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 org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.Terms;
import org.apache.lucene.index.MultiFields;
import org.apache.lucene.util.ToStringUtils;

/** A Query that matches documents containing terms with a specified prefix. A PrefixQuery
 * is built by QueryParser for input like <code>app*</code>.
 *
 * <p>This query uses the {@link
 * MultiTermQuery#CONSTANT_SCORE_AUTO_REWRITE_DEFAULT}
 * rewrite method. */
public class PrefixQuery extends MultiTermQuery {
  private Term prefix;

  /** Constructs a query for terms starting with <code>prefix</code>. */
  public PrefixQuery(Term prefix) {
    super(prefix.field());
    this.prefix = prefix;
  }

  /** Returns the prefix of this query. */
  public Term getPrefix() { return prefix; }
  
  @Override  
  protected TermsEnum getTermsEnum(IndexReader reader) throws IOException {
    if (prefix.bytes().length == 0) {
      // no prefix -- match all terms for this field:
      // NOTE: for now, MultiTermQuery enums terms at the
      // MultiReader level, so we must use MultiFields here:
      final Terms terms = MultiFields.getTerms(reader, getField());
      return (terms != null) ? terms.iterator() : TermsEnum.EMPTY;
    }
    return new PrefixTermsEnum(reader, prefix);
  }

  /** 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(prefix.text());
    buffer.append('*');
    buffer.append(ToStringUtils.boost(getBoost()));
    return buffer.toString();
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = super.hashCode();
    result = prime * result + ((prefix == null) ? 0 : prefix.hashCode());
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (!super.equals(obj))
      return false;
    if (getClass() != obj.getClass())
      return false;
    PrefixQuery other = (PrefixQuery) obj;
    if (prefix == null) {
      if (other.prefix != null)
        return false;
    } else if (!prefix.equals(other.prefix))
      return false;
    return true;
  }

}