/**
 * getCode128BarCode
 * 
 * This function generates Code128 barcode for the given string. It uses subsets B and C when generating barcode 
 * string (not subset A). 
 * @param In &strDataToFormat - string to format into the barcode.
 * Returns: ASCII characters needed to represent the barcode.
 *
 * ASSUMPTIONS: The &strDataToFormat string does not contain any invalid characters. Only ASCII characters 32 to 126 are
 * allowed - if there are invalid characters, an empty string is returned. The function itself appends the necessary special 
 * ASCII characters to generate the barcode.
 *
 * The algorithm for creating barcodes is based upon the sample code provided on this site, with slight modifications:
 * http://grandzebu.net/index.php?page=/informatique/codbar-en/code128.htm
**/
Function getCode128BarCode(&strDataToFormat As string) Returns string
   
   Local boolean &boolSubsetB = True;
   Local boolean &boolIsDigits;
   Local string &strBarcode = "";
   Local integer &i;
   Local integer &intCharNum, &charsToCheck, &intCheckSum;
   
   /* No need to process an empty string - simply return what was put in */
   If Len(&strDataToFormat) = 0 Then
      Return &strBarcode;
   End-If;
   
   /* Check for valid characters */
   For &i = 1 To Len(&strDataToFormat)
      &intCharNum = Code(Substring(&strDataToFormat, &i, 1));
      If &intCharNum >= 32 And
            &intCharNum <= 126 Then
      Else
         /* invalid characters found - return empty string */
         Return "";
      End-If;
   End-For;
   
   &i = 1;
   
   While &i <= Len(&strDataToFormat)
      
      If &boolSubsetB Then
         /* see if it's worth it to switch to subset C */
         /* yes for 4 digits at start or end, else if 6 digits */
         If (&i = 1) Or
               (&i + 3) = Len(&strDataToFormat) Then
            &charsToCheck = 4;
         Else
            &charsToCheck = 6;
         End-If;
         
         &boolIsDigits = False;
         If IsDigits(Substring(&strDataToFormat, &i, &charsToCheck)) And
               (Len(Substring(&strDataToFormat, &i, &charsToCheck)) = &charsToCheck) Then
            &boolIsDigits = True;
         End-If;
         
         If &boolIsDigits Then
            
            If &i = 1 Then
               /* Put Start C character, to indicate barcode starts with subset C */
               &strBarcode = Char(210);
            Else
               /* Put Code C character, to indicate switch to subset C */
               &strBarcode = &strBarcode | Char(204);
            End-If;
            &boolSubsetB = False;
            
         Else
            
            If &i = 1 Then
               /* Put Start B character, to indicate barcode starts with subset B */
               &strBarcode = Char(209);
            End-If;
            
         End-If;
         
      End-If;
      
      If Not &boolSubsetB Then
         
         /* We are on subset C, try to process 2 digits */
         &boolIsDigits = False;
         
         If IsDigits(Substring(&strDataToFormat, &i, 2)) And
               (Len(Substring(&strDataToFormat, &i, 2)) = 2) Then
            &boolIsDigits = True;
         End-If;
         
         If &boolIsDigits Then
            /* 2 digits - process using subset C */
            &intCharNum = Value(Substring(&strDataToFormat, &i, 2));
            If &intCharNum = 0 Then
               &intCharNum = 212;
            Else
               If &intCharNum < 95 Then
                  &intCharNum = &intCharNum + 32;
               Else
                  &intCharNum = &intCharNum + 105;
               End-If;
            End-If;
            
            &strBarcode = &strBarcode | Char(&intCharNum);
            &i = &i + 2;
            
         Else
            /* revert back to subset B */
            &strBarcode = &strBarcode | Char(205);
            &boolSubsetB = True;
            
         End-If;
         
      End-If;
      
      If &boolSubsetB Then
         
         /* Process 1 digit with subset B */
         &strBarcode = &strBarcode | Substring(&strDataToFormat, &i, 1);
         &i = &i + 1
      End-If;
      
   End-While;
   
   /* Calculation of the checksum */
   For &i = 1 To Len(&strBarcode)
      
      &intCharNum = Code(Substring(&strBarcode, &i, 1));
      If &intCharNum = 212 Then
         &intCharNum = 0;
      Else
         If &intCharNum < 127 Then
            &intCharNum = &intCharNum - 32;
         Else
            &intCharNum = &intCharNum - 105;
         End-If;
      End-If;
      
      If &i = 1 Then
         &intCheckSum = &intCharNum;
      Else
         &intCheckSum = &intCheckSum + (&intCharNum * (&i - 1));
      End-If;
      
   End-For;
   
   /* Apply modulo 103 to the weighted total to get the checksum */
   &intCheckSum = Mod(&intCheckSum, 103);
   
   /* Calculate checksum ASCII code */
   If &intCheckSum < 95 Then
      &intCheckSum = &intCheckSum + 32;
   Else
      &intCheckSum = &intCheckSum + 105;
   End-If;
   
   /* Add the checksum and the STOP */
   &strBarcode = &strBarcode | Char(&intCheckSum) | Char(211);
   
   Return &strBarcode;
   
End-Function;