/*      $NetBSD: random.c,v 1.16 2021/05/02 12:50:46 rillig Exp $       */

/*
 * Copyright (c) 1994
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Guy Harris at Network Appliance Corp.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#ifndef lint
__COPYRIGHT("@(#) Copyright (c) 1994\
 The Regents of the University of California.  All rights reserved.");
#endif /* not lint */

#ifndef lint
#if 0
static char sccsid[] = "@(#)random.c    8.6 (Berkeley) 6/1/94";
#else
__RCSID("$NetBSD: random.c,v 1.16 2021/05/02 12:50:46 rillig Exp $");
#endif
#endif /* not lint */

#include <sys/types.h>
#include <sys/time.h>

#include <err.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <limits.h>

static void usage(void) __dead;

int
main(int argc, char *argv[])
{
        double denom;
        int ch, random_exit, selected, unbuffer_output;
        char *ep;

        denom = 0;
        random_exit = unbuffer_output = 0;
        while ((ch = getopt(argc, argv, "er")) != -1)
                switch (ch) {
                case 'e':
                        random_exit = 1;
                        break;
                case 'r':
                        unbuffer_output = 1;
                        break;
                default:
                case '?':
                        usage();
                        /* NOTREACHED */
                }

        argc -= optind;
        argv += optind;

        switch (argc) {
        case 0:
                denom = 2;
                break;
        case 1:
                errno = 0;
                denom = strtod(*argv, &ep);
                if (errno == ERANGE)
                        err(1, "%s", *argv);
                if (denom == 0 || *ep != '\0')
                        errx(1, "denominator is not valid.");
                break;
        default:
                usage();
                /* NOTREACHED */
        }

        /* Compute a random exit status between 0 and denom - 1. */
        if (random_exit)
                return arc4random_uniform(denom);

        /*
         * Act as a filter, randomly choosing lines of the standard input
         * to write to the standard output.
         */
        if (unbuffer_output)
                setbuf(stdout, NULL);

        /*
         * Select whether to print the first line.  (Prime the pump.)
         * We find a random number between 0 and denom - 1 and, if it's
         * 0 (which has a 1 / denom chance of being true), we select the
         * line.
         */
        selected = (arc4random_uniform(denom) == 0);
        while ((ch = getchar()) != EOF) {
                if (selected)
                        (void)putchar(ch);
                if (ch == '\n') {
                        /* End of that line.  See if we got an error. */
                        if (ferror(stdout))
                                err(2, "stdout");

                        /* Now see if the next line is to be printed. */
                        selected = (arc4random_uniform(denom) == 0);
                }
        }
        if (ferror(stdin))
                err(2, "stdin");
        exit (0);

        return 0;
}

static void
usage(void)
{

        (void)fprintf(stderr, "usage: random [-er] [denominator]\n");
        exit(1);
}