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Skeleton for a Recommendation Engine
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/*
 * Copyright (c) 2013-2016 GraphAware
 *
 * This file is part of the GraphAware Framework.
 *
 * GraphAware Framework 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 3 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, see
 * .
 */

package com.graphaware.reco.generic.policy;

import com.graphaware.reco.generic.context.Context;
import com.graphaware.reco.generic.result.Recommendations;

/**
 * A participation policy for {@link com.graphaware.reco.generic.engine.RecommendationEngine}s deciding whether to participate
 * in the recommendation process for the given input and context.
 */
public interface ParticipationPolicy {

    static ParticipationPolicy ALWAYS = new ParticipationPolicy() {
        @Override
        public boolean participate(Object input, Context context, Recommendations recommendations) {
            return true;
        }
    };

    static ParticipationPolicy NEVER = new ParticipationPolicy() {
        @Override
        public boolean participate(Object input, Context context, Recommendations recommendations) {
            return false;
        }
    };

    static ParticipationPolicy IF_MORE_RESULTS_NEEDED = new ParticipationPolicy() {
        @Override
        public boolean participate(Object input, Context context, Recommendations recommendations) {
            return !recommendations.hasEnoughResults(context.config().limit());
        }
    };

    static ParticipationPolicy IF_ENOUGH_TIME = new ParticipationPolicy() {
        @Override
        public boolean participate(Object input, Context context, Recommendations recommendations) {
            return context.timeLeft();
        }
    };

    static ParticipationPolicy IF_MORE_RESULTS_NEEDED_AND_ENOUGH_TIME = new ParticipationPolicy() {
        @Override
        public boolean participate(Object input, Context context, Recommendations recommendations) {
            return IF_MORE_RESULTS_NEEDED.participate(input, context, recommendations) && IF_ENOUGH_TIME.participate(input, context, recommendations);
        }
    };

    static ParticipationPolicy IF_MORE_RESULTS_NEEDED_OR_ENOUGH_TIME = new ParticipationPolicy() {
        @Override
        public boolean participate(Object input, Context context, Recommendations recommendations) {
            return IF_MORE_RESULTS_NEEDED.participate(input, context, recommendations) || IF_ENOUGH_TIME.participate(input, context, recommendations);
        }
    };

    /**
     * Decide whether to participate or not.
     *
     * @param input           for which recommendations are being computed.
     * @param context         in which recommendations are being computed.
     * @param recommendations recommendations produced so far.
     * @return true iff participate.
     */
    boolean participate(IN input, Context context, Recommendations recommendations);
}