ScreenToGif/ImageUtil/Decoder/GifFile.cs

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using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace ScreenToGif.ImageUtil.Decoder
{
    public enum FrameDisposalMethod
    {
        None = 0,
        DoNotDispose = 1,
        RestoreBackground = 2,
        RestorePrevious = 3
    }

    public class FrameMetadata
    {
        public int Left { get; set; }
        public int Top { get; set; }
        public int Width { get; set; }
        public int Height { get; set; }
        public TimeSpan Delay { get; set; }
        public FrameDisposalMethod DisposalMethod { get; set; }
    }

    public class GifFile
    {
        public GifHeader Header { get; private set; }
        public GifColor[] GlobalColorTable { get; set; }
        public IList<GifFrame> Frames { get; set; }
        public IList<GifExtension> Extensions { get; set; }
        public ushort RepeatCount { get; set; }

        private GifFile()
        {
        }

        internal static GifFile ReadGifFile(Stream stream, bool metadataOnly)
        {
            var file = new GifFile();
            file.Read(stream, metadataOnly);
            return file;
        }

        private void Read(Stream stream, bool metadataOnly)
        {
            Header = GifHeader.ReadHeader(stream);

            if (Header.LogicalScreenDescriptor.HasGlobalColorTable)
            {
                GlobalColorTable = GifHelpers.ReadColorTable(stream, Header.LogicalScreenDescriptor.GlobalColorTableSize);
            }

            ReadFrames(stream, metadataOnly);

            var netscapeExtension = Extensions.OfType<GifApplicationExtension>()
                                .FirstOrDefault(GifHelpers.IsNetscapeExtension);

            if (netscapeExtension != null)
                RepeatCount = GifHelpers.GetRepeatCount(netscapeExtension);