import Foundation
import Observation
import VelodyDomain
import VelodyNetworking
import VelodyPlayback
import VelodyPersistence
import VelodySync
import VelodyUtilities
#if canImport(UIKit)
import UIKit
#endif

@MainActor
protocol iPhoneLocalAudioPlaying: AnyObject {
    var onStateChange: ((iPhoneNowPlayingState) -> Void)? { get set }
    var state: iPhoneNowPlayingState { get }

    func setCatalogTracks(_ tracks: [LibraryTrack])
    func play(trackID: String)
    func pause()
    func stop()
    func seek(to time: Double)
}

enum iPhonePlaybackState: Equatable {
    case playing
    case paused
    case stopped
    case missingFile
    case failed

    var displayText: String {
        switch self {
        case .playing:
            return "Playing"
        case .paused:
            return "Paused"
        case .stopped:
            return "Stopped"
        case .missingFile:
            return "Missing file"
        case .failed:
            return "Failed"
        }
    }
}

struct iPhoneNowPlayingState: Equatable {
    var trackID: String?
    var title: String?
    var artist: String?
    var playbackState: iPhonePlaybackState
    var currentTime: Double
    var duration: Double
    var errorMessage: String?

    static let empty = iPhoneNowPlayingState(
        trackID: nil,
        title: nil,
        artist: nil,
        playbackState: .stopped,
        currentTime: 0,
        duration: 0,
        errorMessage: nil
    )

    var isPlaying: Bool {
        playbackState == .playing
    }

    var hasTrack: Bool {
        trackID != nil
    }

    var canSeek: Bool {
        hasTrack && duration > 0 && playbackState != .missingFile && playbackState != .failed
    }
}

private struct StorediPhonePlaybackSession: Codable {
    var currentTrackID: String?
    var currentTime: Double
}

struct iPhonePlaybackSessionStore: PlaybackSessionStore, @unchecked Sendable {
    private let userDefaults: UserDefaults
    private let storageKey: String
    private let encoder = JSONEncoder()
    private let decoder = JSONDecoder()

    init(
        userDefaults: UserDefaults = .standard,
        storageKey: String = "velody.iphone.playback.session"
    ) {
        self.userDefaults = userDefaults
        self.storageKey = storageKey
    }

    func loadSession() -> PlaybackSessionSnapshot? {
        guard let data = userDefaults.data(forKey: storageKey),
              let storedSession = try? decoder.decode(StorediPhonePlaybackSession.self, from: data)
        else {
            return nil
        }

        return PlaybackSessionSnapshot(
            queueTrackIDs: [],
            currentTrackID: storedSession.currentTrackID,
            currentTime: storedSession.currentTime,
            isShuffleEnabled: false,
            repeatMode: .off
        )
    }

    func saveSession(_ session: PlaybackSessionSnapshot) {
        guard let currentTrackID = session.currentTrackID,
              !currentTrackID.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
        else {
            clearSession()
            return
        }

        let storedSession = StorediPhonePlaybackSession(
            currentTrackID: currentTrackID,
            currentTime: session.currentTime
        )

        guard let data = try? encoder.encode(storedSession) else {
            return
        }

        userDefaults.set(data, forKey: storageKey)
    }

    func clearSession() {
        userDefaults.removeObject(forKey: storageKey)
    }
}

@MainActor
final class iPhonePlaybackControllerPlayer: iPhoneLocalAudioPlaying {
    var onStateChange: ((iPhoneNowPlayingState) -> Void)?

