/*
 * 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 (c) 2013, Joyent, Inc. All rights reserved.
 */

#include <sys/param.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/statfs.h>
#include <sys/statvfs.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/poll.h>
#include <port.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.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_PORT        1
#define ADD_EVENTS      2

int port;
int action = USE_PORT;

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)) {
                        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)) {
                        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))
                        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) == 0)
                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 && no_files > 1) {
                        if (!qflag)
                                (void) printf("\n==> %s <==\n",
                                    file->file_name);
                        last = file;
                }
                if (putchar(ch) == EOF)
                        oerr();
        }
        (void) fflush(stdout);
        if (ferror(file->fp)) {
                (void) fclose(file->fp);
                file->fp = NULL;
                ierr(file->file_name);
                return (0);
        }
        clearerr(file->fp);
        return (1);
}

static void
associate(file_info_t *file, boolean_t assoc, port_event_t *ev)
{
        char buf[64], *name;
        int i;

        if (action != USE_PORT || file->fp == NULL)
                return;

        if (!S_ISREG(file->st.st_mode)) {
                /*
                 * For FIFOs, we use PORT_SOURCE_FD as our port event source.
                 */
                if (assoc) {
                        (void) port_associate(port, PORT_SOURCE_FD,
                            fileno(file->fp), POLLIN, file);
                } else {
                        (void) port_dissociate(port, PORT_SOURCE_FD,
                            fileno(file->fp));
                }

                return;
        }

        bzero(&file->fobj, sizeof (file->fobj));

        if (!Fflag) {
                /*
                 * PORT_SOURCE_FILE only allows us to specify a file name, not
                 * a file descriptor.  If we are following a specific file (as
                 * opposed to a file name) and we were to specify the name of
                 * the file to port_associate() and that file were moved
                 * aside, we would not be able to reassociate an event because
                 * we would not know a name that would resolve to the new file
                 * (indeed, there might not be such a name -- the file may
                 * have been unlinked).  But there _is_ a name that we know
                 * maps to the file and doesn't change: the name of the
                 * representation of the open file descriptor in /proc.  We
                 * therefore associate with this name (and the underlying
                 * file), not the name of the file as specified at the command
                 * line.  This also has the (desirable) side-effect of
                 * insulating against FILE_RENAME_FROM and FILE_RENAME_TO
                 * events that we need to ignore to assure that we don't lose
                 * FILE_TRUNC events.
                 */
                (void) snprintf(buf,
                    sizeof (buf), "/proc/self/fd/%d", fileno(file->fp));
                name = buf;
        } else {
                name = file->file_name;
        }

        /*
         * Note that portfs uses the address of the specified file_obj_t to
         * tag an association; if one creates a different association with a
         * (different) file_obj_t that happens to be at the same address,
         * the first association will be implicitly removed.  To assure that
         * each association has a disjoint file_obj_t, we allocate the memory
         * for each in the file_info, not on the stack.
         */
        file->fobj[0].fo_name = name;
        file->fobj[1].fo_name = name;

        if (assoc) {
                /*
                 * To assure that we cannot possibly drop a FILE_TRUNC event,
                 * we have two different PORT_SOURCE_FILE associations with the
                 * port:  one to get only FILE_MODIFIED events and another to
                 * get only FILE_TRUNC events.  This assures that we always
                 * have an active association for FILE_TRUNC events when the
                 * seek offset is non-zero.  Note that the association order
                 * _must_ be FILE_TRUNC followed by FILE_MODIFIED:  if a single
                 * event induces both a FILE_TRUNC and a FILE_MODIFIED (as
                 * a VE_CREATE vnode event does), we must process the
                 * FILE_TRUNC before FILE_MODIFIED -- and the order in which
                 * these are processed will be the association order.  So
                 * if we see a FILE_TRUNC, we dissociate/reassociate the
                 * FILE_MODIFIED association.
                 */
                if (ev == NULL || (ev->portev_events & FILE_TRUNC) ||
                    !(ev->portev_events & (FILE_MODIFIED | FILE_TRUNC))) {
                        (void) port_associate(port, PORT_SOURCE_FILE,
                            (uintptr_t)&file->fobj[0], FILE_TRUNC, file);
                        (void) port_dissociate(port, PORT_SOURCE_FILE,
                            (uintptr_t)&file->fobj[1]);
                        ev = NULL;
                }

                if (ev == NULL || (ev->portev_events & FILE_MODIFIED) ||
                    !(ev->portev_events & (FILE_MODIFIED | FILE_TRUNC))) {
                        (void) port_associate(port, PORT_SOURCE_FILE,
                            (uintptr_t)&file->fobj[1], FILE_MODIFIED, file);
                }
        } else {
                for (i = 0; i <= 1; i++) {
                        (void) port_dissociate(port, PORT_SOURCE_FILE,
                            (uintptr_t)&file->fobj[i]);
                }
        }
}

static void
set_events(file_info_t *files)
{
        int i;
        file_info_t *file;

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

                (void) fstat(fileno(file->fp), &file->st);

                associate(file, B_TRUE, NULL);
        }
}

/*
 * 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 = -1;
        struct stat sb2;
        file_info_t *file;
        struct timespec ts;
        port_event_t ev;

        /* Position each of the files */

        file = files;
        active = 0;
        n = 0;
        for (i = 0; i < no_files; i++, file++) {
                if (file->fp) {
                        active = 1;
                        n++;
                        if (no_files > 1 && !qflag)
                                (void) printf("\n==> %s <==\n",
                                    file->file_name);
                        forward(file->fp, file->file_name, style, off,
                            &file->st);
                        if (Fflag && fileno(file->fp) != STDIN_FILENO)
                                n++;
                }
        }
        if (!Fflag && !active)
                return;

        last = --file;

        if (action == USE_PORT &&
            (stat("/proc/self/fd", &sb2) == -1 || !S_ISDIR(sb2.st_mode) ||
            (port = port_create()) == -1))
                action = USE_SLEEP;

        set_events(files);

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

                                if (sb2.st_ino != file->st.st_ino ||
                                    sb2.st_dev != file->st.st_dev ||
                                    sb2.st_nlink == 0) {
                                        (void) show(file);
                                        associate(file, B_FALSE, NULL);
                                        file->fp = freopen(file->file_name, "r",
                                            file->fp);
                                        if (file->fp != NULL) {
                                                (void) memcpy(&file->st, &sb2,
                                                    sizeof (struct stat));
                                        } else if (errno != ENOENT)
                                                ierr(file->file_name);
                                        ev_change++;
                                }
                        }
                }

                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_PORT:
                        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.
                         */
                        n = port_get(port, &ev, Fflag ? &ts : NULL);

                        if (n == 0) {
                                file = (file_info_t *)ev.portev_user;
                                associate(file, B_TRUE, &ev);

                                if (ev.portev_events & FILE_TRUNC)
                                        (void) fseek(file->fp, 0, SEEK_SET);
                        }

                        break;

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