data.php

<?php

require __dir__.'/../vendor/autoload.php';

function uuid() {
  $raw = openssl_random_pseudo_bytes(16);
  $raw[6] = chr(ord($raw[6]) & 0x0f | 0x40);
  $raw[8] = chr(ord($raw[8]) & 0x3f | 0x80);
  return vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($raw), 4));
}

$server_protocol = null;
if (isset($_SERVER['SERVER_PROTOCOL'])) {
  $server_protocol = $_SERVER['SERVER_PROTOCOL'];
}

$selected = null;
if (isset($_GET['selected'])) {
  $selected = $_GET['selected'];
}

$client = new Predis\Client();

$id = uuid();

$request = [
  'id' => $id,
];

if ($selected) {
  $request['selected'] = $selected;
}

$encoded = json_encode($request);
$client->lpush('scc.locator.request', $encoded);

$data = $client->brpop('scc.locator.response.'.$id, 10);

if ($data === null) {
  $client->lrem('scc.locator.request', 0, $encoded);

  if ($server_protocol !== null)
    header($server_protocol.' 503 Service Unavailable');
  exit();
}

header('Content-type: application/json');
print($data[1].PHP_EOL);