using System;
using System.Collections.Generic;
using System.Drawing;

namespace ColorPickerApp
{
    /// <summary>Genere une palette complete (teintes x nuances + niveaux de gris).</summary>
    internal static class Palette
    {
        public static List<Color> Generate()
        {
            var colors = new List<Color>();

            const int hueSteps = 12;
            const int shadeSteps = 8;

            for (int s = 0; s < shadeSteps; s++)
            {
                double lightness = 0.90 - (s * (0.80 / (shadeSteps - 1)));
                for (int h = 0; h < hueSteps; h++)
                {
                    double hue = (360.0 / hueSteps) * h;
                    colors.Add(FromHsl(hue, 0.75, lightness));
                }
            }

            const int grayCount = 12;
            for (int g = 0; g < grayCount; g++)
            {
                int v = (int)Math.Round(255.0 * g / (grayCount - 1));
                colors.Add(Color.FromArgb(v, v, v));
            }

            return colors;
        }

        private static Color FromHsl(double h, double s, double l)
        {
            double c = (1 - Math.Abs(2 * l - 1)) * s;
            double x = c * (1 - Math.Abs((h / 60.0) % 2 - 1));
            double m = l - c / 2;

            double r1, g1, b1;
            if (h < 60) { r1 = c; g1 = x; b1 = 0; }
            else if (h < 120) { r1 = x; g1 = c; b1 = 0; }
            else if (h < 180) { r1 = 0; g1 = c; b1 = x; }
            else if (h < 240) { r1 = 0; g1 = x; b1 = c; }
            else if (h < 300) { r1 = x; g1 = 0; b1 = c; }
            else { r1 = c; g1 = 0; b1 = x; }

            int r = (int)Math.Round((r1 + m) * 255);
            int g = (int)Math.Round((g1 + m) * 255);
            int b = (int)Math.Round((b1 + m) * 255);

            r = Math.Max(0, Math.Min(255, r));
            g = Math.Max(0, Math.Min(255, g));
            b = Math.Max(0, Math.Min(255, b));

            return Color.FromArgb(r, g, b);
        }
    }
}