package org.apache.lucene.search.highlight;

/**
 * Copyright 2002-2004 The Apache Software Foundation
 *
 * 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.
 */

import java.io.IOException;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.BooleanClause;
import org.apache.lucene.search.BooleanQuery;
import org.apache.lucene.search.PhraseQuery;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.TermQuery;
import org.apache.lucene.search.spans.SpanNearQuery;

/**
 * Utility class used to extract the terms used in a query, plus any weights.
 * This class will not find terms for MultiTermQuery, RangeQuery and PrefixQuery
 * classes so the caller must pass a rewritten query (see Query.rewrite) to
 * obtain a list of expanded terms.
 */
public final class QueryTermExtractor
{

	/**
	 * Extracts all terms texts of a given Query into an array of WeightedTerms
	 * 
	 * @param query
	 *        Query to extract term texts from
	 * @return an array of the terms used in a query, plus their weights.
	 */
	public static final WeightedTerm[] getTerms(Query query)
	{
		return getTerms(query, false);
	}

	/**
	 * Extracts all terms texts of a given Query into an array of WeightedTerms
	 * 
	 * @param query
	 *        Query to extract term texts from
	 * @param reader
	 *        used to compute IDF which can be used to a) score selected
	 *        fragments better b) use graded highlights eg chaning intensity of
	 *        font color
	 * @param fieldName
	 *        the field on which Inverse Document Frequency (IDF) calculations
	 *        are based
	 * @return an array of the terms used in a query, plus their weights.
	 */
	public static final WeightedTerm[] getIdfWeightedTerms(Query query,
			IndexReader reader, String fieldName)
	{
		WeightedTerm[] terms = getTerms(query, false, fieldName);
		int totalNumDocs = reader.numDocs();
		for (int i = 0; i < terms.length; i++)
		{
			try
			{
				int docFreq = reader
						.docFreq(new Term(fieldName, terms[i].term));
				// IDF algorithm taken from DefaultSimilarity class
				float idf = (float) (Math.log((float) totalNumDocs
						/ (double) (docFreq + 1)) + 1.0);
				terms[i].weight *= idf;
			}
			catch (IOException e)
			{
				// ignore
			}
		}
		return terms;
	}

	/**
	 * Extracts all terms texts of a given Query into an array of WeightedTerms
	 * 
	 * @param query
	 *        Query to extract term texts from
	 * @param prohibited
	 *        <code>true</code> to extract "prohibited" terms, too
	 * @param fieldName
	 *        The fieldName used to filter query terms
	 * @return an array of the terms used in a query, plus their weights.
	 */
	public static final WeightedTerm[] getTerms(Query query,
			boolean prohibited, String fieldName)
	{
		HashSet terms = new HashSet();
		if (fieldName != null)
		{
			fieldName = fieldName.intern();
		}
		getTerms(query, terms, prohibited, fieldName);
		return (WeightedTerm[]) terms.toArray(new WeightedTerm[0]);
	}

	/**
	 * Extracts all terms texts of a given Query into an array of WeightedTerms
	 * 
	 * @param query
	 *        Query to extract term texts from
	 * @param prohibited
	 *        <code>true</code> to extract "prohibited" terms, too
	 * @return an array of the terms used in a query, plus their weights.
	 */
	public static final WeightedTerm[] getTerms(Query query, boolean prohibited)
	{
		return getTerms(query, prohibited, null);
	}

	// fieldname MUST be interned prior to this call
	private static final void getTerms(Query query, HashSet terms,
			boolean prohibited, String fieldName)
	{
		if (query instanceof BooleanQuery)
			getTermsFromBooleanQuery((BooleanQuery) query, terms, prohibited,
					fieldName);
		else if (query instanceof PhraseQuery)
			getTermsFromPhraseQuery((PhraseQuery) query, terms, fieldName);
		else if (query instanceof TermQuery)
			getTermsFromTermQuery((TermQuery) query, terms, fieldName);
		else if (query instanceof SpanNearQuery)
			getTermsFromSpanNearQuery((SpanNearQuery) query, terms, fieldName);
	}

	private static final void getTermsFromBooleanQuery(BooleanQuery query,
			HashSet terms, boolean prohibited, String fieldName)
	{
		BooleanClause[] queryClauses = query.getClauses();
		int i;

		for (i = 0; i < queryClauses.length; i++)
		{
			// Pre Lucene 2.0 code
			//if (prohibited || !queryClauses[i].prohibited)
			//	getTerms(queryClauses[i].query, terms, prohibited, fieldName);
			// Lucene 2.0 ready code
			 if (prohibited ||
			 queryClauses[i].getOccur()!=BooleanClause.Occur.MUST_NOT)
			 getTerms(queryClauses[i].getQuery(), terms, prohibited,
			 fieldName);
		}
	}

	private static final void getTermsFromPhraseQuery(PhraseQuery query,
			HashSet terms, String fieldName)
	{
		Term[] queryTerms = query.getTerms();
		int i;

		for (i = 0; i < queryTerms.length; i++)
		{
			if ((fieldName == null) || (queryTerms[i].field() == fieldName))
			{
				terms.add(new WeightedTerm(query.getBoost(), queryTerms[i]
						.text()));
			}
		}
	}

	private static final void getTermsFromTermQuery(TermQuery query,
			HashSet terms, String fieldName)
	{
		if ((fieldName == null) || (query.getTerm().field() == fieldName))
		{
			terms
					.add(new WeightedTerm(query.getBoost(), query.getTerm()
							.text()));
		}
	}

	private static final void getTermsFromSpanNearQuery(SpanNearQuery query,
			HashSet terms, String fieldName)
	{

		Collection queryTerms = query.getTerms();

		for (Iterator iterator = queryTerms.iterator(); iterator.hasNext();)
		{

			// break it out for debugging.

			Term term = (Term) iterator.next();

			String text = term.text();

			if ((fieldName == null) || (term.field() == fieldName))
			{
				terms.add(new WeightedTerm(query.getBoost(), text));
			}
		}

	}

}
