/*
*i2ctest.c
*	Raspberry Pi I2C test using wiringPi library.
*
*Copyright (c) Nahid Alam. <nahid.mahfuza.alam@gmail.com>
***********************************************************
*i2ctest is free software: you can redistribute it and/or modify
 *    it under the terms of the GNU Lesser General Public License as published by
 *    the Free Software Foundation, either version 3 of the License, or
 *    (at your option) any later version.
 *
 *    i2ctest is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU Lesser General Public License for more details.
 *
***********************************************************
*/

#include <stdio.h>
#include <wiringPi.h>
#include <wiringPiI2C.h>

uint8_t solve_challenge(uint8_t arg) {
  return (arg >> 3) ^ (arg << 3);
}

uint8_t parse_int(const char *s) { // Convert string to hex
  uint8_t result = 0;
  int c;
  if ('0' == *s && 'x' == *(s + 1)) {
    s += 2;
    while (*s) {
      result = result << 4;
      if (c = (*s - '0'), (c >= 0 && c <= 9)) result |= c;
      else if (c = (*s - 'A'), (c >= 0 && c <= 5)) result |= (c + 10);
      else if (c = (*s - 'a'), (c >= 0 && c <= 5)) result |= (c + 10);
      else break;
      ++s;
    }
  }
  return result;
}

int main(int argc, char *argv[]) {

  int fd; // Linux filehandle to the i2c device
  uint8_t challenge;
  uint8_t response;
  uint8_t i2c_addr;

  if (argc != 2) {
    printf("Usage: \n\ti2c_challenge <i2caddr>");
    return 1;
  }
  i2c_addr = parse_int(argv[1]);

  wiringPiSetup();

  fd = wiringPiI2CSetup(i2c_addr); // Initialize the i2c protocol with the address
  if (fd == -1) { // Failed to contact device
    printf("Can't setup the I2C device\n");
    return -1;
  }

  delay(1);

  challenge = wiringPiI2CRead(fd);
  response = solve_challenge(challenge);
  wiringPiI2CWrite(fd, response);

  return 0;
}