frenzy-ios/Reader/Screens/Login/LoginViewController.swift

//
//  LoginViewController.swift
//  Reader
//
//  Created by Shadowfacts on 11/25/21.
//

@preconcurrency import Foundation
import UIKit
import AuthenticationServices
import Fervor

@MainActor
protocol LoginViewControllerDelegate: AnyObject {
    func didLogin(with controller: FervorController)
}

class LoginViewController: UIViewController {
    
    weak var delegate: LoginViewControllerDelegate?
    
    private var textField: UITextField!
    private var activityIndicator: UIActivityIndicatorView!
    
    private var authSession: ASWebAuthenticationSession?

    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = .systemBackground

        textField = UITextField()
        textField.translatesAutoresizingMaskIntoConstraints = false
        textField.borderStyle = .roundedRect
        textField.backgroundColor = .secondarySystemBackground
        textField.keyboardType = .URL
        textField.returnKeyType = .next
        textField.autocorrectionType = .no
        textField.autocapitalizationType = .none
        textField.placeholder = "example.com"
        textField.addTarget(self, action: #selector(doEnteredURL), for: .primaryActionTriggered)
        view.addSubview(textField)
        
        activityIndicator = UIActivityIndicatorView(style: .medium)
        activityIndicator.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(activityIndicator)
        
        NSLayoutConstraint.activate([
            textField.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            textField.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            textField.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.75),
            
            activityIndicator.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            activityIndicator.topAnchor.constraint(equalTo: textField.bottomAnchor, constant: 8),
        ])
    }
    
    @objc private func doEnteredURL() {
        Task {
            await enteredURL()
        }
    }
    
    @MainActor
    private func enteredURL() async {
        guard let text = textField.text,
              let components = URLComponents(string: text) else {
            let alert = UIAlertController(title: "Invalid URL", message: nil, preferredStyle: .alert)
            self.present(alert, animated: true)
            return
        }
        
        textField.isEnabled = false
        activityIndicator.startAnimating()
        
        let controller = await FervorController(instanceURL: components.url!, account: nil)
        
        let registration: ClientRegistration
        do {
            registration = try await controller.register()
        } catch {
            let alert = UIAlertController(title: "Unable to register client", message: error.localizedDescription, preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
            present(alert, animated: true)
            
            textField.isEnabled = true
            activityIndicator.stopAnimating()
            
            return
        }
        
        var authorizeComponents = components
        authorizeComponents.path = "/oauth/authorize"
        authorizeComponents.queryItems = [
            URLQueryItem(name: "response_type", value: "code"),
            URLQueryItem(name: "client_id", value: registration.clientID),
            URLQueryItem(name: "redirect_uri", value: FervorController.oauthRedirectURI.absoluteString),
        ]
        authSession = ASWebAuthenticationSession(url: authorizeComponents.url!, callbackURLScheme: "frenzy") { (callbackURL, error) in
            let components = URLComponents(url: callbackURL!, resolvingAgainstBaseURL: false)
            guard let codeItem = components?.queryItems?.first(where: { $0.name == "code" }),
                  let codeValue = codeItem.value else {
                Task { @MainActor in
                    let alert = UIAlertController(title: "Unable to retrieve authorization code", message: error?.localizedDescription ?? "Unknown Error", preferredStyle: .alert)
                    alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
                    self.present(alert, animated: true)
                     
                    self.textField.isEnabled = true
                    self.activityIndicator.stopAnimating()
                }
                return
            }
            Task { @MainActor in
                do {
                    try await controller.getToken(authCode: codeValue)
                } catch {
                    let alert = UIAlertController(title: "Unable to retrieve access token", message: error.localizedDescription, preferredStyle: .alert)
                    alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
                    self.present(alert, animated: true)
                    
                    self.textField.isEnabled = true
                    self.activityIndicator.stopAnimating()
                    return
                }
                self.delegate?.didLogin(with: controller)
            }
        }
        
        self.authSession!.presentationContextProvider = self
        self.authSession!.start()
    }

}

extension LoginViewController: ASWebAuthenticationPresentationContextProviding {
    func presentationAnchor(for session: ASWebAuthenticationSession) -> ASPresentationAnchor {
        return self.view.window!
    }
}