using NAudio.Wave;

namespace Robovoice.App;

internal sealed class AudioOutput : IDisposable
{
    private WaveOutEvent? _waveOut;
    private BufferedWaveProvider? _bufferProvider;
    private int _sampleRate;
    private string _deviceName = string.Empty;
    private float _lastSample;
    private bool _disposed;

    public Action<string>? Log { get; set; }

    public void Start(int sampleRate, string? deviceName = null)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);

        _sampleRate = sampleRate;
        _deviceName = deviceName ?? string.Empty;
        _lastSample = 0f;

        Stop();

        int deviceNumber = FindDevice(_deviceName);
        _waveOut = new WaveOutEvent { DeviceNumber = deviceNumber, DesiredLatency = 200 };

        _bufferProvider = new BufferedWaveProvider(
            WaveFormat.CreateIeeeFloatWaveFormat(sampleRate, 1))
        {
            BufferDuration = TimeSpan.FromSeconds(60),
            DiscardOnBufferOverflow = true,
            ReadFully = true,
        };

        _waveOut.Init(_bufferProvider);
        _waveOut.PlaybackStopped += OnPlaybackStopped;
        _waveOut.Play();
    }

    public void WriteSamples(float[] samples)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        if (_bufferProvider is null) return;

        if (samples.Length > 0)
            _lastSample = samples[^1];

        byte[] bytes = new byte[samples.Length * sizeof(float)];
        Buffer.BlockCopy(samples, 0, bytes, 0, bytes.Length);
        _bufferProvider.AddSamples(bytes, 0, bytes.Length);
    }

    public void Flush()
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        if (_bufferProvider is null || _sampleRate == 0) return;

        // Fade out from last sample to zero over 5ms to avoid click
        int fadeSamples = (int)(_sampleRate * 0.005);
        float[] fade = new float[fadeSamples];
        for (int i = 0; i < fadeSamples; i++)
        {
            float t = (float)i / fadeSamples;
            fade[i] = _lastSample * (1f - t);
        }
        WriteSamples(fade);

        // Then 500ms of silence to let NAudio drain
        int padSamples = (int)(_sampleRate * 0.5);
        WriteSamples(new float[padSamples]);
        
        _lastSample = 0f;
    }

    private void OnPlaybackStopped(object? sender, StoppedEventArgs e)
    {
    }

    public void Stop()
    {
        if (_waveOut is not null)
        {
            _waveOut.PlaybackStopped -= OnPlaybackStopped;
            _waveOut.Stop();
            _waveOut.Dispose();
            _waveOut = null;
        }
        _bufferProvider?.ClearBuffer();
        _bufferProvider = null;
        _lastSample = 0f;
    }

    private static int FindDevice(string? deviceName)
    {
        if (string.IsNullOrEmpty(deviceName))
            return -1;

        for (int i = 0; i < WaveOut.DeviceCount; i++)
        {
            var caps = WaveOut.GetCapabilities(i);
            if (caps.ProductName.Contains(deviceName, StringComparison.OrdinalIgnoreCase))
                return i;
        }

        return -1;
    }

    public static IReadOnlyList<(int Index, string Name)> GetDevices()
    {
        var devices = new List<(int, string)>();
        for (int i = 0; i < WaveOut.DeviceCount; i++)
        {
            var caps = WaveOut.GetCapabilities(i);
            devices.Add((i, caps.ProductName));
        }
        return devices;
    }

    public void Dispose()
    {
        if (_disposed) return;
        Stop();
        _disposed = true;
    }
}