    private(set) var state: iPhoneNowPlayingState = .empty {
        didSet {
            onStateChange?(state)
        }
    }

    private let controller: PlaybackController
    private var idleStateHint: iPhonePlaybackState = .stopped

    init(
        controller: PlaybackController? = nil
    ) {
        self.controller = controller ?? PlaybackController(
            sessionStore: iPhonePlaybackSessionStore()
        )
        self.state = Self.makeState(
            from: self.controller.nowPlayingState,
            idleStateHint: .stopped
        )
        self.controller.onStateChange = { [weak self] state in
            self?.apply(state)
        }
    }

    func setCatalogTracks(_ tracks: [LibraryTrack]) {
        controller.setCatalogTracks(tracks)
        apply(controller.nowPlayingState)
    }

    func play(trackID: String) {
        idleStateHint = .paused
        controller.play(trackID: trackID)
        apply(controller.nowPlayingState)
    }

    func pause() {
        idleStateHint = .paused
        controller.pause()
        apply(controller.nowPlayingState)
    }

    func stop() {
        idleStateHint = .stopped
        controller.stop()
        apply(controller.nowPlayingState)
    }

    func seek(to time: Double) {
        controller.seek(to: time)
        apply(controller.nowPlayingState)
    }

    private func apply(_ nowPlayingState: NowPlayingState) {
        let effectiveDuration = max(
            nowPlayingState.duration,
            nowPlayingState.currentTrack?.durationSeconds ?? 0
        )

        if nowPlayingState.isPlaying {
            idleStateHint = .paused
        } else if nowPlayingState.currentTrack == nil {
            idleStateHint = .stopped
        } else if effectiveDuration > 0,
                  nowPlayingState.currentTime >= max(effectiveDuration - 0.25, 0) {
            idleStateHint = .stopped
        }

        state = Self.makeState(
            from: nowPlayingState,
            idleStateHint: idleStateHint
        )
    }

    private static func makeState(
        from nowPlayingState: NowPlayingState,
        idleStateHint: iPhonePlaybackState
    ) -> iPhoneNowPlayingState {
        let effectiveDuration = max(
            nowPlayingState.duration,
            nowPlayingState.currentTrack?.durationSeconds ?? 0
        )
        let playbackState: iPhonePlaybackState

        if let playbackError = nowPlayingState.error {
            switch playbackError {
            case .missingLocalFile:
                playbackState = .missingFile
            default:
                playbackState = .failed
            }
        } else if nowPlayingState.isPlaying {
            playbackState = .playing
        } else if nowPlayingState.currentTrack != nil {
            if nowPlayingState.currentTime > 0,
               effectiveDuration > 0,
               nowPlayingState.currentTime < effectiveDuration {
                playbackState = .paused
            } else {
                playbackState = idleStateHint
            }
        } else {
            playbackState = .stopped
        }

        return iPhoneNowPlayingState(
            trackID: nowPlayingState.currentTrackID,
            title: nowPlayingState.currentTrack?.title,
            artist: nowPlayingState.currentTrack?.artist,
            playbackState: playbackState,
            currentTime: nowPlayingState.currentTime,
            duration: effectiveDuration,
            errorMessage: nowPlayingState.error?.localizedDescription
        )
    }
}

enum NowPlayingDownloadBadge: Equatable {
    case downloaded
    case missing
    case offline

    var title: String {
        switch self {
        case .downloaded:
            return "Downloaded"
        case .missing:
            return "Missing"
        case .offline:
            return "Offline"
        }
    }
}

struct NowPlayingCardViewData: Equatable {
    let trackID: String
    let title: String
    let artist: String
    let artworkLocalFilePath: String?
    let playbackStateText: String
    let downloadBadge: NowPlayingDownloadBadge
    let currentTime: Double
    let duration: Double
    let currentTimeText: String
    let durationText: String
    let progress: Double
    let isPlaying: Bool
    let canSeek: Bool
    let errorMessage: String?
}

struct LibrarySectionMessage: Equatable {
    let title: String
    let body: String
    let systemImage: String
}

@MainActor
@Observable
final class iPhoneLibraryViewModel {
    enum ViewState: Equatable {
        case idle
        case loading
        case success
        case empty
        case networkError(String)
    }

    var remoteTracks: [RemoteTrackRowViewData] = []
    var availableOfflineTracks: [AvailableOfflineTrackRowViewData] = []
    var searchText = "" {
        didSet {
            guard searchText != oldValue else {
                return
            }

            rebuildRows()
        }
    }
    var syncStatus = "Sync your remote library to see your tracks here."
    var state: ViewState = .idle
    var nowPlaying: iPhoneNowPlayingState = .empty
    var nowPlayingFavoriteTrackID: String?
    var isNowPlayingTrackFavorite = false

