//Konwersja pomiedzy EAN13 <=> EAN14
//www.algorytm.org
//(c) 2007 by Tomasz Lubinski

program ean14;
{$APPTYPE CONSOLE}
uses
  SysUtils;

var
   ean_13, ean_14: String;
   variant, i: Integer;

//calculates EAN-13 checksum
function checkSum13(EAN: String): String;
var
   sum : Integer;
begin
   sum := 1 * StrToInt(EAN[1]) +
         3 * StrToInt(EAN[2]) +
         1 * StrToInt(EAN[3]) +
	 3 * StrToInt(EAN[4]) +
	 1 * StrToInt(EAN[5]) +
	 3 * StrToInt(EAN[6]) +
	 1 * StrToInt(EAN[7]) +
	 3 * StrToInt(EAN[8]) +
	 1 * StrToInt(EAN[9]) +
	 3 * StrToInt(EAN[10]) +
	 1 * StrToInt(EAN[11]) +
	 3 * StrToInt(EAN[12]);

   sum := sum mod 10;
   sum := 10 - sum;
   sum := sum mod 10;

   Result := IntToStr(sum);
end;

//calculates EAN-14 checksum
function checkSum14(EAN: String): String;
var
   sum : Integer;
begin
   sum := 3 * StrToInt(EAN[1]) +
         1 * StrToInt(EAN[2]) +
         3 * StrToInt(EAN[3]) +
         1 * StrToInt(EAN[4]) +
	 3 * StrToInt(EAN[5]) +
	 1 * StrToInt(EAN[6]) +
	 3 * StrToInt(EAN[7]) +
	 1 * StrToInt(EAN[8]) +
	 3 * StrToInt(EAN[9]) +
	 1 * StrToInt(EAN[10]) +
	 3 * StrToInt(EAN[11]) +
	 1 * StrToInt(EAN[12]) +
	 3 * StrToInt(EAN[13]);

   sum := sum mod 10;
   sum := 10 - sum;
   sum := sum mod 10;

   Result := IntToStr(sum);
end;


//EAN-13 => EAN-14
function convertToEAN14(ean13: String; variant: Integer): String;
var
   i: Integer;
begin
   Result := '00000000000000';

   //check length of code
   if (length(ean13) <> 13) then
   begin
      Result := 'Nieprawidlowa dlugosc kodu EAN-13 (powinno byc 13 znakow)';
      exit;
   end;

   //check variant
   if ((variant < 0) or (variant >9)) then
   begin
      Result := 'Nieprawidlowa wartosc wariantu (powinno byc 0-9)';
      exit;
   end;

   //check control digit
   if (checkSum13(ean13)[1] <> ean13[13]) then
   begin
      Result := 'Nieprawidlowa cyfra kontrolna w kodzie EAN-13';
      exit;
   end;

   //convert EAN-13 to EAN-14
   for i:=12 downto 1 do
   	Result[i+1] := ean13[i];

   Result[1] := IntToStr(variant)[1];
   Result[14] := checkSum14(Result)[1];
end;

//EAN-14 => EAN-13
function convertToEAN13(ean14: String): String;
var
   i: Integer;
begin
   Result := '0000000000000';

   //check code length
   if (length(ean14) <> 14) then
   begin
      Result := 'Nieprawidlowa dlugosc kodu EAN-14 (powinno byc 14 znakow)';
      exit;
   end;

   //control check digit
   if (checkSum14(ean14)[1] <> ean14[14]) then
   begin
      Result := 'Nieprawidlowa suma kontrolna w kodzie EAN-14';
      exit;
   end;

   //convert EAN-14 to EAN-13
   for i:=1 to 12 do
   	Result[i] := ean14[i+1];

   Result[13] := checkSum13(Result)[1];
end;

begin

   writeln('1. EAN-13 => EAN-14');
   writeln('2. EAN-14 => EAN-13');
   readln(i);

   if (i=1) then
   begin
      writeln('Podaj kod EAN-13');
      readln(ean_13);
      writeln('Podaj wariant');
      readln(variant);
      ean_14 := convertToEAN14(ean_13, variant);
      writeln('Kod EAN-14 to: ');
      writeln(ean_14);
   end
   else
   begin
      writeln('Podaj kod EAN-14');
      readln(ean_14);
      ean_13 := convertToEAN13(ean_14);
      writeln('Kod EAN-13 to: ');
      writeln(ean_13);
   end;

end.