namespace DeepDrftPublic.Client.Controls;

/// <summary>
/// Pure mapping between the Mix visualizer's zoom slider position [0, 1] and the visible time-span in
/// seconds. The span range is wide (0.333 s … 30 s, ~90×), so the mapping is logarithmic — equal
/// slider travel changes the span by an equal *ratio*, which feels even to the hand. Slider
/// orientation: fraction 0 = most zoomed-out (longest span), fraction 1 = most zoomed-in (the
/// 0.333 s quarter-note-@-180-BPM anchor). Extracted from the component so the math is unit-testable.
/// </summary>
public static class MixZoomMapping
{
    /// <summary>Shortest span (max zoom): one quarter note at 180 BPM = 60/180 s. Hard anchor.</summary>
    public const double MinVisibleSeconds = 60.0 / 180.0;

    /// <summary>Longest span (min zoom). Tunable.</summary>
    public const double MaxVisibleSeconds = 30.0;

    /// <summary>Slider position [0, 1] -> visible seconds. 0 = zoomed out, 1 = zoomed in.</summary>
    public static double FractionToSeconds(double fraction)
    {
        fraction = Math.Clamp(fraction, 0, 1);
        var logMax = Math.Log(MaxVisibleSeconds);
        var logMin = Math.Log(MinVisibleSeconds);
        // Interpolate in log space from out (frac 0 -> logMax) to in (frac 1 -> logMin).
        return Math.Exp(logMax + (logMin - logMax) * fraction);
    }

    /// <summary>Visible seconds -> slider position [0, 1]. Inverse of <see cref="FractionToSeconds"/>.</summary>
    public static double SecondsToFraction(double seconds)
    {
        seconds = Math.Clamp(seconds, MinVisibleSeconds, MaxVisibleSeconds);
        var logMax = Math.Log(MaxVisibleSeconds);
        var logMin = Math.Log(MinVisibleSeconds);
        return (logMax - Math.Log(seconds)) / (logMax - logMin);
    }
}