    private let environment: ServerEnvironment
    private let apiClient: any VelodyAPIClient
    private let syncService: RemoteLibrarySyncService
    private let offlineLibraryService: OfflineLibraryService
    private let favoriteTrackStore: any FavoriteTrackStore
    private let keychainService: any KeychainService
    private let player: any iPhoneLocalAudioPlaying
    private var cachedRemoteTracksByID: [String: RemoteTrack] = [:]
    private var cachedRemoteLibraryTracks: [OfflineLibraryRemoteTrack] = []
    private var cachedAvailableOfflineTracks: [OfflineLibraryTrack] = []
    private var cachedFavoriteTrackRecordsByID: [String: FavoriteTrackRecord] = [:]
    private var hasLoaded = false

    var hasActiveSearch: Bool {
        !searchText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
    }

    var hasCachedRemoteTracks: Bool {
        !cachedRemoteLibraryTracks.isEmpty
    }

    var isSyncing: Bool {
        state == .loading
    }

    var syncButtonTitle: String {
        isSyncing ? "Syncing..." : "Sync Remote Library"
    }

    var remoteSectionTitle: String {
        let count = remoteTracks.count
        return hasActiveSearch
            ? "Remote Library Results (\(count))"
            : "Remote Library (\(count))"
    }

    var availableOfflineSectionTitle: String {
        let count = availableOfflineTracks.count
        return hasActiveSearch
            ? "Offline Results (\(count))"
            : "Available Offline (\(count))"
    }

    var inlineSyncErrorMessage: LibrarySectionMessage? {
        guard hasCachedRemoteTracks, case .networkError = state else {
            return nil
        }

        return Self.connectionFailedMessage
    }

    var remoteEmptyStateMessage: LibrarySectionMessage? {
        guard remoteTracks.isEmpty else {
            return nil
        }

        if hasActiveSearch {
            return Self.searchEmptyMessage
        }

        switch state {
        case .loading:
            return nil
        case .networkError:
            return Self.connectionFailedMessage
        case .idle, .success, .empty:
            return Self.remoteLibraryEmptyMessage
        }
    }

    var availableOfflineEmptyStateMessage: LibrarySectionMessage? {
        guard availableOfflineTracks.isEmpty else {
            return nil
        }

        return hasActiveSearch
            ? Self.searchEmptyMessage
            : Self.availableOfflineEmptyMessage
    }

    var nowPlayingCard: NowPlayingCardViewData? {
        guard let trackID = nowPlaying.trackID,
              let title = nowPlaying.title
        else {
            return nil
        }

        let remoteTrack = cachedRemoteLibraryTracks.first(where: {
            $0.remoteTrack.trackId == trackID
        })
        let fallbackOfflineTrack = cachedAvailableOfflineTracks.first(where: {
            $0.remoteTrackId == trackID
        })
        let artist = nowPlaying.artist
            ?? remoteTrack?.remoteTrack.artist
            ?? fallbackOfflineTrack?.artist
            ?? "Unknown Artist"
        let duration = max(
            nowPlaying.duration,
            Double(remoteTrack?.remoteTrack.durationSeconds ?? fallbackOfflineTrack?.durationSeconds ?? 0)
        )
        let clampedCurrentTime: Double

        if duration > 0 {
            clampedCurrentTime = min(max(nowPlaying.currentTime, 0), duration)
        } else {
            clampedCurrentTime = max(nowPlaying.currentTime, 0)
        }
        let progress: Double

        if duration > 0 {
            progress = min(max(clampedCurrentTime / duration, 0), 1)
        } else {
            progress = 0
        }

