using System;

namespace ytLive.Helpers;

/// <summary>The fader scale for the audio dock: the model stores LINEAR gain (0..1), the dock
/// shows and edits DECIBELS, because "−6 dB" means something to a person and "0.50" does not.
///
/// <para>Range: −∞ (silence) to +6 dB of headroom above unity. 0 dB is unity gain, which is what
/// the old 1.0 meant — so a persisted 0.8 comes back as ≈ −1.9 dB and nothing about the stored
/// data changes.</para>
///
/// <para>Creator context (2026-10-30): nearly deaf on the right, so the fader number is read, not
/// heard. The scale therefore has to be the true one, not a cosmetic curve.</para></summary>
public static class GainDb
{
    /// <summary>Silence floor. Anything at or below this reads as −∞ and writes as 0 gain.</summary>
    public const double FloorDb = -60;

    public const double MaxDb = 6;

    /// <summary>Linear gain → dB, clamped to the fader's range. Zero becomes <see cref="FloorDb"/>.</summary>
    public static double ToDb(double gain)
    {
        if (gain <= 0) return FloorDb;
        var db = 20 * Math.Log10(gain);
        return Math.Clamp(db, FloorDb, MaxDb);
    }

    /// <summary>dB → linear gain. At the floor the result is exactly 0 (true silence), so the
    /// bottom of the fader cannot leave a residue of noise.</summary>
    public static double FromDb(double db)
    {
        if (db <= FloorDb) return 0;
        return Math.Pow(10, Math.Clamp(db, FloorDb, MaxDb) / 20);
    }

    /// <summary>"−∞", "−6.0", "+1.5" — the label beside a fader.</summary>
    public static string Label(double db) =>
        db <= FloorDb ? "−∞" : (db > 0 ? "+" : string.Empty) + db.ToString("0.0");

    /// <summary>Mono fold: the accessible downmix. Averages the pair so hard-panned content is
    /// audible on both sides at half amplitude instead of absent from one.</summary>
    public static float MonoFold(float left, float right) => (left + right) * 0.5f;
}