/*
MIT License

Copyright (c) 2019 Weravech

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

https://github.com/Netthaw/TOTP-MCU
*/
#include "sha1.h"
#include "topt.h"



uint8_t* _hmacKey;
uint8_t _keyLength;
uint8_t _timeZoneOffset;
uint32_t _timeStep;

// Init the library with the private key, its length and the timeStep duration
void TOTP(uint8_t* hmacKey, uint8_t keyLength, uint32_t timeStep) {
  _hmacKey = hmacKey;
  _keyLength = keyLength;
  _timeStep = timeStep;
}

void setTimezone(uint8_t timezone) { _timeZoneOffset = timezone; }

uint32_t TimeStruct2Timestamp(struct tm time) {
  // time.tm_mon -= 1;
  // time.tm_year -= 1900;
  return mktime(&(time)) - (_timeZoneOffset * 3600) - 2208988800;
}

// Generate a code, using the timestamp provided
uint32_t getCodeFromTimestamp(uint32_t timeStamp) {
  uint32_t steps = timeStamp / _timeStep;
  return getCodeFromSteps(steps);
}

// Generate a code, using the timestamp provided
uint32_t getCodeFromTimeStruct(struct tm time) {
  return getCodeFromTimestamp(TimeStruct2Timestamp(time));
}

// Generate a code, using the number of steps provided
uint32_t getCodeFromSteps(uint32_t steps) {
  // STEP 0, map the number of steps in a 8-bytes array (counter value)
  uint8_t _byteArray[8];
  _byteArray[0] = 0x00;
  _byteArray[1] = 0x00;
  _byteArray[2] = 0x00;
  _byteArray[3] = 0x00;
  _byteArray[4] = (uint8_t)((steps >> 24) & 0xFF);
  _byteArray[5] = (uint8_t)((steps >> 16) & 0xFF);
  _byteArray[6] = (uint8_t)((steps >> 8) & 0XFF);
  _byteArray[7] = (uint8_t)((steps & 0XFF));

  // STEP 1, get the HMAC-SHA1 hash from counter and key
  initHmac(_hmacKey, _keyLength);
  writeArray(_byteArray, 8);
  uint8_t* _hash = resultHmac();

  // STEP 2, apply dynamic truncation to obtain a 4-bytes string
  uint32_t _truncatedHash = 0;
  uint8_t _offset = _hash[20 - 1] & 0xF;
  uint8_t j;
  for (j = 0; j < 4; ++j) {
    _truncatedHash <<= 8;
    _truncatedHash |= _hash[_offset + j];
  }

  // STEP 3, compute the OTP value
  _truncatedHash &= 0x7FFFFFFF;  // Disabled
  _truncatedHash %= 1000000;

  return _truncatedHash;
}