//
//  MainTabBarController.swift
//  Mastodon
//
//  Created by Cirno MainasuK on 2021-1-27.
//

import UIKit
import Combine
import CoreDataStack
import SafariServices
import MastodonAsset
import MastodonCore
import MastodonLocalization
import MastodonUI

class MainTabBarController: UITabBarController {

    public var disposeBag = Set<AnyCancellable>()
    
    weak var context: AppContext!
    weak var coordinator: SceneCoordinator!
    
    var authContext: AuthContext?
    
    private let largeContentViewerInteraction = UILargeContentViewerInteraction()
    
    static let avatarButtonSize = CGSize(width: 25, height: 25)
    let avatarButton = CircleAvatarButton()
    let accountSwitcherChevron = UIImageView(
        image: .chevronUpChevronDown?.withConfiguration(
            UIImage.SymbolConfiguration(weight: .bold)
        )
    )
    
    @Published var currentTab: Tab = .home
        
    enum Tab: Int, CaseIterable {
        case home
        case search
        case compose
        case notifications
        case me

        var tag: Int {
            return rawValue
        }
        
        var title: String {
            switch self {
            case .home:             return L10n.Common.Controls.Tabs.home
            case .search:           return L10n.Common.Controls.Tabs.searchAndExplore
            case .compose:          return L10n.Common.Controls.Actions.compose
            case .notifications:    return L10n.Common.Controls.Tabs.notifications
            case .me:               return L10n.Common.Controls.Tabs.profile
            }
        }

        var inputLabels: [String]? {
            switch self {
            case .home, .compose, .notifications, .me:
                return nil
            case .search:
                return [
                    L10n.Common.Controls.Tabs.A11Y.search,
                    L10n.Common.Controls.Tabs.A11Y.explore,
                    L10n.Common.Controls.Tabs.searchAndExplore
                ]
            }
        }
        
        var image: UIImage {
            switch self {
                case .home:             return UIImage(systemName: "house")!
                case .search:           return UIImage(systemName: "magnifyingglass")!
                case .compose:          return UIImage(systemName: "square.and.pencil")!
                case .notifications:    return UIImage(systemName: "bell")!
                case .me:               return UIImage(systemName: "person")!
            }
        }
        
        var selectedImage: UIImage {
            return image.withTintColor(Asset.Colors.Brand.blurple.color, renderingMode: .alwaysOriginal)
        }

        var largeImage: UIImage {
            return image.withRenderingMode(.alwaysTemplate).resized(size: CGSize(width: 80, height: 80))
        }

        @MainActor
        func viewController(context: AppContext, authContext: AuthContext?, coordinator: SceneCoordinator) async -> UIViewController {
            guard let authContext, let me = authContext.mastodonAuthenticationBox.authentication.account() else {
                return UITableViewController()
            }

            let viewController: UIViewController
            switch self {
                case .home:
                    let _viewController = HomeTimelineViewController()
                    _viewController.context = context
                    _viewController.coordinator = coordinator
                    _viewController.viewModel = .init(context: context, authContext: authContext)
                    viewController = _viewController
                case .search:
                    let _viewController = SearchViewController()
                    _viewController.context = context
                    _viewController.coordinator = coordinator
                    _viewController.viewModel = .init(context: context, authContext: authContext)
                    viewController = _viewController
                case .compose:
                    viewController = UIViewController()
                case .notifications:
                    let _viewController = NotificationViewController()
                    _viewController.context = context
                    _viewController.coordinator = coordinator
                    _viewController.viewModel = .init(context: context, authContext: authContext)
                    viewController = _viewController
                case .me:
                    let _viewController = ProfileViewController()
                    _viewController.context = context
                    _viewController.coordinator = coordinator
                    _viewController.viewModel = ProfileViewModel(context: context, authContext: authContext, account: me, relationship: nil, me: me)
                    viewController = _viewController
            }
            viewController.title = self.title
            return AdaptiveStatusBarStyleNavigationController(rootViewController: viewController)
        }
    }
    
    var _viewControllers: [UIViewController] = []
    
    private(set) var isReadyForWizardAvatarButton = false
    
    // output
    @Published var avatarURL: URL?
    
