import ActivityKit
import Combine
import CoreData
import Foundation
import Swinject
import UIKit

@available(iOS 16.2, *) private struct ActiveActivity {
    let activity: Activity<LiveActivityAttributes>
    let startDate: Date

    func needsRecreation() -> Bool {
        switch activity.activityState {
        case .dismissed,
             .ended,
             .stale:
            return true
        case .active: break
        @unknown default:
            return true
        }

        return -startDate.timeIntervalSinceNow >
            TimeInterval(60 * 60)
    }
}

@available(iOS 16.2, *) final class LiveActivityBridge: Injectable, ObservableObject, SettingsObserver
{
    @Injected() private var settingsManager: SettingsManager!
    @Injected() private var broadcaster: Broadcaster!
    @Injected() private var storage: FileStorage!
    @Injected() private var glucoseStorage: GlucoseStorage!

    private let activityAuthorizationInfo = ActivityAuthorizationInfo()
    @Published private(set) var systemEnabled: Bool

    private var settings: FreeAPSSettings {
        settingsManager.settings
    }

    var determination: DeterminationData?
    private var currentActivity: ActiveActivity?
    private var latestGlucose: GlucoseData?
    var glucoseFromPersistence: [GlucoseData]?
    var override: OverrideData?
    var widgetItems: [LiveActivityAttributes.LiveActivityItem]?

    let context = CoreDataStack.shared.newTaskContext()

    private var coreDataPublisher: AnyPublisher<Set<NSManagedObject>, Never>?
    private var subscriptions = Set<AnyCancellable>()

    init(resolver: Resolver) {
        coreDataPublisher =
            changedObjectsOnManagedObjectContextDidSavePublisher()
                .receive(on: DispatchQueue.global(qos: .background))
                .share()
                .eraseToAnyPublisher()

        systemEnabled = activityAuthorizationInfo.areActivitiesEnabled
        injectServices(resolver)
        setupNotifications()
        registerSubscribers()
        registerHandler()
        monitorForLiveActivityAuthorizationChanges()
        setupGlucoseArray()
        broadcaster.register(SettingsObserver.self, observer: self)
    }

    private func setupNotifications() {
        let notificationCenter = Foundation.NotificationCenter.default
        notificationCenter
            .addObserver(forName: UIApplication.didEnterBackgroundNotification, object: nil, queue: nil) { [weak self] _ in
                Task { @MainActor in
                    self?.forceActivityUpdate()
                }
            }
        notificationCenter
            .addObserver(forName: UIApplication.didBecomeActiveNotification, object: nil, queue: nil) { [weak self] _ in
                Task { @MainActor in
                    self?.forceActivityUpdate()
                }
            }
        notificationCenter.addObserver(
            self,
            selector: #selector(handleLiveActivityOrderChange),
            name: .liveActivityOrderDidChange,
            object: nil
        )
    }

    // TODO: - use a delegate or a custom notification here instead

    func settingsDidChange(_: FreeAPSSettings) {
        Task {
            await updateContentState(determination)
        }
    }

    private func registerHandler() {
        // Since we are only using this info to show if an Override is active or not in the Live Activity it is enough to observe only the 'OverrideStored' Entity
        coreDataPublisher?.filterByEntityName("OverrideStored").sink { [weak self] _ in
            guard let self = self else { return }
            self.overridesDidUpdate()
        }.store(in: &subscriptions)

        coreDataPublisher?.filterByEntityName("OrefDetermination").sink { [weak self] _ in
            guard let self = self else { return }
            self.cobOrIobDidUpdate()
        }.store(in: &subscriptions)
    }

    private func registerSubscribers() {
        glucoseStorage.updatePublisher
            .receive(on: DispatchQueue.global(qos: .background))
            .sink { [weak self] _ in
                guard let self = self else { return }
                self.setupGlucoseArray()
            }
            .store(in: &subscriptions)
    }

    private func cobOrIobDidUpdate() {
        Task { @MainActor in
            self.determination = await fetchAndMapDetermination()
            if let determination = determination {
                await self.updateContentState(determination)
            }
        }
    }

    private func overridesDidUpdate() {
        Task { @MainActor in
            self.override = await fetchAndMapOverride()
            if let determination = determination {
                await self.updateContentState(determination)
            }
        }
    }

    @objc private func handleLiveActivityOrderChange() {
        Task {
            self.widgetItems = UserDefaults.standard
                .loadLiveActivityOrderFromUserDefaults() ?? LiveActivityAttributes.LiveActivityItem.defaultItems
            await self.updateLiveActivityOrder()
        }
    }

    @MainActor private func updateContentState<T>(_ update: T) async {
        guard let latestGlucose = latestGlucose else { return }

        var content: LiveActivityAttributes.ContentState?

