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/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you 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 org.elasticsearch.search.suggest.phrase;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Terms;
import org.apache.lucene.util.BytesRef;
import org.elasticsearch.search.suggest.SuggestUtils;
import org.elasticsearch.search.suggest.phrase.DirectCandidateGenerator.Candidate;

import java.io.IOException;
//TODO public for tests
public final class LaplaceScorer extends WordScorer {
    
    public static final WordScorerFactory FACTORY = new WordScorer.WordScorerFactory() {
        @Override
        public WordScorer newScorer(IndexReader reader, Terms terms, String field, double realWordLikelyhood, BytesRef separator) throws IOException {
            return new LaplaceScorer(reader, terms, field, realWordLikelyhood, separator, 0.5);
        }
    };
    
    private double alpha;

    public LaplaceScorer(IndexReader reader, Terms terms, String field,
            double realWordLikelyhood, BytesRef separator, double alpha) throws IOException {
        super(reader, terms, field, realWordLikelyhood, separator);
        this.alpha = alpha;
    }
    
    @Override
    protected double scoreBigram(Candidate word, Candidate w_1) throws IOException {
        SuggestUtils.join(separator, spare, w_1.term, word.term);
        return (alpha + frequency(spare.get())) / (alpha +  w_1.frequency + vocabluarySize);
    }

    @Override
    protected double scoreTrigram(Candidate word, Candidate w_1, Candidate w_2) throws IOException {
        SuggestUtils.join(separator, spare, w_2.term, w_1.term, word.term);
        long trigramCount = frequency(spare.get());
        SuggestUtils.join(separator, spare, w_1.term, word.term);
        return (alpha + trigramCount) / (alpha  +  frequency(spare.get()) + vocabluarySize);
    }


}