#include "encode.h"

#define PADDING '='

unsigned char b64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" \
                      "abcdefghijklmnopqrstuvwxyz" \
                      "0123456789" \
                      "+/";

unsigned char b64url[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" \
                         "abcdefghijklmnopqrstuvwxyz" \
                         "0123456789" \
                         "-_";

int
encode(unsigned char *op, int olen, unsigned char *sp, int url)
{
    int tmp;
    unsigned char *table;
    unsigned char *sbeg;
    unsigned char *tend;

    table = (!url) ? b64 : b64url;

    sbeg = sp;
    tend = op + olen - (olen % 3);
    while (op < tend) {
        *sp++ = table[(*op & ~3) >> 2];
        tmp = (*op++ & 3) << 4;
        *sp++ = table[tmp + ((*op & ~15) >> 4)];
        tmp = (*op++ & 15) << 2;
        *sp++ = table[tmp + ((*op & 192) >> 6)];
        *sp++ = table[*op++ & ~192];
    }
    switch (olen % 3) {
        case 2:
            *sp++ = table[(*op & ~3) >> 2];
            tmp = (*op++ & 3) << 4;
            *sp++ = table[tmp + ((*op & ~15) >> 4)];
            *sp++ = table[(*op & 15) << 2];
            *sp++ = PADDING;
            break;
        case 1:
            *sp++ = table[(*op & ~3) >> 2];
            *sp++ = table[(*op & 3) << 4];
            *sp++ = PADDING;
            *sp++ = PADDING;
            break;
    }

    return sp-sbeg;
}

int
decode(unsigned char *sp, int slen, unsigned char *op, int url)
{
    int tmp, b, atob(int c, int url);
    unsigned char *obeg;
    unsigned char *qend;

    obeg = op;
    qend = sp + slen - (slen % 4);
    while (sp < qend) {
        tmp = atob(*sp++, url) << 2;
        b = atob(*sp++, url);
        *op++ = tmp + ((b & ~15) >> 4);
        tmp = (b & 15) << 4;
        b = atob(*sp++, url);
        *op++ = tmp + ((b & ~3) >> 2);
        *op++ = ((b & 3) << 6) + atob(*sp++, url);
    }
    switch (slen % 4) {
        case 3:
            tmp = atob(*sp++, url) << 2;
            b = atob(*sp++, url);
            *op++ = tmp + ((b & ~15) >> 4);
            tmp = (b & 15) << 4;
            *op++ = tmp + ((atob(*sp++, url) & ~3) >> 2);
            break;
        case 2:
            tmp = atob(*sp++, url) << 2;
            *op++ = tmp + ((atob(*sp++, url) & ~15) >> 4);
            break;
    }

    return op-obeg;
}

int atob(int c, int url)
{
    if (c >= 'A' && c <= 'Z')
        c -= 'A';
    else if (c >= 'a' && c <= 'z')
        c = c - 'a' + 26;
    else if (c >= '0' && c <= '9')
        c = c - '0' + 26 * 2;
    else if (c == ((!url) ? '+' : '-'))
        c = 62;
    else
        c = 63;

    return c;
}