using System.Runtime.CompilerServices;
using NAudio.Wave;

namespace MeetingAssistant.Recording;

public static class PcmWavAudioChunkReader
{
    private const int MaxChunkDurationMilliseconds = 1000;

    public static async IAsyncEnumerable<AudioChunk> ReadChunksAsync(
        string path,
        [EnumeratorCancellation] CancellationToken cancellationToken = default)
    {
        var reader = new WaveFileReader(path);
        try
        {
            var format = reader.WaveFormat;
            if (format.Encoding != WaveFormatEncoding.Pcm || format.BitsPerSample != 16)
            {
                throw new InvalidDataException(
                    $"Only 16-bit PCM WAV files are supported. Found {format.Encoding} with {format.BitsPerSample} bits per sample.");
            }

            var chunkSize = Math.Max(
                format.BlockAlign,
                format.AverageBytesPerSecond * MaxChunkDurationMilliseconds / 1000);
            chunkSize -= chunkSize % format.BlockAlign;

            var buffer = new byte[chunkSize];
            int read;
            while ((read = await reader.ReadAsync(buffer.AsMemory(0, buffer.Length), cancellationToken)) > 0)
            {
                yield return new AudioChunk(buffer[..read], format.SampleRate, format.Channels);
            }
        }
        finally
        {
            try
            {
                reader.Dispose();
            }
            catch (NotSupportedException)
            {
                // NAudio can throw while disposing reader streams from async iterators after all chunks were read.
            }
        }
    }
}