//
//  ContextOrchestrator.swift
//  iris
//
//  Created by Codex.
//

import CoreLocation
import Foundation
import MediaPlayer
import MusicKit
import os

@available(iOS 16.0, *)
@MainActor
final class ContextOrchestrator: NSObject, ObservableObject {
    @Published private(set) var authorization: CLAuthorizationStatus = .notDetermined
    @Published private(set) var lastLocation: CLLocation? = nil
    @Published private(set) var lastRecomputeAt: Date? = nil
    @Published private(set) var lastRecomputeReason: String? = nil
    @Published private(set) var lastFeed: FeedEnvelope? = nil
    @Published private(set) var lastError: String? = nil
    @Published private(set) var lastWeatherDiagnostics: [String: String] = [:]
    @Published private(set) var lastCalendarDiagnostics: [String: String] = [:]
    @Published private(set) var lastPipelineElapsedMs: Int? = nil
    @Published private(set) var lastFetchFailed: Bool = false
    @Published private(set) var musicAuthorization: MusicAuthorization.Status = .notDetermined
    @Published private(set) var nowPlaying: NowPlayingSnapshot? = nil

    private let logger = Logger(subsystem: Bundle.main.bundleIdentifier ?? "iris", category: "ContextOrchestrator")

    private let locationManager = CLLocationManager()
    private let weatherDataSource = WeatherDataSource()
    private let calendarDataSource = CalendarDataSource()
    private let poiDataSource = POIDataSource()
    private let ranker: HeuristicRanker
    private let store: FeedStore
    private let server: LocalServer
    private let ble: BlePeripheralManager
    private let nowPlayingMonitor = NowPlayingMonitor()

    private var lastRecomputeLocation: CLLocation? = nil
    private var lastRecomputeAccuracy: CLLocationAccuracy? = nil
    private var recomputeInFlight = false
    private var lastRecomputeAttemptAt: Date? = nil

    init(store: FeedStore = FeedStore(),
         server: LocalServer = LocalServer(),
         ble: BlePeripheralManager) {
        self.store = store
        self.server = server
        self.ble = ble
        self.ranker = HeuristicRanker(lastShownAt: { id in store.lastShownAt(feedItemId: id) })
        super.init()

        locationManager.delegate = self
        locationManager.desiredAccuracy = kCLLocationAccuracyBest
        locationManager.distanceFilter = kCLDistanceFilterNone
        locationManager.pausesLocationUpdatesAutomatically = false
        locationManager.allowsBackgroundLocationUpdates = true

        ble.onFirstSubscribe = { [weak self] in
            Task { @MainActor in
                self?.logger.info("BLE subscribed: pushing latest feed")
                self?.pushLatestFeedToBle()
            }
        }
        ble.onControlCommand = { [weak self] command in
            Task { @MainActor in
                self?.handleBleControl(command)
            }
        }

        nowPlayingMonitor.onUpdate = { [weak self] update in
            Task { @MainActor in
                guard let self else { return }
                self.musicAuthorization = update.authorization
                self.nowPlaying = update.snapshot
                self.pushLatestFeedToBle()
            }
        }

        let feed = store.getFeed()
        lastFeed = feed
    }

    func start() {
        authorization = locationManager.authorizationStatus
        logger.info("start auth=\(String(describing: self.authorization), privacy: .public)")
        server.start()
        nowPlayingMonitor.start()
        requestPermissionsIfNeeded()
        locationManager.startUpdatingLocation()
    }

    func stop() {
        locationManager.stopUpdatingLocation()
        nowPlayingMonitor.stop()
    }

    func recomputeNow(reason: String = "manual") {
        guard let location = lastLocation ?? locationManager.location else {
            logger.info("recomputeNow skipped: no location")
            return
        }
        maybeRecompute(for: location, reason: reason, force: true)
    }

    func sendFixtureFeedNow() {
        guard let url = Bundle.main.url(forResource: "full_feed_fixture", withExtension: "json", subdirectory: "ProtocolFixtures")
                ?? Bundle.main.url(forResource: "full_feed_fixture", withExtension: "json"),
              let data = try? Data(contentsOf: url) else {
            logger.error("fixture feed missing in bundle")
            return
        }
        ble.sendOpaque(data.trimmedTrailingWhitespace(), msgType: 1)
        logger.info("sent fixture feed bytes=\(data.count)")
    }