        return NowPlayingCardViewData(
            trackID: trackID,
            title: title,
            artist: artist,
            artworkLocalFilePath: remoteTrack?.localArtworkFilePath ?? fallbackOfflineTrack?.localArtworkFilePath,
            playbackStateText: nowPlaying.playbackState.displayText,
            downloadBadge: nowPlayingDownloadBadge(for: trackID),
            currentTime: clampedCurrentTime,
            duration: duration,
            currentTimeText: Self.formatPlaybackTime(clampedCurrentTime),
            durationText: Self.formatPlaybackTime(duration),
            progress: progress,
            isPlaying: nowPlaying.isPlaying,
            canSeek: nowPlaying.canSeek && duration > 0,
            errorMessage: Self.userFacingPlaybackErrorMessage(for: nowPlaying)
        )
    }

    convenience init(
        player: (any iPhoneLocalAudioPlaying)? = nil,
        keychainService: any KeychainService = SystemKeychainService(
            service: "de.diyaa.velody.iphone"
        )
    ) {
        let environment = ServerEnvironment(
            baseURL: ServerEnvironment.defaultLocalBaseURL,
            appVersion: "0.1.0"
        )
        let apiClient = URLSessionVelodyAPIClient(
            environment: environment,
            deviceAccessTokenProvider: {
                try await keychainService.loadValue(forKey: Self.deviceAccessTokenKey)
            }
        )
        let store = Self.makeRemoteLibraryStore()
        let syncCursorStore = Self.makeRemoteLibrarySyncCursorStore()
        let downloadStateStore = Self.makeRemoteTrackDownloadStateStore()
        let audioFileStore = Self.makeOfflineAudioFileStore()
        let artworkStore = Self.makeArtworkStore()
        let favoriteTrackStore = Self.makeFavoriteTrackStore()
        let repository = DefaultRemoteLibraryRepository(
            apiClient: apiClient,
            store: store,
            syncCursorStore: syncCursorStore
        )
        let syncService = RemoteLibrarySyncService(
            repository: repository,
            downloadStateStore: downloadStateStore,
            audioFileStore: audioFileStore,
            artworkStore: artworkStore
        )

        let offlineLibraryService = OfflineLibraryService(
            syncService: syncService,
            audioFileStore: audioFileStore,
            artworkStore: artworkStore
        )
        self.init(
            environment: environment,
            apiClient: apiClient,
            syncService: syncService,
            offlineLibraryService: offlineLibraryService,
            favoriteTrackStore: favoriteTrackStore,
            player: player ?? iPhonePlaybackControllerPlayer(),
            keychainService: keychainService
        )
    }

    init(
        environment: ServerEnvironment,
        apiClient: any VelodyAPIClient,
        syncService: RemoteLibrarySyncService,
        offlineLibraryService: OfflineLibraryService,
        favoriteTrackStore: any FavoriteTrackStore,
        player: any iPhoneLocalAudioPlaying,
        keychainService: any KeychainService
    ) {
        self.environment = environment
        self.apiClient = apiClient
        self.syncService = syncService
        self.offlineLibraryService = offlineLibraryService
        self.favoriteTrackStore = favoriteTrackStore
        self.keychainService = keychainService
        self.player = player
        self.nowPlaying = player.state
        self.player.onStateChange = { [weak self] state in
            self?.handleNowPlayingStateChange(state)
        }
    }

    func loadIfNeeded() async {
        guard !hasLoaded else { return }
        hasLoaded = true

        var favoriteRestoreError: Error?

        do {
            try await reloadFavoriteTracks()
        } catch {
            favoriteRestoreError = error
        }

        do {
            let snapshot = try await reloadOfflineLibrary()
            applyRestoredTracks(snapshot)
            if let favoriteRestoreError {
                Self.logError(favoriteRestoreError, context: "Favorites restore failed")
                syncStatus += " Favorites may be out of date."
            }
        } catch {
            Self.logError(error, context: "Cached library restore failed")
            state = .idle
            syncStatus = "Could not restore the cached library."
        }
    }

    func refreshSync() async {
        guard !isSyncing else {
            return
        }

        state = .loading
        syncStatus = "Syncing your remote library..."

