shell: Make the "home" button act as a "previous" button

Keep history of the visited panels, when navigating between
them through links, or activated through the shell's menu items,
and go back to the overview when the history is empty.

https://bugzilla.gnome.org/show_bug.cgi?id=643322

shell/cc-window.c

@@ -73,13 +73,14 @@ struct _CcWindowPrivate
   GtkWidget  *main_vbox;
   GtkWidget  *scrolled_window;
   GtkWidget  *search_scrolled;
-  GtkWidget  *home_button;
+  GtkWidget  *previous_button;
   GtkWidget  *top_right_box;
   GtkWidget  *search_entry;
   GtkWidget  *lock_button;
   GtkWidget  *current_panel_box;
   GtkWidget  *current_panel;
   char       *current_panel_id;
+  GQueue     *previous_panels;
 
   GPtrArray  *custom_widgets;
 
@@ -101,6 +102,11 @@ enum
   PROP_ACTIVE_PANEL
 };
 
+static gboolean cc_window_set_active_panel_from_id (CcShell      *shell,
+                                                    const gchar  *start_id,
+                                                    const gchar **argv,
+                                                    GError      **err);
+
 /* Notebook helpers */
 static GtkWidget *
 notebook_get_selected_page (GtkWidget *notebook)
@@ -240,6 +246,24 @@ _shell_remove_all_custom_widgets (CcWindowPrivate *priv)
   g_ptr_array_set_size (priv->custom_widgets, 0);
 }
 
+static void
+add_current_panel_to_history (CcShell    *shell,
+                              const char *start_id)
+{
+  CcWindowPrivate *priv;
+
+  g_return_if_fail (start_id != NULL);
+
+  priv = CC_WINDOW (shell)->priv;
+
+  if (!priv->current_panel_id ||
+      g_strcmp0 (priv->current_panel_id, start_id) == 0)
+    return;
+
+  g_queue_push_head (priv->previous_panels, g_strdup (priv->current_panel_id));
+  g_debug ("Added '%s' to the previous panels", priv->current_panel_id);
+}
+
 static void
 shell_show_overview_page (CcWindow *self)
 {
@@ -253,6 +277,10 @@ shell_show_overview_page (CcWindow *self)
   priv->current_panel_box = NULL;
   g_clear_pointer (&priv->current_panel_id, g_free);
 
+  /* Clear the panel history */
+  g_queue_free_full (self->priv->previous_panels, g_free);
+  self->priv->previous_panels = g_queue_new ();
+
   /* clear the search text */
   g_free (priv->filter_string);
   priv->filter_string = g_strdup ("");
@@ -294,7 +322,7 @@ item_activated_cb (CcShellCategoryView *view,
                    gchar               *id,
                    CcWindow            *shell)
 {
-  cc_shell_set_active_panel_from_id (CC_SHELL (shell), id, NULL, NULL);
+  cc_window_set_active_panel_from_id (CC_SHELL (shell), id, NULL, NULL);
 }
 
 static gboolean
@@ -695,7 +723,7 @@ on_search_row_activated (GtkTreeView       *treeview,
                       -1);
 
   if (id)
-    cc_shell_set_active_panel_from_id (CC_SHELL (shell), id, NULL, NULL);
+    cc_window_set_active_panel_from_id (CC_SHELL (shell), id, NULL, NULL);
 
   gtk_tree_selection_unselect_all (selection);
 
@@ -876,10 +904,20 @@ setup_model (CcWindow *shell)
 }
 
 static void
-home_button_clicked_cb (GtkButton *button,
+previous_button_clicked_cb (GtkButton *button,
-                        CcWindow  *shell)
+                            CcWindow  *shell)
 {
-  shell_show_overview_page (shell);
+  g_debug ("Num previous panels? %d", g_queue_get_length (shell->priv->previous_panels));
+  if (g_queue_is_empty (shell->priv->previous_panels)) {
+    shell_show_overview_page (shell);
+  } else {
+    char *panel_name;
+
+    panel_name = g_queue_pop_head (shell->priv->previous_panels);
+    g_debug ("About to go to previous panel '%s'", panel_name);
+    cc_window_set_active_panel_from_id (CC_SHELL (shell), panel_name, NULL, NULL);
+    g_free (panel_name);
+  }
 }
 
