libmalcontent-ui: Cache and diff the app list when rebuilding it

Instead of removing all the entries in the list store when the set of
installed apps is updated, diff the old and new lists so that removed
apps can be selectively removed from the list store, and added apps can
be selectively added.

This means that we can (in subsequent commits) reload the app list less
conservatively, as doing so will no longer remove in-progress user
modifications to the set of blocked apps. Modifications are still only
saved when the restrict applications dialogue is closed.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

Helps: #18, #28

libmalcontent-ui/restrict-applications-selector.c

@@ -61,6 +61,7 @@ struct _MctRestrictApplicationsSelector
 
   GtkListBox *listbox;
 
+  GList *cached_apps;  /* (nullable) (owned) (element-type GAppInfo) */
   GListStore *apps;  /* (owned) */
   GAppInfoMonitor *app_info_monitor;  /* (owned) */
   gulong app_info_monitor_changed_id;
@@ -151,6 +152,7 @@ mct_restrict_applications_selector_dispose (GObject *object)
 
   g_clear_pointer (&self->blocklisted_apps, g_hash_table_unref);
   g_clear_object (&self->apps);
+  g_clear_list (&self->cached_apps, g_object_unref);
 
   if (self->app_info_monitor != NULL && self->app_info_monitor_changed_id != 0)
     {
@@ -225,6 +227,7 @@ mct_restrict_applications_selector_init (MctRestrictApplicationsSelector *self)
   gtk_widget_init_template (GTK_WIDGET (self));
 
   self->apps = g_list_store_new (G_TYPE_APP_INFO);
+  self->cached_apps = NULL;
 
   self->app_info_monitor = g_app_info_monitor_get ();
   self->app_info_monitor_changed_id =
@@ -392,15 +395,68 @@ app_compare_id_length_cb (gconstpointer a,
     return id_a_len - id_b_len;
 }
 
+/* Elements in @added_out and @removed_out are valid as long as @old_apps and
+ * @new_apps are valid.
+ *
+ * Both lists have to be sorted the same before calling this function. */
+static void
+diff_app_lists (GList      *old_apps,
+                GList      *new_apps,
+                GPtrArray **added_out,
+                GPtrArray **removed_out)
+{
+  g_autoptr(GPtrArray) added = g_ptr_array_new_with_free_func (NULL);
+  g_autoptr(GPtrArray) removed = g_ptr_array_new_with_free_func (NULL);
+  GList *o, *n;
+
+  g_return_if_fail (added_out != NULL);
+  g_return_if_fail (removed_out != NULL);
+
+  for (o = old_apps, n = new_apps; o != NULL || n != NULL;)
+    {
+      int comparison;
+
+      if (o == NULL)
+        comparison = 1;
+      else if (n == NULL)
+        comparison = -1;
+      else
+        comparison = app_compare_id_length_cb (o->data, n->data);
+
+      if (comparison < 0)
+        {
+          g_ptr_array_add (removed, o->data);
+          o = o->next;
+        }
+      else if (comparison > 0)
+        {
+          g_ptr_array_add (added, n->data);
+          n = n->next;
+        }
+      else
+        {
+          o = o->next;
+          n = n->next;
+        }
+    }
+
+  *added_out = g_steal_pointer (&added);
+  *removed_out = g_steal_pointer (&removed);
+}
+
+/* This is quite expensive to call, as there’s no way to avoid calling
+ * g_app_info_get_all() to see if anything’s changed; and that’s quite expensive. */
 static void
 reload_apps (MctRestrictApplicationsSelector *self)
 {
-  g_autolist(GAppInfo) apps = NULL;
+  g_autolist(GAppInfo) old_apps = NULL;
-  GList *iter;
+  g_autolist(GAppInfo) new_apps = NULL;
+  g_autoptr(GPtrArray) added_apps = NULL, removed_apps = NULL;
   g_autoptr(GHashTable) seen_flatpak_ids = NULL;
   g_autoptr(GHashTable) seen_executables = NULL;
 
-  apps = g_app_info_get_all ();
+  old_apps = g_steal_pointer (&self->cached_apps);
+  new_apps = g_app_info_get_all ();
 
   /* Sort the apps by increasing length of #GAppInfo ID. When coupled with the
    * deduplication of flatpak IDs and executable paths, below, this should ensure that we
@@ -409,20 +465,46 @@ reload_apps (MctRestrictApplicationsSelector *self)
    *
    * This is designed to avoid listing all the components of LibreOffice for example,
    * which all share an app ID and hence have the same entry in the parental controls
-   * app filter. */
+   * app filter.
-  apps = g_list_sort (apps, app_compare_id_length_cb);
+   *
+   * Then diff the old and new lists so that the code below doesn’t end up
+   * removing more rows than are necessary, and hence potentially losing
+   * in-progress user input. */
+  new_apps = g_list_sort (new_apps, app_compare_id_length_cb);
+  diff_app_lists (old_apps, new_apps, &added_apps, &removed_apps);
+
+  g_debug ("%s: Diffed old and new app lists: %u apps added, %u apps removed",
+           G_STRFUNC, added_apps->len, removed_apps->len);
+
   seen_flatpak_ids = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
   seen_executables = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
 
-  g_list_store_remove_all (self->apps);
+  /* Remove items first. */
-
+  for (guint i = 0; i < removed_apps->len; i++)
-  for (iter = apps; iter; iter = iter->next)
     {
-      GAppInfo *app;
+      GAppInfo *app = removed_apps->pdata[i];
+      guint pos;
+      gboolean found;
+
+      found = g_list_store_find_with_equal_func (self->apps, app,
+                                                 (GEqualFunc) g_app_info_equal, &pos);
+
+      /* The app being removed may have not passed the condition checks below
+       * to have been added to self->apps. */
+      if (!found)
+        continue;
+
+      g_debug ("Removing app ‘%s’", g_app_info_get_id (app));
+      g_list_store_remove (self->apps, pos);
+    }
+
+  /* Now add the new items. */
+  for (guint i = 0; i < added_apps->len; i++)
+    {
+      GAppInfo *app = added_apps->pdata[i];
       const gchar *app_name;
       const gchar * const *supported_types;
 
-      app = iter->data;
       app_name = g_app_info_get_name (app);
 
       supported_types = g_app_info_get_supported_types (app);
@@ -492,6 +574,9 @@ reload_apps (MctRestrictApplicationsSelector *self)
                                   compare_app_info_cb,
                                   self);
     }
+
+  /* Update the cache for next time. */
+  self->cached_apps = g_steal_pointer (&new_apps);
 }
 
 static void