Song ec

<?php

$input = readline();
$pattern = '/^(?<artistName>[A-Z][a-z\' ]+):(?<songName>[A-Z ]+)$/';
$lowLetters = range("a", "z");
$highLetters = range("A","Z");


while ($input !== "end") {

    if (preg_match($pattern, $input)) {
        list($artist, $songName) = explode(":", $input);
        $encKey = strlen($artist);

        for ($i = 0; $i < strlen($input);$i++){
            $checker = 0;
            if ($input[$i] !== " " && $input[$i] !== "'") {
                if ($input[$i] === ":") {
                    $input[$i] = "@";
                    continue;
                }
                $currLetterAscii = ord($input[$i]);
                $checker = $currLetterAscii + $encKey;

                if (in_array($input[$i], $lowLetters)) {
                    $resUpper = 0;
                    if ($checker > 122) {
                        $resUpper = $checker - 122;
                        $input[$i] = chr(97 + $resUpper - 1);
                        continue;
                    }
                }
                if (in_array($input[$i], $highLetters)) {
                    $resSmall = 0;
                    if ($checker > 90) {
                        $resSmall = $checker - 90;
                        $input[$i] = chr(65 + $resSmall - 1);
                        continue;
                    }
                }
                $input[$i] = chr($currLetterAscii + $encKey);
            }
        }
        echo  "Successful encryption: $input" . PHP_EOL;
    } else {
        echo "Invalid input!" . PHP_EOL;
    }
    $input = readline();
}