public interface ISearchService
{
    Task<SearchResult> Search(string keywords, SearchEngine searchEngine);
}

public class SearchService : ISearchService
{
    private readonly GoogleSearch _googleSearch;
    private readonly BingSearch _bingSearch;
    public SearchService(GoogleSearch googleSearch, BingSearch bingSearch)
    {
        _googleSearch = googleSearch;
        _bingSearch = bingSearch;
    }

    public Task<SearchResult> Search(string keywords, SearchEngine searchEngine)
    {
        if (searchEngine == SearchEngine.Google)
        {
            return _googleSearch.Search(keywords);
        }
        return _bingSearch.Search(keywords);
    }
}