    private func requestPermissionsIfNeeded() {
        switch locationManager.authorizationStatus {
        case .notDetermined:
            logger.info("requestWhenInUseAuthorization")
            locationManager.requestWhenInUseAuthorization()
        case .authorizedWhenInUse:
            logger.info("requestAlwaysAuthorization")
            locationManager.requestAlwaysAuthorization()
        case .authorizedAlways:
            break
        case .restricted, .denied:
            lastError = "Location permission denied."
        @unknown default:
            break
        }
    }

    private func maybeRecompute(for location: CLLocation, reason: String, force: Bool) {
        let now = Date()
        let hardThrottleSec: TimeInterval = 60
        if !force, let lastAttempt = lastRecomputeAttemptAt, now.timeIntervalSince(lastAttempt) < hardThrottleSec {
            logger.info("skip recompute (throttle) reason=\(reason, privacy: .public)")
            return
        }

        lastRecomputeAttemptAt = now
        if recomputeInFlight {
            logger.info("skip recompute (in-flight) reason=\(reason, privacy: .public)")
            return
        }
        recomputeInFlight = true
        lastRecomputeReason = reason

        logger.info("recompute start reason=\(reason, privacy: .public) lat=\(location.coordinate.latitude, format: .fixed(precision: 5)) lon=\(location.coordinate.longitude, format: .fixed(precision: 5)) acc=\(location.horizontalAccuracy, format: .fixed(precision: 1))")

        Task {
            await self.recomputePipeline(location: location, reason: reason)
        }
    }

    private func shouldTriggerRecompute(for location: CLLocation) -> (Bool, String) {
        if lastRecomputeAt == nil {
            return (true, "initial")
        }
        let now = Date()
        let speed = max(0, location.speed)
        let moving = speed >= 1.0
        let maxInterval: TimeInterval = moving ? 5 * 60 : 15 * 60
        if let last = lastRecomputeAt, now.timeIntervalSince(last) > maxInterval {
            return (true, moving ? "timer_5m_moving" : "timer_15m")
        }
        if let lastLoc = lastRecomputeLocation {
            let dist = location.distance(from: lastLoc)
            let distanceThreshold: CLLocationDistance = moving ? 100 : 250
            if dist > distanceThreshold {
                return (true, moving ? "moved_100m_moving" : "moved_250m")
            }
        }
        if let lastAcc = lastRecomputeAccuracy, location.horizontalAccuracy > 0, lastAcc > 0 {
            let improvementThreshold: CLLocationAccuracy = moving ? 30 : 50
            if lastAcc - location.horizontalAccuracy > improvementThreshold {
                return (true, moving ? "accuracy_improved_30m" : "accuracy_improved_50m")
            }
        }
        return (false, "no_trigger")
    }

    private func recomputePipeline(location: CLLocation, reason: String) async {
        defer {
            Task { @MainActor in
                self.recomputeInFlight = false
            }
        }

        let nowEpoch = Int(Date().timeIntervalSince1970)
        let userContext = UserContext(isMoving: location.speed >= 1.0, city: "London")

        let start = Date()
        async let weatherResult = withTimeoutResult(seconds: 6) {
            try await self.weatherDataSource.dataWithDiagnostics(for: location, now: nowEpoch)
        }
        async let calendarResult = withTimeoutResult(seconds: 6) {
            try await self.calendarDataSource.dataWithDiagnostics(now: nowEpoch)
        }
        async let poiResult = withTimeoutResult(seconds: 6) {
            try await self.poiDataSource.data(for: location, now: nowEpoch)
        }

        let wxRes = await weatherResult
        let calRes = await calendarResult
        let poiRes = await poiResult

        func calendarTTL(endAt: Int, now: Int) -> Int {
            let ttl = endAt - now
            return min(max(ttl, 60), 2 * 60 * 60)
        }

        func rainTitle(startAt: Int, now: Int) -> String {
            let minutes = max(0, Int(((TimeInterval(startAt - now)) / 60.0).rounded()))
            if minutes <= 0 { return "Rain now" }
            return "Rain in ~\(minutes) min"
        }

