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//
// AddressCacheTracker.swift
// MullvadVPN
//
// Created by pronebird on 08/12/2021.
// Copyright © 2021 Mullvad VPN AB. All rights reserved.
//
import Logging
import UIKit
extension AddressCache {
class Tracker {
/// Shared instance.
static let shared = AddressCache.Tracker(
apiProxy: REST.ProxyFactory.shared.createAPIProxy(),
store: AddressCache.Store.shared
)
/// Update interval (in seconds).
private static let updateInterval: TimeInterval = 60 * 60 * 24
/// Retry interval (in seconds).
private static let retryInterval: TimeInterval = 60 * 15
/// Logger.
private let logger = Logger(label: "AddressCache.Tracker")
/// REST API proxy.
private let apiProxy: REST.APIProxy
/// Store.
private let store: AddressCache.Store
/// 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 = {
let operationQueue = AsyncOperationQueue()
operationQueue.maxConcurrentOperationCount = 1
return operationQueue
}()
/// Lock used for synchronizing member access.
private let nslock = NSLock()
/// Designated initializer
private init(apiProxy: REST.APIProxy, store: AddressCache.Store) {
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.logFormatDate()).")
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: ((OperationCompletion<Bool, Error>) -> Void)? = nil
) -> Cancellable {
let operation = ResultBlockOperation<Bool, Error> { operation in
guard self.nextScheduleDate() <= Date() else {
operation.finish(completion: .success(false))
return
}
let task = self.apiProxy.getAddressList(retryStrategy: .default) { completion in
self.setEndpoints(from: completion)
let mappedCompletion = completion.map { _ in true }
.eraseFailureType()
operation.finish(completion: mappedCompletion)
}
operation.addCancellationBlock {
task.cancel()
}
}
operation.completionQueue = .main
operation.completionHandler = completionHandler
operation.addObserver(
BackgroundObserver(name: "Update endpoints", cancelUponExpiration: true)
)
operationQueue.addOperation(operation)
return operation
}
func nextScheduleDate() -> Date {
nslock.lock()
defer { nslock.unlock() }
return _nextScheduleDate()
}
private func setEndpoints(from completion: OperationCompletion<[AnyIPEndpoint], REST.Error>)
{
nslock.lock()
defer { nslock.unlock() }
switch completion {
case let .success(endpoints):
store.setEndpoints(endpoints)
case let .failure(error):
logger.error(
chainedError: AnyChainedError(error),
message: "Failed to update address cache."
)
case .cancelled:
break
}
lastFailureAttemptDate = completion.isSuccess ? nil : 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.logFormatDate()).")
self.scheduleEndpointsUpdate(startTime: .now() + scheduleDate.timeIntervalSinceNow)
}
}
private func _nextScheduleDate() -> Date {
let nextDate = lastFailureAttemptDate.map { date in
return Date(
timeInterval: Self.retryInterval,
since: date
)
} ?? Date(
timeInterval: Self.updateInterval,
since: store.getLastUpdateDate()
)
return max(nextDate, Date())
}
}
}
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