//
// 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 Combine
import Foundation
import MatrixRustSDK

class RoomSummaryProvider: RoomSummaryProviderProtocol {
    private let roomListService: RoomListServiceProtocol
    private let eventStringBuilder: RoomEventStringBuilder
    private let name: String
    private let shouldUpdateVisibleRange: Bool
    private let notificationSettings: NotificationSettingsProxyProtocol
    private let appSettings: AppSettings
    
    private let roomListPageSize: UInt32
    
    private let visibleItemRangePublisher = CurrentValueSubject<Range<Int>, Never>(0..<0)
    
    // periphery:ignore - retaining purpose
    private var roomList: RoomListProtocol?
    
    private var cancellables = Set<AnyCancellable>()
    private var roomListServiceStateCancellable: AnyCancellable?
    private var listUpdatesSubscriptionResult: RoomListEntriesWithDynamicAdaptersResult?
    private var stateUpdatesTaskHandle: TaskHandle?
    
    private let roomListSubject = CurrentValueSubject<[RoomSummary], Never>([])
    private let stateSubject = CurrentValueSubject<RoomSummaryProviderState, Never>(.notLoaded)
    
    /// Bridge from the SDK's synchronous callback into Swift Concurrency. Yielding is safe from any
    /// thread; a single long-lived `for await` consumer (set up in `init`) applies the diffs on the
    /// main actor in FIFO order, guaranteeing one in-flight update at a time.
    private let diffsContinuation: AsyncStream<[RoomListEntriesUpdate]>.Continuation
    
    /// Same bridging pattern as `diffsContinuation`, for the room list loading state.
    private let loadingStateContinuation: AsyncStream<RoomListLoadingState>.Continuation
    
    var roomListPublisher: CurrentValuePublisher<[RoomSummary], Never> {
        roomListSubject.asCurrentValuePublisher()
    }
    
    var statePublisher: CurrentValuePublisher<RoomSummaryProviderState, Never> {
        stateSubject.asCurrentValuePublisher()
    }
    
    private var rooms: [RoomSummary] = [] {
        didSet {
            roomListSubject.send(rooms)
        }
    }
    
    /// Build a new summary provider with the given parameters
    /// - Parameters:
    ///   - shouldUpdateVisibleRange: whether this summary provider should forward visible ranges
    ///   to the room list service through the `applyInput(input: .viewport(ranges` api. Only useful for
    ///   lists that need to update the visible range on Sliding Sync
    init(roomListService: RoomListServiceProtocol,
         eventStringBuilder: RoomEventStringBuilder,
         name: String,
         shouldUpdateVisibleRange: Bool = false,
         roomListPageSize: UInt32 = 100,
         notificationSettings: NotificationSettingsProxyProtocol,
         appSettings: AppSettings) {
        self.roomListService = roomListService
        self.eventStringBuilder = eventStringBuilder
        self.name = name
        self.shouldUpdateVisibleRange = shouldUpdateVisibleRange
        self.notificationSettings = notificationSettings
        self.appSettings = appSettings
        self.roomListPageSize = roomListPageSize
        
        let (diffsStream, diffsContinuation) = AsyncStream<[RoomListEntriesUpdate]>.makeStream()
        self.diffsContinuation = diffsContinuation
        
        let (loadingStateStream, loadingStateContinuation) = AsyncStream<RoomListLoadingState>.makeStream()
        self.loadingStateContinuation = loadingStateContinuation
        
        Task { [weak self] in
            for await diffs in diffsStream {
                await self?.updateRoomsWithDiffs(diffs)
            }
        }
        
