element-x-ios/NSE/Sources/NotificationHandler.swift

//
// Copyright 2025 Element Creations Ltd.
// Copyright 2022-2025 New Vector Ltd.
//
// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
// Please see LICENSE files in the repository root for full details.
//

import CallKit
import MatrixRustSDK
import Synchronization
import UserNotifications

nonisolated class NotificationHandler {
    private let userSession: NSEUserSession
    private let contentHandler: (UNNotificationContent) -> Void
    private var notificationContent: UNMutableNotificationContent
    private let tag: String
    
    private let notificationContentBuilder: NotificationContentBuilder
    
    /// Whether this handler has already counted its notification towards the app icon badge.
    private var hasCountedTowardsBadge = false
    
    private var userSettings: UserSettings {
        userSession.userSettings
    }
    
    init(userSession: NSEUserSession,
         contentHandler: @escaping (UNNotificationContent) -> Void,
         notificationContent: UNMutableNotificationContent,
         tag: String) {
        self.userSession = userSession
        self.contentHandler = contentHandler
        self.notificationContent = notificationContent
        self.tag = tag
        
        let eventStringBuilder = RoomMessageEventStringBuilder(attributedStringBuilder: AttributedStringBuilder(mentionBuilder: PlainMentionBuilder()),
                                                               style: .plain)
        
        notificationContentBuilder = NotificationContentBuilder(messageEventStringBuilder: eventStringBuilder,
                                                                userSession: userSession)
    }
    
    func processEvent(_ eventID: String, roomID: String) async {
        MXLog.info("\(tag) Processing event: \(eventID) in room: \(roomID)")
        
        // The pusher of an account with its notifications off can outlive a failed deletion.
        guard userSettings.account.enableNotifications else {
            MXLog.error("\(tag) Received a push for an account with notifications off, discarding.")
            discardNotification()
            return
        }
        
        guard let notificationItemProxy = await userSession.notificationItemProxy(roomID: roomID, eventID: eventID) else {
            MXLog.error("\(tag) Failed retrieving notification item")
            discardNotification()
            return
        }
        
        switch await preprocessNotification(notificationItemProxy) {
        case .processedShouldDiscard, .unsupportedShouldDiscard:
            discardNotification()
        case .shouldDisplay:
            if userSettings.app.hideQuietNotificationAlerts, !notificationItemProxy.isNoisy {
                discardNotification()
                return
            }
            
            await notificationContentBuilder.process(notificationContent: &notificationContent,
                                                     notificationItem: notificationItemProxy,
                                                     mediaProvider: userSession.mediaProvider)
            
            deliverNotification()
        }
    }
    
    func handleTimeExpiration() {
        // Called just before the extension will be terminated by the system.
        // Use this as an opportunity to deliver your "best attempt" at modified content
        MXLog.info("\(tag) Extension time will expire")
        deliverNotification()
    }
    
    // MARK: - Private
    
    private func deliverNotification() {
        notificationContent.badge = NSNumber(value: incrementBadgeCount())
        MXLog.info("\(tag) Delivering notification, new badge value: \(userSettings.app.lastKnownBadgeCount)")
        contentHandler(notificationContent)
    }
    
    private func incrementBadgeCount() -> Int {
        // `handleTimeExpiration` can deliver a notification this handler already delivered.
        guard !hasCountedTowardsBadge else {
            return userSettings.app.lastKnownBadgeCount
        }
        
        hasCountedTowardsBadge = true
        userSettings.app.lastKnownBadgeCount += 1
        
        return userSettings.app.lastKnownBadgeCount
    }
    
    private func discardNotification() {
        MXLog.info("\(tag) Discarding notification")
        
        let content = UNMutableNotificationContent()
        // Nothing new is shown to the user, so leave the badge where the app last put it.
        content.badge = NSNumber(value: userSettings.app.lastKnownBadgeCount)
        MXLog.info("\(tag) New badge value: \(content.badge?.stringValue ?? "nil")")
        
        contentHandler(content)
    }
    
    private func preprocessNotification(_ itemProxy: NotificationItemProxyProtocol) async -> NotificationProcessingResult {
        guard case let .timeline(event) = itemProxy.event else {
            return .shouldDisplay
        }
        
        switch try? event.content() {
        case .messageLike(let messageContent):
            switch messageContent {
            case .poll,
                 .roomEncrypted,
                 .sticker:
                return .shouldDisplay
            case .roomMessage(let messageType, _):
                switch messageType {
                case .emote, .image, .audio, .video, .file, .notice, .text, .location, .gallery:
                    return .shouldDisplay
                case .other:
                    return .unsupportedShouldDiscard
                }
            case .roomRedaction(let redactedEventID, _):
                guard let redactedEventID else {
                    MXLog.error("Unable to handle redact notification due to missing event ID")
                    return .processedShouldDiscard
                }
                
