using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Numerics;
using System.Threading;
using Silk.NET.OpenAL;

namespace Godosa.Audio;

/// <summary>
/// OpenAL Soft output on its own thread (every AL call happens there; other threads post
/// sounds, loops, streams and the listener pose). Mix policy comes from the game's
/// <see cref="IAudioMix"/>. No device or any AL failure → silent (logged, never throws).
/// </summary>
public sealed unsafe partial class OpenAlAudio : IDisposable
{
    private const int SourceCount = 32;
    private const int MaxQueued = 64;
    private const int UpdateMs = 10;
    public const float ReferenceDistance = 2f, MaxDistance = 60f;

    // ALC_SOFT_HRTF (not wrapped by Silk.NET): context attribute + status query.
    private const int AlcHrtfSoft = 0x1992, AlcHrtfStatusSoft = 0x1993, AlcDontCareSoft = 0x0002;
    // Mix at our buffers' rate: no per-source resampling (~15 % of the mixer, measured).
    private const int AlcFrequency = 0x1007;

    public static OpenAlAudio? Current { get; private set; }

    /// <summary>A one-shot sound. <paramref name="Render"/> runs once per <paramref name="Key"/>
    /// (the buffer is cached); no position = heard in the head (2D). Falloff: inverse distance,
    /// gain = Reference / distance, distance clamped to [Reference, Max] (world units of the game).
    /// <paramref name="Falloff"/> (distance → gain factor, audio thread) replaces that curve for a positioned sound:
    /// OpenAL only pans it, the factor is applied every update (the game's own attenuation).</summary>
    public readonly record struct Sound(string Key, Func<PcmClip> Render, int Channel,
        Vector3? Position = null, float Gain = 1f, float Pitch = 1f, float Reference = ReferenceDistance, float Max = MaxDistance,
        Func<float, float>? Falloff = null);

    /// <summary>A looping sound that follows something (a projectile in flight). Posted as the
    /// full set every frame: new keys start, missing keys stop.</summary>
    public readonly record struct LoopEmitter(object Key, Sound Sound, Vector3 Position, Vector3 Velocity);

    private readonly IAudioMix _mix;
    private readonly object _loopLock = new();
    private List<LoopEmitter> _loopsPosted = new(), _loopsWorking = new();
    private readonly Dictionary<object, int> _loopSlots = new(ReferenceEqualityComparer.Instance);
    private readonly HashSet<object> _loopSeen = new(ReferenceEqualityComparer.Instance);
    private readonly List<object> _loopGone = new();
    private readonly ConcurrentQueue<Sound> _queue = new();
    private readonly ConcurrentQueue<int> _stops = new();
    private readonly Thread _thread;
    private readonly object _poseLock = new();
    private volatile bool _running = true;
    private Vector3 _listenerPosition, _listenerForward = -Vector3.UnitZ, _listenerUp = Vector3.UnitY;
    private int _state; // AudioPauseState, written by the UI thread

    private ALContext? _alc;
    private AL? _al;
    private Device* _device;
    private Context* _context;
    private HrtfMode _hrtfApplied;
    private readonly uint[] _sources = new uint[SourceCount];
    private readonly int[] _channel = new int[SourceCount];
    private readonly float[] _gain = new float[SourceCount];
    private readonly float[] _appliedGain = new float[SourceCount]; // last gain sent to AL (skip repeats)
    private readonly Func<float, float>?[] _falloff = new Func<float, float>?[SourceCount]; // null = OpenAL's curve
    private readonly Vector3[] _position = new Vector3[SourceCount];
    private Vector3 _appliedPosition, _appliedForward;
    private readonly bool[] _pausedByUs = new bool[SourceCount];
    private readonly Dictionary<string, uint> _buffers = new();

    public static OpenAlAudio Start(IAudioMix mix) => Current = new OpenAlAudio(mix);

    private OpenAlAudio(IAudioMix mix)
    {
        _mix = mix;
        _thread = new Thread(Run) { IsBackground = true, Name = "audio" };
        _thread.Start();
    }

    public AudioPauseState State
    {
        set => Volatile.Write(ref _state, (int)value);
    }

    public void Play(in Sound sound)
    {
        if (_queue.Count < MaxQueued) _queue.Enqueue(sound);
    }

    /// <summary>Stops the one-shot sounds playing on <paramref name="channel"/> (loops and streams keep going). Applied on
    /// the audio thread before any sound queued after this call starts, so stop-then-play cuts cleanly (a voice line
    /// replaced by the next one).</summary>
    public void StopChannel(int channel) => _stops.Enqueue(channel);

    /// <summary>Replaces the set of loop emitters (UI thread, every rendered frame).</summary>
    public void SetLoops(List<LoopEmitter> loops)
    {
        lock (_loopLock)
        {
            _loopsPosted.Clear();
            _loopsPosted.AddRange(loops);
        }
    }

