view: add view_for_each_reverse() macro

include/view.h

@@ -386,6 +386,22 @@ bool view_matches_query(struct view *view, struct view_query *query);
 	     view;                                    \
 	     view = view_next(head, view, criteria))
 
+/**
+ * for_each_view_reverse() - iterate over all views which match criteria
+ * @view: Iterator.
+ * @head: Head of list to iterate over.
+ * @criteria: Criteria to match against.
+ * Example:
+ *	struct view *view;
+ *	for_each_view_reverse(view, &server->views, LAB_VIEW_CRITERIA_NONE) {
+ *		printf("%s\n", view_get_string_prop(view, "app_id"));
+ *	}
+ */
+#define for_each_view_reverse(view, head, criteria)   \
+	for (view = view_prev(head, NULL, criteria);  \
+	     view;                                    \
+	     view = view_prev(head, view, criteria))
+
 /**
  * view_next() - Get next view which matches criteria.
  * @head: Head of list to iterate over.
@@ -398,6 +414,18 @@ bool view_matches_query(struct view *view, struct view_query *query);
 struct view *view_next(struct wl_list *head, struct view *view,
 	enum lab_view_criteria criteria);
 
+/**
+ * view_prev() - Get previous view which matches criteria.
+ * @head: Head of list to iterate over.
+ * @view: Current view from which to find the previous one. If NULL is provided
+ *        as the view argument, the end of the list will be used.
+ * @criteria: Criteria to match against.
+ *
+ * Returns NULL if there are no views matching the criteria.
+ */
+struct view *view_prev(struct wl_list *head, struct view *view,
+	enum lab_view_criteria criteria);
+
 /*
  * Same as `view_next()` except that they iterate one whole cycle rather than
  * stopping at the list-head

src/view.c

@@ -269,6 +269,22 @@ view_next(struct wl_list *head, struct view *view, enum lab_view_criteria criter
 	return NULL;
 }
 
+struct view *
+view_prev(struct wl_list *head, struct view *view, enum lab_view_criteria criteria)
+{
+	assert(head);
+
+	struct wl_list *elm = view ? &view->link : head;
+
+	for (elm = elm->prev; elm != head; elm = elm->prev) {
+		view = wl_container_of(elm, view, link);
+		if (matches_criteria(view, criteria)) {
+			return view;
+		}
+	}
+	return NULL;
+}
+
 struct view *
 view_next_no_head_stop(struct wl_list *head, struct view *from,
 		enum lab_view_criteria criteria)