#include <gtk/gtk.h>
#include "e-bevel-button-util.h"

static void rgb_to_hls (gdouble *r, gdouble *g, gdouble *b);
static void hls_to_rgb (gdouble *h, gdouble *l, gdouble *s);

void
e_bevel_button_util_shade (GdkColor *a,
			   GdkColor *b,
			   gdouble   k)
{
  gdouble red;
  gdouble green;
  gdouble blue;
  
  red = (gdouble) a->red / 65535.0;
  green = (gdouble) a->green / 65535.0;
  blue = (gdouble) a->blue / 65535.0;
  
  rgb_to_hls (&red, &green, &blue);
  
  green *= k;
  if (green > 1.0)
    green = 1.0;
  else if (green < 0.0)
    green = 0.0;
  
  blue *= k;
  if (blue > 1.0)
    blue = 1.0;
  else if (blue < 0.0)
    blue = 0.0;
  
  hls_to_rgb (&red, &green, &blue);
  
  b->red = red * 65535.0;
  b->green = green * 65535.0;
  b->blue = blue * 65535.0;
}

static void
rgb_to_hls (gdouble *r,
            gdouble *g,
            gdouble *b)
{
  gdouble min;
  gdouble max;
  gdouble red;
  gdouble green;
  gdouble blue;
  gdouble h, l, s;
  gdouble delta;
  
  red = *r;
  green = *g;
  blue = *b;
  
  if (red > green)
    {
      if (red > blue)
        max = red;
      else
        max = blue;
      
      if (green < blue)
        min = green;
      else
        min = blue;
    }
  else
    {
      if (green > blue)
        max = green;
      else
        max = blue;
      
      if (red < blue)
        min = red;
      else
        min = blue;
    }
  
  l = (max + min) / 2;
  s = 0;
  h = 0;
  
  if (max != min)
    {
      if (l <= 0.5)
        s = (max - min) / (max + min);
      else
        s = (max - min) / (2 - max - min);
      
      delta = max -min;
      if (red == max)
        h = (green - blue) / delta;
      else if (green == max)
        h = 2 + (blue - red) / delta;
      else if (blue == max)
        h = 4 + (red - green) / delta;
      
      h *= 60;
      if (h < 0.0)
        h += 360;
    }
  
  *r = h;
  *g = l;
  *b = s;
}

static void
hls_to_rgb (gdouble *h,
            gdouble *l,
            gdouble *s)
{
  gdouble hue;
  gdouble lightness;
  gdouble saturation;
  gdouble m1, m2;
  gdouble r, g, b;
  
  lightness = *l;
  saturation = *s;
  
  if (lightness <= 0.5)
    m2 = lightness * (1 + saturation);
  else
    m2 = lightness + saturation - lightness * saturation;
  m1 = 2 * lightness - m2;
  
  if (saturation == 0)
    {
      *h = lightness;
      *l = lightness;
      *s = lightness;
    }
  else
    {
      hue = *h + 120;
      while (hue > 360)
        hue -= 360;
      while (hue < 0)
        hue += 360;
      
      if (hue < 60)
        r = m1 + (m2 - m1) * hue / 60;
      else if (hue < 180)
        r = m2;
      else if (hue < 240)
        r = m1 + (m2 - m1) * (240 - hue) / 60;
      else
        r = m1;
      
      hue = *h;
      while (hue > 360)
        hue -= 360;
      while (hue < 0)
        hue += 360;
      
      if (hue < 60)
        g = m1 + (m2 - m1) * hue / 60;
      else if (hue < 180)
        g = m2;
      else if (hue < 240)
        g = m1 + (m2 - m1) * (240 - hue) / 60;
      else
        g = m1;
      
      hue = *h - 120;
      while (hue > 360)
        hue -= 360;
      while (hue < 0)
        hue += 360;
      
      if (hue < 60)
        b = m1 + (m2 - m1) * hue / 60;
      else if (hue < 180)
        b = m2;
      else if (hue < 240)
        b = m1 + (m2 - m1) * (240 - hue) / 60;
      else
        b = m1;
      
      *h = r;
      *l = g;
      *s = b;
    }
}