 static void
@@ -897,7 +935,7 @@ notebook_page_notify_cb (GtkNotebook *notebook,
 
   if (child == priv->scrolled_window || child == priv->search_scrolled)
     {
-      gtk_widget_hide (priv->home_button);
+      gtk_widget_hide (priv->previous_button);
       gtk_widget_show (priv->search_entry);
       gtk_widget_hide (priv->lock_button);
 
@@ -908,7 +946,7 @@ notebook_page_notify_cb (GtkNotebook *notebook,
     }
   else
     {
-      gtk_widget_show (priv->home_button);
+      gtk_widget_show (priv->previous_button);
       gtk_widget_hide (priv->search_entry);
       /* set the scrolled window small so that it doesn't force
          the window to be larger than this panel */
@@ -935,10 +973,10 @@ _shell_embed_widget_in_header (CcShell      *shell,
 
 /* CcShell implementation */
 static gboolean
-_shell_set_active_panel_from_id (CcShell      *shell,
+cc_window_set_active_panel_from_id (CcShell      *shell,
-                                 const gchar  *start_id,
+                                    const gchar  *start_id,
-                                 const gchar **argv,
+                                    const gchar **argv,
-                                 GError      **err)
+                                    GError      **err)
 {
   GtkTreeIter iter;
   gboolean iter_valid;
@@ -1021,6 +1059,16 @@ _shell_set_active_panel_from_id (CcShell      *shell,
   return TRUE;
 }
 
+static gboolean
+_shell_set_active_panel_from_id (CcShell      *shell,
+                                 const gchar  *start_id,
+                                 const gchar **argv,
+                                 GError      **err)
+{
+  add_current_panel_to_history (shell, start_id);
+  return cc_window_set_active_panel_from_id (shell, start_id, argv, err);
+}
+
 static GtkWidget *
 _shell_get_toplevel (CcShell *shell)
 {
@@ -1103,6 +1151,12 @@ cc_window_dispose (GObject *object)
   g_clear_object (&priv->search_filter);
   g_clear_object (&priv->active_panel);
 
+  if (priv->previous_panels)
+    {
+      g_queue_free_full (priv->previous_panels, g_free);
+      priv->previous_panels = NULL;
+    }
+
   G_OBJECT_CLASS (cc_window_parent_class)->dispose (object);
 }
 
@@ -1378,14 +1432,14 @@ create_header (CcWindow *self)
 
   image = gtk_image_new_from_icon_name ("go-previous-symbolic", GTK_ICON_SIZE_MENU);
   gtk_widget_show (image);
-  priv->home_button = button = gtk_button_new ();
+  priv->previous_button = button = gtk_button_new ();
   gtk_button_set_image (GTK_BUTTON (button), image);
   gtk_widget_set_no_show_all (button, TRUE);
   accessible = gtk_widget_get_accessible (button);
   atk_object_set_name (accessible, _("All Settings"));
   gd_header_bar_pack_start (GD_HEADER_BAR (priv->header), button);
-  g_signal_connect (button, "clicked", G_CALLBACK (home_button_clicked_cb), self);
+  g_signal_connect (button, "clicked", G_CALLBACK (previous_button_clicked_cb), self);
-  context = gtk_widget_get_style_context (priv->home_button);
+  context = gtk_widget_get_style_context (priv->previous_button);
   gtk_style_context_add_class (context, "image-button");
 
   priv->top_right_box = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 0);
@@ -1451,6 +1505,8 @@ cc_window_init (CcWindow *self)
 
   create_window (self);
 
+  self->priv->previous_panels = g_queue_new ();
+
   /* keep a list of custom widgets to unload on panel change */
   priv->custom_widgets = g_ptr_array_new_with_free_func ((GDestroyNotify) g_object_unref);