/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Edward Sze-Tyan Wang.
 *
 * 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/types.h>
#include <sys/stat.h>
#include <err.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "extern.h"

int Fflag, fflag, qflag, rflag, vflag, rval, no_files;

static void obsolete(char **);
static void usage(void) __dead2;
static void getarg(int, enum STYLE, enum STYLE, enum STYLE *, int *, off_t *);

int
main(int argc, char *argv[])
{
        const char *optstring;
        struct stat sb;
        const char *fn;
        FILE *fp;
        off_t off;
        enum STYLE style;
        int ch, first, style_set;
#ifndef BOOTSTRAPPING
        file_info_t file, *filep, *files;
#endif

        if (strcmp(getprogname(), "tac") == 0) {
                optstring = "";
                qflag = 1;
                rflag = 1;
                vflag = 0;
        } else {
                /* tail */
                optstring = "Fb:c:fn:qrv";
        }

        obsolete(argv);
        style_set = 0;
        off = 0;
        while ((ch = getopt(argc, argv, optstring)) != -1) {
                switch (ch) {
                case 'F':       /* -F is superset of (and implies) -f */
#ifdef BOOTSTRAPPING
                        errx(-1, "follow support disabled");
#else
                        Fflag = fflag = 1;
#endif
                        break;
                case 'b':
                        getarg(512, FBYTES, RBYTES, &style, &style_set, &off);
                        break;
                case 'c':
                        getarg(1, FBYTES, RBYTES, &style, &style_set, &off);
                        break;
                case 'f':
#ifdef BOOTSTRAPPING
                        errx(-1, "follow support disabled");
#else
                        fflag = 1;
#endif
                        break;
                case 'n':
                        getarg(1, FLINES, RLINES, &style, &style_set, &off);
                        break;
                case 'q':
                        qflag = 1;
                        vflag = 0;
                        break;
                case 'r':
                        rflag = 1;
                        break;
                case 'v':
                        vflag = 1;
                        qflag = 0;
                        break;
                case '?':
                default:
                        usage();
                }
        }
        argc -= optind;
        argv += optind;

        no_files = argc ? argc : 1;

        /*
         * If displaying in reverse, don't permit follow option, and convert
         * style values.
         */
        if (rflag) {
                if (fflag)
                        usage();
                if (style == FBYTES)
                        style = RBYTES;
                else if (style == FLINES)
                        style = RLINES;
        }

        /*
         * If style not specified, the default is the whole file for -r, and
         * the last 10 lines if not -r.
         */
        if (!style_set) {
                if (rflag) {
                        off = 0;
                        style = REVERSE;
                } else {
                        off = 10;
                        style = RLINES;
                }
        }

        if (*argv && fflag) {
#ifdef BOOTSTRAPPING
                errx(-1, "follow support disabled");
#else
                files = malloc(no_files * sizeof(struct file_info));
                if (files == NULL)
                        err(1, "failed to allocate memory for file descriptors");

                for (filep = files; (fn = *argv++) != NULL; filep++) {
                        filep->file_name = fn;
                        filep->fp = fopen(filep->file_name, "r");
                        if (filep->fp == NULL ||
                            fstat(fileno(filep->fp), &filep->st) == -1) {
                                if (filep->fp != NULL) {
                                        fclose(filep->fp);
                                        filep->fp = NULL;
                                }
                                if (!Fflag || errno != ENOENT)
                                        ierr(filep->file_name);
                        }
                }
                follow(files, style, off);
                free(files);
#endif
        } else if (*argv) {
                first = 1;
                while ((fn = *argv++) != NULL) {
                        if ((fp = fopen(fn, "r")) == NULL ||
                            fstat(fileno(fp), &sb) == -1) {
                                if (fp != NULL)
                                        fclose(fp);
                                ierr(fn);
                                continue;
                        }
                        if (vflag || (!qflag && argc > 1)) {
                                printfn(fn, !first);
                                first = 0;
                        }

                        if (rflag)
                                reverse(fp, fn, style, off, &sb);
                        else
                                forward(fp, fn, style, off, &sb);
                        fclose(fp);
                }
        } else {
                fn = "stdin";

                if (fstat(fileno(stdin), &sb)) {
                        ierr(fn);
                        exit(1);
                }

