import Foundation
import SwiftData
import Network
@preconcurrency import UserNotifications

@MainActor
final class BackgroundSyncCoordinator: ObservableObject {
    enum Activity: Equatable {
        case idle
        case waiting(String)
        case running(String)

        var title: String {
            switch self {
            case .idle: return "Idle"
            case .waiting(let name): return "Waiting · \(name)"
            case .running(let name): return "Running · \(name)"
            }
        }
    }

    @Published private(set) var activity: Activity = .idle
    @Published private(set) var watchedJobCount = 0
    @Published private(set) var scheduledJobCount = 0
    @Published private(set) var isSyncAllRunning = false
    @Published private(set) var syncAllCompleted = 0
    @Published private(set) var syncAllTotal = 0
    @Published private(set) var syncAllFailed = 0
    @Published private(set) var syncAllSkipped = 0
    @Published private(set) var isNetworkAvailable = true
    @Published private(set) var lastError: String?

    var activityDisplayTitle: String {
        if isSyncAllRunning {
            return "Sync All · \(min(syncAllCompleted + 1, syncAllTotal)) of \(syncAllTotal)"
        }
        return activity.title
    }

    private let modelContext: ModelContext
    private let runner: RsyncRunner
    private let watcher = FileWatchService()
    private var timer: Timer?
    private var pending: [(UUID, SyncRunTrigger)] = []
    private var pendingIDs = Set<UUID>()
    private var isProcessingQueue = false
    private var watchDebounceTasks: [UUID: Task<Void, Never>] = [:]
    private var started = false
    private var notificationToken: NSObjectProtocol?
    private let networkMonitor = NWPathMonitor()
    private let networkQueue = DispatchQueue(label: "net.absdev.RsyncStudio.network")
    private var currentTrigger: SyncRunTrigger?

    init(modelContext: ModelContext, runner: RsyncRunner) {
        self.modelContext = modelContext
        self.runner = runner
        watcher.onChange = { [weak self] jobID, path in
            Task { @MainActor [weak self] in
                self?.fileChanged(jobID: jobID, path: path)
            }
        }
        networkMonitor.pathUpdateHandler = { [weak self] path in
            Task { @MainActor [weak self] in
                self?.isNetworkAvailable = path.status == .satisfied
                if path.status == .satisfied { self?.processQueue() }
            }
        }
        networkMonitor.start(queue: networkQueue)
        notificationToken = NotificationCenter.default.addObserver(
            forName: .syncJobsChanged,
            object: nil,
            queue: .main
        ) { [weak self] _ in
            Task { @MainActor [weak self] in self?.refreshConfiguration() }
        }
    }

    deinit {
        networkMonitor.cancel()
        if let notificationToken { NotificationCenter.default.removeObserver(notificationToken) }
    }

    func start() {
        guard !started else { return }
        started = true
        refreshConfiguration()
        pruneHistoryIfNeeded(force: true)
        checkSchedules()
        timer = Timer.scheduledTimer(withTimeInterval: 20, repeats: true) { [weak self] _ in
            Task { @MainActor [weak self] in
                self?.refreshConfiguration()
                self?.checkSchedules()
                self?.processQueue()
            }
        }
    }

    func stop() {
        timer?.invalidate()
        timer = nil
        watcher.stop()
        watchDebounceTasks.values.forEach { $0.cancel() }
        watchDebounceTasks.removeAll()
        started = false
    }

    func syncAllEnabledJobs() {
        guard !isSyncAllRunning else { return }

        let enabledJobs = fetchJobs().filter(\.isEnabled)
        syncAllCompleted = 0
        syncAllTotal = 0
        syncAllFailed = 0
        syncAllSkipped = 0

        for job in enabledJobs {
            if enqueue(jobID: job.id, trigger: .syncAll) {
                syncAllTotal += 1
            }
        }

        isSyncAllRunning = syncAllTotal > 0
        if !isSyncAllRunning {
            syncAllCompleted = 0
        }
    }

    func cancelSyncAll() {
        guard isSyncAllRunning else { return }
        let before = pending.count
        pending.removeAll { item in
            if item.1 == .syncAll {
                pendingIDs.remove(item.0)
                return true
            }
            return false
        }
        syncAllSkipped += max(0, before - pending.count)
        syncAllTotal = max(syncAllCompleted + syncAllFailed + syncAllSkipped, syncAllTotal)
        if currentTrigger == .syncAll && runner.isRunning { runner.cancel() }
        if currentTrigger != .syncAll {
            isSyncAllRunning = false
        }
    }

