letro-ios/NSE/Sources/NotificationHandler.swift

//
// Copyright 2022-2024 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 UserNotifications

class NotificationHandler {
    private let settings: CommonSettingsProtocol
    private let contentHandler: (UNNotificationContent) -> Void
    private var notificationContent: UNMutableNotificationContent
    private let tag: String
    
    private let notificationContentBuilder: NotificationContentBuilder
    
    init(settings: CommonSettingsProtocol,
         contentHandler: @escaping (UNNotificationContent) -> Void,
         notificationContent: UNMutableNotificationContent,
         tag: String) {
        self.settings = settings
        self.contentHandler = contentHandler
        self.notificationContent = notificationContent
        self.tag = tag
        
        let eventStringBuilder = RoomMessageEventStringBuilder(attributedStringBuilder: AttributedStringBuilder(mentionBuilder: PlainMentionBuilder()),
                                                               destination: .notification)
        
        notificationContentBuilder = NotificationContentBuilder(messageEventStringBuilder: eventStringBuilder,
                                                                settings: settings)
    }
    
    func processEvent(_ eventID: String,
                      roomID: String,
                      userSession: NSEUserSession) async {
        MXLog.info("\(tag) Processing event: \(eventID) in room: \(roomID)")
        
        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:
            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() {
        MXLog.info("\(tag) Delivering notification")
        contentHandler(notificationContent)
    }

    private func discardNotification() {
        MXLog.info("\(tag) Discarding notification")
        
        let content = UNMutableNotificationContent()
        
        if let unreadCount = notificationContent.unreadCount {
            content.badge = NSNumber(value: unreadCount)
        }
        
        contentHandler(content)
    }
    
    private func preprocessNotification(_ itemProxy: NotificationItemProxyProtocol) async -> NotificationProcessingResult {
        guard case let .timeline(event) = itemProxy.event else {
            return .shouldDisplay
        }
        
        switch try? event.eventType() {
        case .messageLike(let content):
            switch content {
            case .poll,
                 .roomEncrypted,
                 .sticker:
                return .shouldDisplay
            case .roomMessage(let messageType, _):
                switch messageType {
                case .emote, .image, .audio, .video, .file, .notice, .text, .location:
                    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])
                }
                
                return .processedShouldDiscard
            case .callNotify(let notifyType):
                return await handleCallNotification(notifyType: notifyType,
                                                    timestamp: event.timestamp(),
                                                    roomID: itemProxy.roomID,
                                                    roomDisplayName: itemProxy.roomDisplayName)
            case .callAnswer,
                 .callInvite,
                 .callHangup,
                 .callCandidates,
                 .keyVerificationReady,
                 .keyVerificationStart,
                 .keyVerificationCancel,
                 .keyVerificationAccept,
                 .keyVerificationKey,
                 .keyVerificationMac,
                 .keyVerificationDone,
                 .reactionContent:
                return .unsupportedShouldDiscard
            }
        case .state:
            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(notifyType: NotifyType,
                                        timestamp: Timestamp,
                                        roomID: String,
                                        roomDisplayName: String) 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 notifyType == .ring else {
            MXLog.info("Non-ringing call notification, handling as push notification")
            return .shouldDisplay
        }
        
        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 payload = [ElementCallServiceNotificationKey.roomID.rawValue: roomID,
                       ElementCallServiceNotificationKey.roomDisplayName.rawValue: roomDisplayName]
        
        do {
            try await CXProvider.reportNewIncomingVoIPPushPayload(payload)
            MXLog.info("Call notification delegated to CallKit")
        } catch {
            MXLog.error("Failed reporting voip call with error: \(error). Handling as push notification")
            return .shouldDisplay
        }
        
        return .processedShouldDiscard
    }
    
    private enum NotificationProcessingResult {
        case shouldDisplay
        case processedShouldDiscard
        case unsupportedShouldDiscard
    }
}