GetMinPredicatesVisitor.h

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/*
 Copyright (2016) Michael Baer, Daniel Bonrath, All rights reserved.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */

#ifndef __M2ETIS_PUBSUB_FILTER_GETMINPREDICATESVISITOR_H__
#define __M2ETIS_PUBSUB_FILTER_GETMINPREDICATESVISITOR_H__

#include <stack>

#include "m2etis/pubsub/filter/FilterPredicate.h"

namespace m2etis {
namespace pubsub {
namespace filter {

        // implementation of GetMinPredicates algorithm in Bittner
        template <typename EventType>
        class GetMinPredicatesVisitor : public FilterVisitor<EventType> {
        public:
                GetMinPredicatesVisitor() {}

                virtual ~GetMinPredicatesVisitor() {}

                virtual void Visit(const FilterExp<EventType> *) override {}

                virtual void Visit(const AndExp<EventType> *) override {
                        int operand1 = operand_stack_.top();
                        operand_stack_.pop();
                        int operand2 = operand_stack_.top();
                        operand_stack_.pop();

                        operand_stack_.push(operand1 + operand2);
                }

                virtual void Visit(const OrExp<EventType> *) override {
                        int operand1 = operand_stack_.top();
                        operand_stack_.pop();
                        int operand2 = operand_stack_.top();
                        operand_stack_.pop();

                        operand_stack_.push((operand1 < operand2) ? operand1 : operand2); // return minimum
                }

                virtual void Visit(const Predicate<EventType> * predicate) override {
                        operand_stack_.push(1);
                }

                int get_result() const {
                        return operand_stack_.empty() ? 0 : operand_stack_.top();
                }

        private:
                std::stack<int> operand_stack_;  // stack to store operands (=results of 2 children) of GetMinPredicates
        }; // class MatchVisitor

} /* namespace filter */
} /* namespace pubsub */
} /* namespace m2etis */

#endif /* __M2ETIS_PUBSUB_FILTER_GETMINPREDICATESVISITOR_H__ */