app_for_reddit/Reddit App/Views/RedditWebView.swift

import AppKit
import SwiftUI
import WebKit

struct RedditWebView: NSViewRepresentable {
    let url: URL
    let reloadTrigger: Int

    func makeCoordinator() -> Coordinator {
        Coordinator()
    }

    func makeNSView(context: Context) -> RedditWebViewContainer {
        let container = RedditWebViewContainer(webView: RedditWebViewManager.makeWebView())
        container.webView.navigationDelegate = context.coordinator
        container.webView.uiDelegate = context.coordinator
        context.coordinator.container = container
        context.coordinator.lastReloadTrigger = reloadTrigger
        container.load(url: url)
        return container
    }

    func updateNSView(_ container: RedditWebViewContainer, context: Context) {
        let urlChanged = context.coordinator.lastLoadedURL != url
        let triggerChanged = context.coordinator.lastReloadTrigger != reloadTrigger
        guard urlChanged || triggerChanged else { return }

        context.coordinator.lastReloadTrigger = reloadTrigger
        context.coordinator.lastLoadedURL = url
        container.load(url: url)
    }

    final class Coordinator: NSObject, WKNavigationDelegate, WKUIDelegate {
        weak var container: RedditWebViewContainer?
        var lastReloadTrigger = -1
        var lastLoadedURL: URL?

        func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
            webView.evaluateJavaScript(RedditPostBoundaryStyle.injectionScript, completionHandler: nil)
        }

        func webViewWebContentProcessDidTerminate(_ webView: WKWebView) {
            container?.reloadLastURL()
        }

        func webView(
            _ webView: WKWebView,
            didFailProvisionalNavigation navigation: WKNavigation!,
            withError error: Error
        ) {
            let nsError = error as NSError
            guard nsError.domain != NSURLErrorDomain || nsError.code != NSURLErrorCancelled else { return }
            container?.reloadLastURL(after: 1.0)
        }

        func webView(
            _ webView: WKWebView,
            decidePolicyFor navigationAction: WKNavigationAction,
            decisionHandler: @escaping (WKNavigationActionPolicy) -> Void
        ) {
            guard let url = navigationAction.request.url else {
                decisionHandler(.allow)
                return
            }

            if RedditWebAuthHelper.isOAuthProviderURL(url) {
                beginOAuthSignIn(url: url)
                decisionHandler(.cancel)
                return
            }

            if navigationAction.targetFrame == nil {
                webView.load(URLRequest(url: url))
                decisionHandler(.cancel)
                return
            }

            if navigationAction.navigationType == .linkActivated,
               !RedditWebAuthHelper.isRedditURL(url) {
                NSWorkspace.shared.open(url)
                decisionHandler(.cancel)
                return
            }

            decisionHandler(.allow)
        }

        func webView(
            _ webView: WKWebView,
            createWebViewWith configuration: WKWebViewConfiguration,
            for navigationAction: WKNavigationAction,
            windowFeatures: WKWindowFeatures
        ) -> WKWebView? {
            guard let url = navigationAction.request.url else { return nil }

            if RedditWebAuthHelper.isOAuthProviderURL(url) {
                beginOAuthSignIn(url: url)
                return nil
            }

            webView.load(URLRequest(url: url))
            return nil
        }

        private func beginOAuthSignIn(url: URL) {
            let presentationWindow = container?.window

            OAuthAuthenticationManager.shared.authenticate(
                url: url,
                presentationWindow: presentationWindow
            ) { [weak self] result in
                guard let self, let container = self.container else { return }

                switch result {
                case .success(let callbackURL):
                    RedditOAuthPanelController.shared.completeSignIn(callbackURL: callbackURL) {
                        container.load(url: RedditWebAuthHelper.redditHomeURL)
                    }
                case .failure(let error as OAuthError) where error == .cancelled:
                    break
                case .failure:
                    break
                }
            }
        }
    }
}

final class RedditWebViewContainer: NSView {
    let webView: WKWebView
    private var pendingURL: URL?
    private var lastLoadedURL: URL?
    private var reloadWorkItem: DispatchWorkItem?

    init(webView: WKWebView) {
        self.webView = webView
        super.init(frame: .zero)
        wantsLayer = true

        addSubview(webView)
        webView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            webView.leadingAnchor.constraint(equalTo: leadingAnchor),
            webView.trailingAnchor.constraint(equalTo: trailingAnchor),
            webView.topAnchor.constraint(equalTo: topAnchor),
            webView.bottomAnchor.constraint(equalTo: bottomAnchor),
        ])
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func load(url: URL) {
        pendingURL = url
        lastLoadedURL = url
        reloadWorkItem?.cancel()
        tryLoadIfReady()
    }

    func reloadLastURL(after delay: TimeInterval = 0) {
        guard let lastLoadedURL else { return }

        reloadWorkItem?.cancel()
        let workItem = DispatchWorkItem { [weak self] in
            self?.load(url: lastLoadedURL)
        }
        reloadWorkItem = workItem
        DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: workItem)
    }

    override func layout() {
        super.layout()
        tryLoadIfReady()
    }

    override func viewDidMoveToWindow() {
        super.viewDidMoveToWindow()
        tryLoadIfReady()
    }

    private func tryLoadIfReady() {
        guard let url = pendingURL else { return }
        guard bounds.width > 1, bounds.height > 1 else { return }

        pendingURL = nil
        webView.load(URLRequest(url: url))
    }
}