/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1987, 1993, 1994
 *      The Regents of the University of California.  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. 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/param.h>
#include <sys/stat.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static bool     fflag;                  /* Unlink existing files. */
static bool     Fflag;                  /* Remove empty directories also. */
static bool     hflag;                  /* Check new name for symlink first. */
static bool     iflag;                  /* Interactive mode. */
static bool     Pflag;                  /* Create hard links to symlinks. */
static bool     sflag;                  /* Symbolic, not hard, link. */
static bool     vflag;                  /* Verbose output. */
static bool     wflag;                  /* Warn if symlink target does not
                                         * exist, and -f is not enabled. */
static char     linkch;

static int      linkit(const char *, const char *, bool);
static void     link_usage(void) __dead2;
static void     usage(void) __dead2;

int
main(int argc, char *argv[])
{
        struct stat sb;
        char *targetdir;
        int ch, exitval;

        /*
         * Test for the special case where the utility is called as
         * "link", for which the functionality provided is greatly
         * simplified.
         */
        if (strcmp(getprogname(), "link") == 0) {
                while (getopt(argc, argv, "") != -1)
                        link_usage();
                argc -= optind;
                argv += optind;
                if (argc != 2)
                        link_usage();
                if (lstat(argv[1], &sb) == 0)
                        errc(1, EEXIST, "%s", argv[1]);
                /*
                 * We could simply call link(2) here, but linkit()
                 * performs additional checks and gives better
                 * diagnostics.
                 */
                exit(linkit(argv[0], argv[1], false));
        }

        while ((ch = getopt(argc, argv, "FLPfhinsvw")) != -1)
                switch (ch) {
                case 'F':
                        Fflag = true;
                        break;
                case 'L':
                        Pflag = false;
                        break;
                case 'P':
                        Pflag = true;
                        break;
                case 'f':
                        fflag = true;
                        iflag = false;
                        wflag = false;
                        break;
                case 'h':
                case 'n':
                        hflag = true;
                        break;
                case 'i':
                        iflag = true;
                        fflag = false;
                        break;
                case 's':
                        sflag = true;
                        break;
                case 'v':
                        vflag = true;
                        break;
                case 'w':
                        wflag = true;
                        break;
                case '?':
                default:
                        usage();
                }

        argv += optind;
        argc -= optind;

        linkch = sflag ? '-' : '=';
        if (!sflag)
                Fflag = false;
        if (Fflag && !iflag) {
                fflag = true;
                wflag = false;          /* Implied when fflag is true */
        }

        switch (argc) {
        case 0:
                usage();
                /* NOTREACHED */
        case 1:                         /* ln source */
                exit(linkit(argv[0], ".", true));
        case 2:                         /* ln source target */
                exit(linkit(argv[0], argv[1], false));
        default:
                ;
        }
                                        /* ln source1 source2 directory */
        targetdir = argv[argc - 1];
        if (hflag && lstat(targetdir, &sb) == 0 && S_ISLNK(sb.st_mode)) {
                /*
                 * We were asked not to follow symlinks, but found one at
                 * the target--simulate "not a directory" error
                 */
                errno = ENOTDIR;
                err(1, "%s", targetdir);
        }
        if (stat(targetdir, &sb))
                err(1, "%s", targetdir);
        if (!S_ISDIR(sb.st_mode))
                usage();
        for (exitval = 0; *argv != targetdir; ++argv)
                exitval |= linkit(*argv, targetdir, true);
        exit(exitval);
}

/*
 * Two pathnames refer to the same directory entry if the directories match
 * and the final components' names match.
 */
static int
samedirent(const char *path1, const char *path2)
{
        const char *file1, *file2;
        char pathbuf[PATH_MAX];
        struct stat sb1, sb2;

        if (strcmp(path1, path2) == 0)
                return 1;
        file1 = strrchr(path1, '/');
        if (file1 != NULL)
                file1++;
        else
                file1 = path1;
        file2 = strrchr(path2, '/');
        if (file2 != NULL)
                file2++;
        else
                file2 = path2;
        if (strcmp(file1, file2) != 0)
                return 0;
        if (file1 - path1 >= PATH_MAX || file2 - path2 >= PATH_MAX)
                return 0;
        if (file1 == path1)
                memcpy(pathbuf, ".", 2);
        else {
                memcpy(pathbuf, path1, file1 - path1);
                pathbuf[file1 - path1] = '\0';
        }
        if (stat(pathbuf, &sb1) != 0)
                return 0;
        if (file2 == path2)
                memcpy(pathbuf, ".", 2);
        else {
                memcpy(pathbuf, path2, file2 - path2);
                pathbuf[file2 - path2] = '\0';
        }
        if (stat(pathbuf, &sb2) != 0)
                return 0;
        return sb1.st_dev == sb2.st_dev && sb1.st_ino == sb2.st_ino;
}

