/*
 * Copyright 2024, Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 */


#include <HSL.h>


hsl_color
hsl_color::from_rgb(const rgb_color& rgb)
{
        hsl_color result;

        float r = rgb.red / 255.0f;
        float g = rgb.green / 255.0f;
        float b = rgb.blue / 255.0f;

        float max = max_c(max_c(r, g), b);
        float min = min_c(min_c(r, g), b);

        result.hue = result.saturation = result.lightness = (max + min) / 2;

        if (max == min) {
                // grayscale
                result.hue = result.saturation = 0;
        } else {
                float diff = max - min;
                result.saturation
                        = (result.lightness > 0.5) ? (diff / (2 - max - min)) : (diff / (max + min));

                if (max == r)
                        result.hue = (g - b) / diff + (g < b ? 6 : 0);
                else if (max == g)
                        result.hue = (b - r) / diff + 2;
                else if (max == b)
                        result.hue = (r - g) / diff + 4;

                result.hue /= 6;
        }

        return result;
}


rgb_color
hsl_color::to_rgb() const
{
        rgb_color result;
        result.alpha = 255;

        if (saturation == 0) {
                // grayscale
                result.red = result.green = result.blue = uint8(lightness * 255);
        } else {
                float q = lightness < 0.5 ? (lightness * (1 + saturation))
                        : (lightness + saturation - lightness * saturation);
                float p = 2 * lightness - q;
                result.red = uint8(hue_to_rgb(p, q, hue + 1./3) * 255);
                result.green = uint8(hue_to_rgb(p, q, hue) * 255);
                result.blue = uint8(hue_to_rgb(p, q, hue - 1./3) * 255);
        }

        return result;
}


// reference: https://en.wikipedia.org/wiki/HSL_and_HSV#Color_conversion_formulae
// (from_rgb() and to_rgb() are derived from the same)
float
hsl_color::hue_to_rgb(float p, float q, float t)
{
        if (t < 0)
                t += 1;
        if (t > 1)
                t -= 1;
        if (t < 1./6)
                return p + (q - p) * 6 * t;
        if (t < 1./2)
                return q;
        if (t < 2./3)
                return p + (q - p) * (2./3 - t) * 6;

        return p;
}