/*-
 * 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/param.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/event.h>

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

#include <libcasper.h>
#include <casper/cap_fileargs.h>

#include "extern.h"

static void rlines(FILE *, const char *fn, off_t, struct stat *);
static int show(file_info_t *);
static void set_events(file_info_t *files);

/* defines for inner loop actions */
#define USE_SLEEP       0
#define USE_KQUEUE      1
#define ADD_EVENTS      2

static struct kevent *ev;
static int action = USE_SLEEP;
static int kq;

static const file_info_t *last;

/*
 * forward -- display the file, from an offset, forward.
 *
 * There are eight separate cases for this -- regular and non-regular
 * files, by bytes or lines and from the beginning or end of the file.
 *
 * FBYTES       byte offset from the beginning of the file
 *      REG     seek
 *      NOREG   read, counting bytes
 *
 * FLINES       line offset from the beginning of the file
 *      REG     read, counting lines
 *      NOREG   read, counting lines
 *
 * RBYTES       byte offset from the end of the file
 *      REG     seek
 *      NOREG   cyclically read characters into a wrap-around buffer
 *
 * RLINES
 *      REG     mmap the file and step back until reach the correct offset.
 *      NOREG   cyclically read lines into a wrap-around array of buffers
 */
void
forward(FILE *fp, const char *fn, enum STYLE style, off_t off, struct stat *sbp)
{
        int ch;

        switch(style) {
        case FBYTES:
                if (off == 0)
                        break;
                if (S_ISREG(sbp->st_mode) && sbp->st_size > 0) {
                        if (sbp->st_size < off)
                                off = sbp->st_size;
                        if (fseeko(fp, off, SEEK_SET) == -1) {
                                ierr(fn);
                                return;
                        }
                } else while (off--)
                        if ((ch = getc(fp)) == EOF) {
                                if (ferror(fp)) {
                                        ierr(fn);
                                        return;
                                }
                                break;
                        }
                break;
        case FLINES:
                if (off == 0)
                        break;
                for (;;) {
                        if ((ch = getc(fp)) == EOF) {
                                if (ferror(fp)) {
                                        ierr(fn);
                                        return;
                                }
                                break;
                        }
                        if (ch == '\n' && !--off)
                                break;
                }
                break;
        case RBYTES:
                if (S_ISREG(sbp->st_mode) && sbp->st_size > 0) {
                        if (sbp->st_size >= off &&
                            fseeko(fp, -off, SEEK_END) == -1) {
                                ierr(fn);
                                return;
                        }
                } else if (off == 0) {
                        while (getc(fp) != EOF);
                        if (ferror(fp)) {
                                ierr(fn);
                                return;
                        }
                } else
                        if (bytes(fp, fn, off))
                                return;
                break;
        case RLINES:
                if (S_ISREG(sbp->st_mode) && sbp->st_size > 0)
                        if (!off) {
                                if (fseeko(fp, (off_t)0, SEEK_END) == -1) {
                                        ierr(fn);
                                        return;
                                }
                        } else
                                rlines(fp, fn, off, sbp);
                else if (off == 0) {
                        while (getc(fp) != EOF);
                        if (ferror(fp)) {
                                ierr(fn);
                                return;
                        }
                } else
                        if (lines(fp, fn, off))
                                return;
                break;
        default:
                break;
        }

        while ((ch = getc(fp)) != EOF)
                if (putchar(ch) == EOF)
                        oerr();
        if (ferror(fp)) {
                ierr(fn);
                return;
        }
        (void)fflush(stdout);
}

/*
 * rlines -- display the last offset lines of the file.
 */
static void
rlines(FILE *fp, const char *fn, off_t off, struct stat *sbp)
{
        struct mapinfo map;
        off_t curoff, size;
        int i;

        if (!(size = sbp->st_size))
                return;
        map.start = NULL;
        map.fd = fileno(fp);
        map.mapoff = map.maxoff = size;

        /*
         * Last char is special, ignore whether newline or not. Note that
         * size == 0 is dealt with above, and size == 1 sets curoff to -1.
         */
        curoff = size - 2;
        while (curoff >= 0) {
                if (curoff < map.mapoff && maparound(&map, curoff) != 0) {
                        ierr(fn);
                        return;
                }
                for (i = curoff - map.mapoff; i >= 0; i--)
                        if (map.start[i] == '\n' && --off == 0)
                                break;
                /* `i' is either the map offset of a '\n', or -1. */
                curoff = map.mapoff + i;
                if (i >= 0)
                        break;
        }
        curoff++;
        if (mapprint(&map, curoff, size - curoff) != 0) {
                ierr(fn);
                exit(1);
        }

