//
//  CalendarManager.swift
//  DynamicIsland
//
//  Created by Harsh Vardhan  Goswami  on 08/09/24.
//

import Defaults
import EventKit
import SwiftUI

// MARK: - CalendarManager

@MainActor
class CalendarManager: ObservableObject {
    static let shared = CalendarManager()

    @Published var currentWeekStartDate: Date
    @Published var events: [EventModel] = []
    @Published var allCalendars: [CalendarModel] = []
    @Published var eventCalendars: [CalendarModel] = []
    @Published var reminderLists: [CalendarModel] = []
    @Published var selectedCalendarIDs: Set<String> = []
    @Published var calendarAuthorizationStatus: EKAuthorizationStatus = .notDetermined
    @Published var reminderAuthorizationStatus: EKAuthorizationStatus = .notDetermined

    private var selectedCalendars: [CalendarModel] = []
    private let calendarService = CalendarService()
    private var lastEventsFetchDate: Date?
    private let reloadRefreshInterval: TimeInterval = 15
    private var eventStoreChangedObserver: NSObjectProtocol?

    var hasCalendarAccess: Bool { isAuthorized(calendarAuthorizationStatus) }
    var hasReminderAccess: Bool { isAuthorized(reminderAuthorizationStatus) }

    private init() {
        currentWeekStartDate = CalendarManager.startOfDay(Date())
        setupEventStoreChangedObserver()
        Task {
            await reloadCalendarAndReminderLists()
        }
    }

    deinit {
        if let observer = eventStoreChangedObserver {
            NotificationCenter.default.removeObserver(observer)
        }
    }

    private func setupEventStoreChangedObserver() {
        eventStoreChangedObserver = NotificationCenter.default.addObserver(
            forName: .EKEventStoreChanged,
            object: nil,
            queue: .main
        ) { [weak self] _ in
            Task {
                guard let self else { return }
                await self.reloadCalendarAndReminderLists()
                await self.maybeRefreshEventsAfterReload()
            }
        }
    }

    @MainActor
    func reloadCalendarAndReminderLists() async {
        let allCalendars = await calendarService.calendars()
        eventCalendars = allCalendars.filter { !$0.isReminder }
        reminderLists = allCalendars.filter { $0.isReminder }
        self.allCalendars = allCalendars
        updateSelectedCalendars()
    }

    @MainActor
    private func maybeRefreshEventsAfterReload() async {
        guard hasCalendarAccess else { return }
        let now = Date()
        if let lastFetch = lastEventsFetchDate, now.timeIntervalSince(lastFetch) < reloadRefreshInterval {
            return
        }
        await updateEvents()
    }

    private func isAuthorized(_ status: EKAuthorizationStatus) -> Bool {
        switch status {
        case .authorized, .fullAccess:
            return true
        default:
            return false
        }
    }

    func checkCalendarAuthorization() async {
        let status = EKEventStore.authorizationStatus(for: .event)
        calendarAuthorizationStatus = status

        switch status {
        case .notDetermined:
            let granted = await calendarService.requestAccess(to: .event)
            calendarAuthorizationStatus = granted ? .fullAccess : .denied
            if granted {
                await reloadCalendarAndReminderLists()
                await updateEvents()
            }
        case .restricted, .denied:
            NSLog("Calendar access denied or restricted")
        case .authorized, .fullAccess:
            await reloadCalendarAndReminderLists()
            await updateEvents()
        case .writeOnly:
            NSLog("Calendar write only")
        @unknown default:
            NSLog("Unknown calendar authorization status")
        }
    }

    func checkReminderAuthorization() async {
        let status = EKEventStore.authorizationStatus(for: .reminder)
        reminderAuthorizationStatus = status

        switch status {
        case .notDetermined:
            let granted = await calendarService.requestAccess(to: .reminder)
            reminderAuthorizationStatus = granted ? .fullAccess : .denied
            if granted {
                await reloadCalendarAndReminderLists()
            }
        case .restricted, .denied:
            NSLog("Reminder access denied or restricted")
        case .authorized, .fullAccess:
            await reloadCalendarAndReminderLists()
        case .writeOnly:
            NSLog("Reminder write only")
        @unknown default:
            NSLog("Unknown reminder authorization status")
        }
    }

    func updateSelectedCalendars() {
        switch Defaults[.calendarSelectionState] {
        case .all:
            selectedCalendarIDs = Set(allCalendars.map { $0.id })
        case .selected(let identifiers):
            selectedCalendarIDs = identifiers
        }

        selectedCalendars = allCalendars.filter { selectedCalendarIDs.contains($0.id) }
    }

    func getCalendarSelected(_ calendar: CalendarModel) -> Bool {
        selectedCalendarIDs.contains(calendar.id)
    }

    func setCalendarSelected(_ calendar: CalendarModel, isSelected: Bool) async {
        var selectionState = Defaults[.calendarSelectionState]

        switch selectionState {
        case .all:
            if !isSelected {
                let identifiers = Set(allCalendars.map { $0.id }).subtracting([calendar.id])
                selectionState = .selected(identifiers)
            }
        case .selected(var identifiers):
            if isSelected {
                identifiers.insert(calendar.id)
            } else {
                identifiers.remove(calendar.id)
            }

            if identifiers.isEmpty || identifiers.count == allCalendars.count {
                selectionState = .all
            } else {
                selectionState = .selected(identifiers)
            }
        }

        Defaults[.calendarSelectionState] = selectionState
        updateSelectedCalendars()
        await updateEvents()
    }

    static func startOfDay(_ date: Date) -> Date {
        Calendar.current.startOfDay(for: date)
    }

    func updateCurrentDate(_ date: Date) async {
        currentWeekStartDate = Calendar.current.startOfDay(for: date)
        await updateEvents()
    }

    private func updateEvents() async {
        let calendarIDs = selectedCalendars.map { $0.id }
        let events = await calendarService.events(
            from: currentWeekStartDate,
            to: Calendar.current.date(byAdding: .day, value: 1, to: currentWeekStartDate)!,
            calendars: calendarIDs
        )
        self.events = events
        lastEventsFetchDate = Date()
    }

    func setReminderCompleted(reminderID: String, completed: Bool) async {
        await calendarService.setReminderCompleted(reminderID: reminderID, completed: completed)
        await updateEvents()
    }
}