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Learing to Rank Query w/ RankLib Models

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/*
 * Copyright [2016] Doug Turnbull
 *
 * 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.
 *
 */
package com.o19s.es.ltr.ranker.ranklib;

import java.io.IOException;
import java.util.Map;
import java.util.Objects;

import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.script.ScriptContext;
import org.elasticsearch.script.ScriptEngine;

import com.o19s.es.ltr.ranker.LtrRanker;
import com.o19s.es.ltr.ranker.parser.LtrRankerParserFactory;

/**
 * Created by doug on 12/30/16.
 * The ranklib models are treated like scripts in that they
 * can be run inline, cached, or stored in files
 * However, we don't use the script query because we need to execute
 * many underlying queries.
 * 
 * So this code acts as a hook for deserializing Ranklib models from ranklib XML
 * and as a convenient means for caching those deserialized model
 */
public class RankLibScriptEngine implements ScriptEngine {

    public static final String NAME = "ranklib";
    public static final String EXTENSION = "ranklib";
    public static final ScriptContext CONTEXT =
            new ScriptContext<>("ranklib", RankLibModelContainer.Factory.class);
    private final LtrRankerParserFactory factory;

    public RankLibScriptEngine(Settings settings, LtrRankerParserFactory factory) {
        this.factory = Objects.requireNonNull(factory);
    }


    @Override
    public String getType() {
        return NAME;
    }

    @Override
    public  T compile(String scriptName, String scriptSource, ScriptContext context, Map params) {

        RankLibModelContainer.Factory retFactory = () -> {
            LtrRanker ltrRanker = factory.getParser(RanklibModelParser.TYPE).parse(null, scriptSource);
            return new RankLibModelContainer(ltrRanker);
        };

        return context.factoryClazz.cast(retFactory);
    }

    @Override
    public void close() throws IOException {

    }

    public static class RankLibModelContainer {

        public interface Factory {
            RankLibModelContainer newInstance();
        }

        LtrRanker _ranker;

        public RankLibModelContainer(LtrRanker ranker) {
            _ranker = ranker;
        }

        public void setNextVar(String name, Object value) {
            _ranker = (LtrRanker) (value);

        }

        public Object run() {
            return _ranker;
        }

    }
}