    // haptic feedback
    private let selectionFeedbackGenerator = UIImpactFeedbackGenerator(style: .medium)
    
    init(
        context: AppContext,
        coordinator: SceneCoordinator,
        authContext: AuthContext?
    ) {
        self.context = context
        self.coordinator = coordinator
        self.authContext = authContext
        super.init(nibName: nil, bundle: nil)
        tabBar.addInteraction(largeContentViewerInteraction)
        
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
}

extension MainTabBarController {
    
    open override var childForStatusBarStyle: UIViewController? {
        return selectedViewController
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()

        delegate = self

        view.backgroundColor = .systemBackground

        // seealso: `ThemeService.apply(theme:)`
        Task { @MainActor in
            let tabs = Tab.allCases
            var viewControllers = [UIViewController]()
            
            for tab in tabs {
                let viewController = await tab.viewController(context: context, authContext: authContext, coordinator: coordinator)
                viewController.tabBarItem.tag = tab.tag
                viewController.tabBarItem.title = tab.title     // needs for acessiblity large content label
                viewController.tabBarItem.image = tab.image.imageWithoutBaseline()
                viewController.tabBarItem.largeContentSizeImage = tab.largeImage.imageWithoutBaseline()
                viewController.tabBarItem.accessibilityLabel = tab.title
                viewController.tabBarItem.accessibilityUserInputLabels = tab.inputLabels
                viewController.tabBarItem.imageInsets = UIEdgeInsets(top: 6, left: 0, bottom: -6, right: 0)
                viewControllers.append(viewController)
            }
            
            _viewControllers = viewControllers
            setViewControllers(viewControllers, animated: false)
            selectedIndex = 0
            
            
            // hacky workaround for FB11986255 (Setting accessibilityUserInputLabels on a UITabBarItem has no effect)
            DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(50)) {
                if let searchItem = self.tabBar.subviews.first(where: { $0.accessibilityLabel == Tab.search.title }) {
                    searchItem.accessibilityUserInputLabels = Tab.search.inputLabels
                }
            }
            
            context.apiService.error
                .receive(on: DispatchQueue.main)
                .sink { [weak self] error in
                    guard let self = self, let coordinator = self.coordinator else { return }
                    switch error {
                    case .implicit:
                        break
                    case .explicit:
                        let alertController = UIAlertController(for: error, title: nil, preferredStyle: .alert)
                        let okAction = UIAlertAction(title: "OK", style: .default, handler: nil)
                        alertController.addAction(okAction)
                        _ = coordinator.present(
                            scene: .alertController(alertController: alertController),
                            from: nil,
                            transition: .alertController(animated: true, completion: nil)
                        )
                    }
                }
                .store(in: &disposeBag)
            
            // handle post failure
            
            // handle push notification.
            // toggle entry when finish fetch latest notification
            Publishers.CombineLatest(
                context.notificationService.unreadNotificationCountDidUpdate,
                $currentTab
            )
            .receive(on: DispatchQueue.main)
            .sink { [weak self] authentication, currentTab in
                guard let self = self else { return }
                guard let notificationViewController = self.notificationViewController else { return }
                
                let authentication = self.authContext?.mastodonAuthenticationBox.userAuthorization
                let hasUnreadPushNotification: Bool = authentication.flatMap { authentication in
                    let count = UserDefaults.shared.getNotificationCountWithAccessToken(accessToken: authentication.accessToken)
                    return count > 0
                } ?? false
                
                let image: UIImage
                if hasUnreadPushNotification {
                    let imageConfiguration = UIImage.SymbolConfiguration(paletteColors: [.red, SystemTheme.tabBarItemNormalIconColor])
                    image = UIImage(systemName: "bell.badge", withConfiguration: imageConfiguration)!
                } else {
                    image = Tab.notifications.image
                }
                
                notificationViewController.tabBarItem.image = image.imageWithoutBaseline()
                notificationViewController.navigationController?.tabBarItem.image = image.imageWithoutBaseline()
            }
            .store(in: &disposeBag)
            layoutAvatarButton()
            
            $avatarURL
                .receive(on: DispatchQueue.main)
                .sink { [weak self] avatarURL in
                    guard let self = self else { return }
                    self.avatarButton.avatarImageView.setImage(
                        url: avatarURL,
                        placeholder: .placeholder(color: .systemFill),
                        scaleToSize: MainTabBarController.avatarButtonSize
                    )
                }
                .store(in: &disposeBag)
            
            NotificationCenter.default.publisher(for: .userFetched)
                .receive(on: DispatchQueue.main)
                .sink { [weak self] _ in
                    guard let self else { return }
                    if let account = self.authContext?.mastodonAuthenticationBox.authentication.account() {
                        self.avatarURL = account.avatarImageURL()
                        
