/* $Id: tail.c,v 1.14 2004/03/27 13:05:10 doug Exp $
 * 
 * This file is part of EXACT.
 *
 * EXACT 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.
 * 
 * EXACT 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 EXACT; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#include "config.h" /* autoconf generated */

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>

/* autoconf default include instructions */

#if TIME_WITH_SYS_TIME
#    include <sys/time.h>
#    include <time.h>
#else
#    if HAVE_SYS_TIME_H
#        include <sys/time.h>
#    else
#        include <time.h>
#    endif
#endif

#include "conffile.h"
#include "logger.h"

#define PAWS_MAX (1 * 1000000)

FILE 			*f;
unsigned long	paws; // useconds
time_t 			last;
char			*tail_buff;
unsigned int	tail_bufflen;

// taken from comp.unix.questions FAQ
// http://www.faqs.org/faqs/unix-faq/faq/part4/
// used to avoid usleep/SIGALRM issues
int nap(long usec){
	struct timeval tv;
	tv.tv_sec = usec / 1000000L;
	tv.tv_usec = usec % 1000000L;
	return(select(0,NULL,NULL,NULL,&tv));
}

int tail_open() {
	f=fopen(conffile_param("maillog"),"r");
	last=time(NULL);
	paws=PAWS_MAX;
	if(f) {
		fseek(f,0,SEEK_END);
		tail_buff=malloc(1024);
	}
	return(f!=NULL);
}

int linecount(char *buff, int len) {
	int i;
	int ctr=0;
	for(i=0;i<len;++i) {
		if(buff[i]=='\n') ctr++;
	}
	return(ctr);
}

void tail_reopen(long current) {
	long end;
	if(f) fclose(f);
	logger(LOG_DEBUG,"suspicious about file, reopening\n");
    // We should really check the file for various exceptional conditions
    // before opening - check for existence, then permissions, then size
	f=fopen(conffile_param("maillog"),"r");
	if(!f) {
		logger(LOG_NOTICE, "log file '%s' has disappeared.\n",conffile_param("maillog"));
		f=NULL;
		return;
	}
	fseek(f,0,SEEK_END);
	end=ftell(f);
	if(end<current) {  // the file has been rotated
		logger(LOG_DEBUG,"the file has been rotated.\n");
		if(fseek(f,0,SEEK_SET)==-1) {
			logger(LOG_ERR, "Unable to seek to beginning of logfile\n");
			exit(71);
		}
	} else { // it hasn't
		logger(LOG_DEBUG, "the file hasn't been rotated\n");
		if(fseek(f,current,SEEK_SET)==-1) {
			logger(LOG_ERR, "Unable to seek to end of logfile\n");
			exit(71);
		}
	}
}

char *tail_read() {
	long current,end;
	size_t read;
	unsigned int lines;

	if(f==NULL) {
		tail_reopen(0);
		last=time(NULL);
		tail_bufflen=0;
        nap(paws);
		return tail_buff;
	}
	nap(paws);
	current=ftell(f);
	if(fseek(f,0,SEEK_END)==-1) {
		logger(LOG_ERR, "Unable to seek to end of logfile\n");
		exit(71);
	}
	end=ftell(f);
	if(fseek(f,current,SEEK_SET)==-1) {
		logger(LOG_ERR, "Unable to seek to current position\n");
		exit(72);
	}
	if(end>current)
		last=time(NULL);
	if(time(NULL) - last > conffile_param_int("suspicious")) {
		tail_reopen(current);
		last=time(NULL);
		tail_bufflen=0;
		return tail_buff;
	}
	tail_bufflen=end-current;
	logger(LOG_DEBUG,"%ld bytes added to file\n", tail_bufflen);
	if(tail_bufflen>0) {
		tail_buff=(char *)realloc(tail_buff,tail_bufflen+1);
	}
	if(!tail_buff) {
		logger(LOG_ERR,"unable to realloc %d bytes\n", tail_bufflen);
		exit(30);
	}
	read=fread(tail_buff,1,tail_bufflen,f);
	if(read!=tail_bufflen) {
		logger(LOG_ERR,"read %d bytes, wanted %d bytes\n", read, tail_bufflen);
		exit(31);
	}
	tail_buff[tail_bufflen]='\0'; // zero terminate it, so it can be matched
	lines=linecount(tail_buff,tail_bufflen);
	logger(LOG_DEBUG, "read %d lines with a pause of %ld usecs\n", lines, paws);
	if(lines>0) {
		// try and read one line per pause
		paws=paws/lines;
        // integer arithmetic issues
        if(paws==0) paws=1;
	} else {
		// exponential back off to a maximum
		paws=paws*2; 
		paws=paws > PAWS_MAX ? PAWS_MAX : paws;
	}
	return(tail_buff);
}