using System;
using System.Collections.Generic;
using System.IO;
using MrWu.Debug;

namespace Server.Net
{
    public class CircularBuffer : Stream
    {
        public int ChunkSize = 8192;

        private readonly Queue<byte[]> bufferQueue = new Queue<byte[]>();
        
        private readonly Queue<byte[]> bufferCache = new Queue<byte[]>();

        /// <summary>
        /// 最多缓存30个
        /// </summary>
        private const int MaxCacheCnt = 30;
        
        public int LastIndex { get; set; }

        public int FirstIndex { get; set; }

        private byte[] lastBuffer;

        public CircularBuffer()
        {
            this.AddLast();
        }

        public override long Length
        {
            get
            {
                int c = 0;
                if (this.bufferQueue.Count == 0)
                {
                    c = 0;
                }
                else
                {
                    c = (this.bufferQueue.Count - 1) * ChunkSize + this.LastIndex - this.FirstIndex;
                }

                if (c < 0)
                {
                    Debug.Error($"CircularBuffer count < 0: {this.bufferQueue.Count}, {this.LastIndex}, {this.FirstIndex}");
                }

                return c;
            }
        }

        public void AddLast()
        {
            byte[] buffer;
            if (this.bufferCache.Count > 0)
            {
                buffer = this.bufferCache.Dequeue();
            }
            else
            {
                buffer = new byte[ChunkSize];
            }
            this.bufferQueue.Enqueue(buffer);
            this.lastBuffer = buffer;
        }

        public void RemoveFirst()
        {
            byte[] buffer = this.bufferQueue.Dequeue();
            if (this.bufferCache.Count < MaxCacheCnt)
            {
                this.bufferCache.Enqueue(buffer);
            }
        }

        public byte[] First
        {
            get
            {
                if (this.bufferQueue.Count == 0)
                {
                    this.AddLast();
                }
                return this.bufferQueue.Peek();
            }
        }

        public byte[] Last
        {
            get
            {
                if (this.bufferQueue.Count == 0)
                {
                    this.AddLast();
                }

                return this.lastBuffer;
            }
        }

        /// <summary>
        /// 从CircularBuffer中读取数据到stream中
        /// </summary>
        /// <param name="stream"></param>
        /// <param name="count"></param>
        public void Read(Stream stream, int count)
        {
            if (count > this.Length)
            {
                throw new Exception($"bufferList length < count, {Length} {count}");
            }

            int alreadyCopyCount = 0;
            while (alreadyCopyCount < count)
            {
                int n = count - alreadyCopyCount;
                if (ChunkSize - this.FirstIndex > n)
                {
                    stream.Write(this.First,this.FirstIndex,n);
                    this.FirstIndex += n;
                    alreadyCopyCount += n;
                }
                else
                {
                    stream.Write(this.First,this.FirstIndex,ChunkSize - this.FirstIndex);
                    alreadyCopyCount += ChunkSize - this.FirstIndex;

                    this.FirstIndex = 0;
                    this.RemoveFirst();
                }
            }
        }

        public void Write(Stream stream)
        {
            int count = (int)(stream.Length - stream.Position);

            int alreadyCopyCount = 0;
            while (alreadyCopyCount < count)
            {
                if (this.LastIndex == ChunkSize)
                {
                    this.AddLast();
                    this.LastIndex = 0;
                }
                
                int n = count - alreadyCopyCount;
                if (ChunkSize - this.LastIndex > n)
                {
                    stream.Read(this.lastBuffer, this.LastIndex, n);
                    this.LastIndex += count - alreadyCopyCount;
                    alreadyCopyCount += n;
                }
                else
                {
                    stream.Read(this.lastBuffer, this.LastIndex, ChunkSize - this.LastIndex);
                    alreadyCopyCount += ChunkSize - this.LastIndex;
                    this.LastIndex = ChunkSize;
                }
            }
        }
        
        // 把CircularBuffer中数据写入buffer
        public override int Read(byte[] buffer, int offset, int count)
        {
	        if (buffer.Length < offset + count)
	        {
		        throw new Exception($"bufferList length < count, buffer length: {buffer.Length} {offset} {count}");
	        }

	        long length = this.Length;
			if (length < count)
            {
	            count = (int)length;
            }

            int alreadyCopyCount = 0;
            while (alreadyCopyCount < count)
            {
                int n = count - alreadyCopyCount;
				if (ChunkSize - this.FirstIndex > n)
                {
                    Array.Copy(this.First, this.FirstIndex, buffer, alreadyCopyCount + offset, n);
                    this.FirstIndex += n;
                    alreadyCopyCount += n;
                }
                else
                {
                    Array.Copy(this.First, this.FirstIndex, buffer, alreadyCopyCount + offset, ChunkSize - this.FirstIndex);
                    alreadyCopyCount += ChunkSize - this.FirstIndex;
                    this.FirstIndex = 0;
                    this.RemoveFirst();
                }
            }

	        return count;
        }

	    // 把buffer写入CircularBuffer中
        public override void Write(byte[] buffer, int offset, int count)
        {
	        int alreadyCopyCount = 0;
            while (alreadyCopyCount < count)
            {
                if (this.LastIndex == ChunkSize)
                {
                    this.AddLast();
                    this.LastIndex = 0;
                }

                int n = count - alreadyCopyCount;
                if (ChunkSize - this.LastIndex > n)
                {
                    Array.Copy(buffer, alreadyCopyCount + offset, this.lastBuffer, this.LastIndex, n);
                    this.LastIndex += count - alreadyCopyCount;
                    alreadyCopyCount += n;
                }
                else
                {
                    Array.Copy(buffer, alreadyCopyCount + offset, this.lastBuffer, this.LastIndex, ChunkSize - this.LastIndex);
                    alreadyCopyCount += ChunkSize - this.LastIndex;
                    this.LastIndex = ChunkSize;
                }
            }
        }

	    public override void Flush()
	    {
		    throw new NotImplementedException();
		}

	    public override long Seek(long offset, SeekOrigin origin)
	    {
			throw new NotImplementedException();
	    }

	    public override void SetLength(long value)
	    {
		    throw new NotImplementedException();
		}

	    public override bool CanRead
	    {
		    get
		    {
			    return true;
		    }
	    }

	    public override bool CanSeek
	    {
		    get
		    {
			    return false;
		    }
	    }

	    public override bool CanWrite
	    {
		    get
		    {
			    return true;
		    }
	    }

	    public override long Position { get; set; }
    }
}