/*   multitail -- Watch the output from a utility such as multilog
 *   Copyright (C) 2000  Bruce Guenter <bruceg@em.ca>
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "systime.h"
#include "bool.h"

#define BLKSZ 4096

const int FD_STDIN = 0;
const int FD_STDOUT = 1;
const int FD_STDERR = 2;

void print(const char* msg)
{
  write(FD_STDERR, msg, strlen(msg));
}

void warn(const char* msg)
{
  print("multitail: ");
  print(msg);
  print("!\n");
}

void die(const char* msg)
{
  warn(msg);
  exit(1);
}

void warn2(const char* msg1, const char* msg2)
{
  print("multitail: ");
  print(msg1);
  print(msg2);
  print("!\n");
}

void usage(const char* error)
{
  if(error)
    warn(error);
  print("Usage: multitail [-Ee] filename\n"
	"  -E  Seek to end of file before output (default)\n"
	"  -e  Do not seek to end of file before output\n");
  exit(1);
}

static const char* opt_filename;
static bool opt_seek_end = true;

void parse_args(int argc, char** argv)
{
  int ch;
  while((ch = getopt(argc, argv, "Ee")) != -1){
    switch(ch) {
    case 'E': opt_seek_end = true; break;
    case 'e': opt_seek_end = false; break;
    default:  usage(0);
    }
  }
  if(optind+1 != argc)
    usage("Must include exactly one filename");
  opt_filename = argv[optind];
}

void copy(int fd)
{
  char buf[BLKSZ];
  ssize_t rd;
  while((rd = read(fd, buf, BLKSZ)) != 0) {
    if(rd == -1)
      die("Could not read from file");
    while(rd) {
      ssize_t wr = write(FD_STDOUT, buf, rd);
      if(wr == -1)
	die("Could not write to stdout");
      rd -= wr;
    }
  }
}

void multitail(void)
{
  int fd = 0;
  ino_t inode = 0;
  bool first = true;
  
  for(;; sleep(1)) {
    struct stat buf;
    if(!fd) {
      while((fd = open(opt_filename, O_RDONLY)) == -1) {
	warn("Could not open file, sleeping for one minute");
	sleep(60);
      }
      if(first && opt_seek_end) {
	if(lseek(fd, 0, SEEK_END) == -1)
	  die("Could not seek to end of file");
	first = false;
      }
      fstat(fd, &buf);
      inode = buf.st_ino;
    }
    copy(fd);
    if(stat(opt_filename, &buf) == -1)
      warn("Could not stat file");
    else if(buf.st_ino != inode) {
      close(fd);
      fd = 0;
    }
  }
}
    
int main(int argc, char* argv[])
{
  parse_args(argc, argv);
  multitail();
  return 1;
}