/*******************************************************************
*                                                                  *
*             This software is part of the ast package             *
*                Copyright (c) 1992-2004 AT&T Corp.                *
*        and it may only be used by you under license from         *
*                       AT&T Corp. ("AT&T")                        *
*         A copy of the Source Code Agreement is available         *
*                at the AT&T Internet web site URL                 *
*                                                                  *
*       http://www.research.att.com/sw/license/ast-open.html       *
*                                                                  *
*    If you have copied or used this software without agreeing     *
*        to the terms of the license you are infringing on         *
*           the license and copyright and are violating            *
*               AT&T's intellectual property rights.               *
*                                                                  *
*            Information and Software Systems Research             *
*                        AT&T Labs Research                        *
*                         Florham Park NJ                          *
*                                                                  *
*               Glenn Fowler <gsf@research.att.com>                *
*                David Korn <dgk@research.att.com>                 *
*                                                                  *
*******************************************************************/
#pragma prototyped
/*
 * common support for tail and rev
 */

#include	<cmdlib.h>

#define BUFSIZE			SF_BUFSIZE
#define rounddown(n,size)	(((n)-1)&~((size)-1))

/*
 * copy the lines starting at offset <start> from in <in> to <out>
 * in reverse order
 */
int rev_line(Sfio_t *in, Sfio_t *out, off_t start)
{
	register char *cp, *cpold;
	register int n, nleft=0;
	char buff[BUFSIZE];
	off_t offset;
	if(sfseek(in,(off_t)0,SEEK_CUR) < 0)
	{
		Sfio_t *tmp = sftmp(4*SF_BUFSIZE);
		if(!tmp)
			return(-1);
		if(start>0 && sfmove(in, (Sfio_t*)0, start, -1) != start)
			return(-1);
		if(sfmove(in, tmp, SF_UNBOUND, -1) < 0 || !sfeof(in) || sferror(tmp))
			return(-1);
		in = tmp;
		start=0;
	}
	if((offset = sfseek(in,(off_t)0,SEEK_END)) <= start)
		return(0);
	offset = rounddown(offset,BUFSIZE);
	while(1)
	{
		n = BUFSIZE;
		if(offset < start)
		{
			n -= (start-offset);
			offset = start;
		}
		sfseek(in, offset, SEEK_SET);
		if((n=sfread(in, buff, n)) <=0)
			break;
		cp = buff+n;
		n = *buff;
		*buff = '\n';
		while(1)
		{
			cpold = cp;
			if(nleft==0)
				cp--;
			if(cp==buff)
			{
				nleft= 1;
				break;
			}
			while(*--cp != '\n');
			if(cp==buff && n!='\n')
			{
				*cp = n;
				nleft += cpold-cp;
				break;
			}
			else
				cp++;
			if(sfwrite(out,cp,cpold-cp) < 0)
				return(-1);
			if(nleft)
			{
				if(nleft==1)
					sfputc(out,'\n');
				else if(sfmove(in,out,nleft,-1) != nleft)
					return(-1);
				nleft = 0;
			}
		}
		if(offset <= start)
			break;
		offset -= BUFSIZE;
	}
	if(nleft)
	{
		sfseek(in, start, SEEK_SET);
		if(sfmove(in,out,nleft,-1) != nleft)
			return(-1);
	}
	return(0);
}