// ProfileController
extension ProfileController {
    override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
        let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: headerIdentifier, for: indexPath) as! ProfileHeader
        header.user = user
        header.delegate = self
        return header
    }
}
// ProfileHeader
class ProfileHeader: UICollectionReusableView {
    var delegate: ProfileHeaderDelegate?
    // weak var delegate: ProfileHeaderDelegate?
    // ... [후략] ...
}

// ActionSheetLauncher
func show() {
    guard let windowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene else { return }
    guard let window = windowScene.windows.first(where: { $0.isKeyWindow }) else { return }
    
    window.addSubview(blackView)
    blackView.frame = window.frame
    
    window.addSubview(tableView)
    tableView.frame = CGRect(x: 0, y: window.frame.height, width: window.frame.width, height: actionSheetHeight)
    
    UIView.animate(withDuration: 0.5) {
        self.blackView.alpha = 1
        self.tableView.frame.origin.y -= self.actionSheetHeight
    }
}

// FeedController
extension FeedController {
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! TweetCell
        cell.delegate = self
        return cell
    }
}
extension FeedController: TweetCellDelegate {
    func handleProfileImageTapped(_ cell: TweetCell) {
        let vc = ProfileController(user: user)
        navigationController?.pushViewController(vc, animated: true)
    }
}

// TweetCell
protocol TweetCellDelegate: AnyObject {
    func handleProfileImageTapped(_ cell: TweetCell)
}
class TweetCell : UICollectionViewCell {
    weak var delegate: TweetCellDelegate?
    
    @objc func handleProfileImageTapped() {
        delegate?.handleProfileImageTapped(self)
    }
}

// UploadTweetViewModel
enum UploadTweetConfiguration {
    case tweet
    case reply(Tweet)
}

class UploadTweetViewModel {
    let actionButtonTitle: String
    init(config: UploadTweetConfiguration) {
        switch config {
        case .tweet:
            actionButtonTitle = "Tweet"
        case .reply(let tweet):
            actionButtonTitle = "Reply"
        }
    }
}

// uploadTweetController
class UploadTweetController: UIViewController {
    private let config: UploadTweetConfiguration
    private lazy var viewModel = UploadTweetViewModel(config: config)
    
    @objc func handleUploadTweet() {
        TweetService.shared.uploadTweet(caption: caption, type: config) 
    }
}

// TweetService
struct TweetService {
    func uploadTweet(caption: String, type: UploadTweetConfiguration, completion: @escaping ( Error?, DatabaseReference) -> Void) {       
        switch type {
        case .tweet:
            REF_TWEETS.childByAutoId().updateChildValues(values) { err, ref in
                REF_USER_TWEETS.child(uid).updateChildValues([tweetID: 1], withCompletionBlock: completion)
            }
        case .reply(let tweet):
            REF_TWEET_REPLIES.child(tweet.tweetID).childByAutoId().updateChildValues(values, withCompletionBlock: completion)
        }
    }
}