/* $Id$ */

/*
 * 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 newgrf_storage.h Functionality related to the temporary and persistent storage arrays for NewGRFs. */

#ifndef NEWGRF_STORAGE_H
#define NEWGRF_STORAGE_H

#include "core/pool_type.hpp"

/**
 * Base class for all persistent NewGRF storage arrays. Nothing fancy, only here
 * so we have a generalised access to the virtual methods.
 */
struct BasePersistentStorageArray {
	virtual ~BasePersistentStorageArray();

	/**
	 * Clear the changes made since the last #ClearChanges.
	 * This can be done in two ways:
	 *  - saving the changes permanently
	 *  - reverting to the previous version
	 * @param keep_changes do we save or revert the changes since the last #ClearChanges?
	 */
	virtual void ClearChanges(bool keep_changes) = 0;
};

/**
 * Class for persistent storage of data.
 * On #ClearChanges that data is either reverted or saved.
 * @tparam TYPE the type of variable to store.
 * @tparam SIZE the size of the array.
 */
template <typename TYPE, uint SIZE>
struct PersistentStorageArray : BasePersistentStorageArray {
	TYPE storage[SIZE]; ///< Memory to for the storage array
	TYPE *prev_storage; ///< Memory to store "old" states so we can revert them on the performance of test cases for commands etc.

	/** Simply construct the array */
	PersistentStorageArray() : prev_storage(NULL)
	{
		memset(this->storage, 0, sizeof(this->storage));
	}

	/** And free all data related to it */
	~PersistentStorageArray()
	{
		free(this->prev_storage);
	}

	/** Resets all values to zero. */
	void ResetToZero()
	{
		memset(this->storage, 0, sizeof(this->storage));
	}

	/**
	 * Stores some value at a given position.
	 * If there is no backup of the data that backup is made and then
	 * we write the data.
	 * @param pos   the position to write at
	 * @param value the value to write
	 */
	void StoreValue(uint pos, int32 value)
	{
		/* Out of the scope of the array */
		if (pos >= SIZE) return;

		/* The value hasn't changed, so we pretend nothing happened.
		 * Saves a few cycles and such and it's pretty easy to check. */
		if (this->storage[pos] == value) return;

		/* We do not have made a backup; lets do so */
		if (this->prev_storage == NULL) {
			this->prev_storage = MallocT<TYPE>(SIZE);
			memcpy(this->prev_storage, this->storage, sizeof(this->storage));

			/* We only need to register ourselves when we made the backup
			 * as that is the only time something will have changed */
			AddChangedPersistentStorage(this);
		}

		this->storage[pos] = value;
	}

	/**
	 * Gets the value from a given position.
	 * @param pos the position to get the data from
	 * @return the data from that position
	 */
	TYPE GetValue(uint pos) const
	{
		/* Out of the scope of the array */
		if (pos >= SIZE) return 0;

		return this->storage[pos];
	}

	/**
	 * Clear the changes, or assign them permanently to the storage.
	 * @param keep_changes Whether to assign or ditch the changes.
	 */
	void ClearChanges(bool keep_changes)
	{
		assert(this->prev_storage != NULL);

		if (!keep_changes) {
			memcpy(this->storage, this->prev_storage, sizeof(this->storage));
		}
		free(this->prev_storage);
		this->prev_storage = NULL;
	}
};


/**
 * Class for temporary storage of data.
 * On #ClearChanges that data is always zero-ed.
 * @tparam TYPE the type of variable to store.
 * @tparam SIZE the size of the array.
 */
template <typename TYPE, uint SIZE>
struct TemporaryStorageArray {
	TYPE storage[SIZE]; ///< Memory to for the storage array
	uint16 init[SIZE];  ///< Storage has been assigned, if this equals 'init_key'.
	uint16 init_key;    ///< Magic key to 'init'.

	/** Simply construct the array */
	TemporaryStorageArray()
	{
		memset(this->storage, 0, sizeof(this->storage)); // not exactly needed, but makes code analysers happy
		memset(this->init, 0, sizeof(this->init));
		this->init_key = 1;
	}

	/**
	 * Stores some value at a given position.
	 * @param pos   the position to write at
	 * @param value the value to write
	 */
	void StoreValue(uint pos, int32 value)
	{
		/* Out of the scope of the array */
		if (pos >= SIZE) return;

		this->storage[pos] = value;
		this->init[pos] = this->init_key;
	}

	/**
	 * Gets the value from a given position.
	 * @param pos the position to get the data from
	 * @return the data from that position
	 */
	TYPE GetValue(uint pos) const
	{
		/* Out of the scope of the array */
		if (pos >= SIZE) return 0;

		if (this->init[pos] != this->init_key) {
			/* Unassigned since last call to ClearChanges */
			return 0;
		}

		return this->storage[pos];
	}

	void ClearChanges()
	{
		/* Increment init_key to invalidate all storage */
		this->init_key++;
		if (this->init_key == 0) {
			/* When init_key wraps around, we need to reset everything */
			memset(this->init, 0, sizeof(this->init));
			this->init_key = 1;
		}
	}
};

void AddChangedPersistentStorage(BasePersistentStorageArray *storage);
void ClearPersistentStorageChanges(bool keep_changes);


typedef PersistentStorageArray<int32, 16> OldPersistentStorage;

typedef uint32 PersistentStorageID;

struct PersistentStorage;
typedef Pool<PersistentStorage, PersistentStorageID, 1, 0xFF000> PersistentStoragePool;

extern PersistentStoragePool _persistent_storage_pool;

/**
 * Class for pooled persistent storage of data.
 * On #ClearChanges that data is always zero-ed.
 */
struct PersistentStorage : PersistentStorageArray<int32, 16>, PersistentStoragePool::PoolItem<&_persistent_storage_pool> {
	uint32 grfid; ///< GRFID associated to this persistent storage. A value of zero means "default".

	/** We don't want GCC to zero our struct! It already is zeroed and has an index! */
	PersistentStorage(const uint32 new_grfid) : grfid(new_grfid)
	{
	}
};

assert_compile(cpp_lengthof(OldPersistentStorage, storage) == cpp_lengthof(PersistentStorage, storage));

#define FOR_ALL_STORAGES_FROM(var, start) FOR_ALL_ITEMS_FROM(PersistentStorage, storage_index, var, start)
#define FOR_ALL_STORAGES(var) FOR_ALL_STORAGES_FROM(var, 0)

#endif /* NEWGRF_STORAGE_H */