using System;
using System.IO;
using System.Collections;

namespace SafeMobileLib
{
	public class FifoStream : Stream
	{
		private const int BlockSize = 65536;
		private const int MaxBlocksInCache = (3 * 1024 * 1024) / BlockSize;

		private int m_Size;
		private int m_RPos;
		private int m_WPos;
		private Stack m_UsedBlocks = new Stack();
		private ArrayList m_Blocks = new ArrayList(); 

		private byte[] AllocBlock()
		{
			byte[] Result = null;
			Result = m_UsedBlocks.Count > 0 ? (byte[])m_UsedBlocks.Pop() : new byte[BlockSize];
			return Result;
		}
		private void FreeBlock(byte[] block)
		{
			if (m_UsedBlocks.Count < MaxBlocksInCache)
				m_UsedBlocks.Push(block);
		}
		private byte[] GetWBlock()
		{
			byte[] Result = null;
			if (m_WPos < BlockSize && m_Blocks.Count > 0)
				Result = (byte[])m_Blocks[m_Blocks.Count - 1];
			else
			{
				Result = AllocBlock();
				m_Blocks.Add(Result);
				m_WPos = 0;
			}
			return Result;
		}

		// Stream members
		public override bool CanRead
		{
			get { return true; }
		}
		public override bool CanSeek
		{
			get { return false; }
		}
		public override bool CanWrite
		{
			get { return true; }
		}
		public override long Length
		{
			get 
			{ 
				lock(this)
					return m_Size;
			}
		}
		public override long Position
		{
			get { throw new InvalidOperationException(); }
			set { throw new InvalidOperationException(); }
		}
		public override void Close()
		{
			Flush();
		}
		public override void Flush()
		{
			lock(this)
			{
				foreach (byte[] block in m_Blocks)
					FreeBlock(block);
				m_Blocks.Clear();
				m_RPos = 0;
				m_WPos = 0;
				m_Size = 0;
			}
		}
		public override void SetLength(long len)
		{
			throw new InvalidOperationException();
		}
		public override long Seek(long pos, SeekOrigin o)
		{
			throw new InvalidOperationException();
		}
		public override int Read(byte[] buf, int ofs, int count)
		{
			lock(this)
			{
				int Result = Peek(buf, ofs, count);
				Advance(Result);
				return Result;
			}
		}
		public override void Write(byte[] buf, int ofs, int count)
		{
			lock(this)
			{
				int Left = count;
				while (Left > 0)
				{
					int ToWrite = Math.Min(BlockSize - m_WPos, Left);
					Array.Copy(buf, ofs + count - Left, GetWBlock(), m_WPos, ToWrite);
					m_WPos += ToWrite;
					Left -= ToWrite;
				}
				m_Size += count;
			}
		}

		// extra stuff
		public int Advance(int count)
		{
			lock(this)
			{
				int SizeLeft = count;
				while (SizeLeft > 0 && m_Size > 0)
				{
					if (m_RPos == BlockSize)
					{
						m_RPos = 0;
						FreeBlock((byte[])m_Blocks[0]);
						m_Blocks.RemoveAt(0);
					}
					int ToFeed = m_Blocks.Count == 1 ? Math.Min(m_WPos - m_RPos, SizeLeft) : Math.Min(BlockSize - m_RPos, SizeLeft);
					m_RPos += ToFeed;
					SizeLeft -= ToFeed;
					m_Size -= ToFeed;
				}
				return count - SizeLeft;
			}
		}
		public int Peek(byte[] buf, int ofs, int count)
		{
			lock(this)
			{
				int SizeLeft = count;
				int TempBlockPos = m_RPos;
				int TempSize = m_Size;

				int CurrentBlock = 0;
				while (SizeLeft > 0 && TempSize > 0)
				{
					if (TempBlockPos == BlockSize)
					{
						TempBlockPos = 0;
						CurrentBlock++;
					}
					int Upper = CurrentBlock < m_Blocks.Count - 1 ? BlockSize : m_WPos;
					int ToFeed = Math.Min(Upper - TempBlockPos, SizeLeft);
					Array.Copy((byte[])m_Blocks[CurrentBlock], TempBlockPos, buf, ofs + count - SizeLeft, ToFeed);
					SizeLeft -= ToFeed;
					TempBlockPos += ToFeed;
					TempSize -= ToFeed;
				}
				return count - SizeLeft;
			}
		}
	}
}