#include <cs50.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

int shift(char c);
char cipher(int x, char y);

int main(int argc, string argv[])
{

  //save argv 1 to key
  string key = argv[1];
  string text;

  //rest of the code only executes if user enters a word without any numbers
  if (argc != 2) {
    printf("Usage: ./vigenere keyword\n");
    return 1;
  } else {
    for (int i = 0, j = strlen(key); i < j; i++) {
      if (!isalpha(key[i])) {
        printf("Usage: ./vigenere keyword\n");
      }

    }
      text = get_string("plaintext: ");
  }

    printf("ciphertext: ");

    for (int i = 0, j = strlen(text); i < j; i++) {
        if(isspace(text[i])) {
            printf(" ");
        }else{
            for (int a = 0, b = strlen(key); a < b; a++) {
                if (a == b) {
                    a = 0;
                }

               printf("%c", cipher(shift(key[a]),text[i]));
            }
        }
    }

}

int shift(char c) {
  int shift = c;
  if (shift >= 65 && shift <= 90) {
    shift -= 65;
  } else {
    shift -= 97;
  }
  return shift;
}

char cipher(int x, char y) {
  int pc = y;

  if (islower(y)) {
    return ((((pc + x) - 97) % 26) + 97);
  } else {
    return ((((pc + x) - 65) % 26) + 65);
  }

}