import UIKit

class ToDoTVCell: UITableViewCell {

    @IBOutlet weak var titleLabel: UILabel!
    @IBOutlet weak var dateLabel: UILabel!
}

import Foundation

struct ToDoItem {
    let title: String
    let deadline: Date
}

import UIKit

class AddToDoVC: UIViewController {

    @IBOutlet weak var titleTextField: UITextField!
    @IBOutlet weak var deadlineDatePicker: UIDatePicker!

    // closure comes to rescue for passing the new item
    // to able to add this to an array (toDoItems in the ViewController)
    // we use type function - optional
    var onSave: ((ToDoItem) -> Void)?

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func addToDo(_ sender: UIButton) {
        guard let title = titleTextField.text, !title.isEmpty else {
            return
        }
        let deadline = deadlineDatePicker.date

        print(deadline)

        // create an instnace of new item
        let newItem = ToDoItem(title: title, deadline: deadline)

        // use closure
        onSave?(newItem)

        // go back to main
        self.navigationController?.popViewController(animated: true)
    }
}

import UIKit

// import this for notification
import UserNotifications

class ViewController: UIViewController {

    var toDoItems: [ToDoItem] = [] {
        didSet {
            tableView.reloadData()
        }
    }

    @IBOutlet weak var tableView: UITableView!

    override func viewDidLoad() {
        super.viewDidLoad()

        tableView.dataSource = self
        tableView.delegate = self
    }

    func scheduleNotification(for item: ToDoItem) {
        let content = UNMutableNotificationContent()
        content.title = "ToDo Reminder"
        content.body = "Don't forget: \(item.title)"
        content.sound = .default

        // get the DateComponents for dateMatching for creating a trigger
        let calender = Calendar.current
        let components = calender.dateComponents([.year, .month, .day, .hour, .minute], from: item.deadline)

        // create a trigger
        let trigger = UNCalendarNotificationTrigger(dateMatching: components, repeats: false)

        // to set the notification -> we need to create a notification request
        // don't use item.title for the indentifier. not recommended. maybe uuid
        let request = UNNotificationRequest(identifier: item.title, content: content, trigger: trigger)

        // add the request to the notification center
        UNUserNotificationCenter.current().add(request) { error in
            if let error = error {
                print("Error scheduling notification: \(error)")
            }
        }
    }

    // *use closure here
    // how to transfer data from destination to source
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        guard let addToDoVC = segue.destination as? AddToDoVC else {
            return
        }

        // will be invoked when onSave() was called in addToDo() of AddToDoVC using closure
        // you can assign code block to onSave()
        addToDoVC.onSave = { newItem in
            self.toDoItems.append(newItem)

            // schedule notification
            self.scheduleNotification(for: newItem)
        }
    }
}

extension ViewController: UITableViewDelegate, UITableViewDataSource {
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return toDoItems.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        guard let cell = tableView.dequeueReusableCell(withIdentifier: "ToDoCell", for: indexPath) as? ToDoTVCell else { return UITableViewCell() }

        let toDoItem = toDoItems[indexPath.row]

        // date formatter
        let formatter = DateFormatter()
        formatter.dateFormat = "dd-MM-yyyy HH:mm"
        let formmattedDate = formatter.string(from: toDoItem.deadline)

        cell.titleLabel.text = toDoItem.title
        cell.dateLabel.text = formmattedDate

        return cell
    }

    // delete the data -> remove pending notification as well
    func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete {
            // cancel the notification
            let item = toDoItems[indexPath.row]
            UNUserNotificationCenter.current().removePendingNotificationRequests(withIdentifiers: [item.title])

            // remove the item from the data source
            toDoItems.remove(at: indexPath.row)
        }
    }
}

import UIKit

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
    // this one is the first one invoked when running the application
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.

        // get the authorization from user to allow notification
        let center = UNUserNotificationCenter.current()
        center.requestAuthorization(options: [.alert, .sound]) { granted, error in
            // handle the response if needed
            // command + shift + h -> minimize the app to see if notification works!

        }
        return true
    }

    // MARK: UISceneSession Lifecycle

    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        // Called when a new scene session is being created.
        // Use this method to select a configuration to create the new scene with.
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }
}