        do {
            let deviceId = try await currentOrRegisterDeviceID()
            _ = try await syncService.syncRemoteLibrary(deviceId: deviceId)
            let snapshot = try await reloadOfflineLibrary()
            applySyncedTracks(snapshot)
        } catch {
            Self.logError(error, context: "Remote library sync failed")
            state = .networkError(error.localizedDescription)
            syncStatus = Self.connectionFailedMessage.body
        }
    }

    func downloadTrack(trackID: String) async {
        guard let track = cachedRemoteTracksByID[trackID] else {
            return
        }

        updateRemoteTrack(trackID: trackID) { remoteTrack in
            var updatedTrack = remoteTrack
            updatedTrack.status = .downloading
            updatedTrack.lastDownloadError = nil
            return updatedTrack
        }
        rebuildRows()
        syncStatus = "Downloading \(track.title)..."

        do {
            let deviceId = try await currentOrRegisterDeviceID()
            _ = try await syncService.downloadTrack(track, deviceId: deviceId)
            _ = try await reloadOfflineLibrary()
            syncStatus = "Downloaded \(track.title)."
        } catch {
            Self.logError(error, context: "Download failed for \(track.title)")
            _ = try? await reloadOfflineLibrary()
            syncStatus = "Could not download \(track.title). Try again."
        }
    }

    func togglePlayback(trackID: String) {
        guard let track = cachedRemoteTracksByID[trackID] else {
            return
        }

        if nowPlaying.trackID == track.trackId, nowPlaying.isPlaying {
            player.pause()
            return
        }

        guard canAttemptPlayback(for: track.trackId) else {
            if remoteTrackStatus(for: track.trackId) == .missing {
                syncStatus = "The downloaded file for \(track.title) is missing. Re-download it to play again."
            } else {
                syncStatus = "Download the track before playing it offline."
            }
            return
        }

        player.play(trackID: track.trackId)
        handlePlaybackResult(for: track)
    }

    func stopPlayback() {
        player.stop()
    }

    func seekPlayback(to time: Double) {
        player.seek(to: time)
    }

    func toggleFavorite(trackID: String) async {
        guard hasTrackInLibrarySnapshot(trackID) else {
            return
        }

        let previousFavorites = cachedFavoriteTrackRecordsByID

        if cachedFavoriteTrackRecordsByID[trackID] != nil {
            cachedFavoriteTrackRecordsByID.removeValue(forKey: trackID)
        } else {
            cachedFavoriteTrackRecordsByID[trackID] = FavoriteTrackRecord(
                remoteTrackId: trackID,
                favoritedAt: Date()
            )
        }
        rebuildRows()

        do {
            try await favoriteTrackStore.saveFavoriteTracks(Array(cachedFavoriteTrackRecordsByID.values))
        } catch {
            Self.logError(error, context: "Favorite update failed")
            cachedFavoriteTrackRecordsByID = previousFavorites
            rebuildRows()
            syncStatus = "Could not update favorites. Try again."
        }
    }

    private func currentOrRegisterDeviceID() async throws -> String {
        if let existingDeviceID = try await keychainService.loadValue(
            forKey: Self.deviceIDKey
        ), !existingDeviceID.isEmpty,
           let existingDeviceAccessToken = try await keychainService.loadValue(
            forKey: Self.deviceAccessTokenKey
           ), !existingDeviceAccessToken.isEmpty {
            return existingDeviceID
        }

        let response = try await apiClient.registerDevice(
            DeviceRegistrationPayload(
                platform: .iphone,
                deviceName: Self.currentDeviceName,
                appVersion: environment.appVersion
            )
        )

        try await keychainService.save(response.deviceId, forKey: Self.deviceIDKey)
        try await keychainService.save(
            response.deviceAccessToken,
            forKey: Self.deviceAccessTokenKey
        )
        try await keychainService.save(
            response.bootstrapToken,
            forKey: Self.bootstrapTokenKey
        )

        return response.deviceId
    }

    private func applyRestoredTracks(_ snapshot: OfflineLibrarySnapshot) {
        if snapshot.remoteTracks.isEmpty {
            state = .idle
            syncStatus = "Sync your remote library to see your tracks here."
        } else {
            state = .success
            syncStatus = "Library restored from local cache."
        }
    }

