Var
  iList: Integer;
  tmpInputFile, tmpOutputFile, tmpEntry: String;
  tmpStrip, tmpListIn, tmpListOut: TStringList;
Const
  ctDelim = '_'; ctSep = ','; ctQuote = '"';
  ctOutputPath = 'C:\Test\Customer\Out\'; // Must end with a \
Begin
  psExitCode:= 0;
  tmpInputFile := psFilePath + psFilename;
  tmpOutputFile := '';
  // BTW_Invites_20231023_1.csv
  tmpStrip := TStringList.Create;
  Try
    tmpStrip.Delimiter := ctDelim; tmpStrip.QuoteChar := #0; tmpStrip.StrictDelimiter := True;
    tmpStrip.DelimitedText := psFilename;
    If tmpStrip.Count >=4 Then
    Begin
      tmpOutputFile := tmpStrip.Strings[0] +
                       ctDelim + 'Merged' +
                       ctDelim + tmpStrip.Strings[2] +
                       ctDelim + tmpStrip.Strings[3];
      psLogWrite(1, '', 'OutputFile : ' + tmpOutputFile);
    End;
  Finally
    tmpStrip.Free;
  End;
  //
  If tmpOutputFile <> '' Then
  Begin
    tmpOutputFile := ctOutPutPath + tmpOutputFile;
    tmpListIn := TStringList.Create;   
    tmpListOut := TStringList.Create;
    Try
      Try
        tmpListIn.LoadFromFile(tmpInputFile);
        // Check Output File
        If FileExists(tmpOutputfile) Then
          tmpListOut.LoadFromFile(tmpOutputFile);
        Try
          For iList := 0 to (tmpListIn.Count - 1) Do
          Begin
            tmpEntry := tmpListIn.Strings[iList] + ctSep + ctQuote + psFilename + ctQuote;
            tmpListOut.Add(tmpEntry);
          End;
          // Save To File
          Try
            tmpListOut.SaveToFile(tmpOutputFile);
            psExitCode := 1;
          Except
            psLogWrite(1, '', 'Exception SaveToFile: ' + tmpOutputFile);
          End;
        Except
          psLogWrite(1, '', 'Exception LoadFromFile: ' + tmpOutputFile);
        End;
      Except
        psLogWrite(1, '', 'Exception LoadFromFile: ' + tmpInputFile);
      End;
    Finally
      tmpListIn.Free; 
      tmpListOut.Free;
    End;
  End Else
    psLogWrite(1, '', 'Error, empty output filename, did something change to the source filename structure?');
End.