app_for_reddit/Reddit App/Managers/RedditOAuthPanelController.swift

import AppKit
import WebKit

@MainActor
final class RedditOAuthPanelController: NSObject {
    static let shared = RedditOAuthPanelController()

    private var panel: NSPanel?
    private var webView: WKWebView?
    private var onComplete: (() -> Void)?
    private var onAuthError: ((String) -> Void)?
    private var finishWorkItem: DispatchWorkItem?

    private override init() {
        super.init()
    }

    func completeSignIn(
        callbackURL: URL,
        onAuthError: @escaping (String) -> Void,
        onFinished: @escaping () -> Void
    ) {
        dismiss()

        self.onComplete = onFinished
        self.onAuthError = onAuthError

        let panel = NSPanel(
            contentRect: NSRect(x: 0, y: 0, width: 520, height: 640),
            styleMask: [.titled, .closable, .fullSizeContentView],
            backing: .buffered,
            defer: false
        )
        panel.title = "Sign in to Reddit"
        panel.isReleasedWhenClosed = false
        panel.center()
        panel.level = .floating

        let webView = WKWebView(frame: panel.contentView?.bounds ?? .zero, configuration: RedditWebViewManager.makeConfiguration())
        webView.navigationDelegate = self
        webView.uiDelegate = self
        webView.autoresizingMask = [.width, .height]
        panel.contentView?.addSubview(webView)

        self.panel = panel
        self.webView = webView

        panel.makeKeyAndOrderFront(nil)
        NSApp.activate(ignoringOtherApps: true)

        webView.load(URLRequest(url: callbackURL))
    }

    func dismiss() {
        finishWorkItem?.cancel()
        finishWorkItem = nil
        panel?.close()
        panel = nil
        webView = nil
        onComplete = nil
        onAuthError = nil
    }

    private func finish() {
        let completion = onComplete
        dismiss()
        completion?()
    }

    private func scheduleFinishIfNeeded(for url: URL) {
        guard RedditWebAuthHelper.shouldCompleteOAuthSignIn(for: url) else { return }

        finishWorkItem?.cancel()
        let workItem = DispatchWorkItem { [weak self] in
            self?.finish()
        }
        finishWorkItem = workItem
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.75, execute: workItem)
    }

    private func beginOAuthSignIn(url: URL, in webView: WKWebView) {
        OAuthAuthenticationManager.shared.authenticate(
            url: url,
            presentationWindow: panel
        ) { [weak self] result in
            guard let self else { return }
            switch result {
            case .success(let callbackURL):
                webView.load(URLRequest(url: callbackURL))
            case .failure(let error as OAuthError) where error == .cancelled:
                break
            case .failure(let error):
                self.onAuthError?(error.localizedDescription)
                self.finish()
            }
        }
    }
}

extension RedditOAuthPanelController: WKNavigationDelegate {
    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
        guard let url = webView.url else { return }
        scheduleFinishIfNeeded(for: url)
    }

    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) {
            decisionHandler(.cancel)
            beginOAuthSignIn(url: url, in: webView)
            return
        }

        decisionHandler(.allow)
    }
}

extension RedditOAuthPanelController: WKUIDelegate {
    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, in: webView)
            return nil
        }

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