// // // // // // // // // // // // // // // // // // // // // // // // 
//
//   CS270 Class Example
//
//   Author: Robert Heckendorn
//           University of Idaho
//
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include <sys/stat.h>  // modes are here
#include <fcntl.h>     // 
void fileprocessing(char *file, int num) 
{
    int fd;
    int len;
    char buf[] = "A fluffy dog is great.";

    // create file and open for writing only
    if (file==NULL) {
	    fd = 1;  // set to stdout
	    printf("stdout is used.\n");
	    file = "stdin";
    }
    else {
	    if ((fd = creat(file, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH))==-1) {
		    fprintf(stderr, "ERROR: could not create file '%s'\n", file);
	    }
	    else {
		    printf("File %s opened returning file descriptor %d\n", file, fd);
	    }
    }

    // close the created file
    if (close(fd)==-1) {
        fprintf(stderr, "ERROR: failed to close file '%s'\n", file);
    }

    // open it again
    if ((fd = open(file, O_WRONLY))==-1) {   // O_RDONLY or O_RDWR
        fprintf(stderr, "ERROR: could not open file '%s' as write only\n", file);
    }
    else {
        printf("File %s opened returning file descriptor %d\n", file, fd);
    }

    // seek to location num
    if (lseek(fd, num, SEEK_SET)==-1) {  
        fprintf(stderr, "ERROR: could not seek in file '%s' to position %d\n", file, num);
    }

    // write the string
    len = strlen(buf);
    if (write(fd, buf, len)!=len) {  
        fprintf(stderr, "ERROR: could not complete write in file '%s' to position %d\n", file, num);
    }

    // close file
    if (close(fd)==-1) {
        fprintf(stderr, "ERROR: failed to close file '%s'\n", file);
    }
}

int main(int argc, char **argv)
{

    // // // // // // // // // // // // //
    // begin of arg processing
    extern char *optarg; // if takes a value that is returned here
    extern int optind;   // index into argv
    extern int optopt;   // invalid character on error
    extern int opterr;   // set to zero to force getopt to be silent on errors

    int c;
    bool aflg, nflg, fflg, zflg, errflg;
    char *file;
    int num;

    aflg = nflg = fflg = zflg = errflg = false;
    file = NULL;
    num = 0;
    opterr = 0;

    // hunt for a string of options
    while ((c = getopt(argc, argv, "n:f:")) != EOF)
        switch (c) {
        case  'n':
            char *endptr;
	    int tmpnum;

            nflg = true;
            tmpnum = strtol(optarg, &endptr, 10);
            if (*endptr!='\0') {
                fprintf(stderr, "number on -n option: %s is not legal.\n", optarg);
            }
	    else {
                num = tmpnum;
	    }
            break;
        case        'f':
            if (fflg) {
                fprintf(stderr, "-f option can be used only once.  First one is used.\n");
            }
            else {
                fflg = true;
                file = strdup(optarg);
            }
            break;
        case        ':':  // missing argument case
            fprintf(stderr, "%s: option -%c requires an option\n", argv[0], optopt);
            errflg = 1;
            break;

        case        '?':  // bad option case
        default:
            fprintf(stderr, "%s: option -%c is not an option\n", argv[0], optopt);
            errflg = 1;
        }

    // report any errors or usage request
    if (errflg) {
        fprintf(stderr, "usage: %s [-a] [-z] [-o <filename>] files...\n", argv[0]);
// do you want to continue?        exit(2);
    }

    // pick off a nonoptions as if they were files
    for (; optind < argc; optind++) {
        (void)printf("file: %s\n", argv[optind]);
    }
    // end of arg processing
    // // // // // // // // // // // // //

//    if (fflg && nflg) {
    if (1) {
        fileprocessing(file, num);
    }
    else {
        fprintf(stderr, "ERROR: both number and file required\n");
    }

    return 0;
}