        if let determination = update as? DeterminationData {
            content = LiveActivityAttributes.ContentState(
                new: latestGlucose,
                prev: latestGlucose,
                units: settings.units,
                chart: glucoseFromPersistence ?? [],
                settings: settings,
                determination: determination,
                override: override,
                widgetItems: widgetItems
            )
        } else if let override = update as? OverrideData {
            content = LiveActivityAttributes.ContentState(
                new: latestGlucose,
                prev: latestGlucose,
                units: settings.units,
                chart: glucoseFromPersistence ?? [],
                settings: settings,
                determination: determination,
                override: override,
                widgetItems: widgetItems
            )
        }

        if let content = content {
            await pushUpdate(content)
        }
    }

    @MainActor private func updateLiveActivityOrder() async {
        Task {
            await updateContentState(determination)
        }
    }

    private func setupGlucoseArray() {
        Task { @MainActor in
            // Fetch and map glucose to GlucoseData struct
            self.glucoseFromPersistence = await fetchAndMapGlucose()

            // Push the update to the Live Activity
            glucoseDidUpdate(glucoseFromPersistence ?? [])
        }
    }

    private func monitorForLiveActivityAuthorizationChanges() {
        Task {
            for await activityState in activityAuthorizationInfo.activityEnablementUpdates {
                if activityState != systemEnabled {
                    await MainActor.run {
                        systemEnabled = activityState
                    }
                }
            }
        }
    }

    /// creates and tries to present a new activity update from the current GlucoseStorage values if live activities are enabled in settings
    /// Ends existing live activities if live activities are not enabled in settings
    @MainActor private func forceActivityUpdate() {
        // just before app resigns active, show a new activity
        // only do this if there is no current activity or the current activity is older than 1h
        if settings.useLiveActivity {
            if currentActivity?.needsRecreation() ?? true
            {
                glucoseDidUpdate(glucoseFromPersistence ?? [])
            }
        } else {
            Task {
                await self.endActivity()
            }
        }
    }

    /// attempts to present this live activity state, creating a new activity if none exists yet
    @MainActor private func pushUpdate(_ state: LiveActivityAttributes.ContentState) async {
//        // End all activities that are not the current one
        for unknownActivity in Activity<LiveActivityAttributes>.activities
            .filter({ self.currentActivity?.activity.id != $0.id })
        {
            await unknownActivity.end(nil, dismissalPolicy: .immediate)
        }

        if let currentActivity = currentActivity {
            if currentActivity.needsRecreation(), UIApplication.shared.applicationState == .active {
                await endActivity()
                await pushUpdate(state)
            } else {
                let content = ActivityContent(
                    state: state,
                    staleDate: min(state.date, Date.now).addingTimeInterval(360) // 6 minutes in seconds
                )
                await currentActivity.activity.update(content)
            }
        } else {
            do {
                // always push a non-stale content as the first update
                // pushing a stale content as the frst content results in the activity not being shown at all
                // apparently this initial state is also what is shown after the live activity expires (after 8h)
                let expired = ActivityContent(
                    state: LiveActivityAttributes.ContentState(
                        bg: "--",
                        direction: nil,
                        change: "--",
                        date: Date.now,
                        highGlucose: settings.high,
                        lowGlucose: settings.low,
                        target: determination?.target ?? 100 as Decimal,
                        glucoseColorScheme: settings.glucoseColorScheme.rawValue,
                        detailedViewState: nil,
                        isInitialState: true
                    ),
                    staleDate: Date.now.addingTimeInterval(60)
                )

                // Request a new activity
                let activity = try Activity.request(
                    attributes: LiveActivityAttributes(startDate: Date.now),
                    content: expired,
                    pushType: nil
                )
                currentActivity = ActiveActivity(activity: activity, startDate: Date.now)

                // then show the actual content
                await pushUpdate(state)
            } catch {
                print("Activity creation error: \(error)")
            }
        }
    }

    /// ends all live activities immediateny
    private func endActivity() async {
        if let currentActivity {
            await currentActivity.activity.end(nil, dismissalPolicy: .immediate)
            self.currentActivity = nil
        }

        // end any other activities
        for unknownActivity in Activity<LiveActivityAttributes>.activities {
            await unknownActivity.end(nil, dismissalPolicy: .immediate)
        }
    }
}

@available(iOS 16.2, *)
extension LiveActivityBridge {
    @MainActor func glucoseDidUpdate(_ glucose: [GlucoseData]) {
        guard settings.useLiveActivity else {
            if currentActivity != nil {
                Task {
                    await self.endActivity()
                }
            }
            return
        }

        // backfill latest glucose if contained in this update
        if glucose.count > 1 {
            latestGlucose = glucose.dropFirst().first
        }
        defer {
            self.latestGlucose = glucose.first
        }

        guard let bg = glucose.first else {
            return
        }

        if let determination = determination {
            let content = LiveActivityAttributes.ContentState(
                new: bg,
                prev: latestGlucose,
                units: settings.units,
                chart: glucose,
                settings: settings,
                determination: determination,
                override: override,
                widgetItems: widgetItems
            )

            if let content = content {
                Task {
                    await self.pushUpdate(content)
                }
            }
        }
    }
}