#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

int main (int argc, char *argv[])
{
    int choice; //command line element 'i', 'o' or 's' interpreted by getopt
    char *ifilename;
        char *ofilename;
    int seed; //stores seed for rand()


    extern char *optarg;
    extern int optind, optopt;



    while((choice = getopt(argc, argv, ":i:o:s:")) != -1)
    //sets variables according to command line arguments
    {
        switch(choice)
        {
        case 'i':
            ifilename = optarg;
            break;
        case 'o':
            ofilename = optarg;
            break;
        case 's':
            seed = atoi(optarg);
            break;
        case ':': //missing operands
            printf("-%c missing operand\n", optopt);
        case '?': //invalid argument
            printf("Invalid argument: -%c\n", optopt);
        }
    }



    FILE *ifile; //file to be encrypted
    FILE *ofile; //storage of encrypted file


    ifile = fopen(ifilename, "r");
    ofile = fopen(ofilename, "w");



    srand(seed);
        int key = rand();

        int c;

    while((c = fgetc(ifile)) != EOF)
    {
        if(ferror(ifile))
        {
            printf("Read error\n");
            clearerr(ifile);
            break;
        }

        else
            fputc(c ^ key, ofile);

        if (ferror(ofile))
        {
            printf("Write error\n");
            clearerr(ofile);
            break;
        }
    }


    fclose(ifile);
    fclose(ofile);

    return 0;
}