using System;
using System.IO;
using System.Text;

namespace Questionable.LgbWorker;

internal static class LgbWorkerFraming
{
	public static void Write(Stream stream, in LgbWorkerMessage message)
	{
		using MemoryStream memoryStream = new MemoryStream();
		using BinaryWriter binaryWriter = new BinaryWriter(memoryStream, Encoding.UTF8, leaveOpen: true);
		binaryWriter.Write((byte)message.Type);
		switch (message.Type)
		{
		case LgbMessageType.Progress:
			binaryWriter.Write(message.Done);
			binaryWriter.Write(message.Total);
			break;
		case LgbMessageType.Final:
			binaryWriter.Write(message.Success);
			binaryWriter.Write(message.DurationMs);
			binaryWriter.Write(message.Error ?? string.Empty);
			break;
		default:
			throw new ArgumentOutOfRangeException("message");
		}
		binaryWriter.Flush();
		byte[] array = memoryStream.ToArray();
		Span<byte> span = stackalloc byte[4];
		BitConverter.TryWriteBytes(span, array.Length);
		stream.Write(span);
		stream.Write(array);
	}

	public static LgbWorkerMessage Read(Stream stream)
	{
		Span<byte> span = stackalloc byte[4];
		ReadExact(stream, span);
		int num = BitConverter.ToInt32(span);
		if ((num <= 0 || num > 65536) ? true : false)
		{
			throw new InvalidDataException($"Invalid frame length: {num}");
		}
		byte[] array = new byte[num];
		ReadExact(stream, array);
		using BinaryReader binaryReader = new BinaryReader(new MemoryStream(array), Encoding.UTF8);
		LgbMessageType lgbMessageType = (LgbMessageType)binaryReader.ReadByte();
		return lgbMessageType switch
		{
			LgbMessageType.Progress => new LgbWorkerMessage
			{
				Type = lgbMessageType,
				Done = binaryReader.ReadInt32(),
				Total = binaryReader.ReadInt32()
			}, 
			LgbMessageType.Final => new LgbWorkerMessage
			{
				Type = lgbMessageType,
				Success = binaryReader.ReadBoolean(),
				DurationMs = binaryReader.ReadInt64(),
				Error = binaryReader.ReadString()
			}, 
			_ => throw new InvalidDataException($"Unknown message type: {lgbMessageType}"), 
		};
	}

	private static void ReadExact(Stream stream, Span<byte> buffer)
	{
		int num;
		for (int i = 0; i < buffer.Length; i += num)
		{
			num = stream.Read(buffer.Slice(i));
			if (num == 0)
			{
				throw new EndOfStreamException();
			}
		}
	}
}