//! \file       ImagePNG.cs
//! \date       Sat Jul 05 00:09:15 2014
//! \brief      PNG image implementation.
//

using System.IO;
using System.Linq;
using System.Text;
using System.ComponentModel.Composition;
using System.Windows.Media.Imaging;
using GameRes.Utility;
using System.Windows.Media;

namespace GameRes
{
    [Export(typeof(ImageFormat))]
    public class PngFormat : ImageFormat
    {
        public override string Tag { get { return "PNG"; } }
        public override string Description { get { return "Portable Network Graphics image"; } }
        public override uint Signature { get { return 0x474e5089; } }

        public override ImageData Read (Stream file, ImageMetaData info)
        {
            var decoder = new PngBitmapDecoder (file,
                BitmapCreateOptions.None, BitmapCacheOption.OnLoad);
            BitmapSource frame = decoder.Frames.First();
            frame.Freeze();
            return new ImageData (frame, info);
        }

        public override void Write (Stream file, ImageData image)
        {
            var encoder = new PngBitmapEncoder();
            encoder.Frames.Add (BitmapFrame.Create (image.Bitmap));
            if (0 == image.OffsetX && 0 == image.OffsetY)
            {
                encoder.Save (file);
                return;
            }
            using (var mem_stream = new MemoryStream())
            {
                encoder.Save (mem_stream);
                byte[] buf = mem_stream.GetBuffer();
                long header_pos = 8;
                mem_stream.Position = header_pos;
                uint header_length = ReadChunkLength (mem_stream);
                file.Write (buf, 0, (int)(header_pos+header_length+12));
                WriteOffsChunk (file, image);
                mem_stream.Position = header_pos+header_length+12;
                mem_stream.CopyTo (file);
            }
        }

        uint ReadChunkLength (Stream file)
        {
            int length = file.ReadByte() << 24;
            length |= file.ReadByte() << 16;
            length |= file.ReadByte() << 8;
            length |= file.ReadByte();
            return (uint)length;
        }

        void WriteOffsChunk (Stream file, ImageData image)
        {
            using (var membuf = new MemoryStream (32))
            {
                using (var bin = new BinaryWriter (membuf, Encoding.ASCII, true))
                {
                    bin.Write (Binary.BigEndian ((uint)9));
                    char[] tag = { 'o', 'F', 'F', 's' };
                    bin.Write (tag);
                    bin.Write (Binary.BigEndian ((uint)image.OffsetX));
                    bin.Write (Binary.BigEndian ((uint)image.OffsetY));
                    bin.Write ((byte)0);
                    bin.Flush();
                    uint crc = Crc32.Compute (membuf.GetBuffer(), 8, 9);
                    bin.Write (Binary.BigEndian (crc));
                }
                file.Write (membuf.GetBuffer(), 0, 9+12); // chunk + size+id+crc
            }
        }

        void SkipBytes (BinaryReader file, uint num)
        {
            if (file.BaseStream.CanSeek)
                file.BaseStream.Seek (num, SeekOrigin.Current);
            else
            {
                for (int i = 0; i < num / 4; ++i)
                    file.ReadInt32();
                for (int i = 0; i < num % 4; ++i)
                    file.ReadByte();
            }
        }

        public override ImageMetaData ReadMetaData (Stream stream)
        {
            ImageMetaData meta = null;
            var file = new ArcView.Reader (stream);
            try
            {
                if (file.ReadUInt32() != Signature)
                    return null;
                if (file.ReadUInt32() != 0x0a1a0a0d)
                    return null;
                uint chunk_size = Binary.BigEndian (file.ReadUInt32());
                char[] chunk_type = new char[4];
                file.Read (chunk_type, 0, 4);
                if (!chunk_type.SequenceEqual ("IHDR"))
                    return null;

                meta = new ImageMetaData();
                meta.Width   = Binary.BigEndian (file.ReadUInt32());
                meta.Height  = Binary.BigEndian (file.ReadUInt32());
                int bpp = file.ReadByte();
                int color_type = file.ReadByte();
                switch (color_type)
                {
                case 2: meta.BPP = bpp*3; break;
                case 3: meta.BPP = 24; break;
                case 4: meta.BPP = bpp*2; break;
                case 6: meta.BPP = bpp*4; break;
                default: meta.BPP = bpp; break;
                }
                SkipBytes (file, 7);

                for (;;)
                {
                    chunk_size = Binary.BigEndian (file.ReadUInt32());
                    file.Read (chunk_type, 0, 4);
                    if (chunk_type.SequenceEqual ("IDAT") || chunk_type.SequenceEqual ("IEND"))
                        break;
                    if (chunk_type.SequenceEqual ("oFFs"))
                    {
                        int x = Binary.BigEndian (file.ReadInt32());
                        int y = Binary.BigEndian (file.ReadInt32());
                        if (0 == file.ReadByte())
                        {
                            meta.OffsetX = x;
                            meta.OffsetY = y;
                        }
                        break;
                    }
                    SkipBytes (file, chunk_size+4);
                }
            }
            catch
            {
                meta = null;
            }
            finally
            {
                file.Dispose();
                if (stream.CanSeek)
                    stream.Position = 0;
            }
            return meta;
        }

        long FindChunk (Stream stream, string chunk)
        {
            char[] find_name = chunk.ToCharArray();
            long found_offset = -1;
            var file = new ArcView.Reader (stream);
            try
            {
                char[] buf = new char[4];
                file.BaseStream.Position = 8;
                while (-1 != file.PeekChar())
                {
                    long chunk_offset = file.BaseStream.Position;
                    uint chunk_size = Binary.BigEndian (file.ReadUInt32());
                    if (4 != file.Read (buf, 0, 4))
                        break;
                    if (chunk.SequenceEqual (buf))
                    {
                        found_offset = chunk_offset;
                        break;
                    }
                    file.BaseStream.Position += chunk_size + 4;
                }
            }
            catch
            {
                // ignore errors
            }
            finally
            {
                file.Dispose();
            }
            return found_offset;
        }
    }
}