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


int main(int argc, string argv[])
{
    //creates alphabetical indexes for both upper and lowercased letters.
    string alphaUpper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    string alphaLower = "abcdefghijklmnopqrstuvwxyz";

    int cipherKey;
    int j = 0;

    if (argc == 2)
    {
        string key = argv[1];
        printf("Argv: %s\n", key);

        //gets input for encryption
        string ptext = get_string("Input: ");
        printf("ciphertext: ");

        //loops thru each character
        for (int i = 0, n = strlen(ptext); i < n; i++)
        {
            //B-A-C-O-N
            //1-0-2-14-13
            printf("J: %i\n", j);

            char c = ptext[i];
            if (isalpha(c))
            {
                //sets the cipherkey based on whether it's upper or lower case
                if (isupper(key[j]))
                {
                    cipherKey = key[j % strlen(key)] - 65;
                    printf("CKey: %i\n", cipherKey);

                }
                else
                {
                    cipherKey = key[j % strlen(key)] - 97;
                    printf("CKey: %i\n", cipherKey);

                }
                //DEFINE THE KEY
                //converts ASCII value to match alphabetical index based on case
                //applies key, then prints result
                if (isupper(c))
                {
                    int alphaIndex = c - 65;
                    int answer = (alphaIndex + cipherKey) % 26;
                    printf("%c", alphaUpper[answer]);
                }
                else
                {
                    int alphaIndex = c - 97;
                    int answer = (alphaIndex + cipherKey) % 26;
                    printf("%c", alphaLower[answer]);
                }

                j++;
            }
            //prints if character is not a letter(i.e. commas, spaces, etc)
            else
            {
                printf("%c", c);
            }
        }
        //pages breaks at end for cleanliness
        printf("\n");
    }
    //Prints error if too many or invalid arguments are given.
    else
    {
        printf("ERROR: Invalid input! Argument must be only one number!\n");
        return 1;
    }

}