/////////////////////////////////////////////////////////////////////////////////
//
// Photoshop PSD FileType Plugin for Paint.NET
// http://psdplugin.codeplex.com/
//
// This software is provided under the MIT License:
//   Copyright (c) 2006-2007 Frank Blumenberg
//   Copyright (c) 2010-2016 Tao Yue
//
// See LICENSE.txt for complete licensing and attribution information.
//
/////////////////////////////////////////////////////////////////////////////////

using System;
using PDNWrapper;
using System.IO;
using System.IO.Compression;

namespace PhotoshopFile.Compression
{
    internal class ZipImage : ImageData
    {
        private MemoryStream zipDataStream;
        private DeflateStream zipStream;

        protected override bool AltersWrittenData
        {
            get { return false; }
        }

        public ZipImage(byte[] data, Size size, int bitDepth)
            : base(size, bitDepth)
        {
            if (data == null)
            {
                InitCompress();
            }
            else
            {
                InitDecompress(data);
            }
        }

        private void InitCompress()
        {
            zipDataStream = new MemoryStream();

            // Write 2-byte zlib (RFC 1950) header
            //
            // CMF Compression Method and flags:
            //   CM     0:3 = 8 = deflate
            //   CINFO  4:7 = 4 = undefined, RFC 1950 only defines CINFO = 8
            //
            // FLG Flags:
            //   FCHECK  0:4 = 9 = check bits for CMF and FLG
            //   FDICT     5 = 0 = no preset dictionary
            //   FLEVEL  6:7 = 2 = default compression level

            zipDataStream.WriteByte(0x48);
            zipDataStream.WriteByte(0x89);
            zipStream = new DeflateStream(zipDataStream, CompressionMode.Compress,
                    true);
        }

        private void InitDecompress(byte[] data)
        {
            zipDataStream = new MemoryStream(data);

            // .NET implements Deflate (RFC 1951) but not zlib (RFC 1950),
            // so we have to skip the first two bytes.
            zipDataStream.ReadByte();
            zipDataStream.ReadByte();
            zipStream = new DeflateStream(zipDataStream, CompressionMode.Decompress,
                    true);
        }

        internal override void Read(byte[] buffer)
        {
            var bytesToRead = (long)Size.Height * BytesPerRow;
            Util.CheckByteArrayLength(bytesToRead);

            var bytesRead = zipStream.Read(buffer, 0, (int)bytesToRead);
            if (bytesRead != bytesToRead)
            {
                throw new Exception("ZIP stream was not fully decompressed.");
            }
        }

        public override byte[] ReadCompressed()
        {
            // Write out the last block.  (Flush leaves the last block open.)
            zipStream.Close();

            // Do not write the zlib header when the image data is empty
            var result = (zipDataStream.Length == 2)
                ? new byte[0]
                : zipDataStream.ToArray();
            return result;
        }
    }
}