outlookcaldavsynchronizer/Unicolour/Utils.cs

using System;
using System.Linq;

namespace Wacton.Unicolour
{

    using System.Globalization;

    internal static class Utils
    {
        internal static double Clamp(this double x, double min, double max) => x < min ? min : x > max ? max : x;
        internal static double Clamp(this int x, int min, int max) => x < min ? min : x > max ? max : x;
        internal static double CubeRoot(double x) => x < 0 ? -Math.Pow(-x, 1 / 3.0) : Math.Pow(x, 1 / 3.0);
        internal static double ToDegrees(double radians) => radians * (180.0 / Math.PI);
        internal static double ToRadians(double degrees) => degrees * (Math.PI / 180.0);

        internal static double Modulo(this double value, double modulus)
        {
            if (double.IsNaN(value))
            {
                return double.NaN;
            }

            var remainder = value % modulus;
            if (remainder == 0.0)
            {
                return remainder;
            }

            // handles negatives, e.g. -10 % 360 returns 350 instead of -10
            // don't "add a negative" if both values are negative
            var useSubtraction = remainder < 0 ^ modulus < 0;
            return useSubtraction ? modulus + remainder : remainder;
        }

        internal static (double r, double g, double b, double a) ParseColourHex(string colourHex)
        {
            var hex = colourHex.TrimStart('#');
            if (hex.Length is not (6 or 8))
            {
                throw new ArgumentException($"{colourHex} contains invalid number of characters");
            }

            var r = Parse(hex, 0) / 255.0;
            var g = Parse(hex, 2) / 255.0;
            var b = Parse(hex, 4) / 255.0;
            var a = hex.Length == 8 ? Parse(hex, 6) / 255.0 : 1.0;
            return (r, g, b, a);
        }

        private static int Parse(string hex, int startIndex)
        {
            var chars = hex.Substring(startIndex, 2).ToUpper();
            if (chars.Any(x => !Uri.IsHexDigit(x)))
            {
                throw new ArgumentException($"{chars} cannot be parsed as hex");
            }

            return int.Parse(chars, NumberStyles.HexNumber);
        }

        internal static ColourTriplet ToLchTriplet(double lightness, double axis1, double axis2)
        {
            var chroma = Math.Sqrt(Math.Pow(axis1, 2) + Math.Pow(axis2, 2));
            var hue = ToDegrees(Math.Atan2(axis2, axis1));
            return new ColourTriplet(lightness, chroma, hue.Modulo(360.0));
        }

        internal static (double lightness, double axis1, double axis2) FromLchTriplet(ColourTriplet lchTriplet)
        {
            var (l, c, h) = lchTriplet;
            var axis1 = c * Math.Cos(ToRadians(h));
            var axis2 = c * Math.Sin(ToRadians(h));
            return (l, axis1, axis2);
        }
    }
}