#include "base64.h"

#include <string.h>

static const char b64chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

size_t b64_encoded_size(size_t inlen) {
    size_t ret;

    ret = inlen;
    if (inlen % 3 != 0)
        ret += 3 - (inlen % 3);
    ret /= 3;
    ret *= 4;

    return ret;
}

char *b64_encode(const uint8_t *in, size_t len) {
    char *out;
    size_t elen;
    size_t i;
    size_t j;
    size_t v;

    if (in == NULL || len == 0)
        return NULL;

    elen      = b64_encoded_size(len);
    out       = (char *) malloc(elen + 1);
    out[elen] = '\0';

    for (i = 0, j = 0; i < len; i += 3, j += 4) {
        v = in[i];
        v = i + 1 < len ? v << 8 | in[i + 1] : v << 8;
        v = i + 2 < len ? v << 8 | in[i + 2] : v << 8;

        out[j]     = b64chars[(v >> 18) & 0x3F];
        out[j + 1] = b64chars[(v >> 12) & 0x3F];
        if (i + 1 < len) {
            out[j + 2] = b64chars[(v >> 6) & 0x3F];
        } else {
            out[j + 2] = '=';
        }
        if (i + 2 < len) {
            out[j + 3] = b64chars[v & 0x3F];
        } else {
            out[j + 3] = '=';
        }
    }

    return out;
}

size_t b64_decoded_size(const char *in) {
    size_t len;
    size_t ret;
    size_t i;

    if (in == NULL)
        return 0;

    len = strlen(in);
    ret = len / 4 * 3;

    for (i = len; i-- > 0;) {
        if (in[i] == '=') {
            ret--;
        } else {
            break;
        }
    }

    return ret;
}

static const int b64invs[] = {
        62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 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, -1, -1, -1, -1, -1,
        -1, 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};

static int b64_isvalidchar(char c) {
    if (c >= '0' && c <= '9')
        return 1;
    if (c >= 'A' && c <= 'Z')
        return 1;
    if (c >= 'a' && c <= 'z')
        return 1;
    if (c == '+' || c == '/' || c == '=')
        return 1;
    return 0;
}

int b64_decode(const char *in, uint8_t *out, size_t outlen) {
    size_t len;
    size_t i;
    size_t j;
    int v;

    if (in == NULL || out == NULL)
        return 0;

    len = strlen(in);
    if (outlen < b64_decoded_size(in) || len % 4 != 0)
        return 0;

    for (i = 0; i < len; i++) {
        if (!b64_isvalidchar(in[i])) {
            return 0;
        }
    }

    for (i = 0, j = 0; i < len; i += 4, j += 3) {
        v = b64invs[in[i] - 43];
        v = (v << 6) | b64invs[in[i + 1] - 43];
        v = in[i + 2] == '=' ? v << 6 : (v << 6) | b64invs[in[i + 2] - 43];
        v = in[i + 3] == '=' ? v << 6 : (v << 6) | b64invs[in[i + 3] - 43];

        out[j] = (v >> 16) & 0xFF;
        if (in[i + 2] != '=')
            out[j + 1] = (v >> 8) & 0xFF;
        if (in[i + 3] != '=')
            out[j + 2] = v & 0xFF;
    }

    return 1;
}