namespace ytLive.Services.Audio;

/// <summary>
/// Computes the smoothed mic level (0..1) from captured samples. Pure —
/// unit-tested; the <see cref="AudioMixer"/> only feeds it and forwards the
/// result. RMS-based so it tracks perceived loudness, smoothed so the meter
/// does not flicker.
/// </summary>
public sealed class AudioLevelMeter
{
    private const float Smoothing = 0.2f;
    private const float DecaySmoothing = 0.5f;
    private float _level;

    public float Level => _level;

    /// <summary>
    /// Maps a linear level (0..1) onto the meter's display scale: -60 dBFS..0 dBFS
    /// spread linearly across 0..1 — an HONEST dBFS scale. Linear RMS of real speech is
    /// ~0.01..0.1 (-40..-20 dBFS), which leaves a flat (linear) meter looking dead; the
    /// log scale makes typical levels occupy the bar. Inputs at or below -60 dBFS
    /// (0.001 linear) read as zero — the meter never idles on background noise.
    /// <para>2026-10-09: the +10 dB "input amplification" that used to sit here is gone.
    /// It made a −30 dBFS voice look dialed in, and a creator's upload came out at
    /// −28.5 LUFS. The speech leveler now puts voice at −20 dBFS, which lands at 2/3 of
    /// the bar (the green/yellow edge); loud peaks reach the red.</para>
    /// </summary>
    public static float ToDisplay(float linear)
    {
        if (linear <= 0.001f)
            return 0f;
        var db = 20f * MathF.Log10(linear);
        return Math.Clamp(1f + db / 60f, 0f, 1f);
    }

    public float Push(AudioSample sample)
    {
        if (sample.Samples.Length == 0)
            return _level;

        double sumSquares = 0;
        var count = 0;
        foreach (var value in sample.Samples)
        {
            sumSquares += value * value;
            count++;
        }

        var rms = (float)Math.Sqrt(sumSquares / count);
        var alpha = rms > _level ? Smoothing : DecaySmoothing;
        _level = _level * (1 - alpha) + rms * alpha;
        return _level;
    }

    public void Reset() => _level = 0;
}