passwordGenerator.php

<?php
function generatePassword(int $nbCharacters): string {
    static $characters = [
      'lower' => 'abcdefghijklmnopqrstuvwxyz',
      'upper' => 'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
      'number' => '0123456789',
      'special' => '@#$%^&+=._-!',
    ];

    // Password must have at least one character of each type
    $passwordComposition = array_keys($characters);

    // We're filling out the list with random character types
    $count = $nbCharacters - count($passwordComposition);
    while ($count--) {
      $passwordComposition[] = array_rand($characters);
    }
    // Shuffle the password composition order
    shuffle($passwordComposition);

    // Building password from password composition 
    $password = '';
    foreach ($passwordComposition as $type) {
      $password .= $characters[$type][mt_rand(0, strlen($characters[$type]) - 1)];
    }

    return $password;
}