// util.cxx - general-purpose utility functions.
// Copyright (C) 2002  Curtis L. Olson  - http://www.flightgear.org/~curt
//
// 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
//
// $Id$

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <simgear/compiler.h>

#include <math.h>

#include <cstdlib>

#include <vector>

#include <simgear/debug/logstream.hxx>
#include <simgear/math/SGLimits.hxx>
#include <simgear/math/SGMisc.hxx>

#include "fg_io.hxx"
#include "fg_props.hxx"
#include "globals.hxx"
#include "util.hxx"

#ifdef OSG_LIBRARY_STATIC
#include "osgDB/Registry"
#endif

using std::vector;

// Originally written by Alex Perry.
double
fgGetLowPass (double current, double target, double timeratio)
{
    if ( timeratio < 0.0 ) {
        if ( timeratio < -1.0 ) {
                                // time went backwards; kill the filter
                current = target;
        } else {
                                // ignore mildly negative time
        }
    } else if ( timeratio < 0.2 ) {
                                // Normal mode of operation; fast
                                // approximation to exp(-timeratio)
        current = current * (1.0 - timeratio) + target * timeratio;
    } else if ( timeratio > 5.0 ) {
                                // Huge time step; assume filter has settled
        current = target;
    } else {
                                // Moderate time step; non linear response
        double keep = exp(-timeratio);
        current = current * keep + target * (1.0 - keep);
    }

    return current;
}

// Write out path to validation node and read it back in. A Nasal
// listener is supposed to replace the path with a validated version
// or an empty string otherwise.
const char *fgValidatePath (const char *str, bool write)
{
    SGPropertyNode_ptr r, w;
    r = fgGetNode("/sim/paths/validate/read", true);
    r->setAttribute(SGPropertyNode::READ, true);
    r->setAttribute(SGPropertyNode::WRITE, true);

    w = fgGetNode("/sim/paths/validate/write", true);
    w->setAttribute(SGPropertyNode::READ, true);
    w->setAttribute(SGPropertyNode::WRITE, true);

    SGPropertyNode *prop = write ? w : r;
    prop->setStringValue(str);
    const char *result = prop->getStringValue();
    return result[0] ? result : 0;
}

// end of util.cxx