        var rightNowCandidates: [HeuristicRanker.Ranked] = []
        var calendarItems: [FeedItem] = []
        var poiItems: [FeedItem] = []
        var weatherNowItem: FeedItem? = nil
        var fetchFailed = false
        var wxDiagnostics: [String: String] = [:]
        var calDiagnostics: [String: String] = [:]

        switch wxRes {
        case .success(let snapshot):
            wxDiagnostics = snapshot.diagnostics
            let weather = snapshot.data

            if let current = weather.current {
                weatherNowItem = FeedItem(
                    id: "wx:now:\(nowEpoch / 60)",
                    type: .currentWeather,
                    title: "Now \(current.temperatureC)°C \(current.condition.description)".truncated(maxLength: TextConstraints.titleMax),
                    subtitle: "Feels \(current.feelsLikeC)°C".truncated(maxLength: TextConstraints.subtitleMax),
                    priority: 0.8,
                    ttlSec: 1800,
                    condition: current.condition,
                    startsAt: nil,
                    bucket: .fyi,
                    actions: ["DISMISS"]
                )
            }

            if let rainSoon = weather.rainSoon {
                let title = rainTitle(startAt: rainSoon.startAt, now: nowEpoch).truncated(maxLength: TextConstraints.titleMax)
                let subtitle = (rainSoon.source == .minutely ? "Carry an umbrella" : "Rain likely soon")
                    .truncated(maxLength: TextConstraints.subtitleMax)
                let confidence: Double = (rainSoon.source == .minutely) ? 0.9 : 0.6

                let item = FeedItem(
                    id: "wx:rain:\(rainSoon.startAt)",
                    type: .weatherAlert,
                    title: title,
                    subtitle: subtitle,
                    priority: confidence,
                    ttlSec: max(1, rainSoon.ttlSec),
                    condition: nil,
                    startsAt: nil,
                    bucket: .rightNow,
                    actions: ["DISMISS"]
                )
                rightNowCandidates.append(.init(item: item, confidence: confidence, isEligibleForRightNow: true))
            }

            if let wind = weather.windAlert {
                let mph = Int((wind.gustMps * 2.236936).rounded())
                let title = "Wind gusts ~\(mph) mph".truncated(maxLength: TextConstraints.titleMax)
                let subtitle = "Use caution outside".truncated(maxLength: TextConstraints.subtitleMax)
                let confidence: Double = 0.8

                let item = FeedItem(
                    id: "wx:wind:\(nowEpoch):\(Int(wind.thresholdMps * 10))",
                    type: .weatherAlert,
                    title: title,
                    subtitle: subtitle,
                    priority: confidence,
                    ttlSec: max(1, wind.ttlSec),
                    condition: nil,
                    startsAt: nil,
                    bucket: .rightNow,
                    actions: ["DISMISS"]
                )
                rightNowCandidates.append(.init(item: item, confidence: confidence, isEligibleForRightNow: true))
            }

            for warning in weather.warnings {
                let confidence = min(max(warning.confidence, 0.0), 1.0)
                let item = FeedItem(
                    id: warning.id,
                    type: .weatherWarning,
                    title: warning.title.truncated(maxLength: TextConstraints.titleMax),
                    subtitle: warning.subtitle.truncated(maxLength: TextConstraints.subtitleMax),
                    priority: confidence,
                    ttlSec: max(1, warning.ttlSec),
                    condition: nil,
                    startsAt: nil,
                    bucket: .rightNow,
                    actions: ["DISMISS"]
                )
                rightNowCandidates.append(.init(item: item, confidence: confidence, isEligibleForRightNow: true))
            }

            if let wxErr = wxDiagnostics["weatherkit_error"] {
                fetchFailed = true
                logger.warning("weather fetch error: \(wxErr, privacy: .public)")
            }
        case .failure(let error):
            fetchFailed = true
            if let weatherError = error as? WeatherDataSource.WeatherError,
               case .weatherKitFailed(_, let diagnostics) = weatherError {
                wxDiagnostics = diagnostics
                logger.warning("weather fetch error: \(weatherError.localizedDescription, privacy: .public)")
            } else {
                logger.error("weather fetch failed: \(String(describing: error), privacy: .public)")
            }
        }