    func refreshConfiguration() {
        let jobs = fetchJobs()
        scheduledJobCount = jobs.filter { $0.isEnabled && $0.scheduleEnabled && $0.scheduleKind != .manual }.count
        watchedJobCount = jobs.filter { $0.isEnabled && $0.watchEnabled }.count

        if UserDefaults.standard.object(forKey: "fileWatchingEnabled") as? Bool ?? true {
            watcher.update(jobs: jobs)
        } else {
            watcher.update(jobs: [])
        }

        for job in jobs where job.scheduleEnabled && job.scheduleKind != .manual && job.nextRunAt == nil {
            job.nextRunAt = job.calculateNextRun(after: Date().addingTimeInterval(-1))
        }
        saveContext("refreshing automation configuration")
    }

    private func checkSchedules() {
        guard UserDefaults.standard.object(forKey: "backgroundSchedulesEnabled") as? Bool ?? true else { return }
        let now = Date()
        for job in fetchJobs() where job.isEnabled && job.scheduleEnabled && job.scheduleKind != .manual {
            guard let next = job.nextRunAt, next <= now else { continue }
            enqueue(jobID: job.id, trigger: .scheduled)

            if job.scheduleKind == .once {
                job.scheduleEnabled = false
                job.nextRunAt = nil
            } else {
                job.nextRunAt = job.calculateNextRun(after: now)
            }
        }
        saveContext("updating scheduled jobs")
    }

    private func fileChanged(jobID: UUID, path: String) {
        guard UserDefaults.standard.object(forKey: "fileWatchingEnabled") as? Bool ?? true else { return }
        guard let job = fetchJob(id: jobID), job.isEnabled, job.watchEnabled else { return }
        job.lastWatchEventAt = Date()
        watchDebounceTasks[jobID]?.cancel()
        let delay = max(1, job.watchDebounceSeconds)
        watchDebounceTasks[jobID] = Task { [weak self] in
            try? await Task.sleep(for: .seconds(delay))
            guard !Task.isCancelled, let self else { return }
            _ = self.enqueue(jobID: jobID, trigger: .watched)
        }
        saveContext("recording file-watch activity")
    }

    @discardableResult
    private func enqueue(jobID: UUID, trigger: SyncRunTrigger) -> Bool {
        guard !pendingIDs.contains(jobID), runner.currentJobID != jobID else { return false }
        pending.append((jobID, trigger))
        pendingIDs.insert(jobID)
        processQueue()
        return true
    }

    private func processQueue() {
        guard !isProcessingQueue, !runner.isRunning, !pending.isEmpty else {
            if (isProcessingQueue || runner.isRunning), let first = pending.first, let job = fetchJob(id: first.0) {
                activity = .waiting(job.name)
            }
            return
        }

        let item = pending.removeFirst()
        pendingIDs.remove(item.0)
        guard let job = fetchJob(id: item.0), job.isEnabled else {
            if item.1 == .syncAll { syncAllSkipped += 1 }
            finishSyncAllItemIfNeeded(item.1, succeeded: false, skipped: true)
            processQueue()
            return
        }

        if job.isRemote && !isNetworkAvailable {
            pending.insert(item, at: 0)
            pendingIDs.insert(item.0)
            activity = .waiting("Network · \(job.name)")
            return
        }

        isProcessingQueue = true
        currentTrigger = item.1
        activity = .running(job.name)
        Task { [weak self] in
            guard let self else { return }
            let succeeded = await self.execute(job: job, trigger: item.1)
            self.finishSyncAllItemIfNeeded(item.1, succeeded: succeeded, skipped: false)
            self.isProcessingQueue = false
            self.currentTrigger = nil
            self.activity = .idle
            self.processQueue()
        }
    }

    private func finishSyncAllItemIfNeeded(_ trigger: SyncRunTrigger, succeeded: Bool, skipped: Bool) {
        guard trigger == .syncAll else { return }
        if skipped { syncAllSkipped += 0 }
        else if succeeded { syncAllCompleted += 1 }
        else { syncAllFailed += 1 }
        if syncAllCompleted + syncAllFailed + syncAllSkipped >= syncAllTotal {
            isSyncAllRunning = false
            sendNotification(title: "Sync All complete", body: "\(syncAllCompleted) succeeded · \(syncAllFailed) failed · \(syncAllSkipped) skipped")
        }
    }

