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

int main(int argc, string argv[])
{
    //handles argv[0] requirements, as per the specifications
    if(argc !=2)
    {
        printf("Error 1: missing, redundant or non-alphabetical command-line argument. Please retry.\n");
        return 1;
    }
    //otherwise go ahead
    string k = argv[1];
    int i;
    int j = 0;
    int sl;
    int p_i;
    int j_mod;
    int k_j;
    int c_i;
    int  rc;

    //prompt user for plaintext
    printf("plaintext: ");
    string p = get_string();


    //ciphertext prompt
    printf("ciphertext: ");

    for(i=0, j=0, sl=strlen(p); i<sl; i++,j++)
    {
        if(isalpha(p[i]))
        {
            p_i = p[i]-65; //convert p[i] to alphabetical index
            j_mod = j % strlen(k);
            k_j = k[j] -65; //convert k[j] to alphabetical index
            c_i = (p_i+k_j)%26; //apply vigenere
            rc = c_i+65; //revert to new ascii index
            printf("%c\n", rc);

            printf("i ia %i, p[i] is %i,%c\n", i, p[i], p[i]);
            printf("j is %i, jmod strlen(k) is %i\n", j, j_mod);
            printf("applying vigenere: c_i = (%i+%i)mod26\n", p_i, k_j);
            printf("rc = %i+65-->%i\n", c_i, rc);

        }
        else
        {
            j--;
            printf("%c", p[i]);
        }
    }


printf("\n");
return 0;
}//END OF MAIN