PHP Color Functions

ColorFunctions.php

<?php 
function rgbToHsl(int $r,int $g, int $b ) {
  $oldR = $r;
  $oldG = $g;
  $oldB = $b;
  
  $r /= 255;
  $g /= 255;
  $b /= 255;

  $max = max( $r, $g, $b );
  $min = min( $r, $g, $b );

	$h;
	$s;
	$l = ( $max + $min ) / 2;
	$d = $max - $min;

    	if( $d == 0 ){
        	$h = $s = 0; // achromatic
    	} else {
        	$s = $d / ( 1 - abs( 2 * $l - 1 ) );

		switch( $max ){
        case $r:
          $h = 60 * fmod( ( ( $g - $b ) / $d ), 6 ); 
                  if ($b > $g) {
                $h += 360;
            }
            break;

        case $g: 
          $h = 60 * ( ( $b - $r ) / $d + 2 ); 
          break;

        case $b: 
          $h = 60 * ( ( $r - $g ) / $d + 4 ); 
          break;
    }			        	        
	}

	return array(max(ceil($h), 0), max(round($s, 2), 0), max(round($l, 2), 0));
}

function hslToRgb( int $h, int $s, int $l ){
    $r; 
    $g; 
    $b;

	$c = ( 1 - abs( 2 * $l - 1 ) ) * $s;
	$x = $c * ( 1 - abs( fmod( ( $h / 60 ), 2 ) - 1 ) );
	$m = $l - ( $c / 2 );

	if ( $h < 60 ) {
		$r = $c;
		$g = $x;
		$b = 0;
	} else if ( $h < 120 ) {
		$r = $x;
		$g = $c;
		$b = 0;			
	} else if ( $h < 180 ) {
		$r = 0;
		$g = $c;
		$b = $x;					
	} else if ( $h < 240 ) {
		$r = 0;
		$g = $x;
		$b = $c;
	} else if ( $h < 300 ) {
		$r = $x;
		$g = 0;
		$b = $c;
	} else { $r = $c; $g = 0; $b = $x; }

	$r = ( $r + $m ) * 255;
	$g = ( $g + $m ) * 255;
	$b = ( $b + $m ) * 255;

  return array( max(ceil($r), 0), max(ceil($g), 0), max(ceil($b), 0) );
}

  function adjustRGB(string $type, string $rgbString, int $amount){
    // covert string to array
    $rgb = explode(',', $rgbString);

    // convert to HSL
    $hsl = rgbToHsl($rgb[0], $rgb[1], $rgb[2]);

    // Extract to named variables
    $hue = $hsl[0];
    $saturation = $hsl[1];

    switch ($type):
      case 'darken':
        $lightness = ($hsl[2] - $amount); // Convert to decimal;
        break;
      case 'brighten':
        $lighteness = ($hsl[2] + $amount); // Convert to decimal;
        break
    endswitch;

    // Convert Back to RGB
    return $darkenedRGB = hslToRgb($hue, $saturation, $lightness);
  };

  function darkenRGB(string $rgbString, int $amount){
    return adjustRGB('darken', $rgbString, $amount);
  };

  function brightenRGB(string $rgbString, int $amount){
    return adjustRGB('brighten', $rgbString, $amount);
  };

?>