/// <summary>
/// Asynchronously read a single line from intake
/// </summary>
/// <returns>A tuple consisting of the line sequence number (1-based), source number (1-based) and the line read from intake; or null as EOD mark</returns>
internal async Task <Tuple <int, int, ExternalLine> > GetLineFromIntakeAsync()
{
// TBD: Intake is from either text file(s) or IntakeSupplier function
// linePlus is a Tuple<ExternalLine,int>: Item1 = line, Item2 = source number
// End-of-data indicators: * non-null linePlus.Item1 means data
// * null linePlus.Item1 means end-of-data for a single source (only if asynchronous)
// * null linePlus means end-of-data for all sources
Tuple <ExternalLine, int> linePlus;
do
{
linePlus = _intakeFromReader ? await _intakeReader.GetNextLineAsync() : await _config.AsyncIntakeSupplier(null);
}while (linePlus != null && linePlus.Item1 == null); // ignore tuples with null lines (which in case of async _intakeFromFile denote end of each file)
if (linePlus == null)
{
return(null); // EOD mark
}
var lineCnt = Interlocked.Increment(ref _lineCnt); // adjustment for header row(s) may be needed
return(Tuple.Create(lineCnt, linePlus.Item2, linePlus.Item1));
}