package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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.
 */

import java.io.IOException;
import java.io.Serializable;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;

import org.apache.lucene.queryParser.QueryParser; // for javadoc

/**
 * An abstract {@link Query} that matches documents
 * containing a subset of terms provided by a {@link
 * FilteredTermEnum} enumeration.
 *
 * <p>This query cannot be used directly; you must subclass
 * it and define {@link #getEnum} to provide a {@link
 * FilteredTermEnum} that iterates through the terms to be
 * matched.
 *
 * <p><b>NOTE</b>: if {@link #setRewriteMethod} is either
 * {@link #CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE} or {@link
 * #SCORING_BOOLEAN_QUERY_REWRITE}, you may encounter a
 * {@link BooleanQuery.TooManyClauses} exception during
 * searching, which happens when the number of terms to be
 * searched exceeds {@link
 * BooleanQuery#getMaxClauseCount()}.  Setting {@link
 * #setRewriteMethod} to {@link #CONSTANT_SCORE_FILTER_REWRITE}
 * prevents this.
 *
 * <p>The recommended rewrite method is {@link
 * #CONSTANT_SCORE_AUTO_REWRITE_DEFAULT}: it doesn't spend CPU
 * computing unhelpful scores, and it tries to pick the most
 * performant rewrite method given the query. If you
 * need scoring (like {@link FuzzyQuery}, use
 * {@link TopTermsScoringBooleanQueryRewrite} which uses
 * a priority queue to only collect competitive terms
 * and not hit this limitation.
 *
 * Note that {@link QueryParser} produces
 * MultiTermQueries using {@link
 * #CONSTANT_SCORE_AUTO_REWRITE_DEFAULT} by default.
 */
public abstract class MultiTermQuery extends Query {
  protected RewriteMethod rewriteMethod = CONSTANT_SCORE_AUTO_REWRITE_DEFAULT;
  transient int numberOfTerms = 0;

  /** Abstract class that defines how the query is rewritten. */
  public static abstract class RewriteMethod implements Serializable {
    public abstract Query rewrite(IndexReader reader, MultiTermQuery query) throws IOException;
    
    /**
     * Returns the {@link MultiTermQuery}s {@link FilteredTermEnum}
     * @see MultiTermQuery#getEnum(IndexReader)
     */
    protected FilteredTermEnum getTermsEnum(IndexReader reader, MultiTermQuery query) throws IOException {
      return query.getEnum(reader); // allow RewriteMethod subclasses to pull a FilteredTermEnum from the MTQ 
    }
  }

  /** A rewrite method that first creates a private Filter,
   *  by visiting each term in sequence and marking all docs
   *  for that term.  Matching documents are assigned a
   *  constant score equal to the query's boost.
   * 
   *  <p> This method is faster than the BooleanQuery
   *  rewrite methods when the number of matched terms or
   *  matched documents is non-trivial. Also, it will never
   *  hit an errant {@link BooleanQuery.TooManyClauses}
   *  exception.
   *
   *  @see #setRewriteMethod */
  public static final RewriteMethod CONSTANT_SCORE_FILTER_REWRITE = new RewriteMethod() {
    @Override
    public Query rewrite(IndexReader reader, MultiTermQuery query) {
      Query result = new ConstantScoreQuery(new MultiTermQueryWrapperFilter<MultiTermQuery>(query));
      result.setBoost(query.getBoost());
      return result;
    }

    // Make sure we are still a singleton even after deserializing
    protected Object readResolve() {
      return CONSTANT_SCORE_FILTER_REWRITE;
    }
  };

  /** A rewrite method that first translates each term into
   *  {@link BooleanClause.Occur#SHOULD} clause in a
   *  BooleanQuery, and keeps the scores as computed by the
   *  query.  Note that typically such scores are
   *  meaningless to the user, and require non-trivial CPU
   *  to compute, so it's almost always better to use {@link
   *  #CONSTANT_SCORE_AUTO_REWRITE_DEFAULT} instead.
   *
   *  <p><b>NOTE</b>: This rewrite method will hit {@link
   *  BooleanQuery.TooManyClauses} if the number of terms
   *  exceeds {@link BooleanQuery#getMaxClauseCount}.
   *
   *  @see #setRewriteMethod */
  public final static RewriteMethod SCORING_BOOLEAN_QUERY_REWRITE = ScoringRewrite.SCORING_BOOLEAN_QUERY_REWRITE;
  
