/*
 * ***** BEGIN GPL LICENSE BLOCK *****
 *
 * This program 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; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * Contributor(s): Peter Schlaile <peter@schlaile.de> 2005
 *
 * ***** END GPL LICENSE BLOCK *****
 */

/** \file memutil/MEM_CacheLimiter.h
 *  \ingroup memutil
 */


#ifndef __MEM_CACHELIMITER_H__
#define __MEM_CACHELIMITER_H__

/**
 * @section MEM_CacheLimiter
 * This class defines a generic memory cache management system
 * to limit memory usage to a fixed global maximum.
 * 
 * Please use the C-API in MEM_CacheLimiterC-Api.h for code written in C.
 *
 * Usage example:
 *
 * class BigFatImage {
 * public:
 *       ~BigFatImage() { tell_everyone_we_are_gone(this); }
 * };
 * 
 * void doit() {
 *     MEM_Cache<BigFatImage> BigFatImages;
 *
 *     MEM_Cache_Handle<BigFatImage>* h = BigFatImages.insert(new BigFatImage);
 * 
 *     BigFatImages.enforce_limits();
 *     h->ref();
 *
 *     work with image...
 *
 *     h->unref();
 *
 *     leave image in cache.
 */

#include <list>
#include "MEM_Allocator.h"

template<class T>
class MEM_CacheLimiter;

#ifndef __MEM_CACHELIMITERC_API_H__
extern "C" {
	extern void MEM_CacheLimiter_set_maximum(size_t m);
	extern size_t MEM_CacheLimiter_get_maximum();
};
#endif

template<class T>
class MEM_CacheLimiterHandle {
public:
	explicit MEM_CacheLimiterHandle(T * data_, 
					 MEM_CacheLimiter<T> * parent_) 
		: data(data_), refcount(0), parent(parent_) { }

	void ref() { 
		refcount++; 
	}
	void unref() { 
		refcount--; 
	}
	T * get() { 
		return data; 
	}
	const T * get() const { 
		return data; 
	}
	int get_refcount() const { 
		return refcount; 
	}
	bool can_destroy() const { 
		return !data || !refcount; 
	}
	bool destroy_if_possible() {
		if (can_destroy()) {
			delete data;
			data = 0;
			unmanage();
			return true;
		}
		return false;
	}
	void unmanage() {
		parent->unmanage(this);
	}
	void touch() {
		parent->touch(this);
	}
private:
	friend class MEM_CacheLimiter<T>;

	T * data;
	int refcount;
	typename std::list<MEM_CacheLimiterHandle<T> *,
	  MEM_Allocator<MEM_CacheLimiterHandle<T> *> >::iterator me;
	MEM_CacheLimiter<T> * parent;
};

template<class T>
class MEM_CacheLimiter {
public:
	typedef typename std::list<MEM_CacheLimiterHandle<T> *,
	  MEM_Allocator<MEM_CacheLimiterHandle<T> *> >::iterator iterator;
	typedef size_t (*MEM_CacheLimiter_DataSize_Func) (void *data);
	MEM_CacheLimiter(MEM_CacheLimiter_DataSize_Func getDataSize_)
		: getDataSize(getDataSize_) {
	}
	~MEM_CacheLimiter() {
		for (iterator it = queue.begin(); it != queue.end(); it++) {
			delete *it;
		}
	}
	MEM_CacheLimiterHandle<T> * insert(T * elem) {
		queue.push_back(new MEM_CacheLimiterHandle<T>(elem, this));
		iterator it = queue.end();
		--it;
		queue.back()->me = it;
		return queue.back();
	}
	void unmanage(MEM_CacheLimiterHandle<T> * handle) {
		queue.erase(handle->me);
		delete handle;
	}
	void enforce_limits() {
		size_t max = MEM_CacheLimiter_get_maximum();
		size_t mem_in_use, cur_size;

		if (max == 0) {
			return;
		}

		if(getDataSize) {
			mem_in_use = total_size();
		} else {
			mem_in_use = MEM_get_memory_in_use();
		}

		for (iterator it = queue.begin(); 
		     it != queue.end() && mem_in_use > max;)
		{
			iterator jt = it;
			++it;

			if(getDataSize) {
				cur_size= getDataSize((*jt)->get()->get_data());
			} else {
				cur_size= mem_in_use;
			}

			(*jt)->destroy_if_possible();

			if(getDataSize) {
				mem_in_use-= cur_size;
			} else {
				mem_in_use-= cur_size - MEM_get_memory_in_use();
			}
		}
	}
	void touch(MEM_CacheLimiterHandle<T> * handle) {
		queue.push_back(handle);
		queue.erase(handle->me);
		iterator it = queue.end();
		--it;
		handle->me = it;
	}
private:
	size_t total_size() {
		size_t size = 0;
		for (iterator it = queue.begin(); it != queue.end(); it++) {
			size+= getDataSize((*it)->get()->get_data());
		}
		return size;
	}

	std::list<MEM_CacheLimiterHandle<T>*,
	  MEM_Allocator<MEM_CacheLimiterHandle<T> *> > queue;
	MEM_CacheLimiter_DataSize_Func getDataSize;
};

#endif // __MEM_CACHELIMITER_H__