using System.Buffers;
using System.IO.Pipelines;
using System.Text;

namespace TheXamlGuy.Framework.Serial;

public class SerialLineReader : SerialReader<string>
{
    private readonly PipeReader reader;

    public SerialLineReader(Stream stream) : base(stream)
    {
        reader = PipeReader.Create(stream);
    }

    public override async IAsyncEnumerable<string> ReadAsync()
    {
        while (true)
        {
            ReadResult result = await reader.ReadAsync();
            ReadOnlySequence<byte> buffer = result.Buffer;

            while (TryReadLine(ref buffer, out ReadOnlySequence<byte> line))
            {
                yield return EncodingExtensions.GetString(Encoding.UTF8, line);
            }

            reader.AdvanceTo(buffer.Start, buffer.End);
            if (result.IsCompleted)
            {
                break;
            }
        }

    }

    private bool TryReadLine(ref ReadOnlySequence<byte> buffer, out ReadOnlySequence<byte> line)
    {
        SequencePosition? position = buffer.PositionOf((byte)'\n');
        if (position == null)
        {
            line = default;
            return false;
        }

        line = buffer.Slice(0, position.Value);
        buffer = buffer.Slice(buffer.GetPosition(1, position.Value));
        return true;
    }
}