EventViewModel.swift

//
//  EventViewModel.swift
//  FOSSAsia
//
//  Created by Jurvis Tan on 29/1/16.
//  Copyright © 2016 FossAsia. All rights reserved.
//

import Foundation
import UserNotifications

typealias EventViewModelCompletionHandler = (EventViewModel?, Error?) -> Void

protocol EventTypePresentable {
    var typeColor: UIColor { get }
}

protocol EventDetailsPresentable {
    var eventName: String { get }
    var speakerNames: String { get }
    var timing: String { get }
    var isFavorite: Bool { get }
}

protocol EventDescriptionPresentable {
    var eventDescription: String { get }
}

protocol EventAddToCalendarPresentable {
    var eventStartTime: String { get }
    var eventEndTime: String { get }
    var eventDay: String { get }
    var eventDate: String { get }
    var eventMonth: String { get }
    var eventStartDate: Date { get }
    var eventEndDate: Date { get }
}

struct EventViewModel: EventTypePresentable, EventDetailsPresentable, EventDescriptionPresentable, EventAddToCalendarPresentable {
    let sessionId: Observable<String>
    let track: Observable<UIColor>
    let title: Observable<String>
    let shortDescription: Observable<String>
    let speakers: Observable<[Speaker]?>
    let location: Observable<String>
    let startDateTime: Observable<Date>
    let endDateTime: Observable<Date>
    let favorite: Observable<Bool>

    // MARK: - Services
    fileprivate var eventsService: EventProvider

    init(_ event: Event) {
        sessionId = Observable(event.id)
        track = Observable(event.trackCode.getTrackColor())
        title = Observable(event.title)
        shortDescription = Observable(event.shortDescription)
        speakers = Observable(event.speakers)
        location = Observable(event.location)
        startDateTime = Observable(event.startDateTime)
        endDateTime = Observable(event.endDateTime)
        favorite = Observable(event.favorite)

        // Dependency Injections
        eventsService = EventProvider()
    }

    func favoriteEvent(_ completionHandler: @escaping EventViewModelCompletionHandler) {
        eventsService.toggleFavorite(self.sessionId.value) { (error) -> Void in
            guard error == nil else {
                completionHandler(nil, error)
                return
            }

            self.updateFavorite()
            completionHandler(self, nil)
        }
    }

    fileprivate func updateFavorite() {
        favorite.value = !favorite.value
        if !favorite.value {
            createLocalNotification()
        } else {
            cancelLocalNotification()
        }
    }

    // MARK: - Create Local Notification
    fileprivate func createLocalNotification() {
        // request authorization for local notification
        let center = UNUserNotificationCenter.current()
        center.requestAuthorization(options: [.alert, .sound]) { (granted, error) in
            // Enable or disable features based on authorization.
        }
        let localNotificationContent = UNMutableNotificationContent()
        localNotificationContent.body = "\(self.title) starts in 15 minutes at \(location)!"
        localNotificationContent.sound = UNNotificationSound.default()
        localNotificationContent.userInfo = ["sessionID": sessionId.value]
        // Trigger notification
        let triggerDate = (self.startDateTime.value as Date).addingTimeInterval(-15 * 60)
        let trigger = UNCalendarNotificationTrigger(dateMatching: Calendar.current.dateComponents([.minute, .hour, .day], from: triggerDate), repeats: false)
        let identifier = Constants.localNotificationIdentifier
        let request = UNNotificationRequest(identifier: identifier, content: localNotificationContent, trigger: trigger)
        center.add(request, withCompletionHandler: { (error) in
            if error != nil {
                print("Something went wrong")
            }
        })

    }

    // MARK: - Remove Notification
    fileprivate func cancelLocalNotification() {
        let center = UNUserNotificationCenter.current()
        center.removeAllPendingNotificationRequests()
    }

}

// MARK: - EventDescriptionPresentable Conformance
extension EventViewModel {
    var eventDescription: String { return shortDescription.value }
}

// MARK: - TypePresentable Conformance
extension EventViewModel {
    var typeColor: UIColor { return self.track.value }
}

// MARK: - EventPresentable Conformance
extension EventViewModel {
    var eventName: String { return self.title.value }
    var speakerNames: String {
        let speakers = self.speakers.value
        var speakersNames: [String] = []
        for speaker in speakers! {
            speakersNames.append(speaker.name)
        }
        return speakersNames.joined(separator: ", ")
    }
    var timing: String {
        if let startTime = (self.startDateTime.value as NSDate).formattedDate(withFormat: "HH:mm"), let endTime = (self.endDateTime.value as NSDate).formattedDate(withFormat: "HH:mm") {
            return "\(String(describing: startTime)) - \(String(describing: endTime)) - \(self.location.value)"
        }
        return "N/A"
    }
    var isFavorite: Bool { return self.favorite.value }
}

// MARK: - EventAddToCalendar Conformance
extension EventViewModel {
    var eventStartTime: String { return (self.startDateTime.value as NSDate).formattedDate(withFormat: "HH:mm") }
    var eventEndTime: String { return (self.endDateTime.value as NSDate).formattedDate(withFormat: "HH:mm") }
    var eventDate: String { return (self.startDateTime.value as NSDate).formattedDate(withFormat: "dd") }
    var eventDay: String { return (self.startDateTime.value as NSDate).formattedDate(withFormat: "EEEE") }
    var eventMonth: String { return (self.startDateTime.value as NSDate).formattedDate(withFormat: "MMM") }
    var eventStartDate: Date { return self.startDateTime.value }
    var eventEndDate: Date { return self.endDateTime.value }
}