Twilio callback script

twilio_callback.php

<?php

// Configuration start
$gdocUrl = 'https://docs.google.com/spreadsheets/d/DOCUMENT_ID_HERE/export?format=csv';

$numbers = [
    'Name 1'     => 'number 1',
    '...'        => '...',
    'Name n'     => 'number n',
];

$onDutyFallback = 'Name x';
// Configuration end


$mode = isset($_REQUEST['mode']) ? $_REQUEST['mode'] : null;

if (!in_array($mode, ['sms', 'calls'], true)) {
    http_response_code(400);
    die("Invalid mode parameter");
}

// Load configuration from Google Spreadsheet document
$fp = fopen($gdocUrl, 'rb');
if (!$fp) {
    http_response_code(503);
    die("Unable to load Google Spreadsheet document");
}

$currentDate = date('Y-m-d');

$onDuty = null;
while (false !== ($row = fgetcsv($fp))) {
    if (count($row) < 2 || !preg_match('/^\d{4}-\d{2}-\d{2}$/', $row[0])) {
        continue; // invalid line
    }

    list($date, $onDuty) = $row;

    if ($date === $currentDate) {
        break;
    }
}

if (null === $onDuty || !isset($numbers[$onDuty])) {
    $onDuty = $onDutyFallback;
}

$number = $numbers[$onDuty];

header('Content-Type: text/xml');
?>
<?xml version="1.0" encoding="UTF-8"?>
<?php if ($mode === 'sms'): ?>
<Response>
  <Message to="<?php echo $number ?>"><?php echo htmlentities($_REQUEST['From'] . " : " . $_REQUEST['Body']) ?></Message>
</Response>
<?php elseif ($mode === 'calls'): ?>
<Response>
  <Dial><?php echo $number ?></Dial>
</Response>
<?php endif; ?>