package org.apache.lucene.index;

/**
 * Copyright 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;

/** TermDocs provides an interface for enumerating <document, frequency>
 pairs for a term.  
 The document portion names each document containing
 the term.  Documents are indicated by number.  The frequency portion gives
 the number of times the term occurred in each document.  
 The pairs are
 ordered by document number.

 @see IndexReader#termDocs
 */

public interface TermDocs {
  /** Sets this to the data for a term.
   * The enumeration is reset to the start of the data for this term.
   */
  void seek(Term term) throws IOException;

  /** Sets this to the data for the current term in a {@link TermEnum}.
   * This may be optimized in some implementations.
   */
  void seek(TermEnum termEnum) throws IOException;

  /** Returns the current document number.  
 This is invalid until {@link
   #next()} is called for the first time.*/
  int doc();

  /** Returns the frequency of the term within the current document.  
 This
   is invalid until {@link #next()} is called for the first time.*/
  int freq();

  /** Moves to the next pair in the enumeration.  
 Returns true iff there is
   such a next pair in the enumeration. */
  boolean next() throws IOException;

  /** Attempts to read multiple entries from the enumeration, up to length of
   * docs.  Document numbers are stored in docs, and term
   * frequencies are stored in freqs.  The freqs array must be as
   * long as the docs array.
   *
   * 
Returns the number of entries read.  Zero is only returned when the
   * stream has been exhausted.  */
  int read(int[] docs, int[] freqs) throws IOException;

  /** Skips entries to the first beyond the current whose document number is
   * greater than or equal to target. 
Returns true iff there is such
   * an entry.  
Behaves as if written: 
   *   boolean skipTo(int target) {
   *     do {
   *       if (!next())
   * 	     return false;
   *     } while (target > doc());
   *     return true;
   *   }
   * 
   * Some implementations are considerably more efficient than that.
   */
  boolean skipTo(int target) throws IOException;

  /** Frees associated resources. */
  void close() throws IOException;
}