  /** Like {@link #SCORING_BOOLEAN_QUERY_REWRITE} except
   *  scores are not computed.  Instead, each matching
   *  document receives a constant score equal to the
   *  query's boost.
   * 
   *  <p><b>NOTE</b>: This rewrite method will hit {@link
   *  BooleanQuery.TooManyClauses} if the number of terms
   *  exceeds {@link BooleanQuery#getMaxClauseCount}.
   *
   *  @see #setRewriteMethod */
  public final static RewriteMethod CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE = ScoringRewrite.CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE;

  /**
   * A rewrite method that first translates each term into
   * {@link BooleanClause.Occur#SHOULD} clause in a BooleanQuery, and keeps the
   * scores as computed by the query.
   * 
   * <p>
   * This rewrite method only uses the top scoring terms so it will not overflow
   * the boolean max clause count. It is the default rewrite method for
   * {@link FuzzyQuery}.
   * 
   * @see #setRewriteMethod
   */
  public static final class TopTermsScoringBooleanQueryRewrite extends TopTermsRewrite<BooleanQuery> {

    /** 
     * Create a TopTermsScoringBooleanQueryRewrite for 
     * at most <code>size</code> terms.
     * <p>
     * NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than 
     * <code>size</code>, then it will be used instead. 
     */
    public TopTermsScoringBooleanQueryRewrite(int size) {
      super(size);
    }
    
    @Override
    protected int getMaxSize() {
      return BooleanQuery.getMaxClauseCount();
    }
    
    @Override
    protected BooleanQuery getTopLevelQuery() {
      return new BooleanQuery(true);
    }
    
    @Override
    protected void addClause(BooleanQuery topLevel, Term term, float boost) {
      final TermQuery tq = new TermQuery(term);
      tq.setBoost(boost);
      topLevel.add(tq, BooleanClause.Occur.SHOULD);
    }
  }
  
  /**
   * A rewrite method that first translates each term into
   * {@link BooleanClause.Occur#SHOULD} clause in a BooleanQuery, but the scores
   * are only computed as the boost.
   * <p>
   * This rewrite method only uses the top scoring terms so it will not overflow
   * the boolean max clause count.
   * 
   * @see #setRewriteMethod
   */
  public static final class TopTermsBoostOnlyBooleanQueryRewrite extends TopTermsRewrite<BooleanQuery> {
    
    /** 
     * Create a TopTermsBoostOnlyBooleanQueryRewrite for 
     * at most <code>size</code> terms.
     * <p>
     * NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than 
     * <code>size</code>, then it will be used instead. 
     */
    public TopTermsBoostOnlyBooleanQueryRewrite(int size) {
      super(size);
    }
    
    @Override
    protected int getMaxSize() {
      return BooleanQuery.getMaxClauseCount();
    }
    
    @Override
    protected BooleanQuery getTopLevelQuery() {
      return new BooleanQuery(true);
    }
    
    @Override
    protected void addClause(BooleanQuery topLevel, Term term, float boost) {
      final Query q = new ConstantScoreQuery(new TermQuery(term));
      q.setBoost(boost);
      topLevel.add(q, BooleanClause.Occur.SHOULD);
    }
  }
    
  /** A rewrite method that tries to pick the best
   *  constant-score rewrite method based on term and
   *  document counts from the query.  If both the number of
   *  terms and documents is small enough, then {@link
   *  #CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE} is used.
   *  Otherwise, {@link #CONSTANT_SCORE_FILTER_REWRITE} is
   *  used.
   */
  public static class ConstantScoreAutoRewrite extends org.apache.lucene.search.ConstantScoreAutoRewrite {}

