#include "encode.h"

#define PADDING '='

static
unsigned char b64toascii[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" \
                             "abcdefghijklmnopqrstuvwxyz" \
                             "0123456789" \
                             "+/";

static
unsigned char b64urltoascii[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" \
                                "abcdefghijklmnopqrstuvwxyz" \
                                "0123456789" \
                                "-_";

static
unsigned char asciitob64[] = {
     0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
     0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
     0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
     0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
     0,  0,  0, 62,  0, 62,  0, 63, 52, 53,
    54, 55, 56, 57, 58, 59, 60, 61,  0,  0,
     0,  0,  0,  0,  0,  0,  1,  2,  3,  4,
     5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
    25,  0,  0,  0,  0, 63,  0, 26, 27, 28,
    29, 30, 31, 32, 33, 34, 35, 36, 37, 38,
    39, 40, 41, 42, 43, 44, 45, 46, 47, 48,
    49, 50, 51
};


int
encode(unsigned char *octbuf, int octbufsize, unsigned char *sxtbuf, int urlencoded)
{
    unsigned char *table;
    unsigned char *sxtbegin;
    unsigned char *octleft;
    int highorderbits;

    table = (!urlencoded) ? b64toascii : b64urltoascii;

    sxtbegin = sxtbuf;
    octleft = octbuf + octbufsize - (octbufsize % 3);
    while (octbuf < octleft) {
        *sxtbuf++ = table[(*octbuf & ~3) >> 2];
        highorderbits = (*octbuf++ & 3) << 4;
        *sxtbuf++ = table[highorderbits + ((*octbuf & ~15) >> 4)];
        highorderbits = (*octbuf++ & 15) << 2;
        *sxtbuf++ = table[highorderbits + ((*octbuf & 192) >> 6)];
        *sxtbuf++ = table[*octbuf++ & ~192];
    }
    switch (octbufsize % 3) {
        case 2:
            *sxtbuf++ = table[(*octbuf & ~3) >> 2];
            highorderbits = (*octbuf++ & 3) << 4;
            *sxtbuf++ = table[highorderbits + ((*octbuf & ~15) >> 4)];
            *sxtbuf++ = table[(*octbuf & 15) << 2];
            *sxtbuf++ = PADDING;
            break;
        case 1:
            *sxtbuf++ = table[(*octbuf & ~3) >> 2];
            *sxtbuf++ = table[(*octbuf & 3) << 4];
            *sxtbuf++ = PADDING;
            *sxtbuf++ = PADDING;
            break;
    }

    return sxtbuf-sxtbegin;
}

int
decode(unsigned char *sxtbuf, int sxtbufsize, unsigned char *octbuf)
{
    unsigned char *octbegin;
    unsigned char *sxtleft;
    int highorderbits;
    int loworderbits;

    octbegin = octbuf;
    sxtleft = sxtbuf + sxtbufsize - (sxtbufsize % 4);
    while (sxtbuf < sxtleft) {
        highorderbits = asciitob64[*sxtbuf++] << 2;
        loworderbits = asciitob64[*sxtbuf++];
        *octbuf++ = highorderbits + ((loworderbits & ~15) >> 4);
        highorderbits = (loworderbits & 15) << 4;
        loworderbits = asciitob64[*sxtbuf++];
        *octbuf++ = highorderbits + ((loworderbits & ~3) >> 2);
        *octbuf++ = ((loworderbits & 3) << 6) + asciitob64[*sxtbuf++];
    }
    switch (sxtbufsize % 4) {
        case 3:
            highorderbits = asciitob64[*sxtbuf++] << 2;
            loworderbits = asciitob64[*sxtbuf++];
            *octbuf++ = highorderbits + ((loworderbits & ~15) >> 4);
            highorderbits = (loworderbits & 15) << 4;
            *octbuf++ = highorderbits + ((asciitob64[*sxtbuf++] & ~3) >> 2);
            break;
        case 2:
            highorderbits = asciitob64[*sxtbuf++] << 2;
            *octbuf++ = highorderbits + ((asciitob64[*sxtbuf++] & ~15) >> 4);
            break;
    }

    return octbuf-octbegin;
}