        Task { [weak self, name] in
            for await state in loadingStateStream {
                MXLog.info("\(name): Received state update: \(state)")
                self?.stateSubject.send(RoomSummaryProviderState(roomListState: state))
            }
        }
        
        setupVisibleRangeObservers()
        
        setupNotificationSettingsSubscription()
    }
    
    deinit {
        diffsContinuation.finish()
        loadingStateContinuation.finish()
    }
    
    func setRoomList(_ roomList: RoomList) {
        guard stateUpdatesTaskHandle == nil else {
            return
        }
        
        self.roomList = roomList
        
        do {
            listUpdatesSubscriptionResult = roomList.entriesWithDynamicAdapters(pageSize: UInt32(roomListPageSize),
                                                                                listener: SDKListener { [diffsContinuation] updates in
                                                                                    diffsContinuation.yield(updates)
                                                                                })
            
            // Forces the listener above to be called with the current state
            setFilter(.all(filters: []))
            
            let stateUpdatesSubscriptionResult = try roomList.loadingState(listener: SDKListener { [loadingStateContinuation] state in
                loadingStateContinuation.yield(state)
            })
            
            stateUpdatesTaskHandle = stateUpdatesSubscriptionResult.stateStream
            
            stateSubject.send(RoomSummaryProviderState(roomListState: stateUpdatesSubscriptionResult.state))
        } catch {
            MXLog.error("Failed setting up room list entry listener with error: \(error)")
        }
    }
    
    func updateVisibleRange(_ range: Range<Int>) {
        visibleItemRangePublisher.send(range)
    }
    
    func setFilter(_ filter: RoomSummaryProviderFilter) {
        let baseFilter: [RoomListEntriesDynamicFilterKind] = [.any(filters: [.all(filters: [.nonSpace, .nonLeft]),
                                                                             .all(filters: [.space, .invite])]),
                                                              .deduplicateVersions]
        
        switch filter {
        case .excludeAll:
            _ = listUpdatesSubscriptionResult?.controller().setFilter(kind: .none)
        case let .search(query):
            let filters = if appSettings.fuzzyRoomListSearchEnabled {
                [.fuzzyMatchRoomName(pattern: query)] + baseFilter
            } else {
                [.normalizedMatchRoomName(pattern: query)] + baseFilter
            }
            _ = listUpdatesSubscriptionResult?.controller().setFilter(kind: .all(filters: filters))
        case .rooms(let roomIDs, let filters):
            var rustFilters = filters.map(\.rustFilter) + baseFilter
            
            rustFilters.append(.identifiers(identifiers: Array(roomIDs)))
            
            if !filters.contains(.lowPriority), appSettings.lowPriorityFilterEnabled {
                rustFilters.append(.nonLowPriority)
            }
            
            _ = listUpdatesSubscriptionResult?.controller().setFilter(kind: .all(filters: rustFilters))
        case let .all(filters):
            var rustFilters = filters.map(\.rustFilter) + baseFilter
            
            if !filters.contains(.lowPriority), appSettings.lowPriorityFilterEnabled {
                rustFilters.append(.nonLowPriority)
            }
            
            _ = listUpdatesSubscriptionResult?.controller().setFilter(kind: .all(filters: rustFilters))
        }
    }
    
    // MARK: - Private
    
    private func setupVisibleRangeObservers() {
        visibleItemRangePublisher
            .throttle(for: 0.5, scheduler: DispatchQueue.main, latest: true)
            .removeDuplicates()
            .sink { [weak self] range in
                guard let self else { return }
                
                MXLog.info("\(self.name): Updating visible range: \(range)")
                
                if range.upperBound >= rooms.count {
                    listUpdatesSubscriptionResult?.controller().addOnePage()
                } else if range.lowerBound == 0 {
                    listUpdatesSubscriptionResult?.controller().resetToOnePage()
                }
            }
            .store(in: &cancellables)
        
        visibleItemRangePublisher
            .throttle(for: 0.5, scheduler: DispatchQueue.main, latest: true)
            .filter { [weak self] range in
                guard let self else { return false }
                return !range.isEmpty && shouldUpdateVisibleRange
            }
            .compactMap { [weak self] (range: Range) -> [String]? in
                guard let self else { return nil }
                
