//Vigenere cipher created for CS50 intro to CS course


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

int main(int argc, string argv[])
{
    //Only accept one key word. No more no less.
    if (argc !=2)
    {
        printf("Gimmie ONE key\n");

        return 1;
    }

    //No numbers allowed in key word
    else
    {
        for (int i = 0, n = strlen(argv[1]); i < n; i++)
        {
            if (isdigit(argv[1][i]))
            {
            printf("No numbers! Geez!\n");

            return 1;
            }
        }
    }

    string k = argv[1];

    string p = get_string("Input plaintext: ");

    printf("ciphertext: ");

    for (int i = 0, j = 0, n = strlen(p), klength = strlen(k); i < n; i++)
    {
        //check if plaintext character is a letter
        if (isalpha(p[i]))
        {
            //check if plaintext character is lowercase
            if (islower(p[i]))
            {
                //Check if cipher character is lowercase and make a = 0, b = 1, etc if so.
                if (islower(k[j]))
                {
                    printf("%c", (((p[i] + ((k[j] - 97) % 26) - 97) % 26) + 97));
                }
                //If cipher character is uppercase, make A = 0, B = 1, etc.
                else
                {
                    printf("%c", (((p[i] + ((k[j] - 65) % 26) - 97) % 26) + 97));
                }
            }
            //Same as above but for uppercase plaintext character
            else
            {
                if (islower(k[j]))
                {
                    printf("%c", (((p[i] + ((k[j] - 97) % 26) - 65) % 26) + 65));
                }
                else
                {
                    printf("%c", (((p[i] + ((k[j] - 65) % 26) - 65) % 26) + 65));
                }
            }
            //loop through cipher key
            j = (j + 1) % klength;
        }
        //Simply print character if non-alpha
        else
        {
            printf("%c", p[i]);
        }
    }
    printf("\n");
}