                        // a11y
                        let _profileTabItem = self.tabBar.items?.first { item in item.tag == Tab.me.tag }
                        guard let profileTabItem = _profileTabItem else { return }
                        profileTabItem.accessibilityHint = L10n.Scene.AccountList.tabBarHint(account.displayNameWithFallback)
                        
                        self.context.authenticationService.updateActiveUserAccountPublisher
                            .sink { [weak self] in
                                self?.updateUserAccount()
                            }
                            .store(in: &self.disposeBag)
                    }
                }
                .store(in: &disposeBag)
            
            let tabBarLongPressGestureRecognizer = UILongPressGestureRecognizer()
            tabBarLongPressGestureRecognizer.addTarget(self, action: #selector(MainTabBarController.tabBarLongPressGestureRecognizerHandler(_:)))
            tabBarLongPressGestureRecognizer.delegate = self
            tabBar.addGestureRecognizer(tabBarLongPressGestureRecognizer)
            
            let tabBarDoubleTapGestureRecognizer = UITapGestureRecognizer()
            tabBarDoubleTapGestureRecognizer.numberOfTapsRequired = 2
            tabBarDoubleTapGestureRecognizer.addTarget(self, action: #selector(MainTabBarController.tabBarDoubleTapGestureRecognizerHandler(_:)))
            tabBarDoubleTapGestureRecognizer.delaysTouchesEnded = false
            tabBar.addGestureRecognizer(tabBarDoubleTapGestureRecognizer)
            
            self.isReadyForWizardAvatarButton = authContext != nil
            
            $currentTab
                .receive(on: DispatchQueue.main)
                .sink { [weak self] tab in
                    guard let self = self else { return }
                    self.updateAvatarButtonAppearance()
                }
                .store(in: &disposeBag)
            
            updateTabBarDisplay()
        }
    }
    
    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)
        
        updateTabBarDisplay()
        updateAvatarButtonAppearance()
    }

    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        .portraitOnPhone
    }
}

extension MainTabBarController {
    
    @objc private func composeButtonDidPressed(_ sender: Any) {

        selectionFeedbackGenerator.impactOccurred()
        guard let authContext = self.authContext else { return }
        let composeViewModel = ComposeViewModel(
            context: context,
            authContext: authContext,
            composeContext: .composeStatus,
            destination: .topLevel
        )
        _ = coordinator.present(scene: .compose(viewModel: composeViewModel), transition: .modal(animated: true, completion: nil))
    }
    
    private func touchedTab(by sender: UIGestureRecognizer) -> Tab? {
        var _tab: Tab?
        let location = sender.location(in: tabBar)
        for item in tabBar.items ?? [] {
            guard let tab = Tab(rawValue: item.tag) else { continue }
            guard let view = item.value(forKey: "view") as? UIView else { continue }
            guard view.frame.contains(location) else { continue}

            _tab = tab
            break
        }

        return _tab
    }
    
    @objc private func tabBarDoubleTapGestureRecognizerHandler(_ sender: UITapGestureRecognizer) {
        guard sender.state == .ended else { return }
        guard let tab = touchedTab(by: sender) else { return }

        switch tab {
        case .search:
            assert(Thread.isMainThread)
            // double tapping search tab opens the search bar without additional taps
            searchViewController?.searchBar.becomeFirstResponder()
        default:
            break
        }
    }
    
    @objc private func tabBarLongPressGestureRecognizerHandler(_ sender: UILongPressGestureRecognizer) {
        guard sender.state == .began else { return }
        guard let tab = touchedTab(by: sender) else { return }

        switch tab {
        case .me:
            guard let authContext = self.authContext else { return }
            let accountListViewModel = AccountListViewModel(context: context, authContext: authContext)
            _ = coordinator.present(scene: .accountList(viewModel: accountListViewModel), from: self, transition: .panModal)
        default:
            break
        }
    }
}

extension MainTabBarController {
    
    private func updateTabBarDisplay() {
        switch traitCollection.horizontalSizeClass {
        case .compact:
            tabBar.isHidden = false
        default:
            tabBar.isHidden = true
        }
    }

    private func layoutAvatarButton() {
        guard avatarButton.superview == nil else { return }
        
        let _profileTabItem = self.tabBar.items?.first { item in item.tag == Tab.me.tag }
        guard let profileTabItem = _profileTabItem else { return }
        guard let view = profileTabItem.value(forKey: "view") as? UIView else {
            return
        }
        