                // The scroll view content size based visible range calculations might create large ranges
                // This is just a safety check to not overload the backend
                var range = range
                if range.upperBound - range.lowerBound > SlidingSyncConstants.maximumVisibleRangeSize {
                    let upperBound = range.lowerBound + SlidingSyncConstants.maximumVisibleRangeSize
                    range = range.lowerBound..<upperBound
                }
                
                return range
                    .filter { $0 < self.rooms.count }
                    .map { self.rooms[$0].id }
            }
            .removeDuplicates()
            .sink { [weak self] roomIDs in
                guard let self else { return }
                
                Task { [weak self] in
                    do {
                        try await self?.roomListService.subscribeToRooms(roomIds: roomIDs)
                    } catch {
                        MXLog.error("Failed subscribing to rooms with error: \(error)")
                    }
                }
            }
            .store(in: &cancellables)
    }
    
    fileprivate func updateRoomsWithDiffs(_ diffs: [RoomListEntriesUpdate]) async {
        // Building the room summaries (SDK fetches + string building) and applying the
        // CollectionDifference can be expensive, so compute off the main actor and only
        // hop back to publish the result.
        rooms = await Self.updatedRooms(from: diffs, on: rooms, eventStringBuilder: eventStringBuilder, name: name)
    }
    
    @concurrent
    private static func updatedRooms(from diffs: [RoomListEntriesUpdate],
                                     on currentRooms: [RoomSummary],
                                     eventStringBuilder: RoomEventStringBuilder,
                                     name: String) async -> [RoomSummary] {
        let span = MXLog.createSpan("\(name).process_room_list_diffs")
        span.enter()
        defer {
            span.exit()
        }
        
        var updatedRooms = currentRooms
        for diff in diffs {
            updatedRooms = await processDiff(diff, on: updatedRooms, eventStringBuilder: eventStringBuilder, name: name)
        }
        return updatedRooms
    }
    
    private nonisolated static func processDiff(_ diff: RoomListEntriesUpdate, on currentItems: [RoomSummary], eventStringBuilder: RoomEventStringBuilder, name: String) async -> [RoomSummary] {
        guard let collectionDiff = await buildDiff(from: diff, on: currentItems, eventStringBuilder: eventStringBuilder) else {
            MXLog.error("\(name): Failed building CollectionDifference from \(diff)")
            return currentItems
        }
        
        guard let updatedItems = currentItems.applying(collectionDiff) else {
            MXLog.error("\(name): Failed applying diff: \(collectionDiff)")
            return currentItems
        }
        
        return updatedItems
    }
    
    private nonisolated static func fetchRoomDetails(from room: Room) async -> (roomInfo: RoomInfo?, latestEvent: LatestEventValue?) {
        do {
            let latestEvent = await room.latestEvent()
            let roomInfo = try await room.roomInfo()
            return (roomInfo, latestEvent)
        } catch {
            MXLog.error("Failed fetching room info with error: \(error)")
            return (nil, nil)
        }
    }
    
    private nonisolated static func buildRoomSummary(from room: Room, eventStringBuilder: RoomEventStringBuilder) async -> RoomSummary {
        let roomDetails = await fetchRoomDetails(from: room)
        
        guard let roomInfo = roomDetails.roomInfo else {
            // The room info can be momentarily unavailable while the client tears down (e.g. on logout),
            // where the SDK still delivers a diff but `room.roomInfo()` throws. Return a placeholder to
            // keep the diff indices aligned with the SDK instead of crashing.
            MXLog.error("Missing room info for \(room.id())")
            return .placeholder(room: room)
        }
        
        var attributedLastMessage: AttributedString?
        var lastMessageDate: Date?
        var lastMessageState: RoomSummary.LastMessageState?
        