        switch poiRes {
        case .success(let pois):
            if pois.isEmpty {
                logger.info("no points of interests found")
            }
            for poi in pois.prefix(2) {
                let subtitle = poiSubtitle(for: poi)
                let confidence = min(max(poi.confidence, 0.0), 1.0)
                let item = FeedItem(
                    id: poi.id,
                    type: .poiNearby,
                    title: poi.name.truncated(maxLength: TextConstraints.titleMax),
                    subtitle: subtitle.truncated(maxLength: TextConstraints.subtitleMax),
                    priority: confidence,
                    ttlSec: max(1, poi.ttlSec),
                    condition: nil,
                    startsAt: nil,
                    poiType: poi.poiType,
                    bucket: .fyi,
                    actions: ["DISMISS"]
                )
                poiItems.append(item)
                rightNowCandidates.append(.init(item: item, confidence: confidence, isEligibleForRightNow: true))
            }
        case .failure(let error):
            fetchFailed = true
            logger.error("poi fetch failed: \(String(describing: error), privacy: .public)")
        }

        switch calRes {
        case .success(let snapshot):
            calDiagnostics = snapshot.diagnostics
            for event in snapshot.data.events {
                let isOngoing = event.startAt <= nowEpoch && event.endAt > nowEpoch
                let startsInSec = event.startAt - nowEpoch
                let eligibleForRightNow = isOngoing || startsInSec <= 30 * 60
                let confidence: Double = isOngoing ? 0.9 : 0.7

                let item = FeedItem(
                    id: event.id,
                    type: .calendarEvent,
                    title: event.title.truncated(maxLength: TextConstraints.titleMax),
                    subtitle: "",
                    priority: confidence,
                    ttlSec: calendarTTL(endAt: event.endAt, now: nowEpoch),
                    condition: nil,
                    startsAt: event.startAt,
                    bucket: .fyi,
                    actions: ["DISMISS"]
                )
                calendarItems.append(item)
                rightNowCandidates.append(.init(item: item, confidence: confidence, isEligibleForRightNow: eligibleForRightNow))
            }
        case .failure(let error):
            fetchFailed = true
            if let calendarError = error as? CalendarDataSource.CalendarError {
                calDiagnostics = calendarError.diagnostics
                logger.warning("calendar error: \(calendarError.localizedDescription, privacy: .public)")
            } else {
                logger.error("calendar fetch failed: \(String(describing: error), privacy: .public)")
            }
        }

        let elapsedMs = Int(Date().timeIntervalSince(start) * 1000)
        lastPipelineElapsedMs = elapsedMs
        lastFetchFailed = fetchFailed
        lastWeatherDiagnostics = wxDiagnostics
        lastCalendarDiagnostics = calDiagnostics

        logger.info("pipeline right_now_candidates=\(rightNowCandidates.count) calendar_items=\(calendarItems.count) poi_items=\(poiItems.count) fetchFailed=\(fetchFailed) elapsed_ms=\(elapsedMs)")

        if fetchFailed, rightNowCandidates.isEmpty, calendarItems.isEmpty, weatherNowItem == nil {
            let fallbackFeed = store.getFeed(now: nowEpoch)
            lastFeed = fallbackFeed
            lastError = "Fetch failed; using previous feed."
            server.broadcastFeed(fallbackFeed)
            ble.sendOpaque((try? JSONEncoder().encode(feedForGlass(base: fallbackFeed, now: nowEpoch))) ?? Data(), msgType: 1)
            return
        }

        let eligibleUnsuppressed = rightNowCandidates.filter { ranked in
            !store.isSuppressed(id: ranked.item.id, type: ranked.item.type, now: nowEpoch)
        }

        let winnerSelection = ranker.pickWinner(from: eligibleUnsuppressed, now: nowEpoch, context: userContext)
        let winnerItem = winnerSelection?.item ?? FeedEnvelope.allQuiet(now: nowEpoch).feed[0]