        let _anchorImageView = view.subviews.first { subview in subview is UIImageView } as? UIImageView
        guard let anchorImageView = _anchorImageView else {
            assertionFailure()
            return
        }
        anchorImageView.alpha = 0
        
        accountSwitcherChevron.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(accountSwitcherChevron)
        
        self.avatarButton.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(self.avatarButton)
        NSLayoutConstraint.activate([
            self.avatarButton.centerXAnchor.constraint(equalTo: anchorImageView.centerXAnchor),
            self.avatarButton.centerYAnchor.constraint(equalTo: anchorImageView.centerYAnchor),
            self.avatarButton.widthAnchor.constraint(equalToConstant: MainTabBarController.avatarButtonSize.width).priority(.required - 1),
            self.avatarButton.heightAnchor.constraint(equalToConstant: MainTabBarController.avatarButtonSize.height).priority(.required - 1),
            accountSwitcherChevron.widthAnchor.constraint(equalToConstant: 10),
            accountSwitcherChevron.heightAnchor.constraint(equalToConstant: 18),
            accountSwitcherChevron.leadingAnchor.constraint(equalTo: avatarButton.trailingAnchor, constant: 8),
            accountSwitcherChevron.centerYAnchor.constraint(equalTo: avatarButton.centerYAnchor)
        ])
        self.avatarButton.setContentHuggingPriority(.required - 1, for: .horizontal)
        self.avatarButton.setContentHuggingPriority(.required - 1, for: .vertical)
        self.avatarButton.isUserInteractionEnabled = false
    }
    
    private func updateAvatarButtonAppearance() {
        if currentTab == .me {
            accountSwitcherChevron.tintColor = Asset.Colors.Brand.blurple.color
            avatarButton.borderColor = Asset.Colors.Brand.blurple.color
        } else {
            accountSwitcherChevron.tintColor = Asset.Theme.System.tabBarItemInactiveIconColor.color
            avatarButton.borderColor = Asset.Theme.System.tabBarItemInactiveIconColor.color
        }

        avatarButton.setNeedsLayout()
    }
    
    private func updateUserAccount() {
        guard let authContext = authContext else { return }
        
        Task { @MainActor in
            let profileResponse = try await context.apiService.authenticatedUserInfo(
                authenticationBox: authContext.mastodonAuthenticationBox
            )
            
            if let user = authContext.mastodonAuthenticationBox.authentication.user(
                in: context.managedObjectContext
            ) {
                user.update(
                    property: .init(
                        entity: profileResponse.value,
                        domain: authContext.mastodonAuthenticationBox.domain
                    )
                )
            }
        }
    }
}

extension MainTabBarController {

    var notificationViewController: NotificationViewController? {
        return viewController(of: NotificationViewController.self)
    }
    
    var searchViewController: SearchViewController? {
        return viewController(of: SearchViewController.self)
    }
    
}

// MARK: - UITabBarControllerDelegate
extension MainTabBarController: UITabBarControllerDelegate {
    func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
        if let tab = Tab(rawValue: viewController.tabBarItem.tag), tab == .compose {
            composeButtonDidPressed(tabBarController)
            return false
        }
        
        // Different tab has been selected, send haptic feedback
        if viewController.tabBarItem.tag != tabBarController.selectedIndex {
            selectionFeedbackGenerator.impactOccurred()
        }

        // Assert index is as same as the tab rawValue. This check needs to be done `shouldSelect`
        // because the nav controller has already popped in `didSelect`.
        if currentTab.rawValue == viewController.tabBarItem.tag,
           let navigationController = viewController as? UINavigationController,
           navigationController.viewControllers.count == 1,
           let scrollViewContainer = navigationController.topViewController as? ScrollViewContainer  {
            scrollViewContainer.scrollToTop(animated: true)
        }

        return true
    }

    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        if let tab = Tab(rawValue: viewController.tabBarItem.tag) {
            currentTab = tab
        }
    }
}

// HIG: keyboard UX
// https://developer.apple.com/design/human-interface-guidelines/macos/user-interaction/keyboard/
extension MainTabBarController {
    
    var switchToTabKeyCommands: [UIKeyCommand] {
        var commands: [UIKeyCommand] = []
        let tabs: [Tab] = [
            .home,
            .search,
            .notifications,
            .me
        ]
        for (i, tab) in tabs.enumerated() {
            let title = L10n.Common.Controls.Keyboard.Common.switchToTab(tab.title)
            let input = String(i + 1)
            let command = UIKeyCommand(
                title: title,
                image: nil,
                action: #selector(MainTabBarController.switchToTabKeyCommandHandler(_:)),
                input: input,
                modifierFlags: .command,
                propertyList: tab.rawValue,
                alternates: [],
                discoverabilityTitle: nil,
                attributes: [],
                state: .off
            )
            commands.append(command)
        }
        return commands
    }
    