    /// <summary>Listener = the camera (UI thread, every rendered frame).</summary>
    public void SetListener(Vector3 position, Vector3 forward, Vector3 up)
    {
        lock (_poseLock) (_listenerPosition, _listenerForward, _listenerUp) = (position, forward, up);
    }

    public void Dispose()
    {
        _running = false;
        _thread.Join(500);
        if (ReferenceEquals(Current, this)) Current = null;
    }

    private void Run()
    {
        try
        {
            Open();
        }
        catch (Exception e)
        {
            Console.Error.WriteLine($"audio: disabled ({e.Message})");
            Close();
        }
        while (_running)
        {
            try
            {
                if (_al is not null) Update();
                else _queue.Clear();
            }
            catch (Exception e)
            {
                Console.Error.WriteLine($"audio: disabled after error ({e.Message})");
                Close();
            }
            Thread.Sleep(UpdateMs);
        }
        Close();
    }

    private void Open()
    {
        _alc = ALContext.GetApi(soft: true);
        _al = AL.GetApi(soft: true);
        _device = _alc.OpenDevice("");
        if (_device == null) throw new InvalidOperationException("no audio device");
        CreateContext(_mix.Hrtf);
    }

    private void CreateContext(HrtfMode mode)
    {
        int hrtf = mode switch { HrtfMode.On => 1, HrtfMode.Off => 0, _ => AlcDontCareSoft };
        int* attributes = stackalloc int[] { AlcHrtfSoft, hrtf, AlcFrequency, Pcm.SampleRate, 0 };
        _context = _alc!.CreateContext(_device, attributes);
        if (_context == null) throw new InvalidOperationException("no audio context");
        _alc.MakeContextCurrent(_context);
        _hrtfApplied = mode;

        var al = _al!;
        al.DistanceModel(DistanceModel.InverseDistanceClamped);
        fixed (uint* ids = _sources) al.GenSources(SourceCount, ids);
        foreach (uint s in _sources)
        {
            al.SetSourceProperty(s, SourceFloat.ReferenceDistance, ReferenceDistance);
            al.SetSourceProperty(s, SourceFloat.MaxDistance, MaxDistance);
            al.SetSourceProperty(s, SourceFloat.RolloffFactor, 1f);
        }
        Array.Clear(_pausedByUs);
        Array.Fill(_appliedGain, -1f);
        (_appliedPosition, _appliedForward) = (new Vector3(float.NaN), Vector3.Zero);
        InitReverb();

        int status = -1;
        _alc.GetContextProperty(_device, (GetContextInteger)AlcHrtfStatusSoft, 1, &status);
        if (EngineDebug.Audio)
            EngineDebug.Write("audio", $"device '{_alc.GetContextProperty(_device, GetContextString.DeviceSpecifier)}' hrtf request {mode} status {status}");
    }

    /// <summary>HRTF only changes on a new context; buffers belong to the device and stay.</summary>
    private void DestroyContext()
    {
        if (_context == null) return;
        ReleaseStreams();
        ReleaseReverb();
        fixed (uint* ids = _sources) _al!.DeleteSources(SourceCount, ids);
        _loopSlots.Clear();
        _alc!.MakeContextCurrent(null);
        _alc.DestroyContext(_context);
        _context = null;
    }

    private void Update()
    {
        var al = _al!;
        if (_mix.Hrtf != _hrtfApplied)
        {
            DestroyContext();
            CreateContext(_mix.Hrtf);
        }

        var state = (AudioPauseState)Volatile.Read(ref _state);
        Vector3 position, forward, up;
        lock (_poseLock) (position, forward, up) = (_listenerPosition, _listenerForward, _listenerUp);
        if (position != _appliedPosition || forward != _appliedForward)
        {
            al.SetListenerProperty(ListenerVector3.Position, position);
            float* orientation = stackalloc float[] { forward.X, forward.Y, forward.Z, up.X, up.Y, up.Z };
            al.SetListenerProperty(ListenerFloatArray.Orientation, orientation);
            (_appliedPosition, _appliedForward) = (position, forward);
        }

        bool pauseEffects = _mix.WorldPaused(state);
        for (int i = 0; i < SourceCount; i++)
        {
            var s = SourceState(_sources[i]);
            if (s is not (Silk.NET.OpenAL.SourceState.Playing or Silk.NET.OpenAL.SourceState.Paused)) continue;
            SetGain(i, _gain[i] * Attenuation(i, position) * _mix.ChannelGain(_channel[i], state));
            if (!_mix.Pausable(_channel[i])) continue;
            if (pauseEffects && s == Silk.NET.OpenAL.SourceState.Playing)
            {
                al.SourcePause(_sources[i]);
                _pausedByUs[i] = true;
            }
            else if (!pauseEffects && _pausedByUs[i])
            {
                al.SourcePlay(_sources[i]);
                _pausedByUs[i] = false;
            }
        }

        while (_stops.TryDequeue(out int stop))
            for (int i = 0; i < SourceCount; i++)
                if (_channel[i] == stop && !_streamSlot[i] && !_loopSlots.ContainsValue(i))
                    al.SourceStop(_sources[i]);
        while (_queue.TryDequeue(out var sound))
        {
            if (pauseEffects && _mix.Pausable(sound.Channel)) continue; // a paused world makes no new sounds
            int slot = FreeSource();
            if (slot < 0) break;
            Start(slot, sound, state);
        }
        UpdateLoops(state);
        UpdateStreams(state);
        UpdateReverb();
    }

