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//
// AddressCacheTracker.swift
// MullvadVPN
//
// Created by pronebird on 08/12/2021.
// Copyright © 2025 Mullvad VPN AB. All rights reserved.
//
import MullvadLogging
import MullvadREST
import MullvadTypes
import Operations
import UIKit
final class AddressCacheTracker: @unchecked Sendable {
/// Update interval.
private static let updateInterval: Duration = .days(1)
/// Retry interval.
private static let retryInterval: Duration = .minutes(15)
/// Logger.
private let logger = Logger(label: "AddressCache.Tracker")
private let backgroundTaskProvider: BackgroundTaskProviding
/// REST API proxy.
private let apiProxy: APIQuerying
/// Address cache.
private let store: REST.AddressCache
/// A flag that indicates whether periodic updates are running
private var isPeriodicUpdatesEnabled = false
/// The date of last failed attempt.
private var lastFailureAttemptDate: Date?
/// Timer used for scheduling periodic updates.
private var timer: DispatchSourceTimer?
/// Operation queue.
private let operationQueue = AsyncOperationQueue.makeSerial()
/// Lock used for synchronizing member access.
private let nslock = NSLock()
/// Designated initializer
init(backgroundTaskProvider: BackgroundTaskProviding, apiProxy: APIQuerying, store: REST.AddressCache) {
self.backgroundTaskProvider = backgroundTaskProvider
self.apiProxy = apiProxy
self.store = store
}
func startPeriodicUpdates() {
nslock.lock()
defer { nslock.unlock() }
guard !isPeriodicUpdatesEnabled else {
return
}
logger.debug("Start periodic address cache updates.")
isPeriodicUpdatesEnabled = true
let scheduleDate = _nextScheduleDate()
logger.debug("Schedule address cache update at \(scheduleDate.logFormatted).")
scheduleEndpointsUpdate(startTime: .now() + scheduleDate.timeIntervalSinceNow)
}
func stopPeriodicUpdates() {
nslock.lock()
defer { nslock.unlock() }
guard isPeriodicUpdatesEnabled else { return }
logger.debug("Stop periodic address cache updates.")
isPeriodicUpdatesEnabled = false
timer?.cancel()
timer = nil
}
func updateEndpoints(completionHandler: ((sending Result<Bool, Error>) -> Void)? = nil) -> Cancellable {
let operation = ResultBlockOperation<Bool> { finish -> Cancellable in
guard self.nextScheduleDate() <= Date() else {
finish(.success(false))
return AnyCancellable()
}
return self.apiProxy.getAddressList(retryStrategy: .default) { result in
self.setEndpoints(from: result)
finish(result.map { _ in true })
}
}
operation.completionQueue = .main
operation.completionHandler = completionHandler
operation.addObserver(
BackgroundObserver(
backgroundTaskProvider: backgroundTaskProvider,
name: "Update endpoints",
cancelUponExpiration: true
)
)
operationQueue.addOperation(operation)
return operation
}
func nextScheduleDate() -> Date {
nslock.lock()
defer { nslock.unlock() }
return _nextScheduleDate()
}
private func setEndpoints(from result: Result<[AnyIPEndpoint], Error>) {
nslock.lock()
defer { nslock.unlock() }
switch result {
case let .success(endpoints):
store.setEndpoints(endpoints)
lastFailureAttemptDate = nil
case let .failure(error as REST.Error):
logger.error(
error: error,
message: "Failed to update address cache."
)
fallthrough
default:
lastFailureAttemptDate = Date()
}
}
private func scheduleEndpointsUpdate(startTime: DispatchWallTime) {
let newTimer = DispatchSource.makeTimerSource()
newTimer.setEventHandler { [weak self] in
self?.handleTimer()
}
newTimer.schedule(wallDeadline: startTime)
newTimer.activate()
timer?.cancel()
timer = newTimer
}
private func handleTimer() {
_ = updateEndpoints { _ in
self.nslock.lock()
defer { self.nslock.unlock() }
guard self.isPeriodicUpdatesEnabled else { return }
let scheduleDate = self._nextScheduleDate()
self.logger
.debug("Schedule next address cache update at \(scheduleDate.logFormatted).")
self.scheduleEndpointsUpdate(startTime: .now() + scheduleDate.timeIntervalSinceNow)
}
}
private func _nextScheduleDate() -> Date {
let nextDate =
lastFailureAttemptDate.map { date in
Date(
timeInterval: Self.retryInterval.timeInterval,
since: date
)
}
?? Date(
timeInterval: Self.updateInterval.timeInterval,
since: store.getLastUpdateDate()
)
return max(nextDate, Date())
}
}
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