#include <string.h>
#include "mimeb64.h"

//---------------------------------------------------------------------------
//  4bit binary to char 0-F
char Hex2Chr( unsigned char n )
{
	n &= 0xF;
    if ( n < 10 )
    	return ( char )( n + '0' );
    else
    	return ( char )( n - 10 + 'A' );
}
//---------------------------------------------------------------------------
//  char 0-F to 4bit binary
unsigned char Chr2Hex( char c )
{
	if ( c >= 'a' && c <= 'z' )  //  it's toupper
    	c = c - 'a' + 'A';
    if ( c >= '0' && c <= '9' )
    	return ( int )( c - '0' );
    else if ( c >= 'A' && c <= 'F' )
    	return ( int )( c - 'A' + 10 );
    else
    	return -1;
}
//---------------------------------------------------------------------------
//  Base64 code table
//  0-63 : A-Z(25) a-z(51), 0-9(61), +(62), /(63)
char  Base2Chr( unsigned char n )
{
	n &= 0x3F;
	if ( n < 26 )
    	return ( char )( n + 'A' );
    else if ( n < 52 )
    	return ( char )( n - 26 + 'a' );
    else if ( n < 62 )
    	return ( char )( n - 52 + '0' );
    else if ( n == 62 )
    	return '+';
    else
    	return '/';
}
//---------------------------------------------------------------------------
unsigned char Chr2Base( char c )
{
	if ( c >= 'A' && c <= 'Z' )
    	return ( unsigned char )( c - 'A' );
    else if ( c >= 'a' && c <= 'z' )
    	return ( unsigned char )( c - 'a' + 26 );
    else if ( c >= '0' && c <= '9' )
    	return ( unsigned char )( c - '0' + 52 );
    else if ( c == '+' )
    	return 62;
    else if ( c == '/' )
    	return 63;
    else
        return 64;  //  無效字元
}
//---------------------------------------------------------------------------
//  aLen 為 aSrc 的大小， aDest 所指的緩衝區必須至少為 aLen 的 3 倍！！！
//  返回 aDest 的長度
int QPEncode( char * const aDest, const unsigned char * aSrc, int aLen )
{
	char * p = aDest;
    int    i = 0;

    while ( i++ < aLen )
    {
    	*p++ = '=';
        *p++ = Hex2Chr( *aSrc >> 4 );
        *p++ = Hex2Chr( *aSrc++ );
    }
    *p = 0;  //  aDest is an ASCIIZ string
	return ( p - aDest );  //  exclude the end of zero
}
//---------------------------------------------------------------------------
//  aDest 所指的緩衝區必須至少為 aSrc 長度的 1/3 ！！！
//  返回 aDest 的長度
int QPDecode( unsigned char * const aDest, const char * aSrc )
{
	unsigned char * p = aDest;
    int             n = strlen( aSrc );
    unsigned char   ch, cl;

    while ( *aSrc )  //  aSrc is an ASCIIZ string
    {
    	if ( ( *aSrc == '=' ) && ( n - 2 > 0 ) )
        {
        	ch = Chr2Hex( aSrc[1] );
            cl = Chr2Hex( aSrc[2] );
            if ( ( ch == ( unsigned char )-1 ) || ( cl == ( unsigned char )-1 ) )
            	*p++ = *aSrc++;
            else
            {
				*p++ = ( ch << 4 ) | cl;
    	        aSrc += 3;
            }
        }
        else
        	*p++ = *aSrc++;
    }
	return ( p - aDest );
}
//---------------------------------------------------------------------------
//  aLen 為 aSrc 的長度， aDest 所指的緩衝區必須至少為 aLen 的 4/3 倍！！！
//  返回 aDest 的長度
int Base64Encode( char * const aDest, const unsigned char * aSrc, int aLen )
{
	char        * p = aDest;
    int           i;
    unsigned char t;

    for ( i = 0; i < aLen; i++ )
    {
    	switch ( i % 3 )
        {
        case 0 :
        	*p++ = Base2Chr( *aSrc >> 2 );
            t = ( *aSrc++ << 4 ) & 0x3F;
            break;
        case 1 :
        	*p++ = Base2Chr( t | ( *aSrc >> 4 ) );
            t = ( *aSrc++ << 2 ) & 0x3F;
            break;
        case 2 :
        	*p++ = Base2Chr( t | ( *aSrc >> 6 ) );
            *p++ = Base2Chr( *aSrc++ );
            break;
        }
    }
    if ( aLen % 3 != 0 )
    {
    	*p++ = Base2Chr( t );
        if ( aLen % 3 == 1 )
        	*p++ = '=';
        *p++ = '=';
    }
    *p = 0;  //  aDest is an ASCIIZ string
	return ( p - aDest );  //  exclude the end of zero
}
//---------------------------------------------------------------------------
//  aDest 所指的緩衝區必須至少為 aSrc 長度的 0.75 倍！！！
//  返回 aDest 的長度
int Base64Decode( unsigned char * const aDest, const char * aSrc )
{
	unsigned char * p = aDest;
    int             i, n = strlen( aSrc );
    unsigned char   c, t;

    for ( i = 0; i < n; i++ )
    {
    	if ( *aSrc == '=' )
        	break;
        do {
        	if ( *aSrc )
		       	c = Chr2Base( *aSrc++ );
            else
            	c = 65;  //  字串結束
        } while ( c == 64 );  //  跳過無效字元，如回車等
        if ( c == 65 )
        	break;
        switch ( i % 4 )
        {
        case 0 :
            t = c << 2;
            break;
        case 1 :
            *p++ = ( unsigned char )( t | ( c >> 4 ) );
            t = ( unsigned char )( c << 4 );
            break;
        case 2 :
            *p++ = ( unsigned char )( t | ( c >> 2 ) );
            t = ( unsigned char )( c << 6 );
            break;
        case 3 :
            *p++ = ( unsigned char )( t | c );
            break;
        }
    }
	return ( p - aDest );
}
//---------------------------------------------------------------------------