namespace ChromeboxFanControl;

/// <summary>
/// Fan curve: 14 control points at 0 °C and 40–100 °C every 5 °C, linear interpolation.
/// </summary>
public static class FanCurve
{
    private const int PointCount = 14;

    /// <summary>Temperature breakpoints (°C): 0, 40, 45, 50, …, 100.</summary>
    public static readonly int[] TempBreakpoints = [0, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100];

    /// <param name="tempC">CPU temperature in °C.</param>
    /// <param name="curve">Exactly 14 values 0–100 (fan duty).</param>
    public static byte CalculateFanPercent(double tempC, ReadOnlySpan<int> curve)
    {
        if (curve.Length != PointCount)
            throw new ArgumentException($"Curve must contain exactly {PointCount} points.", nameof(curve));

        var t = Math.Clamp(tempC, 0, 100);
        if (t <= TempBreakpoints[0])
            return (byte)Math.Clamp(curve[0], 0, 100);
        if (t >= TempBreakpoints[PointCount - 1])
            return (byte)Math.Clamp(curve[PointCount - 1], 0, 100);

        for (var i = 0; i < PointCount - 1; i++)
        {
            var t0 = TempBreakpoints[i];
            var t1 = TempBreakpoints[i + 1];
            if (t >= t0 && t <= t1)
            {
                var d0 = Math.Clamp(curve[i], 0, 100);
                var d1 = Math.Clamp(curve[i + 1], 0, 100);
                var frac = (t - t0) / (t1 - t0);
                return (byte)Math.Round(d0 + (d1 - d0) * frac);
            }
        }

        return (byte)Math.Clamp(curve[PointCount - 1], 0, 100);
    }
}