/*
    Read

        http://z0b.kapsi.fi/snippets.php

    before using this code. Thank you.
*/

#include <algorithm>    // min/max
#include <cmath>        // fabs
#include <stdint.h>

// RGB -> HSL
void convertRGBToHSL(const uint8_t red, const uint8_t green, const uint8_t blue,
                     uint8_t &hue, uint8_t &sat, uint8_t &lum)
{
    const float r = (float)red / 255.0f,
                g = (float)green / 255.0f,
                b = (float)blue / 255.0f;

    // find min/max color values
    const float minColor = std::min(r, std::min(g, b)),
                maxColor = std::max(r, std::max(g, b)),
                diff = maxColor - minColor;

    if (std::fabs(diff) < 0.001f) {
        // colors are same, so it is a shade of grey
        lum = red;
        sat = 0U;
        hue = 0U;

        return;
    }

    // luminance
    const float l = (minColor + maxColor) / 2.0f;

    // saturation
    float s;

    if (l < 0.5f)
        s = diff / (maxColor + minColor);
    else s = diff / (2.0f - maxColor - minColor);

    // hue
    float h;

    if (std::fabs(maxColor - r) < 0.001f)
        h = (g - b) / diff;
    else if (std::fabs(maxColor - g) < 0.001f)
        h = 2.0f + (b - r) / diff;
    else h = 4.0f + (r - g) / diff;

    h /= 6.0f;

    if (h < 0.0f)
        h += 1.0f;

    // convert back to 0...255 range, with proper rounding
    hue = (uint8_t)(int(h * 255.0f + 0.5f) & 0xFF);
    sat = (uint8_t)(int(s * 255.0f + 0.5f) & 0xFF);
    lum = (uint8_t)(int(l * 255.0f + 0.5f) & 0xFF);
}

// HSL -> RGB
void convertHSLToRGB(const uint8_t hue, const uint8_t sat, const uint8_t lum,
                     uint8_t &red, uint8_t &green, uint8_t &blue)
{
    if (sat == 0U) {
        // saturation is zero, so it is a shade of grey
        red = green = blue = lum;
        return;
    }

    // convert from 0...255 to 0...1
    const float h = (float)hue / 255.0f,
                s = (float)sat / 255.0f,
                l = (float)lum / 255.0f;

    float q;

    if (l < 0.5f)
        q = l * (1.0f + s);
    else q = (l + s) - (l * s);

    const float p = (2.0f * l) - q;
    float t[3];

    t[0] = h + (1.0f / 3.0f);
    t[1] = h;
    t[2] = h - (1.0f / 3.0f);

    for (int i = 0; i < 3; i++) {
        if (t[i] < 0.0f)
            t[i] += 1.0f;

        if (t[i] > 1.0f)
            t[i] -= 1.0f;
    }

    float out[3];

    for (int i = 0; i < 3; i++) {
        if (t[i] * 6.0f < 1.0f)
            out[i] = p + (q - p) * 6.0f * t[i];
        else if (t[i] * 2.0f < 1.0f)
            out[i] = q;
        else if (t[i] * 3.0f < 2.0f)
            out[i] = p + (q - p) * ((2.0f / 3.0f) - t[i]) * 6.0f;
        else out[i] = p;
    }

    // convert back to 0...255 range, with proper rounding
    red = (uint8_t)(int(out[0] * 255.0f + 0.5f) & 0xFF);
    green = (uint8_t)(int(out[1] * 255.0f + 0.5f) & 0xFF);
    blue = (uint8_t)(int(out[2] * 255.0f + 0.5f) & 0xFF);
}

#ifdef TEST
#include <cstdio>

// a small test program
int main()
{
    uint8_t r1, g1, b1, r2, g2, b2, h, s, l;

    // input color
    r1 = 77U;
    g1 = 125U;
    b1 = 213U;

    // convert to HSL then back
    convertRGBToHSL(r1, g1, b1, h, s, l);
    convertHSLToRGB(h, s, l, r2, g2, b2);

    // print all values
    printf(" IN: %d, %d, %d\n", r1, g1, b1);
    printf("HSL: %d, %d, %d\n", h, s, l);
    printf("OUT: %d, %d, %d\n", r2, g2, b2);

    return 0;
}

#endif