using System;
using System.Collections.Generic;
using System.Threading;
using ADOFAIRenderer.Util.Audio.Clip;

namespace ADOFAIRenderer.Util.Audio.Mixer;

/// <summary>
/// One playing sound of a <see cref="VoiceMixer"/> (the song, or one sound effect), created by <see cref="VoiceMixer.Play"/>.
///
/// Main thread: the Set methods queue a change that takes effect at a given time (seconds relative to the render start,
/// the time at which the game made the change). Changes of one voice must be queued in non-decreasing time order.
/// Render thread: <see cref="VoiceMixer.Mix"/> applies each change at sample floor(time * OutputRate) (<see cref="VoiceMixer.ToSample"/>).
///
/// Playback model (output samples n, clip positions in frames of the source at the output sample rate):
/// - The voice is silent before its start sample and from its end sample on.
/// - Clip position at sample n = anchor position + (n - anchor sample) * pitch. A position or pitch change sets a new anchor
///   at the sample where it takes effect, so a pitch change keeps the position continuous.
/// - Looping: the position wraps at the clip length (<see cref="AudioClipSource.Duration"/> * output rate, fractional).
///   Not looping: the voice ends when the position reaches <see cref="AudioClipSource.TotalFrames"/>.
/// </summary>
internal sealed class Voice
{
    /// <summary>Kind of a queued <see cref="Change"/>; the meaning of <see cref="Change.Value"/> depends on it.</summary>
    internal enum ChangeKind
    {
        /// <summary>Value: playback rate, at least 0.</summary>
        Pitch,

        /// <summary>Value: linear gain.</summary>
        Volume,

        /// <summary>Value: 1 = loop on, 0 = loop off.</summary>
        Loop,

        /// <summary>Value: clip position in seconds, at least 0.</summary>
        Position,

        /// <summary>Value: end time in seconds relative to the render start.</summary>
        EndTime,

        /// <summary>Value: unused (0). Ends playback at the sample the change is applied at.</summary>
        Stop
    }

    /// <summary>One timed change of a voice, queued by the main Unity thread and applied by the render thread.</summary>
    internal readonly struct Change
    {
        public readonly ChangeKind Kind;

        /// <summary>Output sample at which the change takes effect (<see cref="VoiceMixer.ToSample"/> of the change time).</summary>
        public readonly long Sample;

        /// <summary>Argument of the change (see <see cref="ChangeKind"/>).</summary>
        public readonly double Value;

        public Change(ChangeKind kind, long sample, double value)
        {
            Kind = kind;
            Sample = sample;
            Value = value;
        }
    }

    /// <summary>Mixer that owns this voice; the Set methods queue their changes on it.</summary>
    private readonly VoiceMixer _mixer;

    // ── Render thread state ──

    /// <summary>Changes not yet applied, in time order. Render thread only.</summary>
    internal readonly Queue<Change> Pending = new();

    /// <summary>First output sample of playback.</summary>
    internal long StartSample;

    /// <summary>Output sample at which playback stops (exclusive); long.MaxValue when not set.</summary>
    internal long EndSample = long.MaxValue;

    /// <summary>Output sample of the current anchor (see the class summary).</summary>
    internal long AnchorSample;

    /// <summary>Clip position at <see cref="AnchorSample"/>, in frames at the output sample rate (may be fractional).</summary>
    internal double AnchorPosition;

    /// <summary>Clip frames advanced per output sample (1 = original speed), at least 0.</summary>
    internal double Pitch;

    /// <summary>Linear gain applied to the clip samples.</summary>
    internal double Volume;

    /// <summary>True while the clip repeats at <see cref="Period"/>.</summary>
    internal bool Loop;

    /// <summary>Set by the render thread when playback has ended; the voice is then released and removed from the mixer.</summary>
    internal bool Finished;

    /// <summary>
    /// Playback has ended and the voice was released by the render thread. Readable from any thread;
    /// the value can lag behind the render thread.
    /// </summary>
    public bool IsFinished => Volatile.Read(ref Finished);

    /// <summary>Loop length in frames at the output sample rate (source duration * output rate).</summary>
    internal double Period;

