// Copyright © 2022 Rangeproof Pty Ltd. All rights reserved.

import Foundation
import Combine
import GRDB
import CallKit
import UserNotifications
import BackgroundTasks
import SessionMessagingKit
import SignalUtilitiesKit
import SignalCoreKit
import SessionUtilitiesKit

public final class NotificationServiceExtension: UNNotificationServiceExtension {
    private var didPerformSetup = false
    private var contentHandler: ((UNNotificationContent) -> Void)?
    private var request: UNNotificationRequest?
    private var openGroupPollCancellable: AnyCancellable?
    private var hasCompleted: Atomic<Bool> = Atomic(false)

    public static let isFromRemoteKey = "remote"                                                                   // stringlint:disable
    public static let threadIdKey = "Signal.AppNotificationsUserInfoKey.threadId"                                  // stringlint:disable
    public static let threadVariantRaw = "Signal.AppNotificationsUserInfoKey.threadVariantRaw"                     // stringlint:disable
    public static let threadNotificationCounter = "Session.AppNotificationsUserInfoKey.threadNotificationCounter"  // stringlint:disable
    private static let callPreOfferLargeNotificationSupressionDuration: TimeInterval = 30

    // MARK: Did receive a remote push notification request
    
    override public func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
        Log.info("didReceive called.")
        self.contentHandler = contentHandler
        self.request = request
        
        guard let notificationContent = request.content.mutableCopy() as? UNMutableNotificationContent else {
            return self.completeSilenty()
        }

        // Abort if the main app is running
        guard !(UserDefaults.sharedLokiProject?[.isMainAppActive]).defaulting(to: false) else {
            return self.completeSilenty()
        }
        
        /// Create the context if we don't have it (needed before _any_ interaction with the database)
        if !Singleton.hasAppContext {
            Singleton.setup(appContext: NotificationServiceExtensionContext())
        }
        
        let isCallOngoing: Bool = (UserDefaults.sharedLokiProject?[.isCallOngoing])
            .defaulting(to: false)

        // Perform main setup
        Storage.resumeDatabaseAccess()
        LibSession.resumeNetworkAccess()
        DispatchQueue.main.sync { self.setUpIfNecessary() { } }

        // Handle the push notification
        Singleton.appReadiness.runNowOrWhenAppDidBecomeReady {
            let openGroupPollingPublishers: [AnyPublisher<Void, Error>] = self.pollForOpenGroups()
            defer {
                self.openGroupPollCancellable = Publishers
                    .MergeMany(openGroupPollingPublishers)
                    .subscribe(on: DispatchQueue.global(qos: .background))
                    .subscribe(on: DispatchQueue.main)
                    .sink(
                        receiveCompletion:  { [weak self] _ in self?.completeSilenty() },
                        receiveValue: { _ in }
                    )
            }
            
            let (maybeData, metadata, result) = PushNotificationAPI.processNotification(
                notificationContent: notificationContent
            )
            
            guard
                (result == .success || result == .legacySuccess),
                let data: Data = maybeData
            else {
                switch result {
                    // If we got an explicit failure, or we got a success but no content then show
                    // the fallback notification
                    case .success, .legacySuccess, .failure, .legacyFailure:
                        return self.handleFailure(for: notificationContent, error: .processing(result))
                        
                    // Just log if the notification was too long (a ~2k message should be able to fit so
                    // these will most commonly be call or config messages)
                    case .successTooLong:
                        return Log.info("Received too long notification for namespace: \(metadata.namespace).")
                        
                    case .legacyForceSilent, .failureNoContent: return
                }
            }
            
            // 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
            Storage.shared.write { db in
                do {
                    guard let processedMessage: ProcessedMessage = try Message.processRawReceivedMessageAsNotification(db, data: data, metadata: metadata) else {
                        throw NotificationError.messageProcessing
                    }
                    
                    switch processedMessage {
                        /// Custom handle config messages (as they don't get handled by the normal `MessageReceiver.handle` call
                        case .config(let publicKey, let namespace, let serverHash, let serverTimestampMs, let data):
                            try LibSession.handleConfigMessages(
                                db,
                                messages: [
                                    ConfigMessageReceiveJob.Details.MessageInfo(
                                        namespace: namespace,
                                        serverHash: serverHash,
                                        serverTimestampMs: serverTimestampMs,
                                        data: data
                                    )
                                ],
                                publicKey: publicKey
                            )
                            
                        /// Due to the way the `CallMessage` works we need to custom handle it's behaviour within the notification
                        /// extension, for all other message types we want to just use the standard `MessageReceiver.handle` call
                        case .standard(let threadId, let threadVariant, _, let messageInfo) where messageInfo.message is CallMessage:
                            guard let callMessage = messageInfo.message as? CallMessage else {
                                return self.completeSilenty()
                            }
                            
                            // Throw if the message is outdated and shouldn't be processed
                            try MessageReceiver.throwIfMessageOutdated(
                                db,
                                message: messageInfo.message,
                                threadId: threadId,
                                threadVariant: threadVariant
                            )
                            
