trim_leading_whitespace.php

<?php

function trim_leading_whitespace($code)
{
    $lines = collect(explode("\n", $code));

    $min = collect(explode("\n", $code))->filter(function ($line) {
        return trim($line);
    })->min(function ($line) {
        return strlen($line) - strlen(ltrim($line));
    });

    $code = $lines->map(function ($line) use ($min) {
        return substr($line, $min);
    })->implode("\n");
    
    return htmlspecialchars(trim($code));
}