//
//  SettingsViewModel.swift
//  Mastodon
//
//  Created by ihugo on 2021/4/7.
//

import Combine
import CoreData
import CoreDataStack
import Foundation
import MastodonSDK
import UIKit
import os.log

class SettingsViewModel: NSObject {
    // confirm set only once
    weak var context: AppContext! { willSet { precondition(context == nil) } }
    
    var dataSource: UITableViewDiffableDataSource<SettingsSection, SettingsItem>!
    var disposeBag = Set<AnyCancellable>()
    var updateDisposeBag = Set<AnyCancellable>()
    var createDisposeBag = Set<AnyCancellable>()
    
    let viewDidLoad = PassthroughSubject<Void, Never>()
    lazy var fetchResultsController: NSFetchedResultsController<Setting> = {
        let fetchRequest = Setting.sortedFetchRequest
        if let box =
            self.context.authenticationService.activeMastodonAuthenticationBox.value {
            let domain = box.domain
            fetchRequest.predicate = Setting.predicate(domain: domain, userID: box.userID)
        }
        
        fetchRequest.fetchLimit = 1
        fetchRequest.returnsObjectsAsFaults = false
        let controller = NSFetchedResultsController(
            fetchRequest: fetchRequest,
            managedObjectContext: context.managedObjectContext,
            sectionNameKeyPath: nil,
            cacheName: nil
        )
        controller.delegate = self
        return controller
    }()
    let setting = CurrentValueSubject<Setting?, Never>(nil)
    
    /// create a subscription when:
    /// - does not has one
    /// - does not find subscription for selected trigger when change trigger
    let createSubscriptionSubject = PassthroughSubject<(triggerBy: String, values: [Bool?]), Never>()
    
    /// update a subscription when:
    /// - change switch for specified alerts
    let updateSubscriptionSubject = PassthroughSubject<(triggerBy: String, values: [Bool?]), Never>()
    
    lazy var notificationDefaultValue: [String: [Bool?]] = {
        let followerSwitchItems: [Bool?] = [true, nil, true, true]
        let anyoneSwitchItems: [Bool?] = [true, true, true, true]
        let noOneSwitchItems: [Bool?] = [nil, nil, nil, nil]
        let followSwitchItems: [Bool?] = [true, true, true, true]
        
        let anyone = L10n.Scene.Settings.Section.Notifications.Trigger.anyone
        let follower = L10n.Scene.Settings.Section.Notifications.Trigger.follower
        let follow = L10n.Scene.Settings.Section.Notifications.Trigger.follow
        let noOne = L10n.Scene.Settings.Section.Notifications.Trigger.noone
        return [anyone: anyoneSwitchItems,
                follower: followerSwitchItems,
                follow: followSwitchItems,
                noOne: noOneSwitchItems]
    }()
    
    lazy var privacyURL: URL? = {
        guard let box = AppContext.shared.authenticationService.activeMastodonAuthenticationBox.value else {
            return nil
        }
        
        return Mastodon.API.privacyURL(domain: box.domain)
    }()
    
    /// to store who trigger the notification.
    var triggerBy: String?
    
    struct Input {
    }

    struct Output {
    }
    
    init(context: AppContext) {
        self.context = context
        
        super.init()
    }
    
    func transform(input: Input?) -> Output? {
        typealias SubscriptionResponse = Mastodon.Response.Content<Mastodon.Entity.Subscription>
        createSubscriptionSubject
            .debounce(for: .milliseconds(300), scheduler: DispatchQueue.main)
            .sink { _ in
            } receiveValue: { [weak self] (arg) in
                let (triggerBy, values) = arg
                guard let self = self else {
                    return
                }
                guard let activeMastodonAuthenticationBox =
                        self.context.authenticationService.activeMastodonAuthenticationBox.value else {
                    return
                }
                guard values.count >= 4 else {
                    return
                }
                
                self.createDisposeBag.removeAll()
                typealias Query = Mastodon.API.Subscriptions.CreateSubscriptionQuery
                let domain = activeMastodonAuthenticationBox.domain
                let query = Query(
                    // FIXME: to replace the correct endpoint, p256dh, auth
                    endpoint: "http://www.google.com",
                    p256dh: "BLQELIDm-6b9Bl07YrEuXJ4BL_YBVQ0dvt9NQGGJxIQidJWHPNa9YrouvcQ9d7_MqzvGS9Alz60SZNCG3qfpk=",
                    auth: "4vQK-SvRAN5eo-8ASlrwA==",
                    favourite: values[0],
                    follow: values[1],
                    reblog: values[2],
                    mention: values[3],
                    poll: nil
                )
                self.context.apiService.changeSubscription(
                    domain: domain,
                    mastodonAuthenticationBox: activeMastodonAuthenticationBox,
                    query: query,
                    triggerBy: triggerBy,
                    userID: activeMastodonAuthenticationBox.userID
                )
                .sink { (_) in
                } receiveValue: { (_) in
                }
                .store(in: &self.createDisposeBag)
            }
            .store(in: &disposeBag)
        