                /*
                 * Determine if input is a pipe.  4.4BSD will set the SOCKET
                 * bit in the st_mode field for pipes.  Fix this then.
                 */
                if (lseek(fileno(stdin), 0, SEEK_CUR) == -1 &&
                    errno == ESPIPE) {
                        errno = 0;
                        fflag = 0;              /* POSIX.2 requires this. */
                }

                if (rflag) {
                        reverse(stdin, fn, style, off, &sb);
                } else if (fflag) {
#ifdef BOOTSTRAPPING
                        errx(-1, "follow support disabled");
#else
                        file.file_name = fn;
                        file.fp = stdin;
                        file.st = sb;
                        follow(&file, style, off);
#endif
                } else {
                        forward(stdin, fn, style, off, &sb);
                }
        }
        exit(rval);
}

/*
 * Tail's options are weird.  First, -n10 is the same as -n-10, not
 * -n+10.  Second, the number options are 1 based and not offsets,
 * so -n+1 is the first line, and -c-1 is the last byte.  Third, the
 * number options for the -r option specify the number of things that
 * get displayed, not the starting point in the file.  The one major
 * incompatibility in this version as compared to historical versions
 * is that the 'r' option couldn't be modified by the -lbc options,
 * i.e. it was always done in lines.  This version treats -rc as a
 * number of characters in reverse order.  Finally, the default for
 * -r is the entire file, not 10 lines.
 */
static void
getarg(int units, enum STYLE forward_style, enum STYLE backward_style,
       enum STYLE *style, int *style_set, off_t *off)
{
        char *p;

        if (*style_set)
                usage();

        *off = strtoll(optarg, &p, 10) * units;
        if (*p != '\0')
                errx(1, "illegal offset -- %s", optarg);
        switch (optarg[0]) {
        case '+':
                if (*off != 0)
                        *off -= (units);
                *style = forward_style;
                break;
        case '-':
                *off = -*off;
                /* FALLTHROUGH */
        default:
                *style = backward_style;
                break;
        }

        *style_set = 1;
}

/*
 * Convert the obsolete argument form into something that getopt can handle.
 * This means that anything of the form [+-][0-9][0-9]*[lbc][Ffr] that isn't
 * the option argument for a -b, -c or -n option gets converted.
 */
static void
obsolete(char *argv[])
{
        char *ap, *p, *t;
        size_t len;
        char *start;

        while ((ap = *++argv) != NULL) {
                /* Return if "--" or not an option of any form. */
                if (ap[0] != '-') {
                        if (ap[0] != '+')
                                return;
                } else if (ap[1] == '-')
                        return;

                switch (*++ap) {
                /* Old-style option. */
                case '0': case '1': case '2': case '3': case '4':
                case '5': case '6': case '7': case '8': case '9':

                        /* Malloc space for dash, new option and argument. */
                        len = strlen(*argv);
                        if ((start = p = malloc(len + 3)) == NULL)
                                err(1, "failed to allocate memory");
                        *p++ = '-';

                        /*
                         * Go to the end of the option argument.  Save off any
                         * trailing options (-3lf) and translate any trailing
                         * output style characters.
                         */
                        t = *argv + len - 1;
                        if (*t == 'F' || *t == 'f' || *t == 'r') {
                                *p++ = *t;
                                *t-- = '\0';
                        }
                        switch (*t) {
                        case 'b':
                                *p++ = 'b';
                                *t = '\0';
                                break;
                        case 'c':
                                *p++ = 'c';
                                *t = '\0';
                                break;
                        case 'l':
                                *t = '\0';
                                /* FALLTHROUGH */
                        case '0': case '1': case '2': case '3': case '4':
                        case '5': case '6': case '7': case '8': case '9':
                                *p++ = 'n';
                                break;
                        default:
                                errx(1, "illegal option -- %s", *argv);
                        }
                        *p++ = *argv[0];
                        strcpy(p, ap);
                        *argv = start;
                        continue;

                /*
                 * Options w/ arguments, skip the argument and continue
                 * with the next option.
                 */
                case 'b':
                case 'c':
                case 'n':
                        if (!ap[1])
                                ++argv;
                        /* FALLTHROUGH */
                /* Options w/o arguments, continue with the next option. */
                case 'F':
                case 'f':
                case 'r':
                        continue;

                /* Illegal option, return and let getopt handle it. */
                default:
                        return;
                }
        }
}

static void __dead2
usage(void)
{
        if (strcmp(getprogname(), "tac") == 0) {
                fprintf(stderr, "usage: tac [file ...]\n");
        } else {
                fprintf(stderr,
                        "usage: tail [-F | -f | -r] [-q | -v] "
                        "[-b # | -c # | -n #] [file ...]\n");
        }
        exit(1);
}