import UserNotifications
import SessionMessagingKit
import SignalUtilitiesKit
import PromiseKit

public final class NotificationServiceExtension : UNNotificationServiceExtension {
    private var didPerformSetup = false
    private var areVersionMigrationsComplete = false
    private var contentHandler: ((UNNotificationContent) -> Void)?
    private var notificationContent: UNMutableNotificationContent?

    public static let isFromRemoteKey = "remote"
    public static let threadIdKey = "Signal.AppNotificationsUserInfoKey.threadId"

    // MARK: Did receive a remote push notification request
    
    override public func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
        self.contentHandler = contentHandler
        self.notificationContent = request.content.mutableCopy() as? UNMutableNotificationContent

        // Abort if the main app is running
        guard !(UserDefaults.sharedLokiProject?[.isMainAppActive]).defaulting(to: false) else {
            return self.completeSilenty()
        }

        // Perform main setup
        DispatchQueue.main.sync { self.setUpIfNecessary() { } }

        // Handle the push notification
        AppReadiness.runNowOrWhenAppDidBecomeReady {
            let openGorupPollingPromises = self.pollForOpenGroups()
            defer {
                when(resolved: openGorupPollingPromises).done { _ in
                    self.completeSilenty()
                }
            }
            let notificationContent = self.notificationContent!
            guard
                let base64EncodedData: String = notificationContent.userInfo["ENCRYPTED_DATA"] as? String,
                let data: Data = Data(base64Encoded: base64EncodedData),
                let envelope = try? MessageWrapper.unwrap(data: data)
            else {
                return self.handleFailure(for: notificationContent)
            }
            
            // HACK: It is important to use write synchronously here to avoid a race condition
            // where the completeSilenty() is called before the local notification request
            // is added to notification center
            GRDBStorage.shared.write { db in
                do {
                    guard let processedMessage: ProcessedMessage = try Message.processRawReceivedMessageAsNotification(db, envelope: envelope) else {
                        self.handleFailure(for: notificationContent)
                        return
                    }
                    
                    switch processedMessage.messageInfo.message {
                        case let visibleMessage as VisibleMessage:
                            let interactionId: Int64 = try MessageReceiver.handleVisibleMessage(
                                db,
                                message: visibleMessage,
                                associatedWithProto: processedMessage.proto,
                                openGroupId: nil,
                                isBackgroundPoll: false
                            )
                        
                            // Remove the notifications if there is an outgoing messages from a linked device
                            if
                                let interaction: Interaction = try? Interaction.fetchOne(db, id: interactionId),
                                interaction.variant == .standardOutgoing
                            {
                            let semaphore = DispatchSemaphore(value: 0)
                            let center = UNUserNotificationCenter.current()
                            center.getDeliveredNotifications { notifications in
                                let matchingNotifications = notifications.filter({ $0.request.content.userInfo[NotificationServiceExtension.threadIdKey] as? String == interaction.threadId })
                                center.removeDeliveredNotifications(withIdentifiers: matchingNotifications.map({ $0.request.identifier }))
                                // Hack: removeDeliveredNotifications seems to be async,need to wait for some time before the delivered notifications can be removed.
                                DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) { semaphore.signal() }
                            }
                            semaphore.wait()
                        }
                        
                        case let unsendRequest as UnsendRequest:
                            try MessageReceiver.handleUnsendRequest(db, message: unsendRequest)
                            
                        case let closedGroupControlMessage as ClosedGroupControlMessage:
                            try MessageReceiver.handleClosedGroupControlMessage(db, closedGroupControlMessage)
                            
                        default: break
                    }
                }
                catch {
                    if let error = error as? MessageReceiverError, error.isRetryable {
                        self.handleFailure(for: notificationContent)
                    }
                }
            }
        }
    }

    // MARK: Setup
    
    private func setUpIfNecessary(completion: @escaping () -> Void) {
        AssertIsOnMainThread()

        // The NSE will often re-use the same process, so if we're
        // already set up we want to do nothing; we're already ready
        // to process new messages.
        guard !didPerformSetup else { return }

        didPerformSetup = true

        // This should be the first thing we do.
        SetCurrentAppContext(NotificationServiceExtensionContext())

        _ = AppVersion.sharedInstance()

        Cryptography.seedRandom()

        // We should never receive a non-voip notification on an app that doesn't support
        // app extensions since we have to inform the service we wanted these, so in theory
        // this path should never occur. However, the service does have our push token
        // so it is possible that could change in the future. If it does, do nothing
        // and don't disturb the user. Messages will be processed when they open the app.
        guard GRDBStorage.shared[.isReadyForAppExtensions] else { return completeSilenty() }

        AppSetup.setupEnvironment(
            appSpecificBlock: {
                Environment.shared.notificationsManager.mutate {
                    $0 = NSENotificationPresenter()
                }
            },
            migrationsCompletion: { [weak self] _, needsConfigSync in
                self?.versionMigrationsDidComplete(needsConfigSync: needsConfigSync)
                completion()
            }
        )
    }
    
    @objc
    private func versionMigrationsDidComplete(needsConfigSync: Bool) {
        AssertIsOnMainThread()

        areVersionMigrationsComplete = true
        
        // If we need a config sync then trigger it now
        if needsConfigSync {
            GRDBStorage.shared.write { db in
                try MessageSender.syncConfiguration(db, forceSyncNow: true).retainUntilComplete()
            }
        }

        checkIsAppReady()
    }

    @objc
    private func checkIsAppReady() {
        AssertIsOnMainThread()

        // Only mark the app as ready once.
        guard !AppReadiness.isAppReady() else { return }

        // App isn't ready until storage is ready AND all version migrations are complete.
        guard GRDBStorage.shared.isValid && areVersionMigrationsComplete else { return }

        SignalUtilitiesKit.Configuration.performMainSetup()

        // Note that this does much more than set a flag; it will also run all deferred blocks.
        AppReadiness.setAppIsReady()
    }
    
    // MARK: Handle completion
    
    override public func serviceExtensionTimeWillExpire() {
        // Called just before the extension will be terminated by the system.
        // Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
        completeSilenty()
    }
    
    private func completeSilenty() {
        SNLog("Complete silenty")
        self.contentHandler!(.init())
    }

    private func handleSuccess(for content: UNMutableNotificationContent) {
        contentHandler!(content)
    }

    private func handleFailure(for content: UNMutableNotificationContent) {
        content.body = "You've got a new message"
        content.title = "Session"
        let userInfo: [String:Any] = [ NotificationServiceExtension.isFromRemoteKey : true ]
        content.userInfo = userInfo
        contentHandler!(content)
    }
    
    // MARK: Poll for open groups
    private func pollForOpenGroups() -> [Promise<Void>] {
        var promises: [Promise<Void>] = []
        let servers = Set(Storage.shared.getAllV2OpenGroups().values.map { $0.server })
        servers.forEach { server in
            let poller = OpenGroupPollerV2(for: server)
            let promise = poller.poll().timeout(seconds: 20, timeoutError: NotificationServiceError.timeout)
            promises.append(promise)
        }
        return promises
    }
    
    private enum NotificationServiceError: Error {
        case timeout
    }
}