/**
 * Tencent is pleased to support the open source community by making Tars available.
 *
 * Copyright (C) 2016THL A29 Limited, a Tencent company. All rights reserved.
 *
 * Licensed under the BSD 3-Clause License (the "License"); you may not use this file except 
 * in compliance with the License. You may obtain a copy of the License at
 *
 * https://opensource.org/licenses/BSD-3-Clause
 *
 * Unless required by applicable law or agreed to in writing, software distributed 
 * under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
 * CONDITIONS OF ANY KIND, either express or implied. See the License for the 
 * specific language governing permissions and limitations under the License.
 */
#pragma once

#include <fcntl.h>
#include <errno.h>
#include <stdexcept>
#include <iostream>
#include <assert.h>
#include <iostream>
#include <string>
#include "util/tc_platform.h"

#include "util/tc_ex.h"
/**
 * 结构化的queue，在一边读一边写的情况下可以不用加锁，是线程(进程)安全的
 * 如果多个同时读写，需要加锁
 * 增加一个数量标记，在一边读一边写的情况下不一定准确完全准确 
*/

namespace tars
{

/**
 * @brief 异常
 */
struct TC_SQueue_Exception : public TC_Exception
{
	TC_SQueue_Exception(const std::string &buffer) : TC_Exception(buffer){};
	~TC_SQueue_Exception() throw(){};
};

class UTIL_DLL_API TC_SQueue
{
public:
	TC_SQueue() {_header = NULL;_data = NULL;}
	~TC_SQueue() {_header = NULL;_data = NULL;}

	void attach(char* pBuf, size_t iBufSize) 
	{
		if(iBufSize <= sizeof(Header)+MarkLen+ReserveLen) {
			throw TC_SQueue_Exception("TC_SQueue::attach fail:iBufSize is too small");
		}

		_header = (Header *)pBuf;
		_data = pBuf+sizeof(Header);
		if(_header->iBufSize != iBufSize - sizeof(Header))
			throw TC_SQueue_Exception("TC_SQueue::attach fail: iBufSize != iBufSize - sizeof(Header);");
		if(_header->iReserveLen != ReserveLen)
			throw TC_SQueue_Exception("TC_SQueue::attach fail: iReserveLen != ReserveLen");
		if(_header->iBegin >= _header->iBufSize)
			throw TC_SQueue_Exception("TC_SQueue::attach fail: iBegin > iBufSize - sizeof(Header);");
		if(_header->iEnd > iBufSize - sizeof(Header))
			throw TC_SQueue_Exception("TC_SQueue::attach fail: iEnd > iBufSize - sizeof(Header);");
	}

	void create(char* pBuf, size_t iBufSize) 
	{
		if(iBufSize <= sizeof(Header)+MarkLen+ReserveLen) {
			throw TC_SQueue_Exception("TC_SQueue::create fail:iBufSize is too small");
		}

		_header = (Header *)pBuf;
		_data = pBuf+sizeof(Header);
		_header->iBufSize = iBufSize - sizeof(Header);
		_header->iReserveLen = ReserveLen;
		_header->iBegin = 0;
		_header->iEnd = 0;
		_header->iNum = 0;
	}

	bool pop(std::string& buffer)
	{
		size_t iEnd=_header->iEnd;
		size_t tmp_num;
		if(_header->iBegin == iEnd) {
            _header->iNum = 0;
			return false;
        }
		else if(_header->iBegin<iEnd) {
			assert(_header->iBegin+MarkLen < iEnd);
			size_t len = GetLen(_data+_header->iBegin);
			assert(_header->iBegin+MarkLen+len <= iEnd);
			
			buffer.assign(_data+_header->iBegin+MarkLen, len);
			_header->iBegin += len+MarkLen;
			tmp_num = _header->iNum;
			if(tmp_num > 0) 
				_header->iNum = tmp_num-1;
		} else {
			// 被分段
			assert(iEnd+ReserveLen <= _header->iBegin);
			size_t len = 0;
			size_t new_begin = 0;
			char *data_from = NULL;
			char *data_to = NULL;
			assert(_header->iBegin < _header->iBufSize);
			// 长度字段也被分段
			if(_header->iBegin+MarkLen > _header->iBufSize) { 
				char tmp[16];
				memcpy(tmp,_data+_header->iBegin,_header->iBufSize-_header->iBegin);
				memcpy(tmp+_header->iBufSize-_header->iBegin,_data,_header->iBegin+MarkLen-_header->iBufSize);
				len = GetLen(tmp);
				data_from = _data+(_header->iBegin+MarkLen-_header->iBufSize); //
				new_begin = _header->iBegin+MarkLen-_header->iBufSize+len;
				assert(new_begin <= iEnd);
			} else {
				len = GetLen(_data+_header->iBegin);
				data_from = _data+_header->iBegin+MarkLen;
				if(data_from == _data+_header->iBufSize) data_from = _data;
				if(_header->iBegin+MarkLen+len < _header->iBufSize) { 
					new_begin = _header->iBegin+MarkLen+len;
				} else { // 数据被分段
					new_begin = _header->iBegin+MarkLen+len-_header->iBufSize;
					assert(new_begin <= iEnd);
				}
			}
			data_to = _data+new_begin;

