import Foundation

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

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

    private static let authFlowPathPrefixes = [
        "/login",
        "/register",
        "/password",
        "/account/login",
        "/account/register",
        "/account/signup",
    ]

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

        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 == "apple.com" || host.hasSuffix(".apple.com") {
            let path = url.path.lowercased()
            return path.contains("auth")
                || path.contains("signin")
                || path.contains("sso")
        }

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

        let host = url.host?.lowercased() ?? ""
        let isMainSite = host == "reddit.com"
            || host == "www.reddit.com"
            || host == "new.reddit.com"
            || host == "old.reddit.com"
        guard isMainSite else { return false }

        let path = url.path.lowercased()
        return path.isEmpty || path == "/" || path == "/home"
    }

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

        let path = url.path.lowercased()
        return authFlowPathPrefixes.contains { prefix in
            path == prefix || path.hasPrefix("\(prefix)/")
        }
    }

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

        let path = url.path.lowercased()

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

        return true
    }

    /// Returns true when the OAuth completion panel can close and hand off to the main WebView.
    static func shouldCompleteOAuthSignIn(for url: URL) -> Bool {
        guard isRedditURL(url) else { return false }
        if isAuthFlowURL(url) { return false }

        let host = url.host?.lowercased() ?? ""
        let path = url.path.lowercased()

        if host == "accounts.reddit.com" {
            if path.contains("/oauth")
                || path.contains("/authorize")
                || path.contains("/login")
                || path.hasPrefix("/api/") {
                return false
            }
            return path.isEmpty || path == "/"
        }

        if host == "www.reddit.com"
            || host == "reddit.com"
            || host == "new.reddit.com"
            || host == "old.reddit.com" {
            return true
        }

        return looksLikeLoggedInURL(url)
    }

    static func oauthCallbackHost(for url: URL) -> String {
        if let host = parsedRedirectHost(from: url) {
            return host
        }
        return "accounts.reddit.com"
    }

    private static func parsedRedirectHost(from url: URL) -> String? {
        guard let components = URLComponents(url: url, resolvingAgainstBaseURL: false) else {
            return nil
        }

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

        guard let redirectValue else { return nil }

        let decoded = redirectValue.removingPercentEncoding ?? redirectValue
        if let host = hostFromRedirectString(decoded) {
            return host
        }

        if !decoded.contains("://"), let host = hostFromRedirectString("https://\(decoded)") {
            return host
        }

        return nil
    }

    private static func hostFromRedirectString(_ value: String) -> String? {
        guard let redirectURL = URL(string: value),
              let host = redirectURL.host?.lowercased(),
              isRedditURL(redirectURL) else {
            return nil
        }
        return host
    }
}