This script recursively loops through all the files in a Google Drive folder.

get-google-drive-files.php

<?php
/**
 * This function recursively gets the Google Drive files.
 *
 * @param $id
 * @return array
 */
function getGoogleDriveFiles($id)
{
    $files = openGoogleDriveFolder($id);
    $data = [];

    // Means it is a file already, return the id.
    if (count($files['items']) === 0) {
        return $id;
    }

    // If items there are items, loop through it.
    foreach ($files['items'] as $file) {
        $fileId = getGoogleDriveFiles($file['id']);
        $info['id'] = $fileId;
        $info['title'] = $file['title'];

        $data[] = $info;
    }

    return $data;
}

/**
 * This function opens a Google Drive Folder.
 *
 * @param $id
 * @return bool|mixed|string
 */
function openGoogleDriveFolder($id)
{
    $apiKey = ''; // Your Google API Key
    $format = 'https://www.googleapis.com/drive/v2/files?q="%s"+in+parents&key=%s';
    $url = sprintf($format, $id, $apiKey);

    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    $result = curl_exec($ch);
    $result = json_decode($result, true);

    return $result;
}

$driveId = ''; // The google drive folder ID.
$files = getGoogleDriveFiles($driveId);

var_dump($files);
exit;