added collection, collection proxy and collection resolver implementations

include/matador/object/collection_proxy.hpp

@@ -0,0 +1,82 @@
+#ifndef MATADOR_COLLECTION_PROXY_HPP
+#define MATADOR_COLLECTION_PROXY_HPP
+
+#include <atomic>
+
+#include "matador/object/object_ptr.hpp"
+
+#include "matador/utils/identifier.hpp"
+
+#include <vector>
+
+namespace matador::object {
+
+class abstract_collection_resolver {
+public:
+  virtual ~abstract_collection_resolver() = default;
+
+  [[nodiscard]] const std::type_index& type() const { return type_; }
+
+protected:
+  explicit abstract_collection_resolver(const std::type_index& ti) : type_(ti) {}
+
+public:
+  const std::type_index type_;
+};
+
+
+template<typename Type>
+class collection_resolver : public abstract_collection_resolver {
+public:
+  collection_resolver() : abstract_collection_resolver(typeid(Type)) {}
+
+  virtual std::shared_ptr<Type> resolve(const utils::identifier& id) = 0;
+};
+
+template<typename Type>
+class collection_proxy final {
+public:
+  collection_proxy(std::weak_ptr<object_resolver<Type>> resolver, utils::identifier owner_id)
+  : owner_id_(std::move(owner_id)), resolver_(std::move(resolver)) {}
+
+  collection_proxy(std::weak_ptr<object_resolver<Type>> resolver, std::vector<object_ptr<Type>> items)
+  : items_(std::move(items)), resolver_(std::move(resolver)) {}
+
+  explicit collection_proxy(std::vector<object_ptr<Type>> items)
+  : items_(std::move(items)) {}
+
+  [[nodiscard]] const utils::identifier& owner_id() const {
+    return owner_id_;
+  }
+  const std::vector<object_ptr<Type>>& items() const {
+    return items_;
+  }
+  std::vector<object_ptr<Type>>& items() {
+    return items_;
+  }
+private:
+  void resolve() const {
+    if (loaded_) {
+      return;
+    }
+
+    std::lock_guard lock(mutex_);
+    auto resolver = resolver_.lock();
+    if (!resolver) {
+      return;
+      // Todo: Add states (Detached, Attached, Transient) - if attached an no resolver is available throw runtime exception
+      // throw std::runtime_error("Detached proxy (session expired)");
+    }
+
+    items_ = resolver->resolve(owner_id_);
+  }
+
+private:
+  const utils::identifier owner_id_;
+  std::atomic_bool loaded_{false};
+  std::vector<object_ptr<Type>> items_;
+  std::weak_ptr<object_resolver<Type>> resolver_{};
+  mutable std::mutex mutex_{};
+};
+}
+#endif //MATADOR_COLLECTION_PROXY_HPP