added observer to repository and updated tests

include/matador/object/observer.hpp

@@ -0,0 +1,124 @@
+#ifndef MATADOR_OBSERVER_HPP
+#define MATADOR_OBSERVER_HPP
+
+#include <typeindex>
+
+namespace matador::object {
+class repository_node;
+
+class abstract_observer {
+public:
+  virtual ~abstract_observer() = default;
+
+protected:
+  /**
+   * Constructs a basic_object_store_observer for the
+   * give std::type_index.
+   *
+   * @param ti type index of the observer
+   */
+  explicit abstract_observer(const std::type_index &ti);
+
+public:
+  /**
+ * Return the type index of the observer.
+ *
+ * @return The type index of the observer.
+ */
+  [[nodiscard]] const std::type_index& index() const;
+
+private:
+  std::type_index type_index_;
+};
+
+/**
+ * @class observer
+ * @tparam Type Type of the observer
+ * @brief Base class for typed observer classes
+ *
+ * When interested in observe
+ * - attach (prototype_node)
+ * - detach (prototype_node)
+ * - insert (an object)
+ * - update (an object)
+ * - delete (an object)
+ * actions an observer class instance must be
+ * registered within the repository.
+ * Use this class as a base class for all observer classes.
+ */
+template < class Type >
+class observer : public abstract_observer {
+public:
+  /**
+   * Default constructor
+   */
+  observer() : abstract_observer(std::type_index(typeid(Type))) {}
+
+  /**
+   * @brief Called on repository_node attachment
+   *
+   * When a prototype node is attached to the repository,
+   * this is called after the attaching succeeded.
+   *
+   * @param node The attached repository_node
+   * @param prototype The prototype object of the attached node
+   */
+  virtual void on_attach(repository_node &node, const Type &prototype) = 0;
+
+  /**
+   * @brief Called on repository_node detached
+   *
+   * When a prototype node is detached from the repository,
+   * this is called before the detaching succeeded.
+   *
+   * @param node The to be detached repository_node
+   * @param prototype The prototype object of the detached node
+   */
+  virtual void on_detach(repository_node &node, const Type &prototype) = 0;
+
+  /**
+   * @brief Called on object insertion.
+   *
+   * Called when an object is inserted
+   * into the repository.
+   *
+   * @param obj The proxy of the inserted object.
+   */
+  virtual void on_insert(Type &obj) = 0;
+
+  /**
+   * @brief Called on object update.
+   *
+   * Called when an object is updated
+   * in the repository.
+   *
+   * @param obj The proxy of the updated object.
+   */
+  virtual void on_update(Type &obj) = 0;
+
+  /**
+   * @brief Called on object deletion.
+   *
+   * Called when an object is deleted
+   * from the repository.
+   *
+   * @param obj The proxy of the deleted object.
+   */
+  virtual void on_delete(Type &obj) = 0;
+};
+
+namespace internal {
+template < class Type >
+class null_observer : public observer<Type> {
+public:
+  template < class OtherType >
+  explicit null_observer(const null_observer<OtherType> *) {}
+  void on_attach(repository_node &, Type &) override {}
+  void on_detach(repository_node &, Type &) override {}
+  void on_insert(Type &) override {}
+  void on_update(Type &) override {}
+  void on_delete(Type &) override {}
+};
+}
+}
+#endif //MATADOR_OBSERVER_HPP