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

import Foundation
import Combine
import PushKit
import GRDB
import SignalUtilitiesKit
import SignalCoreKit

public enum PushRegistrationError: Error {
    case assertionError(description: String)
    case pushNotSupported(description: String)
    case timeout
    case publisherNoLongerExists
}

/**
 * Singleton used to integrate with push notification services - registration and routing received remote notifications.
 */
@objc public class PushRegistrationManager: NSObject, PKPushRegistryDelegate {

    // MARK: - Dependencies

    private var notificationPresenter: NotificationPresenter {
        return AppEnvironment.shared.notificationPresenter
    }

    // MARK: - Singleton class

    @objc
    public static var shared: PushRegistrationManager {
        get {
            return AppEnvironment.shared.pushRegistrationManager
        }
    }

    override init() {
        super.init()

        SwiftSingletons.register(self)
    }

    private var vanillaTokenPublisher: AnyPublisher<Data, Error>?
    private var vanillaTokenResolver: ((Result<Data, Error>) -> ())?

    private var voipRegistry: PKPushRegistry?
    private var voipTokenPublisher: AnyPublisher<Data?, Error>?
    private var voipTokenResolver: ((Result<Data?, Error>) -> ())?

    // MARK: - Public interface

    public func requestPushTokens() -> AnyPublisher<(pushToken: String, voipToken: String), Error> {
        Logger.info("")
        
        return registerUserNotificationSettings()
            .subscribe(on: DispatchQueue.global(qos: .default))
            .receive(on: DispatchQueue.main)    // MUST be on main thread
            .setFailureType(to: Error.self)
            .tryFlatMap { _ -> AnyPublisher<(pushToken: String, voipToken: String), Error> in
                #if targetEnvironment(simulator)
                throw PushRegistrationError.pushNotSupported(description: "Push not supported on simulators")
                #endif

                return self.registerForVanillaPushToken()
                    .flatMap { vanillaPushToken -> AnyPublisher<(pushToken: String, voipToken: String), Error> in
                        self.registerForVoipPushToken()
                            .map { voipPushToken in (vanillaPushToken, (voipPushToken ?? "")) }
                            .eraseToAnyPublisher()
                    }
                    .eraseToAnyPublisher()
            }
            .eraseToAnyPublisher()
    }

    // MARK: Vanilla push token

    // Vanilla push token is obtained from the system via AppDelegate
    public func didReceiveVanillaPushToken(_ tokenData: Data) {
        guard let vanillaTokenResolver = self.vanillaTokenResolver else {
            owsFailDebug("publisher completion in \(#function) unexpectedly nil")
            return
        }

        vanillaTokenResolver(Result.success(tokenData))
    }

    // Vanilla push token is obtained from the system via AppDelegate    
    @objc
    public func didFailToReceiveVanillaPushToken(error: Error) {
        guard let vanillaTokenResolver = self.vanillaTokenResolver else {
            owsFailDebug("publisher completion in \(#function) unexpectedly nil")
            return
        }

        vanillaTokenResolver(Result.failure(error))
    }

    // MARK: helpers

    // User notification settings must be registered *before* AppDelegate will
    // return any requested push tokens.
    public func registerUserNotificationSettings() -> AnyPublisher<Void, Never> {
        AssertIsOnMainThread()
        return notificationPresenter.registerNotificationSettings()
    }

    /**
     * When users have disabled notifications and background fetch, the system hangs when returning a push token.
     * More specifically, after registering for remote notification, the app delegate calls neither
     * `didFailToRegisterForRemoteNotificationsWithError` nor `didRegisterForRemoteNotificationsWithDeviceToken`
     * This behavior is identical to what you'd see if we hadn't previously registered for user notification settings, though
     * in this case we've verified that we *have* properly registered notification settings.
     */
    private var isSusceptibleToFailedPushRegistration: Bool {

