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

int main(int argc, char* key[])
{
    string k = key[1];
    // checking if totoal number of arcument in 2
        if (argc != 2 )
    {
        printf("Usage: ./substitution key");
        return 1;
    }
    // checking if all the given arguments are letters loop is to check every element
    for (int i  = 0; i <26; i++)
    {
            if (!isalpha(*(k+i)))
            {
                printf("Usage: ./substitution key");
                return 1;
            }
    }

    int len = strlen(k);
    //checking if given argument has length of 26
    if (len != 26)
    {
        printf("Key must contain 26 characters.\n");
        return 1;
    }
    // checking ig there are any duplicate keys
     for (int i=0; i<25; i++)
    {
      for (int j=i+1; j<26; j++)
      {
        if (k[i] == k[j])
        {
          printf("Key must not contain double character.");
          exit (1);
        }
      }
    }
    //getting user input
    string plaintext = get_string("plaintext: ");
    printf("ciphertext: ");
    //converting plain text into cypher text
    for (int i = 0, j = 0, n = strlen(plaintext); i < n; i++)
    {
             if (islower(plaintext[i]))
        {
            printf("%c", tolower(k[plaintext[i] - 97]));
                 j++;
        }
        else if (isupper(plaintext[i]))
        {
            printf("%c", toupper(k[plaintext[i] - 65]));
            j++;
        }
        else
        {
            printf("%c", plaintext[i]);
            j++;
        }
    }
    printf("\n");
    return 0;
}