                            try MessageReceiver.handleCallMessage(
                                db,
                                threadId: threadId,
                                threadVariant: threadVariant,
                                message: callMessage
                            )
                            
                            guard case .preOffer = callMessage.kind else {
                                return self.completeSilenty()
                            }
                            
                            switch (db[.areCallsEnabled], isCallOngoing) {
                                case (false, _):
                                    if
                                        let sender: String = callMessage.sender,
                                        let interaction: Interaction = try MessageReceiver.insertCallInfoMessage(
                                            db,
                                            for: callMessage,
                                            state: .permissionDenied
                                        )
                                    {
                                        let thread: SessionThread = try SessionThread
                                            .fetchOrCreate(
                                                db,
                                                id: sender,
                                                variant: .contact,
                                                shouldBeVisible: nil
                                            )

                                        // Notify the user if the call message wasn't already read
                                        if !interaction.wasRead {
                                            SessionEnvironment.shared?.notificationsManager.wrappedValue?
                                                .notifyUser(
                                                    db,
                                                    forIncomingCall: interaction,
                                                    in: thread,
                                                    applicationState: .background
                                                )
                                        }
                                    }
                                    
                                case (true, true):
                                    try MessageReceiver.handleIncomingCallOfferInBusyState(
                                        db,
                                        message: callMessage
                                    )
                                    
                                case (true, false):
                                    try MessageReceiver.insertCallInfoMessage(db, for: callMessage)
                                    self.handleSuccessForIncomingCall(db, for: callMessage)
                            }
                            
                            // Perform any required post-handling logic
                            try MessageReceiver.postHandleMessage(
                                db,
                                threadId: threadId,
                                threadVariant: threadVariant,
                                message: messageInfo.message
                            )
                            
                        case .standard(let threadId, let threadVariant, let proto, let messageInfo):
                            try MessageReceiver.handle(
                                db,
                                threadId: threadId,
                                threadVariant: threadVariant,
                                message: messageInfo.message,
                                serverExpirationTimestamp: messageInfo.serverExpirationTimestamp,
                                associatedWithProto: proto
                            )
                    }
                }
                catch {
                    // If an error occurred we want to rollback the transaction (by throwing) and then handle
                    // the error outside of the database
                    let handleError = {
                        switch error {
                            case MessageReceiverError.invalidGroupPublicKey, MessageReceiverError.noGroupKeyPair,
                                MessageReceiverError.outdatedMessage:
                                self.completeSilenty()
                                
                            case NotificationError.messageProcessing:
                                self.handleFailure(for: notificationContent, error: .messageProcessing)
                                
                            case let msgError as MessageReceiverError:
                                self.handleFailure(for: notificationContent, error: .messageHandling(msgError))
                                
                            default: self.handleFailure(for: notificationContent, error: .other(error))
                        }
                    }
                    
                    db.afterNextTransactionNested(
                        onCommit: { _ in  handleError() },
                        onRollback: { _ in handleError() }
                    )
                    throw error
                }
            }
        }
    }

    // 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 }

        Log.info("Performing setup.")
        didPerformSetup = true

        _ = AppVersion.sharedInstance()

        Cryptography.seedRandom()

        AppSetup.setupEnvironment(
            retrySetupIfDatabaseInvalid: true,
            appSpecificBlock: {
                Log.setup(with: Logger(
                    primaryPrefix: "NotificationServiceExtension",                                               // stringlint:disable
                    customDirectory: "\(OWSFileSystem.appSharedDataDirectoryPath())/Logs/NotificationExtension", // stringlint:disable
                    forceNSLog: true
                ))
                
                SessionEnvironment.shared?.notificationsManager.mutate {
                    $0 = NSENotificationPresenter()
                }
                
                // Setup LibSession
                LibSession.addLogger()
                LibSession.createNetworkIfNeeded()
            },
            migrationsCompletion: { [weak self] result, needsConfigSync in
                switch result {
                    case .failure(let error):
                        Log.error("Failed to complete migrations: \(error).")
                        self?.completeSilenty()
                        
                    case .success:
                        // 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 Storage.shared[.isReadyForAppExtensions] else {
                            Log.error("Not ready for extensions.")
                            self?.completeSilenty()
                            return
                        }
                        
                        DispatchQueue.main.async {
                            self?.versionMigrationsDidComplete(needsConfigSync: needsConfigSync)
                        }
                }
                
                completion()
            }
        )
    }
    
    private func versionMigrationsDidComplete(needsConfigSync: Bool) {
        AssertIsOnMainThread()

        // If we need a config sync then trigger it now
        if needsConfigSync {
            Storage.shared.write { db in
                ConfigurationSyncJob.enqueue(db, publicKey: getUserHexEncodedPublicKey(db))
            }
        }

        checkIsAppReady(migrationsCompleted: true)
    }

    private func checkIsAppReady(migrationsCompleted: Bool) {
        AssertIsOnMainThread()

        // Only mark the app as ready once.
        guard !Singleton.appReadiness.isAppReady else { return }

