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 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.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() {
        panel?.close()
        panel = nil
        webView = nil
        onComplete = nil
        onAuthError = nil
    }

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

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

        if shouldFinish(for: url) {
            finish()
        }
    }

    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)
            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):
                    self.onAuthError?(error.localizedDescription)
                    self.finish()
                }
            }
            return
        }

        if shouldFinish(for: url) {
            decisionHandler(.allow)
            DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) { [weak self] in
                self?.finish()
            }
            return
        }

        decisionHandler(.allow)
    }

    private func shouldFinish(for url: URL) -> Bool {
        guard let host = url.host?.lowercased() else { return false }
        let path = url.path.lowercased()

        if host == "www.reddit.com" || host == "reddit.com" {
            return !path.contains("login") && !path.contains("register")
        }

        return RedditWebAuthHelper.looksLikeLoggedInURL(url)
    }
}