    private func applySyncedTracks(_ snapshot: OfflineLibrarySnapshot) {
        if snapshot.remoteTracks.isEmpty {
            state = .empty
            syncStatus = "No music was returned for this library."
        } else {
            state = .success
            syncStatus = "Library synced successfully."
        }
    }

    private static func makeRemoteLibraryStore() -> any RemoteLibraryStore {
        if let store = try? FileRemoteLibraryStore() {
            return store
        }

        return InMemoryRemoteLibraryStore()
    }

    private static func makeRemoteTrackDownloadStateStore() -> any RemoteTrackDownloadStateStore {
        if let store = try? FileRemoteTrackDownloadStateStore() {
            return store
        }

        return InMemoryRemoteTrackDownloadStateStore()
    }

    private static func makeRemoteLibrarySyncCursorStore() -> any RemoteLibrarySyncCursorStore {
        if let store = try? FileRemoteLibrarySyncCursorStore() {
            return store
        }

        return InMemoryRemoteLibrarySyncCursorStore()
    }

    private static func makeOfflineAudioFileStore() -> any OfflineAudioFileStore {
        if let store = try? FileOfflineAudioFileStore() {
            return store
        }

        return InMemoryOfflineAudioFileStore()
    }

    private static func makeArtworkStore() -> any ArtworkStore {
        if let store = try? FileArtworkStore() {
            return store
        }

        return InMemoryArtworkStore()
    }

    private static func makeFavoriteTrackStore() -> any FavoriteTrackStore {
        if let store = try? FileFavoriteTrackStore() {
            return store
        }

        return InMemoryFavoriteTrackStore()
    }

    private func reloadFavoriteTracks() async throws {
        let favoriteTracks = try await favoriteTrackStore.loadFavoriteTracks()
        var favoritesByTrackID: [String: FavoriteTrackRecord] = [:]

        for favoriteTrack in favoriteTracks {
            favoritesByTrackID[favoriteTrack.remoteTrackId] = favoriteTrack
        }

        cachedFavoriteTrackRecordsByID = favoritesByTrackID
    }

    private func reloadOfflineLibrary() async throws -> OfflineLibrarySnapshot {
        let snapshot = try await offlineLibraryService.loadSnapshot()

        cachedRemoteLibraryTracks = snapshot.remoteTracks
        cachedAvailableOfflineTracks = snapshot.availableTracks
        cachedRemoteTracksByID = Dictionary(
            uniqueKeysWithValues: snapshot.remoteTracks.map { ($0.remoteTrack.trackId, $0.remoteTrack) }
        )
        player.setCatalogTracks(Self.makePlaybackCatalog(from: snapshot.remoteTracks))
        rebuildRows()

        return snapshot
    }

    private func rebuildRows() {
        let favoriteTrackIDs = Set(cachedFavoriteTrackRecordsByID.keys)
        let filteredSnapshot = OfflineLibrarySnapshot(
            remoteTracks: cachedRemoteLibraryTracks,
            availableTracks: cachedAvailableOfflineTracks
        ).filtered(searchText: searchText)

        remoteTracks = filteredSnapshot.remoteTracks.map { track in
            RemoteTrackRowViewData(
                track: track,
                nowPlaying: nowPlaying,
                isFavorite: favoriteTrackIDs.contains(track.remoteTrack.trackId)
            )
        }
        availableOfflineTracks = filteredSnapshot.availableTracks.map { track in
            AvailableOfflineTrackRowViewData(
                track: track,
                nowPlaying: nowPlaying,
                isFavorite: favoriteTrackIDs.contains(track.remoteTrackId)
            )
        }
        if let trackID = nowPlaying.trackID, hasTrackInLibrarySnapshot(trackID) {
            nowPlayingFavoriteTrackID = trackID
            isNowPlayingTrackFavorite = favoriteTrackIDs.contains(trackID)
        } else {
            nowPlayingFavoriteTrackID = nil
            isNowPlayingTrackFavorite = false
        }
    }

    private func handleNowPlayingStateChange(_ state: iPhoneNowPlayingState) {
        nowPlaying = state
        rebuildRows()
    }

