// load environment variables from .env file
#include <fstream>
#include <cstdlib>
#include <string>
#include <cstring>

#include <openssl/hmac.h>
#include <openssl/err.h>

void load_env(char const* path)
{
    std::ifstream f(path);
    std::string line;
    while (std::getline(f, line))
    {
        if (line.empty() || line[0] == '#')
            continue;
        auto pos = line.find('=');
        if (pos == std::string::npos)
            continue;

        std::string key = line.substr(0, pos);
        std::string val = line.substr(pos + 1);

#ifdef _WIN32
        _putenv_s(key.c_str(), val.c_str());
#else
        setenv(key.c_str(), val.c_str(), 1);
#endif
    }
}

// hex to byte helper function
int hex_to_bytes_upper(const char *hex, unsigned char *out, size_t out_size)
{
    size_t i = 0;
    while (hex[0] && hex[1])
    {
        if (i >= out_size)
            return -1;
        unsigned char h = hex[0];
        unsigned char l = hex[1];
        int hi = (h <= '9') ? (h - '0') : (h - 'A' + 10);
        int lo = (l <= '9') ? (l - '0') : (l - 'A' + 10);
        // minimal sanity check
        if (hi < 0 || hi > 15 || lo < 0 || lo > 15)
            return -1;
        out[i++] = (unsigned char)((hi << 4) | lo);
        hex += 2;
    }
    return (int)i;
}

char * byte_to_hex(unsigned char *bytes, size_t len)
{
    char *hex = new char[len * 2 + 1];
    for (size_t i = 0; i < len; i++)
    {
        sprintf(hex + i * 2, "%02X", bytes[i]);
    }
    hex[len * 2] = '\0';
    return hex;
}

void cal_hmac(unsigned char *mac, char *message)
{

    /* The secret key for hashing */
    const char *key_str = getenv("HMAC_KEY");
    if (key_str == NULL)
    {
        fprintf(stderr, "HMAC_KEY not set in environment\n");
        return;
    }
    unsigned char key_char[64];
    int key_len = hex_to_bytes_upper(key_str, key_char, sizeof(key_char));
    if (key_len != 64)    {
        fprintf(stderr, "Invalid HMAC_KEY format\n");
        return;
    }
    const char *key = (const char *)key_char;
    // printf("HMAC key: %s\n", byte_to_hex((unsigned char *)key, key_len));

    /* Change the length accordingly with your chosen hash engine.
    * Be careful of the length of string with the chosen hash engine. For
    example, SHA1 needed 20 characters. */
    unsigned int len = 20;
    /* Create and initialize the context */
    HMAC_CTX *ctx = HMAC_CTX_new();
    /* Initialize the HMAC operation. */
    HMAC_Init_ex(ctx, key, key_len, EVP_sha1(), NULL);
    /* Provide the message to HMAC, and start HMAC authentication. */
    HMAC_Update(ctx, (unsigned char *)message, strlen(message));
    /* HMAC_Final() writes the hashed values to md, which must have enough
    space for the hash function output. */
    HMAC_Final(ctx, mac, &len);
    /* Releases any associated resources and finally frees context variable
     */
    HMAC_CTX_free(ctx);
    return;
}