<?php
// MIT License; Copyright 2026 Password Generator Plus. See password-generator.js for notice.
function generatePassword(int $length = 16): string {
    if ($length < 4 || $length > 2048) throw new InvalidArgumentException('Length');
    $groups = ['abcdefghijklmnopqrstuvwxyz', 'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
               '0123456789', '!@#$%^&*()-_=+'];
    $pool = implode('', $groups);
    $out = '';
    foreach ($groups as $group) $out .= $group[random_int(0, strlen($group)-1)];
    while (strlen($out) < $length) $out .= $pool[random_int(0, strlen($pool)-1)];
    for ($i = strlen($out)-1; $i > 0; $i--) {
        $j = random_int(0, $i);
        [$out[$i], $out[$j]] = [$out[$j], $out[$i]];
    }
    return $out;
}