        let fyiCalendar = calendarItems
            .filter { $0.id != winnerItem.id }
            .filter { !store.isSuppressed(id: $0.id, type: $0.type, now: nowEpoch) }
            .sorted(by: { ($0.startsAt ?? Int.max) < ($1.startsAt ?? Int.max) })
            .prefix(3)

        var fyi: [FeedItem] = []
        fyi.append(contentsOf: fyiCalendar.map { item in
            FeedItem(
                id: item.id,
                type: item.type,
                title: item.title.truncated(maxLength: TextConstraints.titleMax),
                subtitle: item.subtitle.truncated(maxLength: TextConstraints.subtitleMax),
                priority: min(max(item.priority, 0.0), 1.0),
                ttlSec: max(1, item.ttlSec),
                condition: item.condition,
                startsAt: item.startsAt,
                poiType: item.poiType,
                bucket: .fyi,
                actions: ["DISMISS"]
            )
        })

        let fyiPOI = poiItems
            .filter { $0.id != winnerItem.id }
            .filter { !store.isSuppressed(id: $0.id, type: $0.type, now: nowEpoch) }
            .prefix(2)

        fyi.append(contentsOf: fyiPOI.map { item in
            FeedItem(
                id: item.id,
                type: item.type,
                title: item.title.truncated(maxLength: TextConstraints.titleMax),
                subtitle: item.subtitle.truncated(maxLength: TextConstraints.subtitleMax),
                priority: min(max(item.priority, 0.0), 1.0),
                ttlSec: max(1, item.ttlSec),
                condition: item.condition,
                startsAt: item.startsAt,
                poiType: item.poiType,
                bucket: .fyi,
                actions: ["DISMISS"]
            )
        })

        if let weatherNowItem,
           weatherNowItem.id != winnerItem.id,
           !store.isSuppressed(id: weatherNowItem.id, type: weatherNowItem.type, now: nowEpoch) {
            fyi.append(weatherNowItem)
        }

        let items = [winnerItem] + fyi
        let feedEnvelope = FeedEnvelope(
            schema: 1,
            generatedAt: nowEpoch,
            feed: items,
            meta: FeedMeta(winnerId: winnerItem.id, unreadCount: items.count)
        )
        store.setFeed(feedEnvelope, now: nowEpoch)
        lastFeed = feedEnvelope
        lastRecomputeAt = Date()
        lastRecomputeLocation = location
        lastRecomputeAccuracy = location.horizontalAccuracy
        lastError = fetchFailed ? "Partial fetch failure." : nil

        logger.info("winner id=\(winnerItem.id, privacy: .public) type=\(winnerItem.type.rawValue, privacy: .public) prio=\(winnerItem.priority, format: .fixed(precision: 2)) ttl=\(winnerItem.ttlSec)")

        server.broadcastFeed(feedEnvelope)
        ble.sendOpaque((try? JSONEncoder().encode(feedForGlass(base: feedEnvelope, now: nowEpoch))) ?? Data(), msgType: 1)
    }

    private func pushLatestFeedToBle() {
        let nowEpoch = Int(Date().timeIntervalSince1970)
        let feed = store.getFeed(now: nowEpoch)
        ble.sendOpaque((try? JSONEncoder().encode(feedForGlass(base: feed, now: nowEpoch))) ?? Data(), msgType: 1)
    }

    private func handleBleControl(_ command: String) {
        guard !command.isEmpty else { return }
        if command == "REQ_FULL" {
            logger.info("BLE control REQ_FULL")
            pushLatestFeedToBle()
            return
        }
        if command.hasPrefix("ACK:") {
            logger.info("BLE control \(command, privacy: .public)")
            return
        }
        logger.info("BLE control unknown=\(command, privacy: .public)")
    }

    private func feedForGlass(base: FeedEnvelope, now: Int) -> FeedEnvelope {
        guard let nowPlayingCard = nowPlaying?.asFeedItem(baseGeneratedAt: base.generatedAt, now: now) else {
            return base
        }

        var cards = base.feed.filter { $0.type != .nowPlaying }

        // Append after existing FYI cards (e.g. weather).
        cards.append(nowPlayingCard)

        return FeedEnvelope(
            schema: base.schema,
            generatedAt: base.generatedAt,
            feed: cards,
            meta: FeedMeta(winnerId: base.meta.winnerId, unreadCount: cards.count)
        )
    }

