using Amphora;
using System;
using System.Runtime.InteropServices.JavaScript;

namespace Susurrus.WebAudio
{
    /// <summary>
    /// A streamed sound that hands the browser a quarter second at a time, which it schedules back to back.  Every
    /// chunk is decoded into the same array.
    /// </summary>
    public class WebAudioStreamedSound : StreamedSound
    {
        /// <summary>
        /// The number of chunks kept scheduled ahead, so a pause of up to a second between updates is covered.
        /// </summary>
        public const int ChunksAhead = 4;

        private readonly byte[] chunk;
        private readonly int bytesPerFrame;

        /// <summary>
        /// Gets how many frames each chunk holds, which is about a quarter of a second.
        /// </summary>
        public int ChunkFrames { get; }

        public WebAudioStreamedSound(ISoundStream stream) : base(stream)
        {
            bytesPerFrame = ChannelCount * StreamFeed.BytesPerSample(stream.Format);
            ChunkFrames = Math.Max(1, stream.SampleRate / 4);
            chunk = new byte[ChunkFrames * bytesPerFrame];
        }

        /// <summary>
        /// Schedules chunks on the browser voice in <paramref name="slot"/> until <see cref="ChunksAhead"/> are
        /// waiting, or the stream has nothing more to give.  A failure, including a chunk the browser refuses, ends the
        /// feeding.
        /// </summary>
        public Status Refill(JSObject engine, int slot)
        {
            int queued = WebAudioInterop.StreamQueued(engine, slot);

            while (!IsFed && queued < ChunksAhead)
            {
                StatusOr<int> filled = Feed(new ByteView(chunk));

                if (!filled.IsOk)
                {
                    return filled.Status;
                }

                if (filled.Value == 0)
                {
                    break;
                }

                try
                {
                    WebAudioInterop.StreamQueue(engine, slot, chunk, filled.Value * bytesPerFrame,
                        Stream.SampleRate, ChannelCount, isFloat: Stream.Format == SampleFormat.Float32);
                }
                catch (JSException exception)
                {
                    IsFed = true;
                    return WebAudioFailures.BufferRejected.Fail(exception.Message);
                }

                ++queued;
            }

            return Status.Ok;
        }
    }
}