OpenGraph.fetch(url: url) { result in
    switch result {
    case .success(let og):
        print(og[.title]) // => og:title of the web site
        print(og[.type])  // => og:type of the web site
        print(og[.image]) // => og:image of the web site
        print(og[.url])   // => og:url of the web site
    case .failure(let error):
        print(error)
    }
}

do {
    let og = try await OpenGraph.fetch(url: url)
    print(og[.title]) // => og:title of the web site
    print(og[.type])  // => og:type of the web site
    print(og[.image]) // => og:image of the web site
    print(og[.url])   // => og:url of the web site
} catch {
    print(error)
}

extension Reactive where Base: OpenGraph {
    static func fetch(url: URL?) -> Observable<OpenGraph> {
        return Observable.create { observer in
            guard let url = url else {
                observer.onCompleted()
                return Disposables.create()
            }

            OpenGraph.fetch(url: url) { result in
                switch result {
                case .success(let og):
                    observer.onNext(og)
                case .failure(let error):
                    observer.onError(error)
                }
                observer.onCompleted()
            }

            return Disposables.create()
        }
    }
}