    private func poiSubtitle(for poi: POIDataSource.POI) -> String {
        let distance = distanceText(meters: poi.distanceMeters)
        let walk = "\(poi.walkingMinutes) min walk"
        let parts = [poi.category, distance, walk]
            .map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
            .filter { !$0.isEmpty }
        return parts.joined(separator: " • ")
    }

    private func distanceText(meters: CLLocationDistance) -> String {
        if meters >= 1000 {
            return String(format: "%.1f km", meters / 1000.0)
        }
        return "\(Int(meters.rounded())) m"
    }
}

extension ContextOrchestrator: CLLocationManagerDelegate {
    func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
        authorization = manager.authorizationStatus
        logger.info("auth changed=\(String(describing: self.authorization), privacy: .public)")
        requestPermissionsIfNeeded()
    }

    func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
        logger.error("location error: \(String(describing: error), privacy: .public)")
        lastError = "Location error: \(error)"
    }

    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard let best = locations.sorted(by: { $0.horizontalAccuracy < $1.horizontalAccuracy }).first else { return }
        lastLocation = best

        let (should, reason) = shouldTriggerRecompute(for: best)
        if should {
            maybeRecompute(for: best, reason: reason, force: false)
        }
    }
}

enum TimeoutError: Error {
    case timedOut
}

func withTimeoutResult<T>(seconds: Double, operation: @escaping () async throws -> T) async -> Result<T, Error> {
    do {
        let value = try await withThrowingTaskGroup(of: T.self) { group in
            group.addTask {
                try await operation()
            }
            group.addTask {
                try await Task.sleep(nanoseconds: UInt64(seconds * 1_000_000_000))
                throw TimeoutError.timedOut
            }
            let result = try await group.next()!
            group.cancelAll()
            return result
        }
        return .success(value)
    } catch {
        return .failure(error)
    }
}

@available(iOS 16.0, *)
struct NowPlayingSnapshot: Equatable, Sendable {
    let itemId: String
    let title: String
    let artist: String?
    let album: String?
    let playbackStatus: MusicKit.MusicPlayer.PlaybackStatus

    func asFeedItem(baseGeneratedAt: Int, now: Int) -> FeedItem {
        let desiredLifetimeSec = 30
        let ttl = max(1, (now - baseGeneratedAt) + desiredLifetimeSec)

        let subtitleParts = [artist, album]
            .compactMap { $0?.trimmingCharacters(in: .whitespacesAndNewlines) }
            .filter { !$0.isEmpty }
        let subtitle = subtitleParts.isEmpty ? "Apple Music" : subtitleParts.joined(separator: " • ")

        return FeedItem(
            id: "music:now:\(itemId)",
            type: .nowPlaying,
            title: title.truncated(maxLength: TextConstraints.titleMax),
            subtitle: subtitle.truncated(maxLength: TextConstraints.subtitleMax),
            priority: playbackStatus == .playing ? 0.35 : 0.2,
            ttlSec: ttl,
            condition: nil,
            startsAt: nil,
            bucket: .fyi,
            actions: ["DISMISS"]
        )
    }
}

@available(iOS 16.0, *)
@MainActor
final class NowPlayingMonitor {
    struct Update: Sendable {
        let authorization: MusicAuthorization.Status
        let snapshot: NowPlayingSnapshot?
    }

    var onUpdate: ((Update) -> Void)? = nil

    private let player = SystemMusicPlayer.shared
    private let mpController = MPMusicPlayerController.systemMusicPlayer
    private var observers: [NSObjectProtocol] = []
    private var pollTimer: DispatchSourceTimer?
    private var isRunning = false

    private var authorization: MusicAuthorization.Status = .notDetermined
    private var lastSnapshot: NowPlayingSnapshot? = nil

    func start() {
        guard !isRunning else { return }
        isRunning = true

        mpController.beginGeneratingPlaybackNotifications()
        observers.append(
            NotificationCenter.default.addObserver(
                forName: .MPMusicPlayerControllerNowPlayingItemDidChange,
                object: mpController,
                queue: .main
            ) { [weak self] _ in
                Task { @MainActor in self?.refresh(reason: "mp_now_playing_changed") }
            }
        )
        observers.append(
            NotificationCenter.default.addObserver(
                forName: .MPMusicPlayerControllerPlaybackStateDidChange,
                object: mpController,
                queue: .main
            ) { [weak self] _ in
                Task { @MainActor in self?.refresh(reason: "mp_playback_state_changed") }
            }
        )

        startPolling()

