using System.IO.MemoryMappedFiles;
using VoiceCat.Core;
using Voicecat.V1;

namespace VoiceCat.iOS;

internal sealed class BroadcastAudioPump : IAsyncDisposable
{
    private const uint Magic = 0x56434252, Version = 1;
    private const int Header = 64, Capacity = 96_000, Frame = 960;
    private readonly CancellationTokenSource stop = new();
    private Task worker = Task.CompletedTask;
    private VoiceCatClient? client;
    private uint streamId;
    private readonly short[] scratch = new short[Frame * 2];

    internal void Start(VoiceCatClient owner) { client = owner; worker = RunAsync(stop.Token); }

    private async Task RunAsync(CancellationToken token)
    {
        while (!token.IsCancellationRequested)
        {
            try { await DrainAsync(token); }
            catch (Exception exception) when (exception is IOException or UnauthorizedAccessException or InvalidDataException) { }
            await Task.Delay(10, token).ConfigureAwait(false);
        }
    }

    private async Task DrainAsync(CancellationToken token)
    {
        NSUrl? root = NSFileManager.DefaultManager.GetContainerUrl(IosConstants.AppGroup);
        if (root?.Path is null) return;
        string path = Path.Combine(root.Path, "voicecat", "broadcast_audio.ring"); if (!File.Exists(path)) return;
        using MemoryMappedFile map = MemoryMappedFile.CreateFromFile(path, FileMode.Open, null, Header + Capacity * sizeof(short), MemoryMappedFileAccess.ReadWrite);
        using MemoryMappedViewAccessor view = map.CreateViewAccessor(0, Header + Capacity * sizeof(short), MemoryMappedFileAccess.ReadWrite);
        if (view.ReadUInt32(0) != Magic || view.ReadUInt32(4) != Version) throw new InvalidDataException("Unsupported broadcast ring.");
        bool active = view.ReadUInt32(16) != 0;
        if (!active) { StopStream(); return; }
        VoiceCatClient owner = client ?? throw new IOException("Client disconnected.");
        if (streamId == 0)
        {
            StreamInfo stream = await owner.StartStreamAsync(StreamKind.StreamScreenAudio, "Screen audio", 2, token).ConfigureAwait(false);
            streamId = stream.StreamId; view.Write(32, view.ReadUInt64(24));
        }
        ulong write = view.ReadUInt64(24), read = view.ReadUInt64(32);
        if (write - read > Capacity) read = write - Capacity;
        while (write - read >= Frame * 2)
        {
            for (int sample = 0; sample < scratch.Length; sample++)
            {
                ulong index = (read + (ulong)sample) % Capacity;
                scratch[sample] = view.ReadInt16(Header + checked((long)index * sizeof(short)));
            }
            if (!owner.Audio.FeedPcm(streamId, scratch, 2)) break;
            read += (ulong)scratch.Length;
            view.Write(32, read);
        }
    }

    private void StopStream()
    {
        uint id = streamId; streamId = 0; if (id == 0 || client?.State != ClientConnectionState.Connected) return;
        try { client.StopStream(id); } catch (Exception exception) when (exception is IOException or InvalidOperationException) { }
    }

    public async ValueTask DisposeAsync()
    {
        stop.Cancel(); try { await worker.ConfigureAwait(false); } catch (OperationCanceledException) { } StopStream(); stop.Dispose();
    }
}