    private void UpdateLoops(AudioPauseState state)
    {
        var al = _al!;
        lock (_loopLock) (_loopsPosted, _loopsWorking) = (_loopsWorking, _loopsPosted);
        _loopSeen.Clear();
        foreach (var loop in _loopsWorking)
        {
            _loopSeen.Add(loop.Key);
            if (!_loopSlots.TryGetValue(loop.Key, out int slot))
            {
                if (_mix.WorldPaused(state) && _mix.Pausable(loop.Sound.Channel)) continue;
                slot = FreeSource();
                if (slot < 0) continue;
                Start(slot, loop.Sound, state, looping: true);
                _loopSlots[loop.Key] = slot;
            }
            _gain[slot] = loop.Sound.Gain; // a fleeing critter gets louder and higher
            al.SetSourceProperty(_sources[slot], SourceFloat.Pitch, loop.Sound.Pitch);
            al.SetSourceProperty(_sources[slot], SourceVector3.Position, loop.Position);
            _position[slot] = loop.Position;
            al.SetSourceProperty(_sources[slot], SourceVector3.Velocity, loop.Velocity); // doppler
        }
        _loopGone.Clear();
        foreach (var (key, slot) in _loopSlots)
            if (!_loopSeen.Contains(key))
            {
                al.SourceStop(_sources[slot]);
                al.SetSourceProperty(_sources[slot], SourceBoolean.Looping, false);
                al.SetSourceProperty(_sources[slot], SourceVector3.Velocity, Vector3.Zero);
                _loopGone.Add(key);
            }
        foreach (var key in _loopGone) _loopSlots.Remove(key);
    }

    /// <summary>The slot's own falloff at the listener; 1 without one.</summary>
    private float Attenuation(int slot, Vector3 listener) =>
        _falloff[slot] is { } f ? f(Vector3.Distance(_position[slot], listener)) : 1f;

    private void SetGain(int slot, float gain)
    {
        if (gain == _appliedGain[slot]) return;
        _al!.SetSourceProperty(_sources[slot], SourceFloat.Gain, gain);
        _appliedGain[slot] = gain;
    }

    private Silk.NET.OpenAL.SourceState SourceState(uint source)
    {
        _al!.GetSourceProperty(source, GetSourceInteger.SourceState, out int s);
        return (Silk.NET.OpenAL.SourceState)s;
    }

    private int FreeSource()
    {
        for (int i = 0; i < SourceCount; i++)
        {
            if (_streamSlot[i]) continue; // a starved stream stops, but its source stays taken
            var s = SourceState(_sources[i]);
            if (s is Silk.NET.OpenAL.SourceState.Initial or Silk.NET.OpenAL.SourceState.Stopped) return i;
        }
        return -1;
    }

    private void Start(int slot, in Sound sound, AudioPauseState state, bool looping = false)
    {
        var al = _al!;
        uint source = _sources[slot];
        if (!_buffers.TryGetValue(sound.Key, out uint buffer))
        {
            buffer = al.GenBuffer();
            var clip = sound.Render();
            al.BufferData(buffer, BufferFormat.Mono16, clip.Samples, clip.SampleRate);
            _buffers[sound.Key] = buffer;
        }
        _channel[slot] = sound.Channel;
        _gain[slot] = sound.Gain;
        _pausedByUs[slot] = false;
        al.SetSourceProperty(source, SourceInteger.Buffer, buffer);
        al.SetSourceProperty(source, SourceFloat.Pitch, sound.Pitch);
        al.SetSourceProperty(source, SourceFloat.ReferenceDistance, sound.Reference);
        al.SetSourceProperty(source, SourceFloat.MaxDistance, sound.Max);
        bool positioned = sound.Position is not null;
        _falloff[slot] = positioned ? sound.Falloff : null;
        _position[slot] = sound.Position ?? Vector3.Zero;
        al.SetSourceProperty(source, SourceFloat.RolloffFactor, _falloff[slot] is null ? 1f : 0f);
        _appliedGain[slot] = -1f; // force
        SetGain(slot, sound.Gain * Attenuation(slot, _appliedPosition) * _mix.ChannelGain(sound.Channel, state));
        al.SetSourceProperty(source, SourceBoolean.SourceRelative, !positioned);
        var at = sound.Position ?? Vector3.Zero;
        al.SetSourceProperty(source, SourceVector3.Position, at);
        al.SetSourceProperty(source, SourceBoolean.Looping, looping);
        SendToReverb(source, positioned);
        al.SourcePlay(source);
        if (EngineDebug.Audio) EngineDebug.Write("audio", $"play {sound.Key} {_mix.ChannelName(sound.Channel)} {(positioned ? at.ToString("F1", null) : "2D")}");
    }

    private void Close()
    {
        if (_al is not null && _alc is not null && _device != null)
        {
            if (_context != null)
                foreach (uint b in _buffers.Values) _al.DeleteBuffer(b); // AL calls need the context
            _buffers.Clear();
            DestroyContext();
            _alc.CloseDevice(_device);
        }
        _device = null;
        _al = null;
    }
}