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

namespace BizHawk.Emulation.Cores.Computers.Commodore64.Media
{
	public static class G64
	{
		public static Disk Read(byte[] source)
		{
			using (var mem = new MemoryStream(source))
			{
				var reader = new BinaryReader(mem);
				var id = new string(reader.ReadChars(8));
				var trackDatas = new List<byte[]>();
				var trackLengths = new List<int>();
				var trackNumbers = new List<int>();
				var trackDensities = new List<int>();

				if (id == @"GCR-1541")
				{
					reader.ReadByte(); // version
					int trackCount = reader.ReadByte();
					reader.ReadInt16(); // max track size in bytes

					var trackOffsetTable = new int[trackCount];
					var trackSpeedTable = new int[trackCount];

					for (var i = 0; i < trackCount; i++)
					{
						trackOffsetTable[i] = reader.ReadInt32();
					}

					for (var i = 0; i < trackCount; i++)
					{
						trackSpeedTable[i] = reader.ReadInt32();
					}

					for (var i = 0; i < trackCount; i++)
					{
						if (trackOffsetTable[i] > 0)
						{
							mem.Position = trackOffsetTable[i];
							int trackLength = reader.ReadInt16();
							var trackData = reader.ReadBytes(trackLength);

							trackDatas.Add(trackData);
							trackLengths.Add(trackLength * 8);
							trackDensities.Add(trackSpeedTable[i]);
							trackNumbers.Add(i);
						}
					}

					if (trackSpeedTable.Any(ts => ts > 3 || ts < 0))
					{
						throw new Exception("Byte-level speeds are not yet supported in the G64 loader.");
					}

					return new Disk(trackDatas, trackNumbers, trackDensities, 84) {WriteProtected = true};
				}

				return new Disk(84) {WriteProtected = false};
			}
		}
		
        public static byte[] Write(IList<byte[]> trackData, IList<int> trackNumbers, IList<int> trackDensities)
        {
            const byte version = 0;
            const byte trackCount = 84;
            const int headerLength = 0xC;
            const byte dataFillerValue = 0xFF;

            var trackMaxLength = (ushort)Math.Max(7928, trackData.Max(d => d.Length));

            using (var mem = new MemoryStream())
            {
                var writer = new BinaryWriter(mem);

                // header ID
                writer.Write("GCR-1541".ToCharArray());

                // version #
                writer.Write(version);

                // tracks in the image
                writer.Write(trackCount);

                // maximum track size in bytes
                writer.Write(trackMaxLength);

                // combine track data
                var offsets = new List<int>();
                var densities = new List<int>();
                using (var trackMem = new MemoryStream())
                {
                    var trackMemWriter = new BinaryWriter(trackMem);
                    for (var i = 0; i < trackCount; i++)
                    {
                        if (trackNumbers.Contains(i))
                        {
                            var trackIndex = trackNumbers.IndexOf(i);
                            offsets.Add((int)trackMem.Length);
                            densities.Add(trackDensities[trackIndex]);

                            var data = trackData[trackIndex];
                            var buffer = Enumerable.Repeat(dataFillerValue, trackMaxLength).ToArray();
                            var dataBytes = data.Select(d => unchecked((byte)d)).ToArray();
                            Array.Copy(dataBytes, buffer, dataBytes.Length);
                            trackMemWriter.Write((ushort)dataBytes.Length);
                            trackMemWriter.Write(buffer);
                        }
                        else
                        {
                            offsets.Add(-1);
                            densities.Add(0);
                        }
                    }
                    trackMemWriter.Flush();

                    // offset table
                    foreach (var offset in offsets.Select(o => o >= 0 ? o + headerLength + trackCount * 8 : 0))
                    {
                        writer.Write(offset);
                    }

                    // speed zone data
                    foreach (var density in densities)
                    {
                        writer.Write(density);
                    }

                    // track data
                    writer.Write(trackMem.ToArray());
                }

                writer.Flush();
                return mem.ToArray();
            }
        }
	}
}