class Color

class Color {
  
  /**
   * Validates whether a hexadecimal color value is syntactically correct.
   *
   * @param string $hex
   *   The hexadecimal string to validate. May contain a leading '#'. May use
   *   the shorthand notation (e.g., '123' for '112233').
   *
   * @return bool
   *   TRUE if $hex is valid or FALSE if it is not.
   */
  public static function validateHex($hex) {
    if (!is_string($hex)) {
      return FALSE;
    }
    return preg_match('/^[#]?([0-9a-fA-F]{3}){1,2}$/', $hex) === 1;
  }
  
  /**
   * Parses a hexadecimal color string like '#abc' or '#aabbcc'.
   *
   * @param string $hex
   *   The hexadecimal color string to parse.
   *
   * @return array
   *   An array containing the values for 'red', 'green', 'blue'.
   *
   * @throws \InvalidArgumentException
   */
  public static function hexToRgb($hex) {
    if (!self::validateHex($hex)) {
      throw new \InvalidArgumentException("'{$hex}' is not a valid hex value.");
    }
    // Ignore '#' prefixes.
    $hex = ltrim($hex, '#');
    // Convert shorthands like '#abc' to '#aabbcc'.
    if (strlen($hex) == 3) {
      $hex = $hex[0] . $hex[0] . $hex[1] . $hex[1] . $hex[2] . $hex[2];
    }
    $c = hexdec($hex);
    return [
      'red' => $c >> 16 & 0xff,
      'green' => $c >> 8 & 0xff,
      'blue' => $c & 0xff,
    ];
  }
  
  /**
   * Converts RGB color arrays or strings to lowercase CSS notation.
   *
   * @param array|string $input
   *   The value to convert. If the value is an array the first three elements
   *   will be used as the red, green and blue components. String values in CSS
   *   notation like '10, 20, 30' are also supported.
   *
   * @return string
   *   The lowercase simple color representation of the given color.
   */
  public static function rgbToHex($input) {
    // Remove named array keys if input comes from Color::hex2rgb().
    if (is_array($input)) {
      $rgb = array_values($input);
    }
    elseif (is_string($input)) {
      preg_match('/(\\d+), ?(\\d+), ?(\\d+)/', $input, $rgb);
      array_shift($rgb);
    }
    $out = 0;
    foreach ($rgb as $k => $v) {
      $out |= $v << 16 - $k * 8;
    }
    return '#' . str_pad(dechex($out), 6, '0', STR_PAD_LEFT);
  }
  
  /**
   * Normalize the hex color length to 6 characters for comparison.
   *
   * @param string $hex
   *   The hex color to normalize.
   *
   * @return string
   *   The 6 character hex color.
   */
  public static function normalizeHexLength($hex) {
    // Ignore '#' prefixes.
    $hex = ltrim($hex, '#');
    if (strlen($hex) === 3) {
      $hex[5] = $hex[2];
      $hex[4] = $hex[2];
      $hex[3] = $hex[1];
      $hex[2] = $hex[1];
      $hex[1] = $hex[0];
    }
    return '#' . $hex;
  }

}