NetNewsWire/Shared/Timeline/FetchRequestOperation.swift

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//
// FetchRequestOperation.swift
// NetNewsWire
//
// Created by Brent Simmons on 6/20/19.
// Copyright © 2019 Ranchero Software. All rights reserved.
//
import Foundation
import RSCore
import Account
import Articles
// Main thread only.
// Runs an asynchronous fetch.
typealias FetchRequestOperationResultBlock = (Set<Article>, FetchRequestOperation) -> Void
final class FetchRequestOperation {
let id: Int
let readFilterEnabledTable: [FeedIdentifier: Bool]
let resultBlock: FetchRequestOperationResultBlock
var isCanceled = false
var isFinished = false
private let fetchers: [ArticleFetcher]
init(id: Int, readFilterEnabledTable: [FeedIdentifier: Bool], fetchers: [ArticleFetcher], resultBlock: @escaping FetchRequestOperationResultBlock) {
precondition(Thread.isMainThread)
self.id = id
self.readFilterEnabledTable = readFilterEnabledTable
self.fetchers = fetchers
self.resultBlock = resultBlock
}
func run(_ completion: @escaping (FetchRequestOperation) -> Void) {
precondition(Thread.isMainThread)
precondition(!isFinished)
var didCallCompletion = false
func callCompletionIfNeeded() {
if !didCallCompletion {
didCallCompletion = true
completion(self)
}
}
if isCanceled {
callCompletionIfNeeded()
return
}
if fetchers.isEmpty {
isFinished = true
resultBlock(Set<Article>(), self)
callCompletionIfNeeded()
return
}
let numberOfFetchers = fetchers.count
var fetchersReturned = 0
var fetchedArticles = Set<Article>()
func process(_ articles: Set<Article>) {
precondition(Thread.isMainThread)
guard !self.isCanceled else {
callCompletionIfNeeded()
return
}
assert(!self.isFinished)
fetchedArticles.formUnion(articles)
fetchersReturned += 1
if fetchersReturned == numberOfFetchers {
self.isFinished = true
self.resultBlock(fetchedArticles, self)
callCompletionIfNeeded()
}
}
for fetcher in fetchers {
if (fetcher as? Feed)?.readFiltered(readFilterEnabledTable: readFilterEnabledTable) ?? true {
fetcher.fetchUnreadArticlesAsync { articleSetResult in
let articles = (try? articleSetResult.get()) ?? Set<Article>()
process(articles)
}
} else {
fetcher.fetchArticlesAsync { articleSetResult in
let articles = (try? articleSetResult.get()) ?? Set<Article>()
process(articles)
}
}
}
}
}