    var showFavoritesKeyCommand: UIKeyCommand {
        UIKeyCommand(
            title: L10n.Common.Controls.Keyboard.Common.showFavorites,
            image: nil,
            action: #selector(MainTabBarController.showFavoritesKeyCommandHandler(_:)),
            input: "f",
            modifierFlags: .command,
            propertyList: nil,
            alternates: [],
            discoverabilityTitle: nil,
            attributes: [],
            state: .off
        )
    }
    
    var openSettingsKeyCommand: UIKeyCommand {
        UIKeyCommand(
            title: L10n.Common.Controls.Keyboard.Common.openSettings,
            image: nil,
            action: #selector(MainTabBarController.openSettingsKeyCommandHandler(_:)),
            input: ",",
            modifierFlags: .command,
            propertyList: nil,
            alternates: [],
            discoverabilityTitle: nil,
            attributes: [],
            state: .off
        )
    }
    
    var composeNewPostKeyCommand: UIKeyCommand {
        UIKeyCommand(
            title: L10n.Common.Controls.Keyboard.Common.composeNewPost,
            image: nil,
            action: #selector(MainTabBarController.composeNewPostKeyCommandHandler(_:)),
            input: "n",
            modifierFlags: .command,
            propertyList: nil,
            alternates: [],
            discoverabilityTitle: nil,
            attributes: [],
            state: .off
        )
    }
    
    override var keyCommands: [UIKeyCommand]? {
        guard let topMost = self.topMost else {
            return []
        }
        
        var commands: [UIKeyCommand] = []
        
        if topMost.isModal {
            
        } else {
            // switch tabs
            commands.append(contentsOf: switchToTabKeyCommands)
            
            // show compose
            if !(self.topMost is ComposeViewController) {
                commands.append(composeNewPostKeyCommand)
            }
            
            // show favorites
            if !(self.topMost is FavoriteViewController) {
                commands.append(showFavoritesKeyCommand)
            }
            
            // open settings
            if context.settingService.currentSetting.value != nil {
                commands.append(openSettingsKeyCommand)
            }
        }

        return commands
    }
    
    @objc private func switchToTabKeyCommandHandler(_ sender: UIKeyCommand) {
        guard let rawValue = sender.propertyList as? Int,
              let tab = Tab(rawValue: rawValue) else { return }

        guard let index = Tab.allCases.firstIndex(of: tab) else { return }
        let previousTab = Tab(rawValue: selectedIndex)
        selectedIndex = index
        if let tab = Tab(rawValue: index) {
            currentTab = tab
        }

        if let previousTab = previousTab {
            switch (tab, previousTab) {
            case (.home, .home):
                guard let navigationController = topMost?.navigationController else { return }
                if navigationController.viewControllers.count > 1 {
                    // pop to top when previous tab position already is home
                    navigationController.popToRootViewController(animated: true)
                } else if let homeTimelineViewController = topMost as? HomeTimelineViewController {
                    // trigger scrollToTop if topMost is home timeline
                    homeTimelineViewController.scrollToTop(animated: true)
                }
            default:
                break
            }
        }
    }
    
    @objc private func showFavoritesKeyCommandHandler(_ sender: UIKeyCommand) {
        guard let authContext = self.authContext else { return }
        let favoriteViewModel = FavoriteViewModel(context: context, authContext: authContext)
        _ = coordinator.present(scene: .favorite(viewModel: favoriteViewModel), from: nil, transition: .show)
    }
    
    @objc private func openSettingsKeyCommandHandler(_ sender: UIKeyCommand) {
        guard let setting = context.settingService.currentSetting.value else { return }

        _ = coordinator.present(scene: .settings(setting: setting), from: self, transition: .none)
    }
    
    @objc private func composeNewPostKeyCommandHandler(_ sender: UIKeyCommand) {
        guard let authContext = self.authContext else { return }
        let composeViewModel = ComposeViewModel(
            context: context,
            authContext: authContext,
            composeContext: .composeStatus,
            destination: .topLevel
        )
        _ = coordinator.present(scene: .compose(viewModel: composeViewModel), from: nil, transition: .modal(animated: true, completion: nil))
    }
    
}

extension MainTabBarController: UIGestureRecognizerDelegate {
    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        true
    }
}