menu_view: generalized data-model-update utility

The utility simplifies the synchronization of a list-based data model
from an XML structure.

repos/gems/src/app/menu_view/list_model_from_xml.h

@@ -0,0 +1,138 @@
+/*
+ * \brief  Utility for updating an internal data model from an XML structure
+ * \author Norman Feske
+ * \date   2017-08-09
+ */
+
+/*
+ * Copyright (C) 2017 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+#ifndef _INCLUDE__UTIL__LIST_MODEL_FROM_XML_H_
+#define _INCLUDE__UTIL__LIST_MODEL_FROM_XML_H_
+
+#include <util/xml_node.h>
+
+namespace Genode {
+
+	template <typename POLICY>
+	static inline void
+	update_list_model_from_xml(POLICY                         &policy,
+	                           List<typename POLICY::Element> &list,
+	                           Xml_node                        node);
+
+	template <typename> struct List_model_update_policy;
+}
+
+
+/**
+ * Policy interface to be supplied to 'update_list_model_from_xml'
+ *
+ * \param ELEM  element type, must be a list element
+ *
+ * This class template is merely a blue print of a policy to document the
+ * interface.
+ */
+template <typename ELEM>
+struct Genode::List_model_update_policy
+{
+	/*
+	 * Types that need to be supplied by the policy implementation
+	 */
+	typedef ELEM Element;
+
+	struct Unknown_element_type : Exception { };
+
+	/**
+	 * Destroy element
+	 *
+	 * When this function is called, the element is no longer contained
+	 * in the model's list.
+	 */
+	void destroy_element(ELEM &elem);
+
+	/**
+	 * Create element of the type given in the 'elem_node'
+	 *
+	 * \throw Unknown_element_type
+	 */
+	ELEM &create_element(Xml_node elem_node);
+
+	/**
+	 * Import element properties from XML node
+	 */
+	void update_element(ELEM &elem, Xml_node elem_node);
+
+	/**
+	 * Return true if element corresponds to XML node
+	 */
+	static bool element_matches_xml_node(Element const &, Xml_node);
+
+	/**
+	 * Return true if XML node should be imported
+	 *
+	 * This method allows the policy to disregard certain XML node types from
+	 * building the data model.
+	 */
+	static bool node_is_element(Xml_node node) { return true; }
+};
+
+
+/**
+ * Update 'list' data model according to XML structure 'node'
+ *
+ * \throw Unknown_element_type
+ */
+template <typename POLICY>
+static inline void
+Genode::update_list_model_from_xml(POLICY                         &policy,
+                                   List<typename POLICY::Element> &list,
+                                   Xml_node                        node)
+{
+	typedef typename POLICY::Element Element;
+
+	List<Element> updated_list;
+
+	Element *last_updated = nullptr; /* used for appending to 'updated_list' */
+
+	node.for_each_sub_node([&] (Xml_node sub_node) {
+
+		/* skip XML nodes that are unrelated to the data model */
+		if (!policy.node_is_element(sub_node))
+			return;
+
+		/* look up corresponding element in original list */
+		Element *curr = list.first();
+		while (curr && !policy.element_matches_xml_node(*curr, sub_node))
+			curr = curr->next();
+
+		/* consume existing element or create new one */
+		if (curr) {
+			list.remove(curr);
+		} else {
+			/* \throw Unknown_element_type */
+			curr = &policy.create_element(sub_node);
+		}
+
+		/* append current element to 'updated_list' */
+		updated_list.insert(curr, last_updated);
+		last_updated = curr;
+
+		policy.update_element(*curr, sub_node);
+	});
+
+	/* remove stale elements */
+	Element *next = nullptr;
+	for (Element *e = list.first(); e; e = next) {
+		next = e->next();
+		policy.destroy_element(*e);
+	}
+
+	/* use 'updated_list' list new data model */
+	list = updated_list;
+}
+
+#endif /* _INCLUDE__UTIL__LIST_MODEL_FROM_XML_H_ */