import Foundation
import Observation
import SwiftData
import WatchConnectivity

/// Watch side of the iPhone↔Watch bridge. The watch never touches iCloud — it
/// keeps a local SwiftData cache fed only by application-context pushes from the
/// phone, updates it optimistically on local edits, and forwards changed workouts
/// to the phone (which is the sole writer of iCloud Drive).
@Observable
@MainActor
final class WatchConnectivityBridge: NSObject {
    private let container: ModelContainer
    private var session: WCSession?

    /// Last time state was received from the phone (for a sync indicator).
    private(set) var lastSyncDate: Date?

    /// Exclusive-edit lock pushed by the phone. While set, the watch parks the matching
    /// run (popping out of its progress view) and blocks re-entry, so the phone owns the
    /// edit and the watch can't clobber it with a stale optimistic write. `editingWorkoutID`
    /// matches a run by its workout id; `editingSplitID` matches any run by its `splitID`.
    private(set) var editingWorkoutID: String?
    private(set) var editingSplitID: String?

    /// Monotonic sequence stamped on each live-run frame, so the phone mirror can drop a
    /// stale / out-of-order delivery.
    private var liveVersion = 0

    private var context: ModelContext { container.mainContext }

    init(container: ModelContainer) {
        self.container = container
        super.init()
    }

    func activate() {
        guard WCSession.isSupported() else { return }
        let session = WCSession.default
        session.delegate = self
        session.activate()
        self.session = session
        // Apply whatever the phone last pushed, then ask for a fresh push.
        let ctx = session.receivedApplicationContext
        applyState(WCPayload.decodeSplits(ctx), workouts: WCPayload.decodeWorkouts(ctx))
        applySettings(ctx)
        editingWorkoutID = WCPayload.decodeEditingWorkoutID(ctx)
        editingSplitID = WCPayload.decodeEditingSplitID(ctx)
        requestSync()
    }

    func requestSync() {
        guard let session, session.activationState == .activated, session.isReachable else { return }
        session.sendMessage(WCPayload.requestSyncMessage(), replyHandler: nil, errorHandler: nil)
    }

    /// Optimistically applies a workout edit to the local cache and forwards it to
    /// the phone for durable persistence in iCloud Drive.
    func update(workout doc: WorkoutDocument) {
        CacheMapper.upsertWorkout(doc, relativePath: doc.relativePath, into: context)
        try? context.save()
        sendToPhone(doc)
    }

    // MARK: - Live run mirror (ephemeral; reachable-only)

    /// Broadcast where the run flow currently is, so a propped-up iPhone can mirror it. Sent
    /// over `sendMessage` only when the phone is reachable — this is throwaway presence, so
    /// there's no guaranteed-delivery fallback (a queued frame would be stale on arrival).
    func sendLiveProgress(_ frame: LiveProgress) {
        guard let session, session.activationState == .activated, session.isReachable else { return }
        liveVersion += 1
        var stamped = frame
        stamped.version = liveVersion
        session.sendMessage(WCPayload.encodeLiveProgress(stamped), replyHandler: nil, errorHandler: { _ in })
    }

    /// Tell the phone to stop mirroring this run (the user left the progress flow).
    func sendLiveEnded(workoutID: String, logID: String) {
        guard let session, session.activationState == .activated, session.isReachable else { return }
        session.sendMessage(WCPayload.encodeLiveEnded(workoutID: workoutID, logID: logID),
                            replyHandler: nil, errorHandler: { _ in })
    }

    // MARK: - Internal

    private func sendToPhone(_ doc: WorkoutDocument) {
        guard let session, session.activationState == .activated else { return }
        let payload = WCPayload.encodeWorkoutUpdate(doc)
        if session.isReachable {
            session.sendMessage(payload, replyHandler: nil, errorHandler: { _ in
                session.transferUserInfo(payload)   // fall back to guaranteed delivery
            })
        } else {
            session.transferUserInfo(payload)
        }
    }

    private func applySettings(_ dict: [String: Any]) {
        if let rest = WCPayload.decodeRestSeconds(dict) {
            UserDefaults.standard.set(rest, forKey: WCPayload.restSecondsKey)
        }
        if let done = WCPayload.decodeDoneCountdownSeconds(dict) {
            UserDefaults.standard.set(done, forKey: WCPayload.doneCountdownSecondsKey)
        }
    }

    private func applyState(_ splits: [SplitDocument], workouts: [WorkoutDocument]) {
        guard !splits.isEmpty || !workouts.isEmpty else { return }
        var liveSplitIDs = Set<String>()
        for s in splits {
            CacheMapper.upsertSplit(s, relativePath: s.relativePath, into: context)
            liveSplitIDs.insert(s.id)
        }
        for w in workouts {
            CacheMapper.upsertWorkout(w, relativePath: w.relativePath, into: context)
        }
        // Splits are sent in full → prune any the phone no longer has. Workouts are
        // sent as a recent window, so they're upserted but never pruned (avoids a
        // race deleting a workout just created on the watch).
        if let allSplits = try? context.fetch(FetchDescriptor<Split>()) {
            for s in allSplits where !liveSplitIDs.contains(s.id) { context.delete(s) }
        }
        try? context.save()
        lastSyncDate = Date()
    }
}

// MARK: - WCSessionDelegate

extension WatchConnectivityBridge: WCSessionDelegate {
    nonisolated func session(_ session: WCSession, activationDidCompleteWith activationState: WCSessionActivationState, error: Error?) {
        Task { @MainActor in self.requestSync() }
    }

    nonisolated func session(_ session: WCSession, didReceiveApplicationContext applicationContext: [String: Any]) {
        let splits = WCPayload.decodeSplits(applicationContext)
        let workouts = WCPayload.decodeWorkouts(applicationContext)
        let rest = WCPayload.decodeRestSeconds(applicationContext)
        let done = WCPayload.decodeDoneCountdownSeconds(applicationContext)
        let editingWorkoutID = WCPayload.decodeEditingWorkoutID(applicationContext)
        let editingSplitID = WCPayload.decodeEditingSplitID(applicationContext)
        Task { @MainActor in
            self.applyState(splits, workouts: workouts)
            if let rest { UserDefaults.standard.set(rest, forKey: WCPayload.restSecondsKey) }
            if let done { UserDefaults.standard.set(done, forKey: WCPayload.doneCountdownSecondsKey) }
            // Absent keys mean "not editing" — set unconditionally so the lock clears.
            self.editingWorkoutID = editingWorkoutID
            self.editingSplitID = editingSplitID
        }
    }
}