                let deliveredNotifications = await UNUserNotificationCenter.current().deliveredNotifications()
                
                if let targetNotification = deliveredNotifications.first(where: { $0.request.content.eventID == redactedEventID }) {
                    UNUserNotificationCenter.current().removeDeliveredNotifications(withIdentifiers: [targetNotification.request.identifier])
                    userSettings.app.lastKnownBadgeCount = max(0, userSettings.app.lastKnownBadgeCount - 1)
                }
                
                return .processedShouldDiscard
            case .rtcNotification(let notificationType, let expirationTimestamp, let callIntent):
                return await handleCallNotification(notificationType: notificationType,
                                                    rtcNotifyEventID: event.eventId(),
                                                    timestamp: event.timestamp(),
                                                    expirationTimestamp: expirationTimestamp,
                                                    roomID: itemProxy.roomID,
                                                    roomDisplayName: itemProxy.roomDisplayName,
                                                    callIntent: callIntent)
            case .callAnswer,
                 .callInvite,
                 .callHangup,
                 .callCandidates,
                 .keyVerificationReady,
                 .keyVerificationStart,
                 .keyVerificationCancel,
                 .keyVerificationAccept,
                 .keyVerificationKey,
                 .keyVerificationMac,
                 .keyVerificationDone,
                 .reactionContent,
                 .beacon:
                return .unsupportedShouldDiscard
            }
        case .state(let stateContent):
            switch stateContent {
            case .beaconInfo:
                return .shouldDisplay
            default:
                return .unsupportedShouldDiscard
            }
        case .none:
            return .unsupportedShouldDiscard
        }
    }
    
    /// Handle incoming call notifications.
    /// - Returns: A boolean indicating whether the notification was handled and should now be discarded.
    private func handleCallNotification(notificationType: RtcNotificationType,
                                        rtcNotifyEventID: String,
                                        timestamp: Timestamp,
                                        expirationTimestamp: Timestamp,
                                        roomID: String,
                                        roomDisplayName: String, callIntent: RtcCallIntent?) async -> NotificationProcessingResult {
        // Handle incoming VoIP calls, show the native OS call screen
        // https://developer.apple.com/documentation/callkit/sending-end-to-end-encrypted-voip-calls
        //
        // The way this works is the following:
        // - the NSE receives the notification and decrypts it
        // - checks if it's still time relevant (max 10 seconds old) and whether it should ring
        // - otherwise it goes on to show it as a normal notification
        // - if it should ring then it discards the notification but invokes `reportNewIncomingVoIPPushPayload`
        // so that the main app can handle it
        // - the main app picks this up in `PKPushRegistry.didReceiveIncomingPushWith` and
        // `CXProvider.reportNewIncomingCall` to show the system UI and handle actions on it.
        // N.B. this flow works properly only when background processing capabilities are enabled
        guard notificationType == .ring else {
            MXLog.info("Non-ringing call notification, handling as push notification")
            return .shouldDisplay
        }
        
        // Check to see if a call is still ongoing
        if let room = userSession.roomForIdentifier(roomID) { // Try to get call details from the room info
            if !room.hasActiveRoomCall() { // If I don't have an active call wait a bit and make sure
                // Local `Mutex` holder for the SDK subscription token — keeps it alive across the
                // await without needing `[weak self]`, which would force this class to be `Sendable`.
                let observationToken = Mutex<TaskHandle?>(nil)
                let expiringTask = ExpiringTaskRunner {
                    await withCheckedContinuation { (continuation: CheckedContinuation<Void, Never>) in
                        observationToken.withLock { state in
                            state = room.subscribeToRoomInfoUpdates(listener: SDKListener { info in
                                if info.hasRoomCall {
                                    MXLog.info("Received room info update and the room has an active call now.")
                                    continuation.resume()
                                } else {
                                    MXLog.info("Received a room info update but the room still doesn't have an ongoing call.")
                                }
                            })
                        }
                    }
                }
                
                try? await expiringTask.run(timeout: Duration.seconds(5)) // Wait 5 seconds or just use whatever is available
                // Release the SDK subscription explicitly once we no longer need updates.
                observationToken.withLock { $0 = nil }
                
