// util/base64.cpp


/*    Copyright 2009 10gen Inc.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */

#include "stdafx.h"
#include "base64.h"

namespace mongo {
    namespace base64 {
        
        Alphabet alphabet;

        void encode( stringstream& ss , const char * data , int size ){
            for ( int i=0; i<size; i+=3 ){
                int left = size - i;
                const unsigned char * start = (const unsigned char*)data + i;
                
                // byte 0
                ss << alphabet.e(start[0]>>2);
                
                // byte 1
                unsigned char temp = ( start[0] << 4 );
                if ( left == 1 ){
                    ss << alphabet.e(temp);
                    break;
                }
                temp |= ( ( start[1] >> 4 ) & 0xF );
                ss << alphabet.e(temp);

                // byte 2
                temp = ( start[1] & 0xF ) << 2;
                if ( left == 2 ){
                    ss << alphabet.e(temp);
                    break;
                }
                temp |= ( ( start[2] >> 6 ) & 0x3 );
                ss << alphabet.e(temp);

                // byte 3
                ss << alphabet.e(start[2] & 0x3f);
            }

            int mod = size % 3;
            if ( mod == 1 ){
                ss << "==";
            }
            else if ( mod == 2 ){
                ss << "=";
            }
        }


        string encode( const char * data , int size ){
            stringstream ss;
            encode( ss , data ,size );
            return ss.str();
        }
        
        string encode( const string& s ){
            return encode( s.c_str() , s.size() );
        }


        void decode( stringstream& ss , const string& s ){
            uassert( 10270 ,  "invalid base64" , s.size() % 4 == 0 );
            const unsigned char * data = (const unsigned char*)s.c_str();
            int size = s.size();
            
            unsigned char buf[3];
            for ( int i=0; i<size; i+=4){
                const unsigned char * start = data + i;
                buf[0] = ( ( alphabet.decode[start[0]] << 2 ) & 0xFC ) | ( ( alphabet.decode[start[1]] >> 4 ) & 0x3 );
                buf[1] = ( ( alphabet.decode[start[1]] << 4 ) & 0xF0 ) | ( ( alphabet.decode[start[2]] >> 2 ) & 0xF );
                buf[2] = ( ( alphabet.decode[start[2]] << 6 ) & 0xC0 ) | ( ( alphabet.decode[start[3]] & 0x3F ) );
                
                int len = 3;
                if ( start[3] == '=' ){
                    len = 2;
                    if ( start[2] == '=' ){
                        len = 1;
                    }
                }
                ss.write( (const char*)buf , len );
            }
        }
        
        string decode( const string& s ){
            stringstream ss;
            decode( ss , s );
            return ss.str();
        }

    }
}