        updateSubscriptionSubject
            .debounce(for: .milliseconds(300), scheduler: DispatchQueue.main)
            .sink { _ in
            } receiveValue: { [weak self] (arg) in
                let (triggerBy, values) = arg
                guard let self = self else {
                    return
                }
                guard let activeMastodonAuthenticationBox =
                        self.context.authenticationService.activeMastodonAuthenticationBox.value else {
                    return
                }
                guard values.count >= 4 else {
                    return
                }
                
                self.updateDisposeBag.removeAll()
                typealias Query = Mastodon.API.Subscriptions.UpdateSubscriptionQuery
                let domain = activeMastodonAuthenticationBox.domain
                let query = Query(
                    favourite: values[0],
                    follow: values[1],
                    reblog: values[2],
                    mention: values[3],
                    poll: nil)
                self.context.apiService.updateSubscription(
                    domain: domain,
                    mastodonAuthenticationBox: activeMastodonAuthenticationBox,
                    query: query,
                    triggerBy: triggerBy,
                    userID: activeMastodonAuthenticationBox.userID
                )
                .sink { (_) in
                } receiveValue: { (_) in
                }
                .store(in: &self.updateDisposeBag)
            }
            .store(in: &disposeBag)
        
        // build data for table view
        buildDataSource()
        
        // request subsription data for updating or initialization
        requestSubscription()
        return nil
    }
    
    // MARK: - Private methods
    fileprivate func processDataSource(_ settings: Setting?) {
        var snapshot = NSDiffableDataSourceSnapshot<SettingsSection, SettingsItem>()
        
        // appearance
        let appearnceMode = SettingsItem.AppearanceMode(rawValue: settings?.appearance ?? "") ?? .automatic
        let appearanceItem = SettingsItem.apperance(item: appearnceMode)
        let appearance = SettingsSection.apperance(title: L10n.Scene.Settings.Section.Appearance.title, selectedMode:appearanceItem)
        snapshot.appendSections([appearance])
        snapshot.appendItems([appearanceItem])
        
        // notifications
        var switches: [Bool?]?
        if let alerts = settings?.subscription?.first(where: { (s) -> Bool in
            return s.type == settings?.triggerBy
        })?.alert {
            var items = [Bool?]()
            items.append(alerts.favourite?.boolValue)
            items.append(alerts.follow?.boolValue)
            items.append(alerts.reblog?.boolValue)
            items.append(alerts.mention?.boolValue)
            switches = items
        } else if let triggerBy = settings?.triggerBy,
                  let values = self.notificationDefaultValue[triggerBy] {
            switches = values
        } else {
            // fallback a default value
            let anyone = L10n.Scene.Settings.Section.Notifications.Trigger.anyone
            switches = self.notificationDefaultValue[anyone]
        }
        
        let notifications = [L10n.Scene.Settings.Section.Notifications.favorites,
                             L10n.Scene.Settings.Section.Notifications.follows,
                             L10n.Scene.Settings.Section.Notifications.boosts,
                             L10n.Scene.Settings.Section.Notifications.mentions,]
        var notificationItems = [SettingsItem]()
        for (i, noti) in notifications.enumerated() {
            var value: Bool? = nil
            if let switches = switches, i < switches.count {
                value = switches[i]
            }
            
            let item = SettingsItem.notification(item: SettingsItem.NotificationSwitch(title: noti, isOn: value == true, enable: value != nil))
            notificationItems.append(item)
        }
        let notificationSection = SettingsSection.notifications(title: L10n.Scene.Settings.Section.Notifications.title, items: notificationItems)
        snapshot.appendSections([notificationSection])
        snapshot.appendItems(notificationItems)
        
        // boring zone
        let boringLinks = [L10n.Scene.Settings.Section.Boringzone.terms,
                           L10n.Scene.Settings.Section.Boringzone.privacy]
        var boringLinkItems = [SettingsItem]()
        for l in boringLinks {
            let item = SettingsItem.boringZone(item: SettingsItem.Link(title: l, color: .systemBlue))
            boringLinkItems.append(item)
        }
        let boringSection = SettingsSection.boringZone(title: L10n.Scene.Settings.Section.Boringzone.title, items: boringLinkItems)
        snapshot.appendSections([boringSection])
        snapshot.appendItems(boringLinkItems)
        
