public async Task <string> GetGridSupplyPointByPostcodeAsync(string postcode)
{
var uri = ComposeGetGridSupplyPointByPostcodeUri(postcode);
var result = await GetCollectionAsync <GridSupplyPoint>(uri);
Debug.Assert(result != null);
if (!result.Any())
{
throw new GspException(Resources.NoGspFound);
}
if (result.Count() > 1)
{
throw new GspException(Resources.MultipleGspFound);
}
var gsp = result.Single().GroupId;
Assertions.AssertValidGsp(gsp);
return(gsp);
}