<?php


function id_rand() {
    static $chars = '0123456789abcdefghijklmnopqrstuvwxyz_';
    $result = '';
    for ($i = 0; $i < 5; ++$i) {
        $result .= $chars[mt_rand(0, 36)];
    }
    return $result;
}

$fp = fopen('id.rtf', 'a');
$ch = curl_init();
curl_setopt_array($ch, [
    CURLOPT_SSL_VERIFYPEER => false,
    CURLOPT_RETURNTRANSFER => true,
]);
$checked = [];

while (true) {
    while (isset($checked[$id = id_rand()]));
    $checked[$id] = true;
    $url = "https://twitter.com/users/username_available?username={$id}";
    curl_setopt($ch, CURLOPT_URL, $url);
    $json = json_decode(curl_exec($ch), true);
    if (!isset($json['reason'])) {
        die('Decode error. Script has been shut down.');
    }
    echo "{$id} is {$json['reason']}\n";
    if ($json['reason'] === 'available') {
        fwrite($fp, "{$id}\n");
    }
}