public async Task <Url> Add(string sourceUrl, string tail, string desc)
{
sourceUrl = sourceUrl.Trim();
tail = string.IsNullOrWhiteSpace(tail) ? await CreateTail() : tail.Trim();
desc = string.IsNullOrWhiteSpace(desc) ? $"Entry added at {DateTime.UtcNow} UTC" : desc.Trim();
var newUrl = new Url(sourceUrl, tail, desc);
if (await _urlRepository.ExistAsync(newUrl))
{
throw new ConflictException("This Short URL already exist.");
}
return(await _urlRepository.Save(newUrl));
}