#include <cstring>
#include <iostream>
#include <algorithm>
#include <cstdlib>

static const char chars[26][2] = {
  "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"
};

static int find_pos_from_char(char *item)
{
  for (int i = 0; i < sizeof(chars)/sizeof(chars[0]); i++)
  {
    if (*chars[i] == *item)
    {
      return i;
    }
  }

  return -1;
}

// n = shift
// plain_src = text source
static int caesar_exec(int n, int eod, char* plain_src)
{
  if (n > (sizeof(chars)/sizeof(chars[0]))) {
    return -1;
  } else if (n < 1) {
    n = 23;
  }

  if (eod < 0 || eod > 1)
  {
    // 0 = e
    // 1 = d
    eod = 0;
  }

  for (int i = 0; i < strlen(plain_src); i++)
  {
    if (!std::isspace(plain_src[i]))
    {
      plain_src[i] = static_cast<char>(std::tolower(static_cast<char>(plain_src[i])));
      if (eod == 0) {
        plain_src[i] = *chars[(find_pos_from_char(&plain_src[i]) + n) % 26];
      } else {
        plain_src[i] = *chars[std::abs((find_pos_from_char(&plain_src[i]) - n) % 26)];
      }
    }
  }

  return 0;
}

int main()
{
  char text[] = "abcdefghijklmnopqrstuvwyz";

  if (caesar_exec(23, 0, text) != -1) {
    std::cout << text << std::endl;
    // decrypt
    if (caesar_exec(23, 1, text) != -1) {
      std:: cout << text << std::endl;
    } else {
      std::cout << "fail to decrypt";
    }
  } else {
    std::cout << "fail to encrypt";
  }
  return 0;
}