PatternTerm.h

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/*
 * PatternTerm.h
 *
 * Copyright (C) 2015 OpenCog Foundation
 * All Rights Reserved
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License v3 as
 * published by the Free Software Foundation and including the exceptions
 * at http://opencog.org/wiki/Licenses
 *
 * 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 Affero General Public License
 * along with this program; if not, write to:
 * Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Created by Jacek Świergocki <jswiergo@gmail.com> July 2015
 */

#ifndef _OPENCOG_PATTERN_TERM_H
#define _OPENCOG_PATTERN_TERM_H

#include <vector>

#include <opencog/atomspace/Handle.h>
#include <opencog/atomspace/Link.h>

namespace opencog {

class PatternTerm;
typedef std::shared_ptr<PatternTerm> PatternTermPtr;
typedef std::vector<PatternTermPtr> PatternTermSeq;

class PatternTerm
{
    protected:
        Handle _handle;
        PatternTermPtr _parent;
        PatternTermSeq _outgoing;

    public:
        static const PatternTermPtr UNDEFINED;

        PatternTerm()
        {
            _handle = Handle::UNDEFINED;
            _parent = PatternTerm::UNDEFINED;
        }

        PatternTerm(const PatternTermPtr& parent, const Handle& h)
        {
            _parent = parent;
            _handle = h;
        }

        void addOutgoingTerm(const PatternTermPtr& ptm)
        {
            _outgoing.push_back(ptm);
        }

        inline Handle getHandle()
        {
            return _handle;
        };
    
        inline PatternTermPtr getParent()
        {
            return _parent;
        };

        inline const PatternTermSeq& getOutgoingSet() const
        {
            return _outgoing;
        }

        inline Arity getArity() const {
            return _outgoing.size();
        }

        inline PatternTermPtr getOutgoingTerm(Arity pos) const
            throw (RuntimeException)
        {
            // Checks for a valid position
            if (pos < getArity()) {
                return _outgoing[pos];
            } else {
                throw RuntimeException(TRACE_INFO,
                                       "invalid outgoing set index %d", pos);
            }
        }

        inline std::string toString(std::string indent = ":") const
        {
            if (_handle == Handle::UNDEFINED) return "-";
            std::string str = _parent->toString();
            str += indent + std::to_string(_handle.value());
            return str;
        }

};

} // namespace opencog

using namespace opencog;

namespace std {

// We need to overload standard comparison operator for PatternTerm pointers.
// Now we do not care much about complexity of this comparison. The cases of
// queries having repeated atoms that are deep should be very rare. So we just
// traverse up towards root node. Typically we compare only the first level
// handles on this path.
template<>
struct less<PatternTermPtr>
{
    bool operator()(const PatternTermPtr& lhs, const PatternTermPtr& rhs) const
    {
        const Handle& lHandle = lhs->getHandle();
        const Handle& rHandle = rhs->getHandle();
        if (lHandle == rHandle)
        {
            if (lHandle == Handle::UNDEFINED) return false;
            return lhs->getParent() < rhs->getParent();
        }
        return lHandle < rHandle;
    }

};

}; // namespace std;

#endif // _OPENCOG_PATTERN_TERM_H