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 org.apache.lucene.index.Term;
import org.apache.lucene.util.ToStringUtils;
import org.apache.lucene.util.automaton.Automaton;
import org.apache.lucene.util.automaton.BasicAutomata;
import org.apache.lucene.util.automaton.BasicOperations;

import java.util.ArrayList;
import java.util.List;

/** Implements the wildcard search query. Supported wildcards are <code>*</code>, which
 * matches any character sequence (including the empty one), and <code>?</code>,
 * which matches any single character. Note this query can be slow, as it
 * needs to iterate over many terms. In order to prevent extremely slow WildcardQueries,
 * a Wildcard term should not start with the wildcard <code>*</code>
 * 
 * <p>This query uses the {@link
 * MultiTermQuery#CONSTANT_SCORE_AUTO_REWRITE_DEFAULT}
 * rewrite method.
 *
 * @see AutomatonQuery
 */
public class WildcardQuery extends AutomatonQuery {
  /** String equality with support for wildcards */
  public static final char WILDCARD_STRING = '*';

  /** Char equality with support for wildcards */
  public static final char WILDCARD_CHAR = '?';

  /**
   * Constructs a query for terms matching <code>term</code>. 
   */
  public WildcardQuery(Term term) {
    super(term, toAutomaton(term));
  }
  
  /**
   * Convert Lucene wildcard syntax into an automaton.
   */
  static Automaton toAutomaton(Term wildcardquery) {
    List<Automaton> automata = new ArrayList<Automaton>();
    
    String wildcardText = wildcardquery.text();
    
    for (int i = 0; i < wildcardText.length();) {
      final int c = wildcardText.codePointAt(i);
      switch(c) {
        case WILDCARD_STRING: 
          automata.add(BasicAutomata.makeAnyString());
          break;
        case WILDCARD_CHAR:
          automata.add(BasicAutomata.makeAnyChar());
          break;
        default:
          automata.add(BasicAutomata.makeChar(c));
      }
      i += Character.charCount(c);
    }
    
    return BasicOperations.concatenate(automata);
  }
  
  /**
   * Returns the pattern term.
   */
  public Term getTerm() {
    return term;
  }
  
  /** Prints a user-readable version of this query. */
  @Override
  public String toString(String field) {
    StringBuilder buffer = new StringBuilder();
    if (!getField().equals(field)) {
      buffer.append(getField());
      buffer.append(":");
    }
    buffer.append(term.text());
    buffer.append(ToStringUtils.boost(getBoost()));
    return buffer.toString();
  }
}