(**
@author Benedikt Bauer <benedikt.bauer@bbauer.eu>
@license GNU AGPL - http://www.gnu.org/licenses/agpl-3.0.txt
*)

FUNCTION dec2bin(dec : Integer) : String;
VAR remainder : Integer;
temp : String;
BEGIN
  remainder := dec;
  WHILE remainder > 0 DO
  BEGIN
    temp := IntToStr(remainder mod 2) + temp;
//    WriteLn('Bin: ' + temp);
    remainder := remainder div 2;
//    WriteLn('Remainder: ' + IntToStr(remainder));
  END;
  WHILE Length(temp) mod 4 > 0 DO
    temp := '0' + temp;

  result := temp;
END;

FUNCTION str2bin(str : String) : String;
VAR temp : String;
i : Integer;
BEGIN
  FOR i := 1 TO Length(str) DO
    temp := temp + dec2bin(Ord(str[i]));

  result := temp;
END;

FUNCTION base64encode(str : String) : String;
VAR binary, sextbin, resulttemp, lookup : String;
multiplier : Float;
i, j, k, len, pow, exp, sextet : Integer;
BEGIN
  // Base64 Lookup Table
  lookup := 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
  binary := str2bin(str);
  WHILE i < Length(binary) DO
  BEGIN
//    WriteLn('i: ' + IntToStr(i));
    // 6 digit binary substring
    sextbin := Copy(binary, i+1, 6);

    // Add padding
    WHILE Length(sextbin) < 6 DO
      sextbin := sextbin + '0';
//    WriteLn('Binary: ' + sextbin);
    // j runs from LSB to MSB
    j := 6;
    // k runs the exponent
    FOR k := 0 TO 5 DO
    BEGIN
//    WriteLn('j: ' + IntToStr(j));
      multiplier := StrToFloat(sextbin[j]);
      exp := k;
      // digit * 2^pos
      pow := StrToInt(FloatToStr(multiplier * Power(2.0, exp)));
//      WriteLn(FloatToStr(multiplier) + ' * 2^' + IntToStr(exp) + '=' + IntToStr(pow));
      sextet := sextet + pow;
      j := j-1;
    END;
//    WriteLn('Number: ' + IntToStr(sextet));
//    WriteLn('Base64: ' + lookup[sextet+1]);
    resulttemp := resulttemp + lookup[sextet+1];
    sextet := 0;
    sextbin := '';
    i := i+6;
  END;
 
  // Add = padding to the base64 string
  WHILE Length(resulttemp) mod 4 > 0 DO
    resulttemp := resulttemp + '=';

  result := resulttemp;
END;

// Example encodings, taken from Wikipedia (https://en.wikipedia.org/wiki/Base64#Examples) for verifying the correctness of my algorithm
//WriteLn(resulttemp);
WriteLn(base64encode('Man'));
WriteLn(base64encode('Ma'));
WriteLn(base64encode('M'));
WriteLn(base64encode('any carnal pleasure.'));

{$INCLUDE 'base64encode.pal'}