  /** Read-only default instance of {@link
   *  ConstantScoreAutoRewrite}, with {@link
   *  ConstantScoreAutoRewrite#setTermCountCutoff} set to
   *  {@link
   *  ConstantScoreAutoRewrite#DEFAULT_TERM_COUNT_CUTOFF}
   *  and {@link
   *  ConstantScoreAutoRewrite#setDocCountPercent} set to
   *  {@link
   *  ConstantScoreAutoRewrite#DEFAULT_DOC_COUNT_PERCENT}.
   *  Note that you cannot alter the configuration of this
   *  instance; you'll need to create a private instance
   *  instead. */
  public final static RewriteMethod CONSTANT_SCORE_AUTO_REWRITE_DEFAULT = new ConstantScoreAutoRewrite() {
    @Override
    public void setTermCountCutoff(int count) {
      throw new UnsupportedOperationException("Please create a private instance");
    }

    @Override
    public void setDocCountPercent(double percent) {
      throw new UnsupportedOperationException("Please create a private instance");
    }

    // Make sure we are still a singleton even after deserializing
    protected Object readResolve() {
      return CONSTANT_SCORE_AUTO_REWRITE_DEFAULT;
    }
  };

  /**
   * Constructs a query matching terms that cannot be represented with a single
   * Term.
   */
  public MultiTermQuery() {
  }

  /** Construct the enumeration to be used, expanding the pattern term. */
  protected abstract FilteredTermEnum getEnum(IndexReader reader)
      throws IOException;

  /**
   * Expert: Return the number of unique terms visited during execution of the query.
   * If there are many of them, you may consider using another query type
   * or reduce your total term count in index.
   * <p>This method is not thread safe, be sure to only call it when no query is running!
   * If you re-use the same query instance for another
   * search, be sure to first reset the term counter
   * with {@link #clearTotalNumberOfTerms}.
   * <p>On single-segment indexes / no MultiReaders, you get the correct number of
   * unique terms for the whole index. Use this number to compare different queries.
   * For multi-segment indexes this number can also be achieved in
   * non-constant-score mode. In constant-score mode you get the total number of
   * terms seeked for all segments / sub-readers.
   * @see #clearTotalNumberOfTerms
   * @deprecated Don't use this method, as its not thread safe and useless.
   */
  @Deprecated
  public int getTotalNumberOfTerms() {
    return numberOfTerms;
  }
  
  /**
   * Expert: Resets the counting of unique terms.
   * Do this before executing the query/filter.
   * @see #getTotalNumberOfTerms
   * @deprecated Don't use this method, as its not thread safe and useless.
   */
  @Deprecated
  public void clearTotalNumberOfTerms() {
    numberOfTerms = 0;
  }
  
  /** 
   * @deprecated Don't use this method, as its not thread safe and useless.
   */
  @Deprecated
  protected void incTotalNumberOfTerms(int inc) {
    numberOfTerms += inc;
  }

  /**
   * To rewrite to a simpler form, instead return a simpler
   * enum from {@link #getEnum(IndexReader)}.  For example,
   * to rewrite to a single term, return a {@link SingleTermEnum}
   */
  @Override
  public final Query rewrite(IndexReader reader) throws IOException {
    return rewriteMethod.rewrite(reader, this);
  }

  /**
   * @see #setRewriteMethod
   */
  public RewriteMethod getRewriteMethod() {
    return rewriteMethod;
  }

  /**
   * Sets the rewrite method to be used when executing the
   * query.  You can use one of the four core methods, or
   * implement your own subclass of {@link RewriteMethod}. */
  public void setRewriteMethod(RewriteMethod method) {
    rewriteMethod = method;
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + Float.floatToIntBits(getBoost());
    result = prime * result;
    result += rewriteMethod.hashCode();
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    MultiTermQuery other = (MultiTermQuery) obj;
    if (Float.floatToIntBits(getBoost()) != Float.floatToIntBits(other.getBoost()))
      return false;
    if (!rewriteMethod.equals(other.rewriteMethod)) {
      return false;
    }
    return true;
  }
 
}
