/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 2000 Dan Papasian.  All rights reserved.
 * Copyright 2023 OmniOS Community Edition (OmniOSce) Association.
 *
 * 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/fcntl.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <err.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define EXIT_USAGE      2

static void     usage(void) __NORETURN;
static bool     print_matches(char *, const char *const);

static bool     silent = false;
static bool     allpaths = false;

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 = true;
                        break;
                case 's':
                        silent = true;
                        break;
                default:
                        usage();
                        break;
                }
        }

        argv += optind;
        argc -= optind;

        if (argc == 0)
                exit(EXIT_SUCCESS);

        if ((p = getenv("PATH")) == NULL)
                errx(EXIT_FAILURE, "Could not find PATH in environment");

        pathlen = strlen(p);
        path = strdup(p);

        if (path == NULL)
                err(EXIT_FAILURE, "Failed to duplicate PATH");

        while (argc > 0) {
                memcpy(path, p, pathlen + 1);

                if (strlen(*argv) >= FILENAME_MAX) {
                        status = EXIT_FAILURE;

                        warnx("operand too long '%s'", *argv);
                } else if (!print_matches(path, *argv)) {
                        status = EXIT_FAILURE;

                        if (!silent) {
                                (void) printf("no %s in", *argv);

                                if (pathlen > 0) {
                                        char *q = path;
                                        const char *d;

                                        memcpy(q, p, pathlen + 1);

                                        while ((d = strsep(&q, ":")) != NULL) {
                                                (void) printf(" %s",
                                                    *d == '\0' ? "." : d);
                                        }
                                }

                                (void) printf("\n");
                        }
                }

                argv++;
                argc--;
        }

        free(path);
        exit(status);
}

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

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

        if (faccessat(AT_FDCWD, candidate, X_OK, AT_EACCESS) == 0 &&
            stat(candidate, &fin) == 0 &&
            S_ISREG(fin.st_mode)) {
                if (!silent)
                        printf("%s\n", candidate);

                return (true);
        }

        return (false);
}

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

        if (strchr(filename, '/') != NULL)
                return (is_there(filename));

        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 = true;
                        if (!allpaths)
                                break;
                }
        }

        return (found);
}