/*
 * 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.
 * 4. 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.
 */

/*
 * Copyright 2017, Joyent, Inc.
 */

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

#include <ctype.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, rval, no_files;

file_info_t *files;

static void obsolete(char **);
static void usage(void);

int
main(int argc, char *argv[])
{
        struct stat sb;
        const char *fn;
        FILE *fp;
        off_t off;
        enum STYLE style;
        int i, ch, first;
        file_info_t *file;
        char *p;

        /*
         * 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.
         */
#define ARG(units, forward, backward) {                                 \
        if (style)                                                      \
                usage();                                                \
        off = strtoll(optarg, &p, 10) * (units);                        \
        if (*p)                                                         \
                errx(1, "illegal offset -- %s", optarg);                \
        switch (optarg[0]) {                                            \
        case '+':                                                       \
                if (off)                                                \
                        off -= (units);                                 \
                style = (forward);                                      \
                break;                                                  \
        case '-':                                                       \
                off = -off;                                             \
                /* FALLTHROUGH */                                       \
        default:                                                        \
                style = (backward);                                     \
                break;                                                  \
        }                                                               \
}

        obsolete(argv);
        style = NOTSET;
        off = 0;
        while ((ch = getopt(argc, argv, "Fb:c:fn:qr")) != -1)
                switch (ch) {
                case 'F':       /* -F is superset of (and implies) -f */
                        Fflag = fflag = 1;
                        break;
                case 'b':
                        ARG(512, FBYTES, RBYTES);
                        break;
                case 'c':
                        ARG(1, FBYTES, RBYTES);
                        break;
                case 'f':
                        fflag = 1;
                        break;
                case 'n':
                        ARG(1, FLINES, RLINES);
                        break;
                case 'q':
                        qflag = 1;
                        break;
                case 'r':
                        rflag = 1;
                        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 == NOTSET) {
                if (rflag) {
                        off = 0;
                        style = REVERSE;
                } else {
                        off = 10;
                        style = RLINES;
                }
        }

        if (*argv && fflag) {
                files = (struct file_info *)malloc(no_files *
                    sizeof (struct file_info));
                if (!files)
                        err(1, "Couldn't malloc space for file descriptors.");

                for (file = files; (fn = *argv++); file++) {
                        file->file_name = strdup(fn);
                        if (! file->file_name)
                                errx(1, "Couldn't malloc space for file name.");
                        if ((file->fp = fopen(file->file_name, "r")) == NULL ||
                            fstat(fileno(file->fp), &file->st)) {
                                if (file->fp != NULL) {
                                        (void) fclose(file->fp);
                                        file->fp = NULL;
                                }
                                if (!Fflag || errno != ENOENT)
                                        ierr(file->file_name);
                        }
                }
                follow(files, style, off);
                for (i = 0, file = files; i < no_files; i++, file++) {
                    free(file->file_name);
                }
                free(files);
        } else if (*argv) {
                for (first = 1; (fn = *argv++); ) {
                        if ((fp = fopen(fn, "r")) == NULL ||
                            fstat(fileno(fp), &sb)) {
                                ierr(fn);
                                continue;
                        }
                        if (argc > 1 && !qflag) {
                                (void) printf("%s==> %s <==\n",
                                    first ? "" : "\n", fn);
                                first = 0;
                                (void) fflush(stdout);
                        }

                        if (rflag)
                                reverse(fp, fn, style, off, &sb);
                        else
                                forward(fp, fn, style, off, &sb);
                }
        } 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), (off_t)0, SEEK_CUR) == -1 &&
                    errno == ESPIPE) {
                        errno = 0;
                        fflag = 0;              /* POSIX.2 requires this. */
                }

                if (rflag)
                        reverse(stdin, fn, style, off, &sb);
                else
                        forward(stdin, fn, style, off, &sb);
        }
        exit(rval);
}

static boolean_t
iscount(const char *ap)
{
        char c;

        if (ap == NULL) {
                return (B_FALSE);
        }

        c = ap[0];

        if (c == '+' || c == '-') {
                c = ap[1];
        }

        return (isdigit(c) ? B_TRUE : B_FALSE);
}

/*
 * 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)) {
                /* 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, "malloc");
                        *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];
                        (void) strcpy(p, ap);
                        *argv = start;
                        continue;

                /*
                 * Legacy Solaris tail supports "+c" "-c", "+l", "-l",
                 * "+b", and "-b" with a default value of 10. We need
                 * to determine here whether or not a count has been
                 * provided after the flag, and create a new, explicit
                 * argument as appropriate. [+-]l isn't allowed to have
                 * any numbers after it, but [+-][bc] can, potentially
                 * in the next command-line argument. We therefore
                 * handle them in two separate cases below.
                 */
                case 'l':
                        len = strlen(ap);
                        start = NULL;

                        if (len > 2) {
                                errx(1, "illegal option -- %s", *argv);
                        }

                        /* The only characters following should be flags */
                        if (len == 2 && !isalpha(ap[1])) {
                                errx(1, "illegal option -- %s", *argv);
                        }

                        if (asprintf(&start, "-%sn%c10",
                            ap + 1, *argv[0]) == -1) {
                                err(1, "asprintf");
                        }

                        *argv = start;

                        continue;
                case 'b':
                case 'c':
                        len = strlen(ap);
                        start = NULL;

                        if (len == 1) {
                                /*
                                 * The option is just the flag name. Check if
                                 * the next argument is a count, so we know
                                 * whether we need to default to 10.
                                 */
                                if (iscount(argv[1])) {
                                        ++argv;
                                        continue;
                                } else {
                                        if (asprintf(&start,
                                            "-%c%c10", ap[0], *argv[0]) == -1) {
                                                err(1, "asprintf");
                                        }
                                }
                        } else {
                                /*
                                 * The option has characters following the c/b.
                                 * If the characters following the option are a
                                 * count, then we use those. This invocation is
                                 * only allowed when '-' is used.
                                 *
                                 * Otherwise, we need to honor the following
                                 * flags, and default to 10.
                                 */
                                if (iscount(ap + 1)) {
                                        if (*argv[0] != '-') {
                                                errx(1, "illegal option -- %s",
                                                    *argv);
                                        }

                                        if (asprintf(&start, "-%c%s",
                                            ap[0], ap + 1) == -1) {
                                                err(1, "asprintf");
                                        }
                                } else {
                                        if (asprintf(&start, "-%s%c%c10",
                                            ap + 1, ap[0], *argv[0]) == -1) {
                                                err(1, "asprintf");
                                        }
                                }
                        }

                        *argv = start;

                        continue;
                /*
                 * Options w/ arguments, skip the argument and continue
                 * with the next option.
                 */
                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
usage(void)
{
        (void) fprintf(stderr,
            "usage: tail [-F | -f | -r] [-q] [-b # | -c # | -n #]"
            " [file ...]\n");
        exit(1);
}