        if let latestRoomMessage = roomDetails.latestEvent {
            switch latestRoomMessage {
            case .local(let timestamp, let senderID, let profile, let content, let state):
                let sender = TimelineItemSender(senderID: senderID, senderProfile: profile)
                attributedLastMessage = eventStringBuilder.buildAttributedString(for: content, sender: sender, isOutgoing: true)
                lastMessageDate = Date(timeIntervalSince1970: TimeInterval(timestamp / 1000))
                
                switch state {
                case .isSending:
                    lastMessageState = .sending
                case .cannotBeSent:
                    lastMessageState = .failed
                case .hasBeenSent:
                    lastMessageState = nil
                }
            case .remote(let timestamp, let senderID, let isOwn, let profile, let content):
                let sender = TimelineItemSender(senderID: senderID, senderProfile: profile)
                attributedLastMessage = eventStringBuilder.buildAttributedString(for: content, sender: sender, isOutgoing: isOwn)
                lastMessageDate = Date(timeIntervalSince1970: TimeInterval(timestamp / 1000))
            case .remoteInvite(let timestamp, let senderID, let profile):
                lastMessageDate = Date(timeIntervalSince1970: TimeInterval(timestamp / 1000))
                
                if let senderID {
                    let sender = TimelineItemSender(senderID: senderID, senderProfile: profile)
                    let senderDisplayName = sender.displayName ?? sender.id
                    let invitedYouString = eventStringBuilder.stateEventStringBuilder.buildInvitedYouString(senderDisplayName)
                    attributedLastMessage = AttributedString(invitedYouString)
                }
            case .none:
                break
            }
        }
        
        var inviterProxy: RoomMemberProxyProtocol?
        if let inviter = roomInfo.inviter {
            inviterProxy = RoomMemberProxy(member: inviter)
        }
        
        let notificationMode = roomInfo.cachedUserDefinedNotificationMode.flatMap { RoomNotificationModeProxy.from(roomNotificationMode: $0) }
        
        let joinRequestType: RoomSummary.JoinRequestType? = switch roomInfo.membership {
        case .invited: .invite(inviter: inviterProxy)
        case .knocked: .knock
        default: nil
        }
        
        let activeCallIntent: RtcCallIntent? = switch roomInfo.activeRoomCallConsensusIntent {
        case .full(let intent):
            intent
        case .partial(intent: let intent, _, _):
            intent
        case .none:
            nil
        }
        
        return RoomSummary(room: room,
                           id: roomInfo.id,
                           joinRequestType: joinRequestType,
                           name: roomInfo.displayName ?? roomInfo.id,
                           isDirect: roomInfo.isDirect,
                           isSpace: roomInfo.isSpace,
                           avatarURL: roomInfo.avatarUrl.flatMap(URL.init(string:)),
                           heroes: roomInfo.heroes.map(UserProfile.init),
                           activeMembersCount: UInt(roomInfo.activeMembersCount),
                           lastMessage: attributedLastMessage,
                           lastMessageDate: lastMessageDate,
                           lastMessageState: lastMessageState,
                           unreadMessagesCount: UInt(roomInfo.numUnreadMessages),
                           unreadMentionsCount: UInt(roomInfo.numUnreadMentions),
                           unreadNotificationsCount: UInt(roomInfo.numUnreadNotifications),
                           notificationMode: notificationMode,
                           canonicalAlias: roomInfo.canonicalAlias,
                           alternativeAliases: .init(roomInfo.alternativeAliases),
                           hasOngoingCall: roomInfo.hasRoomCall,
                           activeCallIntent: activeCallIntent.map { .init(rustCallIntent: $0) },
                           isMarkedUnread: roomInfo.isMarkedUnread,
                           isFavourite: roomInfo.isFavourite,
                           isTombstoned: roomInfo.successorRoom != nil)
    }
    
    private nonisolated static func buildDiff(from diff: RoomListEntriesUpdate, on rooms: [RoomSummary], eventStringBuilder: RoomEventStringBuilder) async -> CollectionDifference<RoomSummary>? {
        var changes = [CollectionDifference<RoomSummary>.Change]()
        