        // Only affects users who have disabled both: background refresh *and* notifications
        guard UIApplication.shared.backgroundRefreshStatus == .denied else {
            return false
        }

        guard let notificationSettings = UIApplication.shared.currentUserNotificationSettings else {
            return false
        }

        guard notificationSettings.types == [] else {
            return false
        }

        return true
    }

    private func registerForVanillaPushToken() -> AnyPublisher<String, Error> {
        AssertIsOnMainThread()
        
        // Use the existing publisher if it exists
        if let vanillaTokenPublisher: AnyPublisher<Data, Error> = self.vanillaTokenPublisher {
            return vanillaTokenPublisher
                .map { $0.toHexString() }
                .eraseToAnyPublisher()
        }
        
        UIApplication.shared.registerForRemoteNotifications()
        
        // No pending vanilla token yet; create a new publisher
        let publisher: AnyPublisher<Data, Error> = Deferred {
            Future<Data, Error> { self.vanillaTokenResolver = $0 }
        }
        .eraseToAnyPublisher()
        self.vanillaTokenPublisher = publisher
        
        return publisher
            .timeout(
                .seconds(10),
                scheduler: DispatchQueue.main,
                customError: { PushRegistrationError.timeout }
            )
            .catch { error -> AnyPublisher<Data, Error> in
                switch error {
                    case PushRegistrationError.timeout:
                        guard self.isSusceptibleToFailedPushRegistration else {
                            // Sometimes registration can just take a while.
                            // If we're not on a device known to be susceptible to push registration failure,
                            // just return the original publisher.
                            guard let originalPublisher: AnyPublisher<Data, Error> = self.vanillaTokenPublisher else {
                                return Fail(error: PushRegistrationError.publisherNoLongerExists)
                                    .eraseToAnyPublisher()
                            }
                            
                            return originalPublisher
                        }
                        
                        // If we've timed out on a device known to be susceptible to failures, quit trying
                        // so the user doesn't remain indefinitely hung for no good reason.
                        return Fail(
                            error: PushRegistrationError.pushNotSupported(
                                description: "Device configuration disallows push notifications"
                            )
                        ).eraseToAnyPublisher()
                        
                    default:
                        return Fail(error: error)
                            .eraseToAnyPublisher()
                }
            }
            .map { tokenData -> String in
                if self.isSusceptibleToFailedPushRegistration {
                    // Sentinal in case this bug is fixed
                    OWSLogger.debug("Device was unexpectedly able to complete push registration even though it was susceptible to failure.")
                }
                
                return tokenData.toHexString()
            }
            .handleEvents(
                receiveCompletion: { _ in
                    self.vanillaTokenPublisher = nil
                    self.vanillaTokenResolver = nil
                }
            )
            .eraseToAnyPublisher()
    }
    
    public func createVoipRegistryIfNecessary() {
        AssertIsOnMainThread()

        guard voipRegistry == nil else { return }
        let voipRegistry = PKPushRegistry(queue: nil)
        self.voipRegistry = voipRegistry
        voipRegistry.desiredPushTypes = [.voIP]
        voipRegistry.delegate = self
    }
    
    private func registerForVoipPushToken() -> AnyPublisher<String?, Error> {
        AssertIsOnMainThread()
        
        // Use the existing publisher if it exists
        if let voipTokenPublisher: AnyPublisher<Data?, Error> = self.voipTokenPublisher {
            return voipTokenPublisher
                .map { $0?.toHexString() }
                .eraseToAnyPublisher()
        }
        
        // We don't create the voip registry in init, because it immediately requests the voip token,
        // potentially before we're ready to handle it.
        createVoipRegistryIfNecessary()
        
        guard let voipRegistry: PKPushRegistry = self.voipRegistry else {
            owsFailDebug("failed to initialize voipRegistry")
            return Fail(
                error: PushRegistrationError.assertionError(description: "failed to initialize voipRegistry")
            ).eraseToAnyPublisher()
        }
        
