app_for_reddit/Reddit App/Utilities/RedditWebAuthHelper.swift

import Foundation

enum RedditWebAuthHelper {
    static let redditHomeURL = URL(string: "https://www.reddit.com")!

    static func isOAuthProviderURL(_ url: URL) -> Bool {
        guard let host = url.host?.lowercased() else { return false }

        let oauthHosts = [
            "accounts.google.com",
            "appleid.apple.com",
            "idmsa.apple.com",
            "login.microsoftonline.com",
            "login.live.com",
            "account.live.com",
            "login.microsoft.com",
            "www.facebook.com",
            "m.facebook.com",
            "facebook.com",
            "auth0.com",
        ]

        if oauthHosts.contains(where: { host == $0 || host.hasSuffix(".\($0)") }) {
            return true
        }

        if host == "google.com" || host.hasSuffix(".google.com") {
            let path = url.path.lowercased()
            return path.contains("oauth")
                || path.contains("signin")
                || path.contains("gsi")
        }

        if host == "facebook.com" || host.hasSuffix(".facebook.com") {
            let path = url.path.lowercased()
            return path.contains("oauth") || path.contains("login") || path.contains("dialog")
        }

        if host.hasSuffix(".auth0.com") {
            return true
        }

        return false
    }

    static func isRedditURL(_ url: URL) -> Bool {
        guard let host = url.host?.lowercased() else { return false }

        let redditHosts = [
            "reddit.com",
            "www.reddit.com",
            "old.reddit.com",
            "new.reddit.com",
            "accounts.reddit.com",
            "oauth.reddit.com",
            "reddit.app.link",
            "redd.it",
        ]

        return redditHosts.contains(where: { host == $0 || host.hasSuffix(".\($0)") })
    }

    static func looksLikeLoggedInURL(_ url: URL) -> Bool {
        guard isRedditURL(url) else { return false }

        let path = url.path.lowercased()
        let blockedPaths = [
            "/login",
            "/register",
            "/password",
            "/account/login",
        ]

        if blockedPaths.contains(where: { path.hasPrefix($0) }) {
            return false
        }

        if url.host?.lowercased() == "accounts.reddit.com" {
            return path.isEmpty || path == "/" || path.hasPrefix("/api/")
        }

        return true
    }

    static func oauthCallbackHost(for url: URL) -> String {
        guard let components = URLComponents(url: url, resolvingAgainstBaseURL: false) else {
            return "accounts.reddit.com"
        }

        let redirectURI = components.queryItems?.first(where: { $0.name == "redirect_uri" })?.value
            ?? components.queryItems?.first(where: { $0.name == "redirect_url" })?.value

        if let redirectURI,
           let redirectURL = URL(string: redirectURI),
           let host = redirectURL.host?.lowercased(),
           isRedditURL(redirectURL) {
            return host
        }

        return "accounts.reddit.com"
    }
}