feat(Cmake/Database): separate database lib from common (#5334)

* feat(Core/Database): separate databse lib from common

* 1

src/server/database/Database/DatabaseLoader.h

@@ -0,0 +1,56 @@
+/*
+ * 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 DatabaseLoader_h__
+#define DatabaseLoader_h__
+
+#include "Define.h"
+#include <functional>
+#include <queue>
+#include <stack>
+#include <string>
+
+template <class T>
+class DatabaseWorkerPool;
+
+// A helper class to initiate all database worker pools,
+// handles updating, delays preparing of statements and cleans up on failure.
+class DatabaseLoader
+{
+public:
+    // Register a database to the loader (lazy implemented)
+    template <class T>
+    DatabaseLoader& AddDatabase(DatabaseWorkerPool<T>& pool, std::string const& name);
+
+    // Load all databases
+    bool Load();
+
+    enum DatabaseTypeFlags
+    {
+        DATABASE_NONE       = 0,
+
+        DATABASE_LOGIN      = 1,
+        DATABASE_CHARACTER  = 2,
+        DATABASE_WORLD      = 4,
+
+        DATABASE_MASK_ALL   = DATABASE_LOGIN | DATABASE_CHARACTER | DATABASE_WORLD
+    };
+
+private:
+    bool OpenDatabases();
+    bool PrepareStatements();
+
+    using Predicate = std::function<bool()>;
+    using Closer = std::function<void()>;
+
+    // Invokes all functions in the given queue and closes the databases on errors.
+    // Returns false when there was an error.
+    bool Process(std::queue<Predicate>& queue);
+
+    std::queue<Predicate> _open, _prepare;
+    std::stack<Closer> _close;
+};
+
+#endif // DatabaseLoader_h__