        /* Set the file pointer to reflect the length displayed. */
        if (fseeko(fp, sbp->st_size, SEEK_SET) == -1) {
                ierr(fn);
                return;
        }
        if (map.start != NULL && munmap(map.start, map.maplen)) {
                ierr(fn);
                return;
        }
}

static int
show(file_info_t *file)
{
        int ch;

        while ((ch = getc(file->fp)) != EOF) {
                if (last != file) {
                        if (vflag || (qflag == 0 && no_files > 1))
                                printfn(file->file_name, 1);
                        last = file;
                }
                if (putchar(ch) == EOF)
                        oerr();
        }
        (void)fflush(stdout);
        if (ferror(file->fp)) {
                fclose(file->fp);
                file->fp = NULL;
                ierr(file->file_name);
                return 0;
        }
        clearerr(file->fp);
        return 1;
}

static void
set_events(file_info_t *files)
{
        int i, n = 0;
        file_info_t *file;
        struct timespec ts;
        struct statfs sf;

        ts.tv_sec = 0;
        ts.tv_nsec = 0;

        action = USE_KQUEUE;
        for (i = 0, file = files; i < no_files; i++, file++) {
                if (!file->fp)
                        continue;

                if (fstatfs(fileno(file->fp), &sf) == 0 &&
                    (sf.f_flags & MNT_LOCAL) == 0) {
                        action = USE_SLEEP;
                        return;
                }

                if (Fflag && fileno(file->fp) != STDIN_FILENO) {
                        EV_SET(&ev[n], fileno(file->fp), EVFILT_VNODE,
                            EV_ADD | EV_ENABLE | EV_CLEAR,
                            NOTE_DELETE | NOTE_RENAME, 0, 0);
                        n++;
                }
                EV_SET(&ev[n], fileno(file->fp), EVFILT_READ,
                    EV_ADD | EV_ENABLE | EV_CLEAR, 0, 0, 0);
                n++;
        }

        if (kevent(kq, ev, n, NULL, 0, &ts) < 0) {
                action = USE_SLEEP;
        }
}

/*
 * follow -- display the file, from an offset, forward.
 *
 */
void
follow(file_info_t *files, enum STYLE style, off_t off)
{
        int active, ev_change, i, n;
        struct stat sb2;
        file_info_t *file;
        FILE *ftmp;
        struct timespec ts;

        /* Position each of the files */
        active = 0;
        for (i = 0, file = files; i < no_files; i++, file++) {
                if (!file->fp)
                        continue;
                active = 1;
                if (vflag || (qflag == 0 && no_files > 1))
                        printfn(file->file_name, 1);
                forward(file->fp, file->file_name, style, off, &file->st);
        }
        if (!Fflag && !active)
                return;

        last = --file;

        kq = kqueue();
        if (kq < 0)
                err(1, "kqueue");
        /*
         * The number of kqueue events we track may vary over time and may
         * even grow past its initial value in the -F case, but it will
         * never exceed two per file, so just preallocate that.
         */
        ev = malloc(no_files * 2 * sizeof(struct kevent));
        if (ev == NULL)
                err(1, "failed to allocate memory for kevents");
        set_events(files);

        for (;;) {
                ev_change = 0;
                if (Fflag) {
                        for (i = 0, file = files; i < no_files; i++, file++) {
                                if (!file->fp) {
                                        file->fp =
                                            fileargs_fopen(fa, file->file_name,
                                            "r");
                                        if (file->fp != NULL &&
                                            fstat(fileno(file->fp), &file->st)
                                            == -1) {
                                                fclose(file->fp);
                                                file->fp = NULL;
                                        }
                                        if (file->fp != NULL)
                                                ev_change++;
                                        continue;
                                }
                                if (fileno(file->fp) == STDIN_FILENO)
                                        continue;
                                ftmp = fileargs_fopen(fa, file->file_name, "r");
                                if (ftmp == NULL ||
                                    fstat(fileno(ftmp), &sb2) == -1) {
                                        if (errno != ENOENT)
                                                ierr(file->file_name);
                                        show(file);
                                        if (file->fp != NULL) {
                                                fclose(file->fp);
                                                file->fp = NULL;
                                        }
                                        if (ftmp != NULL) {
                                                fclose(ftmp);
                                        }
                                        ev_change++;
                                        continue;
                                }

                                if (sb2.st_ino != file->st.st_ino ||
                                    sb2.st_dev != file->st.st_dev ||
                                    sb2.st_nlink == 0) {
                                        show(file);
                                        if (file->fp != NULL)
                                                fclose(file->fp);
                                        file->fp = ftmp;
                                        memcpy(&file->st, &sb2,
                                            sizeof(struct stat));
                                        ev_change++;
                                } else {
                                        fclose(ftmp);
                                }
                        }
                }

                for (i = 0, file = files; i < no_files; i++, file++)
                        if (file->fp && !show(file))
                                ev_change++;

                if (ev_change)
                        set_events(files);

                switch (action) {
                case USE_KQUEUE:
                        ts.tv_sec = 1;
                        ts.tv_nsec = 0;
                        /*
                         * In the -F case we set a timeout to ensure that
                         * we re-stat the file at least once every second.
                         * If we've received EINTR, ignore it. Both reasons
                         * for its generation are transient.
                         */
                        do {
                                n = kevent(kq, NULL, 0, ev, 1, Fflag ? &ts : NULL);
                                if (n < 0 && errno != EINTR)
                                        err(1, "kevent");
                        } while (n < 0);
                        if (n == 0) {
                                /* timeout */
                                break;
                        } else if (ev->filter == EVFILT_READ && ev->data < 0) {
                                /* file shrank, reposition to end */
                                if (lseek(ev->ident, (off_t)0, SEEK_END) == -1) {
                                        ierr(file->file_name);
                                        continue;
                                }
                        }
                        break;

                case USE_SLEEP:
                        (void) usleep(250000);
                        break;
                }
        }
}