        Task { @MainActor in
            await ensureAuthorization()
            refresh(reason: "start")
        }
    }

    func stop() {
        guard isRunning else { return }
        isRunning = false

        pollTimer?.cancel()
        pollTimer = nil

        for token in observers {
            NotificationCenter.default.removeObserver(token)
        }
        observers.removeAll()

        mpController.endGeneratingPlaybackNotifications()
    }

    private func startPolling() {
        guard pollTimer == nil else { return }
        let timer = DispatchSource.makeTimerSource(queue: .main)
        timer.schedule(deadline: .now() + 2, repeating: 2)
        timer.setEventHandler { [weak self] in
            guard let self else { return }
            self.refresh(reason: "poll")
        }
        timer.resume()
        pollTimer = timer
    }

    private func ensureAuthorization() async {
        if authorization == .notDetermined {
            authorization = await MusicAuthorization.request()
            onUpdate?(Update(authorization: authorization, snapshot: lastSnapshot))
        }
    }

    private func refresh(reason: String) {
        guard authorization == .authorized else {
            if lastSnapshot != nil {
                lastSnapshot = nil
                onUpdate?(Update(authorization: authorization, snapshot: nil))
            }
            return
        }

        let playback = player.state.playbackStatus
        guard playback != .stopped else {
            if lastSnapshot != nil {
                lastSnapshot = nil
                onUpdate?(Update(authorization: authorization, snapshot: nil))
            }
            return
        }

        let mpItem = mpController.nowPlayingItem
        let musicKitItem = player.queue.currentEntry?.item

        let itemId = sanitizeId(
            musicKitItem.map { String(describing: $0.id) }
                ?? mpItem.map { "mp:\($0.persistentID)" }
                ?? UUID().uuidString
        )

        let musicKitTitle = musicKitItem.map(nowPlayingTitle(from:))
        let title = normalizeTitle(musicKitTitle) ?? normalizeTitle(mpItem?.title) ?? "Now Playing"

        let artist = normalizePart(musicKitItem.flatMap(nowPlayingArtist(from:))) ?? normalizePart(mpItem?.artist)
        let album = normalizePart(musicKitItem.flatMap(nowPlayingAlbum(from:))) ?? normalizePart(mpItem?.albumTitle)

        let snapshot = NowPlayingSnapshot(itemId: itemId, title: title, artist: artist, album: album, playbackStatus: playback)

        guard snapshot != lastSnapshot else { return }
        lastSnapshot = snapshot
        onUpdate?(Update(authorization: authorization, snapshot: snapshot))
    }

    private func nowPlayingTitle(from item: MusicItem) -> String {
        if let song = item as? Song { return song.title }
        if let album = item as? Album { return album.title }
        if let playlist = item as? Playlist { return playlist.name }
        return "Now Playing"
    }

    private func nowPlayingArtist(from item: MusicItem) -> String? {
        if let song = item as? Song { return song.artistName }
        if let album = item as? Album { return album.artistName }
        return nil
    }

    private func nowPlayingAlbum(from item: MusicItem) -> String? {
        if let song = item as? Song { return song.albumTitle }
        return nil
    }

    private func sanitizeId(_ raw: String) -> String {
        raw
            .replacingOccurrences(of: " ", with: "_")
            .replacingOccurrences(of: "\n", with: "_")
            .replacingOccurrences(of: "\t", with: "_")
    }

    private func normalizePart(_ raw: String?) -> String? {
        guard let raw else { return nil }
        let trimmed = raw.trimmingCharacters(in: .whitespacesAndNewlines)
        return trimmed.isEmpty ? nil : trimmed
    }

    private func normalizeTitle(_ raw: String?) -> String? {
        guard let value = normalizePart(raw) else { return nil }
        if value == "Now Playing" { return nil }
        return value
    }
}