        // If we've already completed registering for a voip token, resolve it immediately,
        // rather than waiting for the delegate method to be called.
        if let voipTokenData: Data = voipRegistry.pushToken(for: .voIP) {
            Logger.info("using pre-registered voIP token")
            return Just(voipTokenData.toHexString())
                .setFailureType(to: Error.self)
                .eraseToAnyPublisher()
        }
        
        // No pending voip token yet. Create a new publisher
        let publisher: AnyPublisher<Data?, Error> = Deferred {
            Future<Data?, Error> { self.voipTokenResolver = $0 }
        }
        .eraseToAnyPublisher()
        self.voipTokenPublisher = publisher
        
        return publisher
            .map { voipTokenData -> String? in
                Logger.info("successfully registered for voip push notifications")
                return voipTokenData?.toHexString()
            }
            .handleEvents(
                receiveCompletion: { _ in
                    self.voipTokenPublisher = nil
                    self.voipTokenResolver = nil
                }
            )
            .eraseToAnyPublisher()
    }
    
    // MARK: - PKPushRegistryDelegate
    
    public func pushRegistry(_ registry: PKPushRegistry, didUpdate pushCredentials: PKPushCredentials, for type: PKPushType) {
        Logger.info("")
        owsAssertDebug(type == .voIP)
        owsAssertDebug(pushCredentials.type == .voIP)

        voipTokenResolver?(Result.success(pushCredentials.token))
    }
    
    // NOTE: This function MUST report an incoming call.
    public func pushRegistry(_ registry: PKPushRegistry, didReceiveIncomingPushWith payload: PKPushPayload, for type: PKPushType) {
        SNLog("[Calls] Receive new voip notification.")
        owsAssertDebug(CurrentAppContext().isMainApp)
        owsAssertDebug(type == .voIP)
        let payload = payload.dictionaryPayload
        
        guard
            let uuid: String = payload["uuid"] as? String,
            let caller: String = payload["caller"] as? String,
            let timestampMs: Int64 = payload["timestamp"] as? Int64
        else {
            SessionCallManager.reportFakeCall(info: "Missing payload data")
            return
        }
        
        // Resume database
        NotificationCenter.default.post(name: Database.resumeNotification, object: self)
        
        let maybeCall: SessionCall? = Storage.shared.write { db in
            let messageInfo: CallMessage.MessageInfo = CallMessage.MessageInfo(
                state: (caller == getUserHexEncodedPublicKey(db) ?
                    .outgoing :
                    .incoming
                )
            )
            
            let messageInfoString: String? = {
                if let messageInfoData: Data = try? JSONEncoder().encode(messageInfo) {
                   return String(data: messageInfoData, encoding: .utf8)
                } else {
                    return "Incoming call." // TODO: We can do better here.
                }
            }()
            
            let call: SessionCall = SessionCall(db, for: caller, uuid: uuid, mode: .answer)
            let thread: SessionThread = try SessionThread
                .fetchOrCreate(db, id: caller, variant: .contact, shouldBeVisible: nil)
            
            let interaction: Interaction = try Interaction(
                messageUuid: uuid,
                threadId: thread.id,
                authorId: caller,
                variant: .infoCall,
                body: messageInfoString,
                timestampMs: timestampMs
            ).inserted(db)
            call.callInteractionId = interaction.id
            
            return call
        }
        
        guard let call: SessionCall = maybeCall else {
            SessionCallManager.reportFakeCall(info: "Could not retrieve call from database")
            return
        }
        
        // NOTE: Just start 1-1 poller so that it won't wait for polling group messages
        (UIApplication.shared.delegate as? AppDelegate)?.startPollersIfNeeded(shouldStartGroupPollers: false)
        
        call.reportIncomingCallIfNeeded { error in
            if let error = error {
                SNLog("[Calls] Failed to report incoming call to CallKit due to error: \(error)")
            }
        }
    }
}

// We transmit pushToken data as hex encoded string to the server
fileprivate extension Data {
    var hexEncodedString: String {
        return map { String(format: "%02hhx", $0) }.joined()
    }
}