			if(data_to > data_from) {
				assert(data_to - data_from == (long)len);
				buffer.assign(data_from, len);
			} else {
				buffer.assign(data_from, _data+_header->iBufSize-data_from);
				buffer.append(_data, data_to-_data);
				assert(_header->iBufSize-(data_from-data_to)== len);
			}
			_header->iBegin = new_begin;
			tmp_num = _header->iNum;
			if(tmp_num > 0) 
				_header->iNum = tmp_num-1;
		}

		return true;
	}
	
	bool push(const std::string& buffer)
	{
		return push(buffer.c_str(), buffer.length());
	}
	// 写端使用
	bool push(const char *buffer, size_t len)
	{
		if(len == 0) return true;
		size_t iBegin = _header->iBegin;
		if(_header->iEnd == iBegin) {
            _header->iNum = 0;
			if(MarkLen+len+ReserveLen>_header->iBufSize) 
				return false;
		} else if(_header->iEnd > iBegin) {
			assert(iBegin+MarkLen < _header->iEnd);
			if(_header->iBufSize - _header->iEnd + iBegin < MarkLen+len+ReserveLen)
				return false;
		} else {
			assert(_header->iEnd+ReserveLen <= iBegin);
			if(iBegin - _header->iEnd < MarkLen+len+ReserveLen)
				return false;
		}

		// 长度字段被分段
		if(_header->iEnd+MarkLen > _header->iBufSize) {
			char tmp[16]; SetLen(tmp,len);
			memcpy(_data+_header->iEnd,tmp,_header->iBufSize-_header->iEnd);
			memcpy(_data,tmp+_header->iBufSize-_header->iEnd,_header->iEnd+MarkLen-_header->iBufSize);
			memcpy(_data+_header->iEnd+MarkLen-_header->iBufSize,buffer,len);
			_header->iEnd = len+_header->iEnd+MarkLen-_header->iBufSize;
			assert(_header->iEnd+ReserveLen <= iBegin);
			_header->iNum++;
		} 
		// 数据被分段
		else if(_header->iEnd+MarkLen+len > _header->iBufSize){
			SetLen(_data+_header->iEnd,len);
			memcpy(_data+_header->iEnd+MarkLen,buffer,_header->iBufSize-_header->iEnd-MarkLen);
			memcpy(_data,buffer+_header->iBufSize-_header->iEnd-MarkLen,len-(_header->iBufSize-_header->iEnd-MarkLen));
			_header->iEnd = len-(_header->iBufSize-_header->iEnd-MarkLen);
			assert(_header->iEnd+ReserveLen <= iBegin);
			_header->iNum++;
		} else {
			SetLen(_data+_header->iEnd,len);
			memcpy(_data+_header->iEnd+MarkLen,buffer,len);
			_header->iEnd = (_header->iEnd+MarkLen+len)%_header->iBufSize;
			_header->iNum++;
		}
		return true;
	}

	// 读端使用
	//bool isEmpty() const {size_t iEnd=_header->iEnd;return _header->iBegin == iEnd;}
	bool empty() const {size_t iEnd=_header->iEnd;return _header->iBegin == iEnd;}
	// 写端使用
	bool full(size_t len) const
	{
		size_t iBegin = _header->iBegin;
		if(len==0) return false;

		if(_header->iEnd == iBegin) {
			if(len+MarkLen+ReserveLen > _header->iBufSize) return true;
			return false;
		} else if(_header->iEnd > iBegin) {
			assert(iBegin+MarkLen < _header->iEnd);
			return _header->iBufSize - _header->iEnd + iBegin < MarkLen+len+ReserveLen;
		}
		assert(_header->iEnd+ReserveLen <= iBegin);
		return (iBegin - _header->iEnd < MarkLen+len+ReserveLen);
	}
	// 返回队列里的元素数量，不一定绝对准确，只能作为参考
	size_t size() const 
    {
        if (empty()) {
			_header->iNum = 0;
        }
        return _header->iNum;
    } 

private:
	size_t GetLen(char *buf) {size_t u; memcpy((void *)&u,buf,MarkLen); return u;}
	void SetLen(char *buf, size_t u) {memcpy(buf,(void *)&u,MarkLen);}

private:
	const static size_t ReserveLen = 8;
	const static size_t MarkLen = sizeof(size_t);
	struct Header
	{
		size_t iBufSize;
		size_t iReserveLen; // must be 8
		size_t iBegin;
		size_t iEnd;
		size_t iNum;		// 增加一个数量标记，不一定准确
	};

	Header *_header;
	char *_data;
};

}
