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

int main(int argc, string argv[])

{
    // checks if command line input is 2 or less
    if (argc != 2)
    {
        printf("Usage: ./caesar key\n");
        printf("1");
        return 1;
    }
    else if (argc == 2)
    {
        // check key for validity (positive int)
        // convert argv to int
        const int KEY = atoi(argv[1]);
        // store boolean
        bool KeyValid = true;
        // store key len
        int len = strlen(argv[1]);

        // Loop checking each digit
        for (int i = 0; i < len; i++)
        {
            // if isdigit (part of ctype.h) detects a non-digit turns bool to false
            if (isdigit(argv[1][i]) == false)
            {
                // if anything besides positive int is entered the program will print false and end
                KeyValid = false;
                printf("false\n");
                return 0;
            }
        }
        // if input is positive int, this condition will execute
        if (KeyValid == true)
        {
            // this will prompt user for input
            string plain = get_string("plaintext: ");
            // this determines the length of the user input
            int plainLength = strlen(plain);
            // print "ciphertext: " once before the iteration loop happens
            printf("ciphertext: ");
            // iterate i against the length of plain text entered, basically scanning every character
            for (int i = 0; i < plainLength; i++)
            {
                // turn plain[i] into a character variable, so it can be scanned individually and printed
                char p = plain[i];
                //int ci = (p + KEY) % 26;
                if (isalpha(p) == false)
                {
                    printf("%c", plain[i]);
                }
                if (isupper(p) == true)
                {
                    printf("%c", p + KEY);
                }
                else
                {
                    printf("%c", p + KEY);
                }
            }
            printf("\n");
        }
    }
}