import Combine
import Foundation
import WatchConnectivity

@MainActor
public final class WatchConnectivityService: NSObject, ObservableObject {
  @Published public private(set) var activationState: WCSessionActivationState = .notActivated
  @Published public private(set) var isReachable = false
  @Published public private(set) var lastSynchronizedAt: Date?
  @Published public private(set) var lastError: String?

  public var onEnvelope: ((WatchSyncEnvelopeV1) -> Void)?
  public var onAcknowledgement: ((Set<UUID>) -> Void)?

  private let session: WCSession?
  private let encoder = WatchCoding.encoder
  private let decoder = WatchCoding.decoder

  public override init() {
    session = WCSession.isSupported() ? .default : nil
    super.init()
  }

  public func activate() {
    guard let session else { return }
    session.delegate = self
    session.activate()
    activationState = session.activationState
    isReachable = session.isReachable
  }

  public func sendLive(_ envelope: WatchSyncEnvelopeV1) {
    guard let session, session.isReachable else { return }
    do {
      let data = try encoder.encode(envelope)
      session.sendMessageData(data, replyHandler: nil) { [weak self] error in
        Task { @MainActor in self?.lastError = error.localizedDescription }
      }
    } catch {
      lastError = error.localizedDescription
    }
  }

  /// Guaranteed delivery for durable mutations. WatchConnectivity persists these while offline.
  public func transfer(_ envelope: WatchSyncEnvelopeV1) {
    guard let session else { return }
    do {
      session.transferUserInfo(["envelope": try encoder.encode(envelope)])
    } catch {
      lastError = error.localizedDescription
    }
  }

  public func flush(outbox: [WatchSyncEnvelopeV1]) {
    for envelope in outbox { transfer(envelope) }
  }

  public func updateApplicationContext(preferences: WatchPreferencesV1) {
    guard let session else { return }
    do {
      try session.updateApplicationContext(["preferences": try encoder.encode(preferences)])
    } catch {
      lastError = error.localizedDescription
    }
  }

  private func receive(_ data: Data) {
    do {
      let envelope = try decoder.decode(WatchSyncEnvelopeV1.self, from: data)
      lastSynchronizedAt = Date()
      if envelope.kind == .acknowledgement,
         let acknowledgement = try? envelope.decodePayload(WatchAcknowledgementV1.self) {
        onAcknowledgement?(Set(acknowledgement.eventIDs))
      } else {
        onEnvelope?(envelope)
      }
    } catch {
      lastError = error.localizedDescription
    }
  }
}

extension WatchConnectivityService: WCSessionDelegate {
  nonisolated public func session(
    _ session: WCSession,
    activationDidCompleteWith activationState: WCSessionActivationState,
    error: Error?
  ) {
    Task { @MainActor [weak self] in
      self?.activationState = activationState
      self?.isReachable = session.isReachable
      self?.lastError = error?.localizedDescription
    }
  }

  nonisolated public func sessionReachabilityDidChange(_ session: WCSession) {
    Task { @MainActor [weak self] in self?.isReachable = session.isReachable }
  }

  nonisolated public func session(_ session: WCSession, didReceiveMessageData messageData: Data) {
    Task { @MainActor [weak self] in self?.receive(messageData) }
  }

  nonisolated public func session(_ session: WCSession, didReceiveUserInfo userInfo: [String: Any] = [:]) {
    guard let data = userInfo["envelope"] as? Data else { return }
    Task { @MainActor [weak self] in self?.receive(data) }
  }

  nonisolated public func session(
    _ session: WCSession,
    didReceiveApplicationContext applicationContext: [String: Any]
  ) {
    guard let data = applicationContext["preferences"] as? Data else { return }
    Task { @MainActor [weak self] in
      guard let self,
            let preferences = try? self.decoder.decode(WatchPreferencesV1.self, from: data) else { return }
      let payload = try? self.encoder.encode(preferences)
      if let payload {
        self.onEnvelope?(.init(
          deviceID: "iphone",
          sequence: 0,
          kind: .preferences,
          payload: payload
        ))
      }
      self.lastSynchronizedAt = Date()
    }
  }
}