        // App isn't ready until storage is ready AND all version migrations are complete.
        guard Storage.shared.isValid && migrationsCompleted else {
            Log.error("Storage invalid.")
            self.completeSilenty()
            return
        }

        SignalUtilitiesKit.Configuration.performMainSetup()

        // Note that this does much more than set a flag; it will also run all deferred blocks.
        Singleton.appReadiness.setAppReady()
    }
    
    // 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.
        Log.warn("Execution time expired.")
        openGroupPollCancellable?.cancel()
        completeSilenty()
    }
    
    private func completeSilenty() {
        // Ensure we on'y run this once
        guard
            hasCompleted.mutate({ hasCompleted in
                let wasCompleted: Bool = hasCompleted
                hasCompleted = true
                return wasCompleted
            }) == false
        else { return }
        
        let silentContent: UNMutableNotificationContent = UNMutableNotificationContent()
        silentContent.badge = Storage.shared
            .read { db in try Interaction.fetchUnreadCount(db) }
            .map { NSNumber(value: $0) }
            .defaulting(to: NSNumber(value: 0))
        Log.info("Complete silently.")
        LibSession.suspendNetworkAccess()
        Storage.suspendDatabaseAccess()
        Log.flush()
        
        self.contentHandler!(silentContent)
    }
    
    private func handleSuccessForIncomingCall(_ db: Database, for callMessage: CallMessage) {
        if #available(iOSApplicationExtension 14.5, *), Preferences.isCallKitSupported {
            guard let caller: String = callMessage.sender, let timestamp = callMessage.sentTimestamp else { return }
            
            let payload: JSON = [
                "uuid": callMessage.uuid,   // stringlint:disable
                "caller": caller,           // stringlint:disable
                "timestamp": timestamp      // stringlint:disable
            ]
            
            CXProvider.reportNewIncomingVoIPPushPayload(payload) { error in
                if let error = error {
                    self.handleFailureForVoIP(db, for: callMessage)
                    Log.error("Failed to notify main app of call message: \(error).")
                }
                else {
                    Log.info("Successfully notified main app of call message.")
                    UserDefaults.sharedLokiProject?[.lastCallPreOffer] = Date()
                    self.completeSilenty()
                }
            }
        }
        else {
            self.handleFailureForVoIP(db, for: callMessage)
        }
    }
    
    private func handleFailureForVoIP(_ db: Database, for callMessage: CallMessage) {
        let notificationContent = UNMutableNotificationContent()
        notificationContent.userInfo = [ NotificationServiceExtension.isFromRemoteKey : true ]
        notificationContent.title = "Session"
        notificationContent.badge = (try? Interaction.fetchUnreadCount(db))
            .map { NSNumber(value: $0) }
            .defaulting(to: NSNumber(value: 0))
        
        if let sender: String = callMessage.sender {
            let senderDisplayName: String = Profile.displayName(db, id: sender, threadVariant: .contact)
            notificationContent.body = "\(senderDisplayName) is calling..."
        }
        else {
            notificationContent.body = "Incoming call..."
        }
        
        let identifier = self.request?.identifier ?? UUID().uuidString
        let request = UNNotificationRequest(identifier: identifier, content: notificationContent, trigger: nil)
        let semaphore = DispatchSemaphore(value: 0)
        
        UNUserNotificationCenter.current().add(request) { error in
            if let error = error {
                Log.error("Failed to add notification request due to error: \(error).")
            }
            semaphore.signal()
        }
        semaphore.wait()
        Log.info("Add remote notification request.")
        Log.flush()
    }

    private func handleFailure(for content: UNMutableNotificationContent, error: NotificationError) {
        Log.error("Show generic failure message due to error: \(error).")
        LibSession.suspendNetworkAccess()
        Storage.suspendDatabaseAccess()
        Log.flush()
        
        content.title = "Session"
        content.body = "APN_Message".localized()
        let userInfo: [String: Any] = [ NotificationServiceExtension.isFromRemoteKey: true ]
        content.userInfo = userInfo
        contentHandler!(content)
    }
    
    // MARK: - Poll for open groups
    
    private func pollForOpenGroups() -> [AnyPublisher<Void, Error>] {
        return Storage.shared
            .read { db in
                // The default room promise creates an OpenGroup with an empty `roomToken` value,
                // we don't want to start a poller for this as the user hasn't actually joined a room
                try OpenGroup
                    .select(.server)
                    .filter(OpenGroup.Columns.roomToken != "")
                    .filter(OpenGroup.Columns.isActive)
                    .distinct()
                    .asRequest(of: String.self)
                    .fetchSet(db)
            }
            .defaulting(to: [])
            .map { server -> AnyPublisher<Void, Error> in
                OpenGroupAPI.Poller(for: server)
                    .poll(calledFromBackgroundPoller: true, isPostCapabilitiesRetry: false)
                    .timeout(
                        .seconds(20),
                        scheduler: DispatchQueue.global(qos: .default),
                        customError: { NotificationServiceError.timeout }
                    )
                    .eraseToAnyPublisher()
            }
    }
    
    private enum NotificationServiceError: Error {
        case timeout
    }
}