    /// <summary>Read position registered on <see cref="Source"/> so the decoder thread keeps the chunks ahead loaded; null without a usable source.</summary>
    internal AudioCursor? Cursor;

    /// <summary>Chunk of <see cref="Source"/> currently held for reading (invalid when none). Render thread only.</summary>
    internal ChunkView View;

    internal Voice(VoiceMixer mixer, AudioClipSource? source, string name)
    {
        _mixer = mixer;
        Source = source;
        Name = name;
    }

    /// <summary>Clip played by this voice; null plays silence (the clip could not be loaded).</summary>
    public AudioClipSource? Source { get; }

    /// <summary>Name for logs (the game's clip key).</summary>
    public string Name { get; }

    /// <summary>Sets the playback rate (1 = original speed). Negative values are treated as 0.</summary>
    public void SetPitch(double pitch, double time) => _mixer.Enqueue(this, ChangeKind.Pitch, time, Math.Max(0.0, pitch));

    /// <summary>Sets the linear gain applied to the clip samples.</summary>
    public void SetVolume(double volume, double time) => _mixer.Enqueue(this, ChangeKind.Volume, time, volume);

    /// <summary>Turns looping on or off. Turning it off lets the current repetition play to the end of the clip.</summary>
    public void SetLoop(bool loop, double time) => _mixer.Enqueue(this, ChangeKind.Loop, time, loop ? 1.0 : 0.0);

    /// <summary>
    /// Moves playback to <paramref name="clipSeconds"/> seconds into the clip.
    /// Before the voice starts, this sets the position playback starts from.
    /// </summary>
    public void SetPosition(double clipSeconds, double time) => _mixer.Enqueue(this, ChangeKind.Position, time, Math.Max(0.0, clipSeconds));

    /// <summary>Stops playback at <paramref name="endTime"/> (seconds relative to the render start).</summary>
    public void SetEndTime(double endTime, double time) => _mixer.Enqueue(this, ChangeKind.EndTime, time, endTime);

    /// <summary>Stops playback at <paramref name="time"/>.</summary>
    public void Stop(double time) => _mixer.Enqueue(this, ChangeKind.Stop, time, 0.0);

    /// <summary>Unwrapped clip position at output sample <paramref name="sample"/> (sample at or after the anchor).</summary>
    internal double PositionAt(long sample) => AnchorPosition + (sample - AnchorSample) * Pitch;

    /// <summary>Clip position at <paramref name="sample"/>, wrapped into the loop when looping.</summary>
    internal double WrappedPositionAt(long sample)
    {
        var position = PositionAt(sample);
        if (Loop && Period > 0 && position >= Period) position %= Period;
        return position;
    }

    /// <summary>
    /// Applies <paramref name="change"/> at output sample <paramref name="sample"/> (its own sample, or a later one when the change
    /// arrived after its sample was mixed). Before the start sample, changes replace the starting state. Render thread only.
    /// </summary>
    internal void Apply(in Change change, long sample, int outputRate)
    {
        // Anchor changes made before the start take effect at the start sample (playback starts from the new state).
        // EndTime uses the change's own value; Stop ends at the sample it is applied at, so a Stop before the start
        // ends the voice before it plays.
        var at = Math.Max(sample, StartSample);
        switch (change.Kind)
        {
            case ChangeKind.Pitch:
                Reanchor(at);
                Pitch = change.Value;
                break;
            case ChangeKind.Volume:
                Volume = change.Value;
                break;
            case ChangeKind.Loop:
                Reanchor(at);
                Loop = change.Value != 0.0;
                break;
            case ChangeKind.Position:
                AnchorSample = at;
                AnchorPosition = change.Value * outputRate;
                break;
            case ChangeKind.EndTime:
                EndSample = VoiceMixer.ToSample(change.Value, outputRate);
                break;
            case ChangeKind.Stop:
                EndSample = Math.Min(EndSample, sample);
                break;
        }
    }

    /// <summary>Moves the anchor to <paramref name="sample"/>, keeping the (wrapped) position there, before a pitch or loop change.</summary>
    private void Reanchor(long sample)
    {
        AnchorPosition = WrappedPositionAt(sample);
        AnchorSample = sample;
    }
}