Google Drive - Get folder ID

GoogleDriveGetFolderID.swift

func getFolderID(
    name: String,
    service: GTLRDriveService,
    user: GIDGoogleUser,
    completion: @escaping (String?) -> Void) {
    
    let query = GTLRDriveQuery_FilesList.query()

    // Comma-separated list of areas the search applies to. E.g., appDataFolder, photos, drive.
    query.spaces = "drive"
    
    // Comma-separated list of access levels to search in. Some possible values are "user,allTeamDrives" or "user"
    query.corpora = "user"
        
    let withName = "name = '\(name)'" // Case insensitive!
    let foldersOnly = "mimeType = 'application/vnd.google-apps.folder'"
    let ownedByUser = "'\(user.profile!.email!)' in owners"
    query.q = "\(withName) and \(foldersOnly) and \(ownedByUser)"
    
    service.executeQuery(query) { (_, result, error) in
        guard error == nil else {
            fatalError(error!.localizedDescription)
        }
                                 
        let folderList = result as! GTLRDrive_FileList

        // For brevity, assumes only one folder is returned.
        completion(folderList.files?.first?.identifier)
    }
}