//	Spludlow Software
//	Copyright © Samuel P. Ludlow 2020 All Rights Reserved
//	Distributed under the terms of the GNU General Public License version 3
//	Distributed WITHOUT ANY WARRANTY; without implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE
//	https://www.spludlow.co.uk/LICENCE.TXT
//	The Spludlow logo is a registered trademark of Samuel P. Ludlow and may not be used without permission
//	v1.14

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using System.IO;
using System.Windows.Media.Imaging;     //	Ref	PresentationCore	WindowsBase

namespace Spludlow.Drawing
{
	public class GIF
	{
		private static byte[] _ApplicationExtension = new byte[] { 33, 255, 11, 78, 69, 84, 83, 67, 65, 80, 69, 50, 46, 48, 3, 1, 0, 0, 0 };

		public static void MakeGif(MemoryStream[] frameMemoryStreams, Stream outputStream)
		{
			using (MemoryStream intemediateStream = new MemoryStream())
			{
				GifBitmapEncoder encoder = new GifBitmapEncoder();

				foreach (MemoryStream memoryStream in frameMemoryStreams)
					encoder.Frames.Add(BitmapFrame.Create(memoryStream));

				encoder.Save(intemediateStream);

				intemediateStream.Position = 0;

				//
				//	Fix the GIF to allow looping
				//

				//	Copy first 13 bytes
				byte[] headerBuffer = new byte[13];
				intemediateStream.Read(headerBuffer, 0, headerBuffer.Length);
				outputStream.Write(headerBuffer, 0, headerBuffer.Length);

				//	Inject the extra bit
				outputStream.Write(_ApplicationExtension, 0, _ApplicationExtension.Length);

				//	Copy remaining
				intemediateStream.CopyTo(outputStream);
			}
		}
	}
}