                guard room.hasActiveRoomCall() else {
                    MXLog.info("The room no longer has an ongoing call, handling as push notification")
                    return .shouldDisplay
                }
            }
        } else { // Otherwise fallback to the old timeout mechanism
            let timestamp = Date(timeIntervalSince1970: TimeInterval(timestamp / 1000))
            
            guard abs(timestamp.timeIntervalSinceNow) < ElementCallServiceNotificationDiscardDelta else {
                MXLog.info("Call notification is too old, handling as push notification")
                return .shouldDisplay
            }
        }
        
        let expirationDate = Date(timeIntervalSince1970: TimeInterval(expirationTimestamp / 1000))
        let payload = [ElementCallServiceNotificationKey.roomID.rawValue: roomID,
                       ElementCallServiceNotificationKey.roomDisplayName.rawValue: roomDisplayName,
                       ElementCallServiceNotificationKey.expirationDate.rawValue: expirationDate,
                       ElementCallServiceNotificationKey.rtcNotifyEventID.rawValue: rtcNotifyEventID,
                       ElementCallServiceNotificationKey.isVoiceCall.rawValue: callIntent == RtcCallIntent.audio] as [String: Any]
        
        do {
            try await CXProvider.reportNewIncomingVoIPPushPayload(payload)
            MXLog.info("Call notification delegated to CallKit")
        } catch {
            // HealthChat: without the notification filtering entitlement CallKit rejects the hand-off,
            // so ask the push gateway for a PushKit push instead and keep the alert visible.
            MXLog.error("Failed reporting voip call with error: \(error). Requesting a VoIP push instead")
            await requestVoIPPush(roomID: roomID,
                                  roomDisplayName: roomDisplayName,
                                  rtcNotifyEventID: rtcNotifyEventID,
                                  expirationDate: expirationDate,
                                  isVoiceCall: callIntent == RtcCallIntent.audio)
            return .shouldDisplay
        }
        
        return .processedShouldDiscard
    }
    
    /// Asks the push gateway to deliver a PushKit push with the call details, the way the legacy
    /// element-ios app did. The app's `PKPushRegistryDelegate` then reports the call to CallKit.
    private func requestVoIPPush(roomID: String, roomDisplayName: String, rtcNotifyEventID: String, expirationDate: Date, isVoiceCall: Bool) async {
        guard let token = userSettings.app.pushKitDeviceToken,
              let notifyURL = userSettings.app.voipPushGatewayNotifyURL.flatMap(URL.init(string:)) else {
            MXLog.warning("No PushKit token or push gateway stored by the app, cannot request a VoIP push")
            return
        }
        
        // The gateway merges `default_payload` into the push verbatim, so the keys match what the app expects.
        let defaultPayload: [String: Any] = [ElementCallServiceNotificationKey.roomID.rawValue: roomID,
                                             ElementCallServiceNotificationKey.roomDisplayName.rawValue: roomDisplayName,
                                             ElementCallServiceNotificationKey.rtcNotifyEventID.rawValue: rtcNotifyEventID,
                                             ElementCallServiceNotificationKey.expirationDate.rawValue: expirationDate.timeIntervalSince1970,
                                             ElementCallServiceNotificationKey.isVoiceCall.rawValue: isVoiceCall]
        let body: [String: Any] = ["notification": ["event_id": rtcNotifyEventID,
                                                    "room_id": roomID,
                                                    "prio": "high",
                                                    "devices": [["app_id": userSettings.app.voipPusherAppID,
                                                                 "pushkey": token,
                                                                 "data": ["format": "event_id_only",
                                                                          "default_payload": defaultPayload]]]]]
        
        var request = URLRequest(url: notifyURL, timeoutInterval: 5)
        request.httpMethod = "POST"
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        
        do {
            request.httpBody = try JSONSerialization.data(withJSONObject: body)
            let (data, response) = try await URLSession.shared.data(for: request)
            let statusCode = (response as? HTTPURLResponse)?.statusCode ?? 0
            let rejected = (try? JSONSerialization.jsonObject(with: data) as? [String: Any])?["rejected"] as? [String] ?? []
            guard statusCode == 200, rejected.isEmpty else {
                MXLog.error("Push gateway refused the VoIP push: status \(statusCode), rejected \(rejected.count) pushkey(s)")
                return
            }
            MXLog.info("Requested a VoIP push for the call in \(roomID)")
        } catch {
            MXLog.error("Failed requesting a VoIP push: \(error)")
        }
    }
    
    private enum NotificationProcessingResult {
        case shouldDisplay
        case processedShouldDiscard
        case unsupportedShouldDiscard
    }
}