/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 2000 Dan Papasian.  All rights reserved.
 *
 * 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. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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/param.h>
#include <sys/stat.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static void      usage(void);
static int       print_matches(char *, char *);

static int       silent;
static int       allpaths;

int
main(int argc, char **argv)
{
        char *p, *path;
        size_t pathlen;
        int opt, status;

        status = EXIT_SUCCESS;

        while ((opt = getopt(argc, argv, "as")) != -1) {
                switch (opt) {
                case 'a':
                        allpaths = 1;
                        break;
                case 's':
                        silent = 1;
                        break;
                default:
                        usage();
                        break;
                }
        }

        argv += optind;
        argc -= optind;

        if (argc == 0)
                usage();

        if ((p = getenv("PATH")) == NULL)
                exit(EXIT_FAILURE);
        pathlen = strlen(p) + 1;
        path = malloc(pathlen);
        if (path == NULL)
                err(EXIT_FAILURE, NULL);

        while (argc > 0) {
                memcpy(path, p, pathlen);

                if (strlen(*argv) >= FILENAME_MAX ||
                    print_matches(path, *argv) == -1)
                        status = EXIT_FAILURE;

                argv++;
                argc--;
        }

        exit(status);
}

static void
usage(void)
{

        (void)fprintf(stderr, "usage: which [-as] program ...\n");
        exit(EXIT_FAILURE);
}

static int
is_there(char *candidate)
{
        struct stat fin;

        /* XXX work around access(2) false positives for superuser */
        if (access(candidate, X_OK) == 0 &&
            stat(candidate, &fin) == 0 &&
            S_ISREG(fin.st_mode) &&
            (getuid() != 0 ||
            (fin.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH)) != 0)) {
                if (!silent)
                        printf("%s\n", candidate);
                return (1);
        }
        return (0);
}

static int
print_matches(char *path, char *filename)
{
        char candidate[PATH_MAX];
        const char *d;
        int found;

        if (strchr(filename, '/') != NULL)
                return (is_there(filename) ? 0 : -1);
        found = 0;
        while ((d = strsep(&path, ":")) != NULL) {
                if (*d == '\0')
                        d = ".";
                if (snprintf(candidate, sizeof(candidate), "%s/%s", d,
                    filename) >= (int)sizeof(candidate))
                        continue;
                if (is_there(candidate)) {
                        found = 1;
                        if (!allpaths)
                                break;
                }
        }
        return (found ? 0 : -1);
}