using System;
using System.IO;

namespace SharpCompress.Compressors.Xz
{
    [CLSCompliant(false)]
    public sealed class XZStream : XZReadOnlyStream
    {
        public static bool IsXZStream(Stream stream)
        {
            try
            {
                return null != XZHeader.FromStream(stream);
            }
            catch (Exception)
            {
                return false;
            }
        }

        private void AssertBlockCheckTypeIsSupported()
        {
            switch (Header.BlockCheckType)
            {
                case CheckType.NONE:
                    break;
                case CheckType.CRC32:
                    break;
                case CheckType.CRC64:
                    break;
                case CheckType.SHA256:
                    throw new NotImplementedException();
                default:
                    throw new NotSupportedException("Check Type unknown to this version of decoder.");
            }
        }
        public XZHeader Header { get; private set; }
        public XZIndex Index { get; private set; }
        public XZFooter Footer { get; private set; }
        public bool HeaderIsRead { get; private set; }
        private XZBlock _currentBlock;

        private bool _endOfStream;

        public XZStream(Stream stream) : base(stream)
        {
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            int bytesRead = 0;
            if (_endOfStream)
                return bytesRead;
            if (!HeaderIsRead)
                ReadHeader();
            bytesRead = ReadBlocks(buffer, offset, count);
            if (bytesRead < count)
            {
                _endOfStream = true;
                ReadIndex();
                ReadFooter();
            }
            return bytesRead;
        }

        private void ReadHeader()
        {
            Header = XZHeader.FromStream(BaseStream);
            AssertBlockCheckTypeIsSupported();
            HeaderIsRead = true;
        }

        private void ReadIndex()
        {
            Index = XZIndex.FromStream(BaseStream, true);
            // TODO veryfy Index
        }

        private void ReadFooter()
        {
            Footer = XZFooter.FromStream(BaseStream);
            // TODO verify footer
        }

        private int ReadBlocks(byte[] buffer, int offset, int count)
        {
            int bytesRead = 0;
            if (_currentBlock == null)
                NextBlock();
            for (;;)
            {
                try
                {
                    if (bytesRead >= count)
                        break;
                    int remaining = count - bytesRead;
                    int newOffset = offset + bytesRead;
                    int justRead = _currentBlock.Read(buffer, newOffset, remaining);
                    if (justRead < remaining)
                        NextBlock();
                    bytesRead += justRead;
                }
                catch (XZIndexMarkerReachedException)
                {
                    break;
                }
            }
            return bytesRead;
        }

        private void NextBlock()
        {
            _currentBlock = new XZBlock(BaseStream, Header.BlockCheckType, Header.BlockCheckSize);
        }
    }
}