<?php

/**
 * @file
 * Functions to support theming in the Olivero theme.
 */

/**
 * Converts hex color strings to array of HSL values.
 *
 * @param string $hex_string
 *   The 6-character hexadecimal color code, optionally with a leading hash.
 *
 * @return array
 *   Array containing hue, saturation, and lightness values.
 *   $hue: integer of value 0-360 indicating the hue on a color wheel.
 *   $saturation: string of saturation as a percentage (0% all gray, 100% full
 *   color).
 *   $lightness: string of lightness as a percentage (0% darkened to black, 50%
 *   full color, 100% lightened to white).
 *
 * @see https://css-tricks.com/converting-color-spaces-in-javascript
 *   Code based on JS version.
 * @see https://www.rapidtables.com/convert/color/rgb-to-hsl.html
 *   Mathematical formula for rgb-to-hsl conversion.
 *
 * @internal
 */
function _olivero_hex_to_hsl(string $hex_string) {
  // Convert hexcode pairs to rgb values (0-255).
  $hex_val = trim($hex_string, '#');

  $r0 = $g0 = $b0 = '00';

  if (strlen($hex_val) === 6) {
    $r0 = hexdec($hex_val[0] . $hex_val[1]);
    $g0 = hexdec($hex_val[2] . $hex_val[3]);
    $b0 = hexdec($hex_val[4] . $hex_val[5]);
  }

  if (strlen($hex_val) === 3) {
    $r0 = hexdec($hex_val[0] . $hex_val[0]);
    $g0 = hexdec($hex_val[1] . $hex_val[1]);
    $b0 = hexdec($hex_val[2] . $hex_val[2]);
  }

  // Convert rgb's 0-255 to decimal values.
  $r = fdiv($r0, 255);
  $g = fdiv($g0, 255);
  $b = fdiv($b0, 255);

  // Calculate Hue.
  $c_min = min($r, $g, $b);
  $c_max = max($r, $g, $b);
  $delta = $c_max - $c_min;

  if ($delta == 0) {
    $h = 0;
  }
  else {
    switch ($c_max) {
      case $r:
        $h = fmod((($g - $b) / $delta), 6);
        break;

      case $g:
        $h = (($b - $r) / $delta) + 2;
        break;

      case $b:
        $h = (($r - $g) / $delta) + 4;
        break;

      default:
        $h = 0;
        break;
    }
  }

  $h = round($h * 60);

  // Shift hue range from [-60 - 300] to [0 - 360].
  if ($h < 0) {
    $h += 360;
  }

  // Calculate Lightness.
  $l = ($c_max + $c_min) / 2;

  // Calculate Saturation.
  $s = $delta == 0 ? 0 : $delta / (1 - abs((2 * $l) - 1));

  // Convert Saturation and Lightness to percentages.
  $s = round($s * 100);
  $l = round($l * 100);

  return [$h, $s, $l];
}