utils: Add utility function for creating activate signal and shortcuts

The current way of adding activation shortcuts is cumbersome,
as it is a for-loop pasted in the middle of class initializers.
The utility function addresses this problem by simply allowing us
to declaratively add these shortcuts with minimal effort.

Furthermore, the implementation is also simpler, thanks to the
`gtk_widget_class_add_binding_signal()` wrapper function.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/747>

src/utils/gcal-utils.c

@@ -1449,3 +1449,44 @@ gcal_get_email_from_mailto_uri (const gchar *mailto_uri)
 
   return address;
 }
+
+/**
+ * gcal_create_activate_signal_shortcuts:
+ * @widget_class: the class to add the bindings to
+ * @widget_type: the type this signal pertains to
+ *
+ * Adds activate signal and shortcuts to the desired widget during class instantiation.
+ *
+ * The primary use case is for custom widgets desiring to have activation functionality.
+ *
+ * Returns: the signal ID
+ */
+guint
+gcal_create_activate_signal_and_shortcuts (GtkWidgetClass *widget_class,
+                                           GType           widget_type)
+{
+  const guint activate_keyvals[] = {
+    GDK_KEY_space,
+    GDK_KEY_KP_Space,
+    GDK_KEY_Return,
+    GDK_KEY_ISO_Enter,
+    GDK_KEY_KP_Enter,
+  };
+
+  guint signal_id =
+    g_signal_new ("activate",
+                  widget_type,
+                  G_SIGNAL_RUN_FIRST | G_SIGNAL_ACTION,
+                  0,
+                  NULL, NULL,
+                  g_cclosure_marshal_VOID__VOID,
+                  G_TYPE_NONE,
+                  0);
+
+  gtk_widget_class_set_activate_signal (widget_class, signal_id);
+
+  for (size_t i = 0; i < G_N_ELEMENTS (activate_keyvals); i++)
+    gtk_widget_class_add_binding_signal (widget_class, activate_keyvals[i], 0, "activate", NULL);
+
+  return signal_id;
+}

src/utils/gcal-utils.h

@@ -141,4 +141,7 @@ SoupSession *        gcal_create_soup_session                    (void);
 GListModel *         gcal_create_writable_calendars_model        (GcalManager        *manager);
 
 const gchar *        gcal_get_email_from_mailto_uri              (const gchar        *mailto_uri);
+
+guint                gcal_create_activate_signal_and_shortcuts   (GtkWidgetClass *widget_class,
+                                                                  GType           widget_type);
 #endif /* __GCAL_UTILS_H__ */