app_for_reddit/Reddit App/Views/RedditWebView.swift

import AppKit
import SwiftUI
import WebKit

struct RedditWebView: NSViewRepresentable {
    let url: URL
    let reloadTrigger: Int
    var goBackTrigger: Int = 0
    var onCanGoBackChange: (Bool) -> Void = { _ in }
    var onAuthError: (String) -> Void = { _ in }

    func makeCoordinator() -> Coordinator {
        Coordinator(
            onCanGoBackChange: onCanGoBackChange,
            onAuthError: onAuthError
        )
    }

    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
        context.coordinator.startObservingNavigation(in: container.webView)
        container.load(url: url)
        return container
    }

    func updateNSView(_ container: RedditWebViewContainer, context: Context) {
        context.coordinator.onCanGoBackChange = onCanGoBackChange

        if context.coordinator.lastGoBackTrigger != goBackTrigger {
            context.coordinator.lastGoBackTrigger = goBackTrigger
            if container.webView.canGoBack {
                container.webView.goBack()
            }
        }

        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 lastGoBackTrigger = 0
        var lastLoadedURL: URL?
        private var prefillWorkItem: DispatchWorkItem?
        private var canGoBackObservation: NSKeyValueObservation?
        private var urlObservation: NSKeyValueObservation?
        var onCanGoBackChange: (Bool) -> Void
        private let onAuthError: (String) -> Void

        init(
            onCanGoBackChange: @escaping (Bool) -> Void,
            onAuthError: @escaping (String) -> Void
        ) {
            self.onCanGoBackChange = onCanGoBackChange
            self.onAuthError = onAuthError
        }

        func startObservingNavigation(in webView: WKWebView) {
            guard canGoBackObservation == nil else { return }

            canGoBackObservation = webView.observe(\.canGoBack, options: [.initial, .new]) { [weak self] webView, _ in
                DispatchQueue.main.async {
                    self?.reportBackButtonVisibility(for: webView)
                }
            }

            urlObservation = webView.observe(\.url, options: [.new]) { [weak self] webView, _ in
                DispatchQueue.main.async {
                    self?.reportBackButtonVisibility(for: webView)
                }
            }
        }

        private func reportBackButtonVisibility(for webView: WKWebView) {
            let isOnHome = webView.url.map(RedditWebAuthHelper.isRedditHomeURL) ?? false
            onCanGoBackChange(webView.canGoBack && !isOnHome)
        }

        func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
            startObservingNavigation(in: webView)
            reportBackButtonVisibility(for: webView)
            webView.evaluateJavaScript(RedditPostBoundaryStyle.injectionScript, completionHandler: nil)
            webView.evaluateJavaScript(RedditHomeChromeStyle.injectionScript, completionHandler: nil)
            webView.evaluateJavaScript(RedditAuthChromeStyle.injectionScript, completionHandler: nil)
            scheduleSubmitPrefillIfNeeded(on: webView)
        }

        private func scheduleSubmitPrefillIfNeeded(on webView: WKWebView) {
            guard
                let url = webView.url,
                RedditSubmitURLBuilder.isSubmitPage(url),
                let prefill = RedditSubmitPrefillManager.pending
            else { return }

            prefillWorkItem?.cancel()

            let script = RedditSubmitPrefillScript.make(prefill: prefill)
            guard !script.isEmpty else {
                RedditSubmitPrefillManager.clear()
                return
            }

            attemptSubmitPrefill(on: webView, script: script, remainingAttempts: 6)
        }

        private func attemptSubmitPrefill(on webView: WKWebView, script: String, remainingAttempts: Int) {
            guard remainingAttempts > 0, RedditSubmitPrefillManager.pending != nil else { return }

            webView.evaluateJavaScript(script) { result, _ in
                let succeeded = (result as? Bool) == true
                if succeeded {
                    RedditSubmitPrefillManager.clear()
                    return
                }

                guard remainingAttempts > 1 else {
                    RedditSubmitPrefillManager.clear()
                    return
                }

                let workItem = DispatchWorkItem { [weak self, weak webView] in
                    guard let self, let webView else { return }
                    self.attemptSubmitPrefill(on: webView, script: script, remainingAttempts: remainingAttempts - 1)
                }
                self.prefillWorkItem = workItem
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.6, execute: workItem)
            }
        }

        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) {
                // Always route OAuth through ASWebAuthenticationSession. Reddit's login
                // modal runs in a subframe; letting WebKit handle Google/Apple SSO there
                // triggers SOAuthorizationCoordinator subframe errors and breaks sign-in.
                decisionHandler(.cancel)
                beginOAuthSignIn(url: url)
                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,
                        onAuthError: onAuthError
                    ) {
                        container.load(url: RedditWebAuthHelper.redditHomeURL)
                    }
                case .failure(let error as OAuthError) where error == .cancelled:
                    break
                case .failure(let error):
                    onAuthError(error.localizedDescription)
                }
            }
        }
    }
}

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))
    }
}