feat(Core/Database): port TrinityCore database API (#5611)

src/common/Utilities/AsyncCallbackProcessor.h

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2016+ AzerothCore <www.azerothcore.org>, released under GNU AGPL v3 license: https://github.com/azerothcore/azerothcore-wotlk/blob/master/LICENSE-AGPL3
+ * Copyright (C) 2021+ WarheadCore <https://github.com/WarheadCore>
+ */
+
+#ifndef AsyncCallbackProcessor_h__
+#define AsyncCallbackProcessor_h__
+
+#include "Define.h"
+#include <algorithm>
+#include <vector>
+
+//template <class T>
+//concept AsyncCallback = requires(T t) { { t.InvokeIfReady() } -> std::convertible_to<bool> };
+
+template<typename T> // requires AsyncCallback<T>
+class AsyncCallbackProcessor
+{
+public:
+    AsyncCallbackProcessor() = default;
+    ~AsyncCallbackProcessor() = default;
+
+    T& AddCallback(T&& query)
+    {
+        _callbacks.emplace_back(std::move(query));
+        return _callbacks.back();
+    }
+
+    void ProcessReadyCallbacks()
+    {
+        if (_callbacks.empty())
+            return;
+
+        std::vector<T> updateCallbacks{ std::move(_callbacks) };
+
+        updateCallbacks.erase(std::remove_if(updateCallbacks.begin(), updateCallbacks.end(), [](T& callback)
+        {
+            return callback.InvokeIfReady();
+        }), updateCallbacks.end());
+
+        _callbacks.insert(_callbacks.end(), std::make_move_iterator(updateCallbacks.begin()), std::make_move_iterator(updateCallbacks.end()));
+    }
+
+private:
+    AsyncCallbackProcessor(AsyncCallbackProcessor const&) = delete;
+    AsyncCallbackProcessor& operator=(AsyncCallbackProcessor const&) = delete;
+
+    std::vector<T> _callbacks;
+};
+
+#endif // AsyncCallbackProcessor_h__