NetNewsWire/iOS/Article/WebViewProvider.swift

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//
// WebViewProvider.swift
// NetNewsWire-iOS
//
// Created by Maurice Parker on 9/21/19.
// Copyright © 2019 Ranchero Software. All rights reserved.
//
import Foundation
import RSCore
import WebKit
/// WKWebView has an awful behavior of a flash to white on first load when in dark mode.
/// Keep a queue of WebViews where we've already done a trivial load so that by the time we need them in the UI, they're past the flash-to-shite part of their lifecycle.
class WebViewProvider: NSObject {
private let articleIconSchemeHandler: ArticleIconSchemeHandler
private let operationQueue = MainThreadOperationQueue()
private var queue = UIView()
init(coordinator: SceneCoordinator, viewController: UIViewController) {
articleIconSchemeHandler = ArticleIconSchemeHandler(coordinator: coordinator)
super.init()
viewController.view.insertSubview(queue, at: 0)
replenishQueueIfNeeded()
}
func flushQueue() {
operationQueue.add(WebViewProviderFlushQueueOperation(queue: queue))
}
func replenishQueueIfNeeded() {
operationQueue.add(WebViewProviderReplenishQueueOperation(queue: queue, articleIconSchemeHandler: articleIconSchemeHandler))
}
func dequeueWebView(completion: @escaping (PreloadedWebView) -> ()) {
operationQueue.add(WebViewProviderDequeueOperation(queue: queue, articleIconSchemeHandler: articleIconSchemeHandler, completion: completion))
operationQueue.add(WebViewProviderReplenishQueueOperation(queue: queue, articleIconSchemeHandler: articleIconSchemeHandler))
}
}
class WebViewProviderFlushQueueOperation: MainThreadOperation {
// MainThreadOperation
public var isCanceled = false
public var id: Int?
public weak var operationDelegate: MainThreadOperationDelegate?
public var name: String? = "WebViewProviderFlushQueueOperation"
public var completionBlock: MainThreadOperation.MainThreadOperationCompletionBlock?
private var queue: UIView
init(queue: UIView) {
self.queue = queue
}
func run() {
queue.subviews.forEach { $0.removeFromSuperview() }
self.operationDelegate?.operationDidComplete(self)
}
}
class WebViewProviderReplenishQueueOperation: MainThreadOperation {
// MainThreadOperation
public var isCanceled = false
public var id: Int?
public weak var operationDelegate: MainThreadOperationDelegate?
public var name: String? = "WebViewProviderReplenishQueueOperation"
public var completionBlock: MainThreadOperation.MainThreadOperationCompletionBlock?
private let minimumQueueDepth = 3
private var queue: UIView
private var articleIconSchemeHandler: ArticleIconSchemeHandler
init(queue: UIView, articleIconSchemeHandler: ArticleIconSchemeHandler) {
self.queue = queue
self.articleIconSchemeHandler = articleIconSchemeHandler
}
func run() {
while queue.subviews.count < minimumQueueDepth {
let webView = PreloadedWebView(articleIconSchemeHandler: articleIconSchemeHandler)
queue.insertSubview(webView, at: 0)
webView.preload()
}
self.operationDelegate?.operationDidComplete(self)
}
}
class WebViewProviderDequeueOperation: MainThreadOperation {
// MainThreadOperation
public var isCanceled = false
public var id: Int?
public weak var operationDelegate: MainThreadOperationDelegate?
public var name: String? = "WebViewProviderFlushQueueOperation"
public var completionBlock: MainThreadOperation.MainThreadOperationCompletionBlock?
private var queue: UIView
private var articleIconSchemeHandler: ArticleIconSchemeHandler
private var completion: (PreloadedWebView) -> ()
init(queue: UIView, articleIconSchemeHandler: ArticleIconSchemeHandler, completion: @escaping (PreloadedWebView) -> ()) {
self.queue = queue
self.articleIconSchemeHandler = articleIconSchemeHandler
self.completion = completion
}
func run() {
if let webView = queue.subviews.last as? PreloadedWebView {
webView.ready { preloadedWebView in
preloadedWebView.removeFromSuperview()
self.completion(preloadedWebView)
}
self.operationDelegate?.operationDidComplete(self)
return
}
assertionFailure("Creating PreloadedWebView in \(#function); queue has run dry.")
let webView = PreloadedWebView(articleIconSchemeHandler: articleIconSchemeHandler)
webView.preload()
webView.ready { preloadedWebView in
self.completion(preloadedWebView)
}
self.operationDelegate?.operationDidComplete(self)
}
}