    private func handlePlaybackResult(for track: RemoteTrack) {
        switch nowPlaying.playbackState {
        case .missingFile:
            syncStatus = "The downloaded file for \(track.title) is missing. Re-download it to play again."
            refreshOfflineLibraryInBackground()
        case .failed:
            syncStatus = "Playback couldn't start for \(track.title). Try again."
        case .playing, .paused, .stopped:
            break
        }
    }

    private func canAttemptPlayback(for trackID: String) -> Bool {
        guard let remoteTrack = cachedRemoteLibraryTracks.first(where: {
            $0.remoteTrack.trackId == trackID
        }) else {
            return false
        }

        return remoteTrack.isFileAvailable || remoteTrack.status == .missing
    }

    private func remoteTrackStatus(for trackID: String) -> OfflineLibraryRemoteTrackStatus? {
        cachedRemoteLibraryTracks.first(where: {
            $0.remoteTrack.trackId == trackID
        })?.status
    }

    private func nowPlayingDownloadBadge(for trackID: String) -> NowPlayingDownloadBadge {
        switch remoteTrackStatus(for: trackID) {
        case .downloaded:
            return .downloaded
        case .missing:
            return .missing
        default:
            return .offline
        }
    }

    private func updateRemoteTrack(
        trackID: String,
        transform: (OfflineLibraryRemoteTrack) -> OfflineLibraryRemoteTrack
    ) {
        guard let index = cachedRemoteLibraryTracks
            .firstIndex(where: { $0.remoteTrack.trackId == trackID })
        else {
            return
        }

        cachedRemoteLibraryTracks[index] = transform(cachedRemoteLibraryTracks[index])
    }

    private func hasTrackInLibrarySnapshot(_ trackID: String) -> Bool {
        cachedRemoteTracksByID[trackID] != nil
    }

    private func refreshOfflineLibraryInBackground() {
        Task { @MainActor [weak self] in
            guard let self else {
                return
            }

            _ = try? await self.reloadOfflineLibrary()
        }
    }

    private static func makePlaybackCatalog(
        from tracks: [OfflineLibraryRemoteTrack]
    ) -> [LibraryTrack] {
        tracks.map { track in
            LibraryTrack(
                id: track.remoteTrack.trackId,
                title: track.remoteTrack.title,
                artist: track.remoteTrack.artist,
                durationSeconds: Double(track.remoteTrack.durationSeconds),
                localFilePath: track.localFilePath,
                remoteTrackId: track.remoteTrack.trackId
            )
        }
    }

    private static func formatPlaybackTime(_ seconds: Double) -> String {
        guard seconds.isFinite, seconds > 0 else {
            return "0:00"
        }

        let totalSeconds = Int(seconds.rounded(.towardZero))
        let minutes = totalSeconds / 60
        let remainingSeconds = totalSeconds % 60
        return "\(minutes):\(String(format: "%02d", remainingSeconds))"
    }

    private static func userFacingPlaybackErrorMessage(for state: iPhoneNowPlayingState) -> String? {
        switch state.playbackState {
        case .missingFile:
            return "This downloaded file is missing. Re-download the track to play it again."
        case .failed:
            return "Playback couldn't start. Try again."
        case .playing, .paused, .stopped:
            return nil
        }
    }

    private static func logError(_ error: Error, context: String) {
        print("iPhoneLibraryViewModel \(context): \(error.localizedDescription)")
    }

    #if canImport(UIKit)
    private static var currentDeviceName: String {
        UIDevice.current.name
    }
    #else
    private static let currentDeviceName = "Velody iPhone"
    #endif

    private static let deviceIDKey = "velody.iphone.device-id"
    private static let deviceAccessTokenKey = "velody.iphone.device-access-token"
    private static let bootstrapTokenKey = "velody.iphone.bootstrap-token"
    private static let remoteLibraryEmptyMessage = LibrarySectionMessage(
        title: "No music synced yet",
        body: "Sync your remote library to see your tracks here.",
        systemImage: "music.note.list"
    )
    private static let availableOfflineEmptyMessage = LibrarySectionMessage(
        title: "No offline tracks yet",
        body: "Download tracks to listen without internet.",
        systemImage: "arrow.down.circle"
    )
    private static let searchEmptyMessage = LibrarySectionMessage(
        title: "No matching tracks",
        body: "Try a different title or artist.",
        systemImage: "magnifyingglass"
    )
    private static let connectionFailedMessage = LibrarySectionMessage(
        title: "Connection failed",
        body: "Could not reach the backend. Check that the server is running and try again.",
        systemImage: "wifi.exclamationmark"
    )
}

