Move EngineOverrideManager to separate header

src/engine_override.h

@@ -0,0 +1,40 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file engine_override.h Engine override functionality. */
+
+#ifndef ENGINE_OVERRIDE_H
+#define ENGINE_OVERRIDE_H
+
+#include "engine_type.h"
+#include "vehicle_type.h"
+
+#include <vector>
+
+struct EngineIDMapping {
+	uint32_t grfid;          ///< The GRF ID of the file the entity belongs to
+	uint16_t internal_id;    ///< The internal ID within the GRF file
+	VehicleType type;        ///< The engine type
+	uint8_t  substitute_id;  ///< The (original) entity ID to use if this GRF is not available (currently not used)
+};
+
+/**
+ * Stores the mapping of EngineID to the internal id of newgrfs.
+ * Note: This is not part of Engine, as the data in the EngineOverrideManager and the engine pool get resetted in different cases.
+ */
+struct EngineOverrideManager : std::vector<EngineIDMapping> {
+	static const uint NUM_DEFAULT_ENGINES; ///< Number of default entries
+
+	void ResetToDefaultMapping();
+	EngineID GetID(VehicleType type, uint16_t grf_local_id, uint32_t grfid);
+
+	static bool ResetToCurrentNewGRFConfig();
+};
+
+extern EngineOverrideManager _engine_mngr;
+
+#endif /* ENGINE_BASE_H */