namespace ytLive.Services.Audio;

/// <summary>
/// Master output limiter — the last stage before the live mix reaches the
/// encoder pipe: a peak ceiling of -1 dBFS so mic + loopback (game + TRAX music)
/// can never sum past 0 dBFS and clip in the AAC encode. Instant attack per frame
/// (a hot frame is scaled exactly to the ceiling — no overshoot), smoothed release
/// toward unity so loud passages don't pump. Pure — unit-tested.
/// </summary>
public sealed class MasterLimiter
{
    /// <summary>-1 dBFS: standard streaming headroom for encoder overshoot.</summary>
    public const float Ceiling = 0.891f;

    private const float Release = 0.005f;
    private float _gain = 1f;

    /// <summary>The current gain multiplier (≤ 1, so the limiter never boosts).</summary>
    public float Gain => _gain;

    /// <summary>Scales the frame by the current gain. Gain drops instantly to
    /// <c>ceiling/peak</c> when the frame exceeds the ceiling and recovers
    /// toward unity slowly.</summary>
    public void Process(float[] samples)
    {
        var peak = 0f;
        foreach (var s in samples)
        {
            var abs = MathF.Abs(s);
            if (abs > peak)
                peak = abs;
        }

        var target = peak > Ceiling ? Ceiling / peak : 1f;
        if (target < _gain)
            _gain = target;
        else
            _gain += (target - _gain) * Release;

        for (var i = 0; i < samples.Length; i++)
            samples[i] *= _gain;
    }

    public void Reset() => _gain = 1f;
}