using System.Collections.Generic;
using System.Net.Sockets;

namespace HaoYueNet.ClientNetwork.IOCPMode
{
    public class BufferManager
    {
        int m_numBytes;                 // the total number of bytes controlled by the buffer pool  
        byte[] m_buffer;                // the underlying byte array maintained by the Buffer Manager  
        Stack<int> m_freeIndexPool;     //   
        int m_currentIndex;
        int m_bufferSize;

        public BufferManager(int totalBytes, int bufferSize)
        {
            m_numBytes = totalBytes;
            m_currentIndex = 0;
            m_bufferSize = bufferSize;
            m_freeIndexPool = new Stack<int>();
        }

        // Allocates buffer space used by the buffer pool  
        public void InitBuffer()
        {
            // create one big large buffer and divide that   
            // out to each SocketAsyncEventArg object  
            m_buffer = new byte[m_numBytes];
        }

        // Assigns a buffer from the buffer pool to the   
        // specified SocketAsyncEventArgs object  
        //  
        // <returns>true if the buffer was successfully set, else false</returns>  
        public bool SetBuffer(SocketAsyncEventArgs args)
        {

            if (m_freeIndexPool.Count > 0)
            {
                args.SetBuffer(m_buffer, m_freeIndexPool.Pop(), m_bufferSize);
            }
            else
            {
                if (m_numBytes - m_bufferSize < m_currentIndex)
                {
                    return false;
                }
                args.SetBuffer(m_buffer, m_currentIndex, m_bufferSize);
                m_currentIndex += m_bufferSize;
            }
            return true;
        }

        // Removes the buffer from a SocketAsyncEventArg object.    
        // This frees the buffer back to the buffer pool  
        public void FreeBuffer(SocketAsyncEventArgs args)
        {
            m_freeIndexPool.Push(args.Offset);
            args.SetBuffer(null, 0, 0);
        }
    }
}