GCLID decode / get timestamp from GCLID

gclid.php

<?php

/**
 * Function decodes GCLID (Google Click ID) and extract timestamp from it.
 *
 * @param string $gclid
 *
 * @return int|null
 */
function getTimestampFromGclid(string $gclid): ?int
{
    // Decode the base64/web encoded gclid
    $decodedBytes = base64_decode(str_replace(['-', '_'], ['+', '/'], $gclid));

    // Check if the gclid is valid and determine its type
    $type = ord($decodedBytes[0]);

    switch ($type) {
        case 0x08: // Old gclid Type with Microsecond-Timestamp
            if (strlen($decodedBytes) >= 9) {
                $bytes = substr($decodedBytes, 1, 8); // Extract the timestamp at offset 1
                $microseconds = decodeVLQ($bytes); // Decode timestamp bytes into integer
                return (int)ceil($microseconds / 1000000); // Convert to seconds
            }
            break;
        case 0x10: // Version with Old gclid Message in a Sub-Sub-Message
            $oldMessageOffset = strpos($decodedBytes, "\x08", 8); // Find timestamp offset
            if ($oldMessageOffset !== false && strlen($decodedBytes) >= $oldMessageOffset + 9) {
                $bytes = substr($decodedBytes, $oldMessageOffset + 1, 8); // Extract the timestamp at offset $oldMessageOffset + 1
                $microseconds = decodeVLQ($bytes); // Decode timestamp bytes into integer
                return (int)ceil($microseconds / 1000000); // Convert to seconds
            }
            break;
        case 0x0A: // gclid version with Seconds-Since-Epoch
            if (strlen($decodedBytes) >= 9) {
                $bytes = substr($decodedBytes, 5, 8); // Extract the timestamp at offset 5
                return decodeVLQ($bytes); // Decode timestamp bytes into integer (already in seconds)
            }
            break;
    }

    return null; // Invalid gclid
}

/**
 * Decode binary data including variable-length quantities.
 *
 * @param $bytes
 *
 * @return int
 */
function decodeVLQ($bytes): int
{
//     $val = 0;
//     foreach (str_split($bytes) as $i => $byte) {
//         $val = PHP_INT_SIZE < 8 && function_exists('bcadd') ?
//             bcadd($val, bcmul(ord($byte) & 0x7f, bcpow(2, $i * 7))) :
//             $val + ((ord($byte) & 0x7f) * pow(2, $i * 7));
//         if (!(ord($byte) & 0x80)) break;
//     }
//     return $val;
  
  
    // Unpack the bytes using the 'C*' format to treat each byte as an unsigned char
    $unpacked = unpack('C*', $bytes);

    $val = 0;
    $shift = 0;

    // Iterate over each unpacked byte
    foreach ($unpacked as $byte) {
        // Add the lower 7 bits of the byte to the decoded value
        $val |= ($byte & 0x7F) << $shift;

        // Shift by 7 bits for the next byte
        $shift += 7;

        // If the MSB is 0, stop decoding (end of the VLQ)
        if (!($byte & 0x80)) {
            break;
        }
    }

    return $val;
}