using System.Runtime.InteropServices;
using Microsoft.Win32.SafeHandles;

namespace VoiceCat.Dsp;

public sealed unsafe partial class RnnoiseProcessor : IDisposable
{
    public const int SampleRate = 48000;
    public const int FrameSamples = 480;
    private readonly RnnoiseHandle handle;
    private readonly float[] input = new float[FrameSamples];
    private readonly float[] output = new float[FrameSamples];

    public RnnoiseProcessor()
    {
        handle = new(Create());
        if (handle.IsInvalid) { handle.Dispose(); throw new OutOfMemoryException(); }
    }

    public void Process(Span<short> pcm, int sampleRate = SampleRate)
    {
        ObjectDisposedException.ThrowIf(handle.IsClosed, this);
        if (sampleRate != SampleRate) return;
        if (pcm.Length % FrameSamples != 0) throw new ArgumentException("RNNoise requires complete 480-sample mono chunks.", nameof(pcm));
        fixed (float* source = input)
        fixed (float* destination = output)
        {
            for (int offset = 0; offset < pcm.Length; offset += FrameSamples)
            {
                for (int i = 0; i < FrameSamples; i++) input[i] = pcm[offset + i];
                ProcessFrame(handle, destination, source);
                for (int i = 0; i < FrameSamples; i++)
                    pcm[offset + i] = (short)Math.Clamp(MathF.Round(output[i], MidpointRounding.AwayFromZero), short.MinValue, short.MaxValue);
            }
        }
    }

    public void Dispose() => handle.Dispose();

    [LibraryImport("voicecat_media", EntryPoint = "vcm_rnnoise_create")]
    private static partial nint Create();
    [LibraryImport("voicecat_media", EntryPoint = "vcm_rnnoise_destroy")]
    private static partial void Destroy(nint state);
    [LibraryImport("voicecat_media", EntryPoint = "vcm_rnnoise_process")]
    private static partial float ProcessFrame(RnnoiseHandle state, float* output, float* input);

    private sealed class RnnoiseHandle : SafeHandleZeroOrMinusOneIsInvalid
    {
        public RnnoiseHandle() : base(true) { }
        internal RnnoiseHandle(nint value) : this() => SetHandle(value);
        protected override bool ReleaseHandle() { Destroy(handle); return true; }
    }
}