NetNewsWire/Shared/Timeline/FetchRequestQueue.swift

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//
// FetchRequestQueue.swift
// NetNewsWire
//
// Created by Brent Simmons on 6/20/19.
// Copyright © 2019 Ranchero Software. All rights reserved.
//
import Foundation
// Main thread only.
final class FetchRequestQueue {
private var pendingRequests = [FetchRequestOperation]()
private var currentRequest: FetchRequestOperation? = nil
func cancelAllRequests() {
precondition(Thread.isMainThread)
pendingRequests.forEach { $0.isCanceled = true }
currentRequest?.isCanceled = true
pendingRequests = [FetchRequestOperation]()
}
func add(_ fetchRequestOperation: FetchRequestOperation) {
precondition(Thread.isMainThread)
pendingRequests.append(fetchRequestOperation)
runNextRequestIfNeeded()
}
}
private extension FetchRequestQueue {
func runNextRequestIfNeeded() {
precondition(Thread.isMainThread)
removeCanceledAndFinishedRequests()
guard currentRequest == nil, let requestToRun = pendingRequests.first else {
return
}
currentRequest = requestToRun
pendingRequests.removeFirst()
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currentRequest!.run { (fetchRequestOperation) in
precondition(fetchRequestOperation === self.currentRequest)
self.currentRequest = nil
self.runNextRequestIfNeeded()
}
}
func removeCanceledAndFinishedRequests() {
pendingRequests = pendingRequests.filter{ !$0.isCanceled && !$0.isFinished }
}
}