        switch diff {
        case .append(let values):
            for (index, value) in values.enumerated() {
                let summary = await buildRoomSummary(from: value, eventStringBuilder: eventStringBuilder)
                changes.append(.insert(offset: rooms.count + index, element: summary, associatedWith: nil))
            }
        case .clear:
            for (index, value) in rooms.enumerated() {
                changes.append(.remove(offset: index, element: value, associatedWith: nil))
            }
        case .insert(let index, let value):
            let summary = await buildRoomSummary(from: value, eventStringBuilder: eventStringBuilder)
            changes.append(.insert(offset: Int(index), element: summary, associatedWith: nil))
        case .popBack:
            guard let value = rooms.last else {
                fatalError()
            }
            
            changes.append(.remove(offset: rooms.count - 1, element: value, associatedWith: nil))
        case .popFront:
            let summary = rooms[0]
            changes.append(.remove(offset: 0, element: summary, associatedWith: nil))
        case .pushBack(let value):
            let summary = await buildRoomSummary(from: value, eventStringBuilder: eventStringBuilder)
            changes.append(.insert(offset: rooms.count, element: summary, associatedWith: nil))
        case .pushFront(let value):
            let summary = await buildRoomSummary(from: value, eventStringBuilder: eventStringBuilder)
            changes.append(.insert(offset: 0, element: summary, associatedWith: nil))
        case .remove(let index):
            let summary = rooms[Int(index)]
            changes.append(.remove(offset: Int(index), element: summary, associatedWith: nil))
        case .reset(let values):
            for (index, summary) in rooms.enumerated() {
                changes.append(.remove(offset: index, element: summary, associatedWith: nil))
            }
            
            for (index, value) in values.enumerated() {
                await changes.append(.insert(offset: index, element: buildRoomSummary(from: value, eventStringBuilder: eventStringBuilder), associatedWith: nil))
            }
        case .set(let index, let value):
            let summary = await buildRoomSummary(from: value, eventStringBuilder: eventStringBuilder)
            changes.append(.remove(offset: Int(index), element: summary, associatedWith: nil))
            changes.append(.insert(offset: Int(index), element: summary, associatedWith: nil))
        case .truncate(let length):
            for (index, value) in rooms.enumerated() {
                if index < length {
                    continue
                }
                
                changes.append(.remove(offset: index, element: value, associatedWith: nil))
            }
        }
        
        return CollectionDifference(changes)
    }
    
    private func setupNotificationSettingsSubscription() {
        notificationSettings.callbacks
            .receive(on: DispatchQueue.main)
            .dropFirst() // drop the first one to avoid rebuilding the summaries during the first synchronization
            .sink { [weak self] callback in
                guard let self else { return }
                switch callback {
                case .settingsDidChange:
                    Task { await self.rebuildRoomSummaries() }
                }
            }
            .store(in: &cancellables)
    }
    
    private func rebuildRoomSummaries() async {
        MXLog.info("\(name): Rebuilding room summaries for \(rooms.count) rooms")
        
        rooms = await Self.rebuiltRoomSummaries(from: rooms, eventStringBuilder: eventStringBuilder, name: name)
        
        MXLog.info("\(name): Finished rebuilding room summaries (\(rooms.count) rooms)")
    }
    
    @concurrent
    private static func rebuiltRoomSummaries(from rooms: [RoomSummary], eventStringBuilder: RoomEventStringBuilder, name: String) async -> [RoomSummary] {
        let span = MXLog.createSpan("\(name).rebuild_room_summaries")
        span.enter()
        defer {
            span.exit()
        }
        
        var rebuiltRooms = [RoomSummary]()
        rebuiltRooms.reserveCapacity(rooms.count)
        for room in rooms {
            await rebuiltRooms.append(buildRoomSummary(from: room.room, eventStringBuilder: eventStringBuilder))
        }
        return rebuiltRooms
    }
}

extension RoomSummaryProviderState {
    init(roomListState: RoomListLoadingState) {
        switch roomListState {
        case .notLoaded:
            self = .notLoaded
        case .loaded(let maximumNumberOfRooms):
            self = .loaded(totalNumberOfRooms: UInt(maximumNumberOfRooms ?? 0))
        }
    }
}