/*************************************************************************
 * Copyright (c) 2011 AT&T Intellectual Property 
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors: Details at https://graphviz.org
 *************************************************************************/

#include	<sfio/sfhdr.h>
#include <stddef.h>

/*	Push/pop streams
**
**	Written by Kiem-Phong Vo.
*/

/**
 * @param f1 base of stack
 * @param f2 top of stack
 */
Sfio_t *sfstack(Sfio_t * f1, Sfio_t * f2)
{
    int n;
    Sfio_t *rf;
    Sfrsrv_t *rsrv;

    if (f1 && (f1->mode & SF_RDWR) != f1->mode && _sfmode(f1, 0, 0) < 0)
	return NULL;
    if (f2 && (f2->mode & SF_RDWR) != f2->mode && _sfmode(f2, 0, 0) < 0)
	return NULL;
    if (!f1)
	return f2;

    /* give access to other internal functions */
    _Sfstack = sfstack;

    if (f2 == SF_POPSTACK) {
	if (!(f2 = f1->push))
	    return NULL;
	f2->mode &= ~SF_PUSH;
    } else {
	if (f2->push)
	    return NULL;
	if (f1->pool && f1->pool != &_Sfpool && f1->pool != f2->pool && f1 == f1->pool->sf[0]) {	/* get something else to pool front since f1 will be locked */
	    for (n = 1; n < f1->pool->n_sf; ++n) {
		if (SFFROZEN(f1->pool->sf[n]))
		    continue;
		_Sfpmove(f1->pool->sf[n], 0);
		break;
	    }
	}
    }

    if (f2->pool && f2->pool != &_Sfpool && f2 != f2->pool->sf[0])
	_Sfpmove(f2, 0);

    /* swap streams */
    sfswap(f1, f2);

    /* but the reserved buffer and mutex must remain the same */
    rsrv = f1->rsrv;
    f1->rsrv = f2->rsrv;
    f2->rsrv = rsrv;

    SFLOCK(f1, 0);
    SFLOCK(f2, 0);

    if (f2->push != f2) {	/* freeze the pushed stream */
	f2->mode |= SF_PUSH;
	f1->push = f2;
	rf = f1;
    } else {			/* unfreeze the just exposed stream */
	f1->mode &= ~SF_PUSH;
	f2->push = NULL;
	rf = f2;
    }

    SFOPEN(f1, 0);
    SFOPEN(f2, 0);

    return rf;
}
