+  c_time_string[strlen(c_time_string) - 1] = '\0';
+  char path[MAX_PATH];
+  snprintf(path, MAX_PATH, "%s/%s %s.png", folder, "Swappshot", c_time_string);
+  write_file(pixbuf, path);
+}
+
 void pixbuf_save_to_stdout(GdkPixbuf *pixbuf) {
   GOutputStream *out;
   GError *error = NULL;
@@ -61,6 +64,6 @@ void pixbuf_save_to_file(GdkPixbuf *pixbuf, char *file) {
   if (g_strcmp0(file, "-") == 0) {
     pixbuf_save_to_stdout(pixbuf);
   } else {
-    pixbuf_save_to_file(pixbuf, file);
+    write_file(pixbuf, file);
   }
-}
+}