import Foundation
import Observation
import VelodyDomain
import VelodyNetworking
import VelodyPersistence
import VelodyUtilities

@MainActor
@Observable
final class MacLibraryViewModel {
    var tracks: [LibraryTrack] = []
    var selectedFolderPath = "No folder selected"
    var scanStatus = "Choose a folder to begin local discovery."
    var discoveredTrackCount = 0
    var isScanning = false

    var serverURLString: String
    var deviceRegistrationStatus = "Not registered."
    var registeredDeviceId: String?
    var lastHeartbeatStatus = "No heartbeat sent yet."
    var lastSyncBootstrapStatus = "No sync bootstrap run yet."
    var lastBootstrapTrackCount: Int?
    var lastBootstrapCursor: String?
    var isRegisteringDevice = false
    var isSendingHeartbeat = false
    var isRunningSyncBootstrap = false

    private let folderAccessService: any VelodyPersistence.FolderAccessService
    private let catalogService: any LocalCatalogService
    private let localMusicScanner: any LocalMusicScanner
    private let keychainService: any KeychainService
    private let userDefaults: UserDefaults
    private var hasLoaded = false

    init(
        userDefaults: UserDefaults = .standard,
        keychainService: any KeychainService = SystemKeychainService(service: "de.diyaa.velody.mac")
    ) {
        let folderAccessService = FolderAccessService()
        let localMusicScanner = FileSystemLocalMusicScanner(
            metadataReader: AVFoundationMetadataReader()
        )
        let repository = Self.makeTrackRepository()

        self.folderAccessService = folderAccessService
        self.catalogService = DefaultLocalCatalogService(repository: repository)
        self.localMusicScanner = localMusicScanner
        self.keychainService = keychainService
        self.userDefaults = userDefaults
        self.serverURLString = userDefaults.string(forKey: Self.serverURLDefaultsKey)
            ?? ServerEnvironment.defaultLocalBaseURL.absoluteString

        if let url = folderAccessService.storedFolderURL() {
            selectedFolderPath = url.path
            scanStatus = "Folder restored. Run a manual scan to discover MP3 files."
        }
    }

    func loadIfNeeded() async {
        guard !hasLoaded else { return }
        hasLoaded = true
        do {
            tracks = try await catalogService.loadActiveLocalTracks()
            discoveredTrackCount = tracks.count
        } catch {
            scanStatus = "Failed to load saved catalog: \(error.localizedDescription)"
        }

        await restoreDeviceIdentity()
    }

    func chooseFolder() {
        if let url = folderAccessService.chooseFolder() {
            selectedFolderPath = url.path
            scanStatus = "Folder selected. Run a manual scan to discover MP3 files."
            tracks = []
            discoveredTrackCount = 0
            Task {
                do {
                    try await catalogService.resetLocalCatalog()
                } catch {
                    scanStatus = "Failed to reset saved catalog: \(error.localizedDescription)"
                }
            }
        }
    }

    func scanMP3Files() async {
        guard let folderURL = folderAccessService.storedFolderURL() else {
            scanStatus = "Choose a folder before scanning."
            return
        }

        isScanning = true
        scanStatus = "Scanning MP3 files..."
        defer {
            isScanning = false
        }

        do {
            let discoveredTracks = try await localMusicScanner.scanFolder(at: folderURL)
            let scanResult = try await catalogService.reconcileScanResults(
                discoveredTracks,
                in: folderURL,
                scannedAt: Date()
            )
            tracks = scanResult.tracks
            discoveredTrackCount = tracks.count
            scanStatus = Self.scanStatus(
                for: scanResult,
                activeTrackCount: discoveredTrackCount
            )
        } catch {
            scanStatus = "Scan failed: \(error.localizedDescription)"
        }
    }

    func persistServerURLSelection() {
        guard let serverURL = Self.normalizedServerURL(from: serverURLString) else {
            return
        }

        serverURLString = serverURL.absoluteString
        userDefaults.set(serverURLString, forKey: Self.serverURLDefaultsKey)
    }

    func registerThisMac() async {
        isRegisteringDevice = true
        deviceRegistrationStatus = "Registering this Mac..."
        defer {
            isRegisteringDevice = false
        }

        do {
            let environment = try currentEnvironment()
            let payload = DeviceRegistrationPayload(
                platform: .macos,
                deviceName: Self.currentDeviceName,
                appVersion: environment.appVersion
            )
            let response = try await makeAPIClient(for: environment).registerDevice(payload)

            try await keychainService.save(response.deviceId, forKey: Self.deviceIdKey)
            try await keychainService.save(response.bootstrapToken, forKey: Self.bootstrapTokenKey)

            registeredDeviceId = response.deviceId
            deviceRegistrationStatus = "Registered successfully at \(response.serverTime)."
        } catch {
            deviceRegistrationStatus = "Registration failed: \(error.localizedDescription)"
        }
    }

    func sendHeartbeat() async {
        isSendingHeartbeat = true
        lastHeartbeatStatus = "Sending heartbeat..."
        defer {
            isSendingHeartbeat = false
        }

        do {
            let environment = try currentEnvironment()
            let deviceId = try await currentDeviceId()
            let response = try await makeAPIClient(for: environment).sendHeartbeat(
                DeviceHeartbeatPayload(
                    deviceId: deviceId,
                    appVersion: environment.appVersion
                )
            )