        // spicy zone
        let spicyLinks = [L10n.Scene.Settings.Section.Spicyzone.clear,
                          L10n.Scene.Settings.Section.Spicyzone.signout]
        var spicyLinkItems = [SettingsItem]()
        for l in spicyLinks {
            let item = SettingsItem.spicyZone(item: SettingsItem.Link(title: l, color: .systemRed))
            spicyLinkItems.append(item)
        }
        let spicySection = SettingsSection.spicyZone(title: L10n.Scene.Settings.Section.Spicyzone.title, items: spicyLinkItems)
        snapshot.appendSections([spicySection])
        snapshot.appendItems(spicyLinkItems)
        
        self.dataSource.apply(snapshot, animatingDifferences: false)
    }
    
    private func buildDataSource() {
        setting.sink { [weak self] (settings) in
            guard let self = self else { return }
            self.processDataSource(settings)
        }
        .store(in: &disposeBag)
    }
    
    private func requestSubscription() {
        setting.sink { [weak self] (settings) in
            guard let self = self else { return }
            guard settings != nil else { return }
            guard self.triggerBy != settings?.triggerBy else { return }
            self.triggerBy = settings?.triggerBy
            
            var switches: [Bool?]?
            var who: String?
            if let alerts = settings?.subscription?.first(where: { (s) -> Bool in
                return s.type == settings?.triggerBy
            })?.alert {
                var items = [Bool?]()
                items.append(alerts.favourite?.boolValue)
                items.append(alerts.follow?.boolValue)
                items.append(alerts.reblog?.boolValue)
                items.append(alerts.mention?.boolValue)
                switches = items
                who = settings?.triggerBy
            } else if let triggerBy = settings?.triggerBy,
                      let values = self.notificationDefaultValue[triggerBy] {
                switches = values
                who = triggerBy
            } else {
                // fallback a default value
                let anyone = L10n.Scene.Settings.Section.Notifications.Trigger.anyone
                switches = self.notificationDefaultValue[anyone]
                who = anyone
            }
            
            // should create a subscription whenever change trigger
            if let values = switches, let triggerBy = who {
                self.createSubscriptionSubject.send((triggerBy: triggerBy, values: values))
            }
        }
        .store(in: &disposeBag)
        
        guard let activeMastodonAuthenticationBox = self.context.authenticationService.activeMastodonAuthenticationBox.value else {
            return
        }
        let domain = activeMastodonAuthenticationBox.domain
        let userId = activeMastodonAuthenticationBox.userID
        
        do {
            try fetchResultsController.performFetch()
            if nil == fetchResultsController.fetchedObjects?.first {
                let anyone = L10n.Scene.Settings.Section.Notifications.Trigger.anyone
                setting.value =  self.context.apiService.createSettingIfNeed(domain: domain,
                                                                             userId: userId,
                                                                             triggerBy: anyone)
            } else {
                setting.value = fetchResultsController.fetchedObjects?.first
            }
        } catch {
            assertionFailure(error.localizedDescription)
        }
    }
    
    deinit {
        os_log(.info, log: .debug, "%{public}s[%{public}ld], %{public}s:", ((#file as NSString).lastPathComponent), #line, #function)
    }
}

// MARK: - NSFetchedResultsControllerDelegate
extension SettingsViewModel: NSFetchedResultsControllerDelegate {
    
    func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
         os_log("%{public}s[%{public}ld], %{public}s", ((#file as NSString).lastPathComponent), #line, #function)
    }

    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        guard controller === fetchResultsController else {
            return
        }
        
        setting.value = fetchResultsController.fetchedObjects?.first
    }
    
}

enum SettingsSection: Hashable {
    case apperance(title: String, selectedMode: SettingsItem)
    case notifications(title: String, items: [SettingsItem])
    case boringZone(title: String, items: [SettingsItem])
    case spicyZone(title: String, items: [SettingsItem])
    
    var title: String {
        switch self {
        case .apperance(let title, _),
             .notifications(let title, _),
             .boringZone(let title, _),
             .spicyZone(let title, _):
            return title
        }
    }
}

enum SettingsItem: Hashable {
    enum AppearanceMode: String {
        case automatic
        case light
        case dark
    }
    
    struct NotificationSwitch: Hashable {
        let title: String
        let isOn: Bool
        let enable: Bool
    }
    
    struct Link: Hashable {
        let title: String
        let color: UIColor
    }
    
    case apperance(item: AppearanceMode)
    case notification(item: NotificationSwitch)
    case boringZone(item: Link)
    case spicyZone(item: Link)
}