/**
 * @copyright
 *
 * Tencent is pleased to support the open source community by making IoT Hub available.
 * Copyright(C) 2018 - 2021 THL A29 Limited, a Tencent company.All rights reserved.
 *
 * Licensed under the MIT License(the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 * http://opensource.org/licenses/MIT
 *
 * 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.
 *
 * @file utils_base64.c
 * @brief base64 encdoe & decode. Reference mbedtls/base64.c.
 * @author fancyxu (fancyxu@tencent.com)
 * @version 1.0
 * @date 2021-05-27
 *
 * @par Change Log:
 * <table>
 * <tr><th>Date       <th>Version <th>Author    <th>Description
 * <tr><td>2021-05-27 <td>1.0     <td>fancyxu   <td>first commit
 * </table>
 */

#include "utils_base64.h"

static const unsigned char base64_enc_map[64] = {
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
    'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
    's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'};

static const unsigned char base64_dec_map[128] = {
    127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
    127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 62,
    127, 127, 127, 63,  52,  53,  54,  55,  56,  57,  58,  59,  60,  61,  127, 127, 127, 64,  127, 127, 127, 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,  127, 127, 127, 127, 127, 127, 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,  127, 127, 127, 127, 127};

#define BASE64_SIZE_T_MAX ((size_t)-1) /* SIZE_T_MAX is not standard */

/**
 * @brief Check if src buf and dst buf.
 *
 * @param[in] dst destination buffer
 * @param[in] dlen size of the destination buffer
 * @param[in] src source buffer
 * @param[in] slen amount of data to be encoded
 * @return 0 for valid, -1 for invalid
 */
static int _utils_base64_check_valid(unsigned char *dst, size_t dlen, const unsigned char *src, size_t slen)
{
    size_t   i, n;
    uint32_t j, x;

    /* First pass: check for validity and get output length */
    for (i = n = j = 0; i < slen; i++) {
        /* Skip spaces before checking for EOL */
        x = 0;
        while (i < slen && src[i] == ' ') {
            ++i;
            ++x;
        }

        /* Spaces at end of buffer are OK */
        if (i == slen)
            break;

        if ((slen - i) >= 2 && src[i] == '\r' && src[i + 1] == '\n')
            continue;

        if (src[i] == '\n')
            continue;

        /* Space inside a line is an error */
        if (x != 0)
            return -1;

        if (src[i] == '=' && ++j > 2)
            return -1;

        if (src[i] > 127 || base64_dec_map[src[i]] == 127)
            return -1;

        if (base64_dec_map[src[i]] < 64 && j != 0)
            return -1;

        n++;
    }

    // if no useful data, means error
    if (n == 0) {
        return -1;
    }

    /* The following expression is to calculate the following formula without
     * risk of integer overflow in n:
     *     n = ( ( n * 6 ) + 7 ) >> 3;
     */
    n = (6 * (n >> 3)) + ((6 * (n & 0x7) + 7) >> 3);
    n -= j;

    if (!dst || dlen < n) {
        return -1;
    }

    return 0;
}

/**
 * @brief Encode a buffer into base64 format.
 *
 * @param[out] dst destination buffer
 * @param[in] dlen size of the destination buffer
 * @param[out] olen number of bytes written
 * @param[in] src source buffer
 * @param[in] slen amount of data to be encoded
 * @return 0 if successful, or MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL.
 *         *olen is always updated to reflect the amount
 *         of data that has (or would have) been written.
 *         If that length cannot be represented, then no data is
 *         written to the buffer and *olen is set to the maximum
 *         length representable as a size_t.
 *
 * @note Call this function with dlen = 0 to obtain the
 *       required buffer size in *olen
 */
int utils_base64encode(unsigned char *dst, size_t dlen, size_t *olen, const unsigned char *src, size_t slen)
{
    size_t         i, n;
    unsigned char *p;

    if (slen == 0) {
        *olen = 0;
        return 0;
    }

    n = slen / 3 + (slen % 3 != 0);

    if (n > (BASE64_SIZE_T_MAX - 1) / 4) {
        *olen = BASE64_SIZE_T_MAX;
        return -1;
    }

    n *= 4;

    if ((dlen < n + 1) || (NULL == dst)) {
        *olen = n + 1;
        return -1;
    }

    n = (slen / 3) * 3;

    int C1, C2, C3;
    for (i = 0, p = dst; i < n; i += 3) {
        C1 = *src++;
        C2 = *src++;
        C3 = *src++;

        *p++ = base64_enc_map[(C1 >> 2) & 0x3F];
        *p++ = base64_enc_map[(((C1 & 3) << 4) + (C2 >> 4)) & 0x3F];
        *p++ = base64_enc_map[(((C2 & 15) << 2) + (C3 >> 6)) & 0x3F];
        *p++ = base64_enc_map[C3 & 0x3F];
    }

    if (i < slen) {
        C1 = *src++;
        C2 = ((i + 1) < slen) ? *src++ : 0;

        *p++ = base64_enc_map[(C1 >> 2) & 0x3F];
        *p++ = base64_enc_map[(((C1 & 3) << 4) + (C2 >> 4)) & 0x3F];

        if ((i + 1) < slen)
            *p++ = base64_enc_map[((C2 & 15) << 2) & 0x3F];
        else
            *p++ = '=';

        *p++ = '=';
    }

    *olen = p - dst;
    *p    = 0;

    return 0;
}

/**
 * @brief Decode a base64-formatted buffer.
 *
 * @param[out] dst destination buffer (can be NULL for checking size)
 * @param[in] dlen size of the destination buffer
 * @param[out] olen number of bytes written
 * @param[in] src source buffer
 * @param[in] slen amount of data to be decoded
 * @return 0 if successful, MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL, or
 *         MBEDTLS_ERR_BASE64_INVALID_CHARACTER if the input data is
 *         not correct. *olen is always updated to reflect the amount
 *         of data that has (or would have) been written.
 *
 * @note Call this function with *dst = NULL or dlen = 0 to obtain
 *       the required buffer size in *olen
 */
int utils_base64decode(unsigned char *dst, size_t dlen, size_t *olen, const unsigned char *src, size_t slen)
{
    size_t         i, n;
    uint32_t       j, x;
    unsigned char *p;

    /* First pass: check for validity and get output length */
    if (_utils_base64_check_valid(dst, dlen, src, slen)) {
        *olen = 0;
        return -1;
    }

    for (i = slen, j = 3, n = x = 0, p = dst; i > 0; i--, src++) {
        if (*src == '\r' || *src == '\n' || *src == ' ')
            continue;

        j -= (base64_dec_map[*src] == 64);
        x = (x << 6) | (base64_dec_map[*src] & 0x3F);

        if (++n == 4) {
            n = 0;
            if (j > 0)
                *p++ = (unsigned char)(x >> 16);
            if (j > 1)
                *p++ = (unsigned char)(x >> 8);
            if (j > 2)
                *p++ = (unsigned char)(x);
        }
    }

    *olen = p - dst;

    return 0;
}