using System;
using System.IO;
using Matroska.Enumerations;

namespace Matroska.Models;

/// <summary>
/// http://matroska.sourceforge.net/technical/specs/index.html#block_structure
/// </summary>
public class Block : IParseRawBinary
{
	private const byte LacingBits = 0b0000110;
	private const byte InvisibleBit = 0b00010000;

	/// <summary>
	/// Track Number (Track Entry)
	/// </summary>
	public ulong TrackNumber { get; private set; }

	public byte Flags { get; private set; }

	/// <summary>
	/// Number of frames in the lace-1 (uint8)
	/// </summary>
	public int NumFrames { get; private set; }

	/// <summary>
	/// Lace-coded size of each frame of the lace, except for the last one (multiple uint8). 
	/// *This is not used with Fixed-size lacing as it is calculated automatically from (total size of lace) / (number of frames in lace).
	/// </summary>
	public byte LaceCodedSizeOfEachFrame { get; private set; }

	/// <summary>
	/// Timecode (relative to Cluster timecode, signed int16)
	/// </summary>
	public short TimeCode { get; private set; }

	/// <summary>
	/// Invisible, the codec should decode this frame but not display it
	/// </summary>
	public bool IsInvisible { get; private set; }

	/// <summary>
	/// Lacing
	/// </summary>
	public Lacing Lacing { get; private set; }

	public byte[]? Data { get; private set; }

	public virtual void Parse(Span<byte> span)
	{
		var spanReader = new SpanReader(span);

		TrackNumber = spanReader.ReadVInt().Value;
		TimeCode = spanReader.ReadShort(true); // EBML integer datatypes are big-endian
		Flags = spanReader.ReadByte();

		IsInvisible = (Flags & InvisibleBit) == InvisibleBit;
		Lacing = (Lacing)(Flags & LacingBits);

		if (Lacing != Lacing.No)
		{
			NumFrames = spanReader.ReadByte();

			if (Lacing != Lacing.FixedSize)
			{
				LaceCodedSizeOfEachFrame = spanReader.ReadByte();
			}
		}

		Data = span.Slice(spanReader.Position).ToArray();
	}
}