            registeredDeviceId = deviceId
            lastHeartbeatStatus = response.ok
                ? "Heartbeat succeeded at \(response.serverTime)."
                : "Heartbeat did not succeed."
        } catch {
            lastHeartbeatStatus = "Heartbeat failed: \(error.localizedDescription)"
        }
    }

    func syncBootstrap() async {
        isRunningSyncBootstrap = true
        lastSyncBootstrapStatus = "Running sync bootstrap..."
        defer {
            isRunningSyncBootstrap = false
        }

        do {
            let environment = try currentEnvironment()
            let response = try await makeAPIClient(for: environment).fetchSyncBootstrap()

            lastBootstrapTrackCount = response.tracks.count
            lastBootstrapCursor = response.nextCursor.value
            lastSyncBootstrapStatus = "Sync bootstrap succeeded. Tracks: \(response.tracks.count). Next cursor: \(response.nextCursor.value)."
        } catch {
            lastSyncBootstrapStatus = "Sync bootstrap failed: \(error.localizedDescription)"
        }
    }

    private func restoreDeviceIdentity() async {
        do {
            let deviceId = try await keychainService.loadValue(forKey: Self.deviceIdKey)
            let bootstrapToken = try await keychainService.loadValue(forKey: Self.bootstrapTokenKey)

            registeredDeviceId = deviceId

            if let deviceId {
                if let bootstrapToken, !bootstrapToken.isEmpty {
                    deviceRegistrationStatus = "Registered locally."
                } else {
                    deviceRegistrationStatus = "Device ID restored (\(deviceId)). Bootstrap token is missing."
                }
            } else {
                deviceRegistrationStatus = "Not registered."
            }
        } catch {
            deviceRegistrationStatus = "Failed to load saved device identity: \(error.localizedDescription)"
        }
    }

    private func currentEnvironment() throws -> ServerEnvironment {
        guard let serverURL = Self.normalizedServerURL(from: serverURLString) else {
            throw BackendConnectionError.invalidServerURL
        }

        serverURLString = serverURL.absoluteString
        userDefaults.set(serverURLString, forKey: Self.serverURLDefaultsKey)

        return ServerEnvironment(
            baseURL: serverURL,
            appVersion: Self.currentAppVersion
        )
    }

    private func currentDeviceId() async throws -> String {
        if let registeredDeviceId, !registeredDeviceId.isEmpty {
            return registeredDeviceId
        }

        if let savedDeviceId = try await keychainService.loadValue(forKey: Self.deviceIdKey),
           !savedDeviceId.isEmpty
        {
            registeredDeviceId = savedDeviceId
            return savedDeviceId
        }

        throw BackendConnectionError.missingDeviceIdentity
    }

    private func makeAPIClient(for environment: ServerEnvironment) -> URLSessionVelodyAPIClient {
        URLSessionVelodyAPIClient(environment: environment)
    }

    private static func makeTrackRepository() -> any TrackRepository {
        if let repository = try? SwiftDataTrackRepository() {
            return repository
        }

        return InMemoryTrackRepository()
    }

    private static func scanStatus(
        for result: LocalCatalogScanResult,
        activeTrackCount: Int
    ) -> String {
        "Scan finished. Active: \(activeTrackCount). Added: \(result.insertedTrackCount). Updated: \(result.updatedTrackCount). Reactivated: \(result.reactivatedTrackCount). Deleted: \(result.deletedTrackCount). Duplicates skipped: \(result.skippedDuplicateTrackCount)."
    }

    private static var currentAppVersion: String {
        if let shortVersion = Bundle.main.object(forInfoDictionaryKey: "CFBundleShortVersionString") as? String,
           !shortVersion.isEmpty
        {
            return shortVersion
        }

        if let buildVersion = Bundle.main.object(forInfoDictionaryKey: "CFBundleVersion") as? String,
           !buildVersion.isEmpty
        {
            return buildVersion
        }

        return "0.1.0"
    }

    private static var currentDeviceName: String {
        let localizedName = Host.current().localizedName?
            .trimmingCharacters(in: .whitespacesAndNewlines)

        if let localizedName, !localizedName.isEmpty {
            return localizedName
        }

        return "Velody Mac"
    }

    private static func normalizedServerURL(from rawValue: String) -> URL? {
        let trimmed = rawValue.trimmingCharacters(in: .whitespacesAndNewlines)

        guard
            !trimmed.isEmpty,
            let url = URL(string: trimmed),
            let scheme = url.scheme?.lowercased(),
            ["http", "https"].contains(scheme),
            url.host != nil
        else {
            return nil
        }

        return url
    }

    private static let serverURLDefaultsKey = "velody.server-environment.base-url"
    private static let deviceIdKey = "velody.device-id"
    private static let bootstrapTokenKey = "velody.bootstrap-token"
}

private enum BackendConnectionError: LocalizedError {
    case invalidServerURL
    case missingDeviceIdentity

    var errorDescription: String? {
        switch self {
        case .invalidServerURL:
            return "Enter a valid backend URL, such as http://localhost:3000."
        case .missingDeviceIdentity:
            return "Register this Mac before sending a heartbeat."
        }
    }
}