struct RemoteTrackRowViewData: Identifiable, Equatable {
    let id: String
    let title: String
    let artist: String
    let durationText: String
    let isFavorite: Bool
    let status: OfflineLibraryRemoteTrackStatus
    let statusBadgeTitle: String
    let statusDetailText: String?
    let canDownload: Bool
    let downloadButtonTitle: String
    let canPlay: Bool
    let playButtonTitle: String
    let artworkLocalFilePath: String?

    init(
        track: OfflineLibraryRemoteTrack,
        nowPlaying: iPhoneNowPlayingState,
        isFavorite: Bool
    ) {
        id = track.remoteTrack.trackId
        title = track.remoteTrack.title
        artist = track.remoteTrack.artist
        durationText = Self.formatDuration(seconds: track.remoteTrack.durationSeconds)
        self.isFavorite = isFavorite
        status = track.status
        statusBadgeTitle = Self.statusBadgeTitle(for: track.status)
        statusDetailText = Self.statusDetailText(for: track.status)
        canDownload = track.status == .notDownloaded || track.status == .failed || track.status == .missing
        downloadButtonTitle = Self.downloadButtonTitle(for: track.status)
        canPlay = track.isFileAvailable
        playButtonTitle = nowPlaying.trackID == track.remoteTrack.trackId && nowPlaying.isPlaying
            ? "Pause"
            : "Play"
        artworkLocalFilePath = track.localArtworkFilePath
    }

    static func formatDuration(seconds: Int) -> String {
        let minutes = seconds / 60
        let remainingSeconds = seconds % 60
        return "\(minutes):\(String(format: "%02d", remainingSeconds))"
    }

    private static func statusBadgeTitle(for status: OfflineLibraryRemoteTrackStatus) -> String {
        switch status {
        case .notDownloaded:
            return "Offline"
        case .downloading:
            return "Downloading"
        case .downloaded:
            return "Downloaded"
        case .missing:
            return "Missing"
        case .failed:
            return "Failed"
        }
    }

    private static func statusDetailText(for status: OfflineLibraryRemoteTrackStatus) -> String? {
        switch status {
        case .missing:
            return "Downloaded file missing. Re-download to restore offline playback."
        case .failed:
            return "Download failed. Try again."
        case .notDownloaded, .downloading, .downloaded:
            return nil
        }
    }

    private static func downloadButtonTitle(for status: OfflineLibraryRemoteTrackStatus) -> String {
        switch status {
        case .notDownloaded:
            return "Download"
        case .downloading:
            return "Downloading..."
        case .downloaded:
            return "Play"
        case .missing:
            return "Re-download"
        case .failed:
            return "Retry"
        }
    }
}

struct AvailableOfflineTrackRowViewData: Identifiable, Equatable {
    let id: String
    let title: String
    let artist: String
    let durationText: String
    let isFavorite: Bool
    let statusBadgeTitle: String
    let playButtonTitle: String
    let artworkLocalFilePath: String?

    init(
        track: OfflineLibraryTrack,
        nowPlaying: iPhoneNowPlayingState,
        isFavorite: Bool
    ) {
        id = track.remoteTrackId
        title = track.title
        artist = track.artist
        durationText = RemoteTrackRowViewData.formatDuration(seconds: track.durationSeconds)
        self.isFavorite = isFavorite
        statusBadgeTitle = "Downloaded"
        playButtonTitle = nowPlaying.trackID == track.remoteTrackId && nowPlaying.isPlaying
            ? "Pause"
            : "Play"
        artworkLocalFilePath = track.localArtworkFilePath
    }
}