Where can a sandboxed Mac app save files?

Question

My Mac app is sandboxed and I need to save a file. Where do I save this file? I can\'t seem to find the specific place where this is allowed without using an open panel. This is

Answer 1

Converting @Mazyod's answer into Swift (5.1):

var appPath: URL? {
    //Create App directory if not exists:
    let fileManager = FileManager()
    let urlPaths = fileManager.urls(for: .applicationSupportDirectory, in: .userDomainMask)
    if let bundleID = Bundle.main.bundleIdentifier, let appDirectory = urlPaths.first?.appendingPathComponent(bundleID,isDirectory: true) {
        var objCTrue: ObjCBool = true
        let path = appDirectory.path
        if !fileManager.fileExists(atPath: path,isDirectory: &objCTrue) {
            do {
                try fileManager.createDirectory(atPath: path, withIntermediateDirectories: true, attributes: nil)
            } catch {
                return nil
            }
        }
        return appDirectory
    }
    return nil
}

However, the directory has changed and I am not sure that the additonal repetition of the bundle ID is needed as the path is

"/Users/**user name**/Library/Containers/**bundleID**/Data/Library/Application Support/**bundleID**". 

But it seems to work.