package org.apache.lucene.index;

/*
 * 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.util.BytesRef;

/**
 * A per-document byte[] with presorted values.
 * <p>
 * Per-Document values in a SortedDocValues are deduplicated, dereferenced,
 * and sorted into a dictionary of unique values. A pointer to the
 * dictionary value (ordinal) can be retrieved for each document. Ordinals
 * are dense and in increasing sorted order.
 */
public abstract class SortedDocValues extends BinaryDocValues {

  /** Sole constructor. (For invocation by subclass 
   * constructors, typically implicit.) */
  protected SortedDocValues() {}

  /**
   * Returns the ordinal for the specified docID.
   * @param  docID document ID to lookup
   * @return ordinal for the document: this is dense, starts at 0, then
   *         increments by 1 for the next value in sorted order. Note that
   *         missing values are indicated by -1.
   */
  public abstract int getOrd(int docID);

  /** Retrieves the value for the specified ordinal. The returned
   * {@link BytesRef} may be re-used across calls to {@link #lookupOrd(int)}
   * so make sure to {@link BytesRef#deepCopyOf(BytesRef) copy it} if you want
   * to keep it around.
   * @param ord ordinal to lookup (must be &gt;= 0 and &lt {@link #getValueCount()})
   * @see #getOrd(int) 
   */
  public abstract BytesRef lookupOrd(int ord);

  /**
   * Returns the number of unique values.
   * @return number of unique values in this SortedDocValues. This is
   *         also equivalent to one plus the maximum ordinal.
   */
  public abstract int getValueCount();

  private final BytesRef empty = new BytesRef();

  @Override
  public BytesRef get(int docID) {
    int ord = getOrd(docID);
    if (ord == -1) {
      return empty;
    } else {
      return lookupOrd(ord);
    }
  }

  /** If {@code key} exists, returns its ordinal, else
   *  returns {@code -insertionPoint-1}, like {@code
   *  Arrays.binarySearch}.
   *
   *  @param key Key to look up
   **/
  public int lookupTerm(BytesRef key) {
    int low = 0;
    int high = getValueCount()-1;

    while (low <= high) {
      int mid = (low + high) >>> 1;
      final BytesRef term = lookupOrd(mid);
      int cmp = term.compareTo(key);

      if (cmp < 0) {
        low = mid + 1;
      } else if (cmp > 0) {
        high = mid - 1;
      } else {
        return mid; // key found
      }
    }

    return -(low + 1);  // key not found.
  }
  
  /** 
   * Returns a {@link TermsEnum} over the values.
   * The enum supports {@link TermsEnum#ord()} and {@link TermsEnum#seekExact(long)}.
   */
  public TermsEnum termsEnum() {
    return new SortedDocValuesTermsEnum(this);
  }
}