function hexToHsl($hex) {
    $hex = array($hex[0].$hex[1], $hex[2].$hex[3], $hex[4].$hex[5]);
    $rgb = array_map(function($part) {
        return hexdec($part) / 255;
    }, $hex);

    $max = max($rgb);
    $min = min($rgb);

    $l = ($max + $min) / 2;

    if ($max == $min) {
        $h = $s = 0;
    } else {
        $diff = $max - $min;
        $s = $l > 0.5 ? $diff / (2 - $max - $min) : $diff / ($max + $min);

        switch($max) {
            case $rgb[0]:
                $h = ($rgb[1] - $rgb[2]) / $diff + ($rgb[1] < $rgb[2] ? 6 : 0);
                break;
            case $rgb[1]:
                $h = ($rgb[2] - $rgb[0]) / $diff + 2;
                break;
            case $rgb[2]:
                $h = ($rgb[0] - $rgb[1]) / $diff + 4;
                break;
        }

        $h = round($h * 60);
    }

    return array($h, $s, $l);
}

function hslToHex($hsl)
{
    list($h, $s, $l) = $hsl;

    if ($s == 0) {
        $r = $g = $b = 1;
    } else {
        $q = $l < 0.5 ? $l * (1 + $s) : $l + $s - $l * $s;
        $p = 2 * $l - $q;

        $r = hue2rgb($p, $q, $h + 1/3);
        $g = hue2rgb($p, $q, $h);
        $b = hue2rgb($p, $q, $h - 1/3);
    }

    return rgb2hex($r) . rgb2hex($g) . rgb2hex($b);
}

function hue2rgb($p, $q, $t) {
    if ($t < 0) $t += 1;
    if ($t > 1) $t -= 1;
    if ($t < 1/6) return $p + ($q - $p) * 6 * $t;
    if ($t < 1/2) return $q;
    if ($t < 2/3) return $p + ($q - $p) * (2/3 - $t) * 6;

    return $p;
}

function rgb2hex($rgb) {
    return str_pad(dechex($rgb * 255), 2, '0', STR_PAD_LEFT);
}