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

int key_to_int_reduced(string s_key);
void rotate(string plaintext, int i_key);

int main(int argc, string argv[])
{
    // Print usage and exit if argc is not 2 or key is not integer
    if (argc != 2 || key_to_int_reduced(argv[1]) < 0)
    {
        printf("Usage: ./caesar key\n");
        return 1;
    }
    else
    {
        string s_key = argv[1];
        int i_key = key_to_int_reduced(s_key);
        string plaintext = get_string("plaintext:  ");
        rotate(plaintext, i_key);
    }
    return 0;
}

// Convert a string of numbers to integer
int key_to_int_reduced(string s_key)
{
    int key = 0;

    // Iterate each string element
    for (int i = 0; i < strlen(s_key); i++)
    {
        if (isdigit(s_key[i]))
        {
            key += ((int) s_key[i] - 48);
            if (i < strlen(s_key) - 1)
            {
                key *= 10;
            }
        }
        // Cancel if not digit
        else
        {
            return -1;
        }
    }

    // Reduce key size to < 26
    while (key >= 26)
    {
        key %= 26;
    }
    return key;
}

void rotate(string plaintext, int i_key)
{
    printf("ciphertext: ");

    // Iterate each plaintext element
    for (int i = 0; i < strlen(plaintext); i++)
    {
        // Apply key for text characters only
        if (isalpha(plaintext[i]))
        {
            // Rollover and rotate characters, upper- and lowercase
            if ((isupper(plaintext[i]) && plaintext[i] + i_key > 90) || (islower(plaintext[i]) && plaintext[i] + i_key > 122))
            {
                printf("%c", plaintext[i] + i_key - 26);
            }
            // Rotate characters
            else
            {
                printf("%c", plaintext[i] + i_key);
            }
        }
        // Leave non-alphanumerics as-is
        else
        {
            printf("%c", plaintext[i]);
        }
    }
    printf("\n");
}