    private func execute(job: SyncJob, trigger: SyncRunTrigger) async -> Bool {
        let executable = RsyncLocator.locate()
        let command = RsyncCommandBuilder.displayCommand(job: job, dryRun: false, executable: executable)
        let run = SyncRun(job: job, command: command, wasDryRun: false, trigger: trigger)
        modelContext.insert(run)
        saveContext("creating run history")

        let automatic = trigger == .scheduled || trigger == .watched
        let maxAttempts = automatic ? max(1, job.retryCount + 1) : 1
        var finalSuccess = false
        var combinedOutput = ""
        var combinedError = ""

        for attempt in 1...maxAttempts {
            if attempt > 1 {
                let delay = max(1, job.retryDelaySeconds) * (attempt - 1)
                combinedError += "\nRetry \(attempt - 1) of \(maxAttempts - 1) after \(delay)s…\n"
                try? await Task.sleep(for: .seconds(delay))
            }
            do {
                let preflight = await runner.preflight(job: job)
                guard preflight.passed else {
                    combinedError += preflight.checks.filter { $0.severity == .error }.map(\.detail).joined(separator: "\n")
                    break
                }
                let result = try await runner.run(job: job, dryRun: false, trigger: trigger)
                combinedOutput += result.stdout
                combinedError += result.stderr
                run.exitCode = Int(result.exitCode)
                run.wasCancelled = result.wasCancelled
                if result.exitCode == 0 {
                    finalSuccess = true
                    break
                }
                if result.wasCancelled { break }
            } catch {
                combinedError += "\n\(error.localizedDescription)\n"
                run.exitCode = -1
            }
        }

        run.output = SyncRun.sanitizedLog(combinedOutput)
        run.errorOutput = SyncRun.sanitizedLog(combinedError)
        run.finishedAt = Date()
        job.lastRunAt = run.finishedAt
        job.lastExitCode = run.exitCode
        job.updatedAt = Date()
        saveContext("saving run history")
        pruneHistoryIfNeeded()

        if finalSuccess, job.notifyOnSuccess { sendNotification(title: "Sync complete", body: job.name) }
        if !finalSuccess, job.notifyOnFailure { sendNotification(title: "Sync failed", body: job.name) }
        return finalSuccess
    }

    private func sendNotification(title: String, body: String) {
        Task { @MainActor in
            do {
                let center = UNUserNotificationCenter.current()
                let granted = try await center.requestAuthorization(options: [.alert, .sound])
                guard granted else { return }

                let content = UNMutableNotificationContent()
                content.title = title
                content.body = body
                content.sound = .default

                let request = UNNotificationRequest(
                    identifier: UUID().uuidString,
                    content: content,
                    trigger: nil
                )
                try await center.add(request)
            } catch {
                lastError = "Could not deliver notification: \(error.localizedDescription)"
            }
        }
    }

    private func pruneHistoryIfNeeded(force: Bool = false) {
        let now = Date()
        if !force, let last = UserDefaults.standard.object(forKey: "lastHistoryPruneAt") as? Date, now.timeIntervalSince(last) < 3600 { return }

        let configuredDays = UserDefaults.standard.integer(forKey: "historyRetentionDays")
        let days = configuredDays == 0 ? 90 : max(7, min(configuredDays, 3650))
        let cutoff = now.addingTimeInterval(-TimeInterval(days) * 86_400)

        do {
            let runs = try modelContext.fetch(FetchDescriptor<SyncRun>())
            for run in runs where run.finishedAt != nil && run.startedAt < cutoff {
                modelContext.delete(run)
            }
            try modelContext.save()
            UserDefaults.standard.set(now, forKey: "lastHistoryPruneAt")
        } catch {
            lastError = "Could not prune run history: \(error.localizedDescription)"
        }
    }

    private func saveContext(_ operation: String) {
        do {
            try modelContext.save()
        } catch {
            lastError = "Database error while \(operation): \(error.localizedDescription)"
        }
    }

    private func fetchJobs() -> [SyncJob] {
        (try? modelContext.fetch(FetchDescriptor<SyncJob>(sortBy: [SortDescriptor(\SyncJob.name)]))) ?? []
    }

    private func fetchJob(id: UUID) -> SyncJob? {
        fetchJobs().first { $0.id == id }
    }
}

extension Notification.Name {
    static let syncJobsChanged = Notification.Name("RsyncStudio.syncJobsChanged")
}