/*
 * Create a link to source.  If target is a directory (and some additional
 * conditions apply, see comments within) the link will be created within
 * target and have the basename of source.  Otherwise, the link will be
 * named target.  If isdir is true, target has already been determined to
 * be a directory; otherwise, we will check, if needed.
 */
static int
linkit(const char *source, const char *target, bool isdir)
{
        char path[PATH_MAX];
        char wbuf[PATH_MAX];
        char bbuf[PATH_MAX];
        struct stat sb;
        const char *p;
        int ch, first;
        bool append, exists;

        if (!sflag) {
                /* If source doesn't exist, quit now. */
                if ((Pflag ? lstat : stat)(source, &sb)) {
                        warn("%s", source);
                        return (1);
                }
                /* Only symbolic links to directories. */
                if (S_ISDIR(sb.st_mode)) {
                        errno = EISDIR;
                        warn("%s", source);
                        return (1);
                }
        }

        /*
         * Append a slash and the source's basename if:
         * - the target is "." or ends in "/" or "/.", or
         * - the target is a directory (and not a symlink if hflag) and
         *   Fflag is not set
         */
        if ((p = strrchr(target, '/')) == NULL)
                p = target;
        else
                p++;
        append = false;
        if (p[0] == '\0' || (p[0] == '.' && p[1] == '\0')) {
                append = true;
        } else if (!Fflag) {
                if (isdir || (lstat(target, &sb) == 0 && S_ISDIR(sb.st_mode)) ||
                    (!hflag && stat(target, &sb) == 0 && S_ISDIR(sb.st_mode))) {
                        append = true;
                }
        }
        if (append) {
                if (strlcpy(bbuf, source, sizeof(bbuf)) >= sizeof(bbuf) ||
                    (p = basename(bbuf)) == NULL /* can't happen */ ||
                    snprintf(path, sizeof(path), "%s/%s", target, p) >=
                    (ssize_t)sizeof(path)) {
                        errno = ENAMETOOLONG;
                        warn("%s", source);
                        return (1);
                }
                target = path;
        }

        /*
         * If the link source doesn't exist, and a symbolic link was
         * requested, and -w was specified, give a warning.
         */
        if (sflag && wflag) {
                if (*source == '/') {
                        /* Absolute link source. */
                        if (stat(source, &sb) != 0)
                                 warn("warning: %s inaccessible", source);
                } else {
                        /*
                         * Relative symlink source.  Try to construct the
                         * absolute path of the source, by appending `source'
                         * to the parent directory of the target.
                         */
                        strlcpy(bbuf, target, sizeof(bbuf));
                        p = dirname(bbuf);
                        if (p != NULL) {
                                (void)snprintf(wbuf, sizeof(wbuf), "%s/%s",
                                                p, source);
                                if (stat(wbuf, &sb) != 0)
                                        warn("warning: %s", source);
                        }
                }
        }

        /*
         * If the file exists, first check it is not the same directory entry.
         */
        exists = lstat(target, &sb) == 0;
        if (exists) {
                if (!sflag && samedirent(source, target)) {
                        warnx("%s and %s are the same directory entry",
                            source, target);
                        return (1);
                }
        }
        /*
         * Then unlink it forcibly if -f was specified
         * and interactively if -i was specified.
         */
        if (fflag && exists) {
                if (Fflag && S_ISDIR(sb.st_mode)) {
                        if (rmdir(target)) {
                                warn("%s", target);
                                return (1);
                        }
                } else if (unlink(target)) {
                        warn("%s", target);
                        return (1);
                }
        } else if (iflag && exists) {
                fflush(stdout);
                fprintf(stderr, "replace %s? ", target);

                first = ch = getchar();
                while(ch != '\n' && ch != EOF)
                        ch = getchar();
                if (first != 'y' && first != 'Y') {
                        fprintf(stderr, "not replaced\n");
                        return (1);
                }

                if (Fflag && S_ISDIR(sb.st_mode)) {
                        if (rmdir(target)) {
                                warn("%s", target);
                                return (1);
                        }
                } else if (unlink(target)) {
                        warn("%s", target);
                        return (1);
                }
        }

        /* Attempt the link. */
        if (sflag ? symlink(source, target) :
            linkat(AT_FDCWD, source, AT_FDCWD, target,
            Pflag ? 0 : AT_SYMLINK_FOLLOW)) {
                warn("%s", target);
                return (1);
        }
        if (vflag)
                (void)printf("%s %c> %s\n", target, linkch, source);
        return (0);
}

static void
link_usage(void)
{
        (void)fprintf(stderr, "usage: link source_file target_file\n");
        exit(1);
}

static void
usage(void)
{
        (void)fprintf(stderr, "%s\n%s\n",
            "usage: ln [-s [-F] | -L | -P] [-f | -i] [-hnv] source_file [target_file]",
            "       ln [-s [-F] | -L | -P] [-f | -i] [-hnv] source_file ... target_dir");
        exit(1);
}