import UIKit

import Swiftagram

/// A `class` defining a view controller capable of displaying the authentication web view.
class LoginViewController: UIViewController {
    /// The completion handler.
    var completion: ((Secret) -> Void)? {
        didSet {
            guard oldValue == nil, let completion = completion else { return }
            // Authenticate.
            DispatchQueue.main.asyncAfter(deadline: .now()) {
                // We're using `Authentication.keyhcain`, being encrypted,
                // but you can rely on different ones.
                Authenticator.keychain
                    .visual(filling: self.view)
                    .authenticate()
                    .sink(receiveCompletion: { _ in }, receiveValue: completion)
                    .store(in: &self.bin)
            }
        }
    }

    /// The dispose bag.
    private var bin: Set<AnyCancellable> = []
}

let controller = LoginViewController()
controller.completion = { _ in /* do something */ }
// Present/push the controller.

import SwiftagramCrypto

/// A retained dispose bag.
/// **You need to retain this.**
private var bin: Set<AnyCancellable> = []

// We're using `Authentication.keyhcain`, being encrypted,
// but you can rely on different ones.
Authenticator.keychain
    .basic(username: /* username */,
           password: /* password */)
    .authenticate()
    .sink(receiveCompletion: {
            switch $0 {
            case .failure(let error):
                // Deal with two factor authentication.
                switch error {
                case Authenticator.Error.twoFactorChallenge(let challenge):
                    // Once you receive the challenge,
                    // ask the user for the 2FA code
                    // then just call:
                    // `challenge.code(/* the code */).authenticate()`
                    // and deal with the publisher.
                    break
                default:
                    break
                }
            default:
                break
            }
          }, 
          receiveValue: { _ in /* do something */ })
    .store(in: &self.bin)
}