/*
 * 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.
 */
package org.apache.lucene.util;

import java.util.Arrays;
import java.util.Comparator;

A simple append only random-access BytesRef array that stores full copies of the appended bytes in a ByteBlockPool. Note: This class is not Thread-Safe!
@lucene.internal
@lucene.experimental
/**
 * A simple append only random-access {@link BytesRef} array that stores full
 * copies of the appended bytes in a {@link ByteBlockPool}.
 * 
 * 
 * <b>Note: This class is not Thread-Safe!</b>
 * 
 * @lucene.internal
 * @lucene.experimental
 */
public final class BytesRefArray implements SortableBytesRefArray {
  private final ByteBlockPool pool;
  private int[] offsets = new int[1];
  private int lastElement = 0;
  private int currentOffset = 0;
  private final Counter bytesUsed;

  
Creates a new BytesRefArray with a counter to track allocated bytes /**
   * Creates a new {@link BytesRefArray} with a counter to track allocated bytes
   */
  public BytesRefArray(Counter bytesUsed) {
    this.pool = new ByteBlockPool(new ByteBlockPool.DirectTrackingAllocator(
        bytesUsed));
    pool.nextBuffer();
    bytesUsed.addAndGet(RamUsageEstimator.NUM_BYTES_ARRAY_HEADER * Integer.BYTES);
    this.bytesUsed = bytesUsed;
  }
 
  
Clears this BytesRefArray /**
   * Clears this {@link BytesRefArray}
   */
  @Override
  public void clear() {
    lastElement = 0;
    currentOffset = 0;
    // TODO: it's trappy that this does not return storage held by int[] offsets array!
    Arrays.fill(offsets, 0);
    pool.reset(false, true); // no need to 0 fill the buffers we control the allocator
  }
  
  
Appends a copy of the given BytesRef to this BytesRefArray. 
Params:
bytes – the bytes to append
Returns:
the index of the appended bytes/**
   * Appends a copy of the given {@link BytesRef} to this {@link BytesRefArray}.
   * @param bytes the bytes to append
   * @return the index of the appended bytes
   */
  @Override
  public int append(BytesRef bytes) {
    if (lastElement >= offsets.length) {
      int oldLen = offsets.length;
      offsets = ArrayUtil.grow(offsets, offsets.length + 1);
      bytesUsed.addAndGet((offsets.length - oldLen) * Integer.BYTES);
    }
    pool.append(bytes);
    offsets[lastElement++] = currentOffset;
    currentOffset += bytes.length;
    return lastElement-1;
  }
  
  
Returns the current size of this BytesRefArray 
Returns:
the current size of this BytesRefArray/**
   * Returns the current size of this {@link BytesRefArray}
   * @return the current size of this {@link BytesRefArray}
   */
  @Override
  public int size() {
    return lastElement;
  }
  
  
Returns the n'th element of this BytesRefArray 
Params:
spare – a spare BytesRef instance
index – the elements index to retrieve
Returns:
the n'th element of this BytesRefArray/**
   * Returns the <i>n'th</i> element of this {@link BytesRefArray}
   * @param spare a spare {@link BytesRef} instance
   * @param index the elements index to retrieve 
   * @return the <i>n'th</i> element of this {@link BytesRefArray}
   */
  public BytesRef get(BytesRefBuilder spare, int index) {
    FutureObjects.checkIndex(index, lastElement);
    int offset = offsets[index];
    int length = index == lastElement - 1 ? currentOffset - offset
        : offsets[index + 1] - offset;
    spare.grow(length);
    spare.setLength(length);
    pool.readBytes(offset, spare.bytes(), 0, spare.length());
    return spare.get();
  }

  
Used only by sort below, to set a BytesRef with the specified slice, avoiding copying bytes in the common case when the slice is contained in a single block in the byte block pool. /** Used only by sort below, to set a {@link BytesRef} with the specified slice, avoiding copying bytes in the common case when the slice
   *  is contained in a single block in the byte block pool. */
  private void setBytesRef(BytesRefBuilder spare, BytesRef result, int index) {
    FutureObjects.checkIndex(index, lastElement);
    int offset = offsets[index];
    int length;
    if (index == lastElement - 1) {
      length = currentOffset - offset;
    } else {
      length = offsets[index + 1] - offset;
    }
    pool.setBytesRef(spare, result, offset, length);
  }
  
  private int[] sort(final Comparator<BytesRef> comp) {
    final int[] orderedEntries = new int[size()];
    for (int i = 0; i < orderedEntries.length; i++) {
      orderedEntries[i] = i;
    }
    new IntroSorter() {
      @Override
      protected void swap(int i, int j) {
        final int o = orderedEntries[i];
        orderedEntries[i] = orderedEntries[j];
        orderedEntries[j] = o;
      }
      
      @Override
      protected int compare(int i, int j) {
        final int idx1 = orderedEntries[i], idx2 = orderedEntries[j];
        setBytesRef(scratch1, scratchBytes1, idx1);
        setBytesRef(scratch2, scratchBytes2, idx2);
        return comp.compare(scratchBytes1, scratchBytes2);
      }
      
      @Override
      protected void setPivot(int i) {
        final int index = orderedEntries[i];
        setBytesRef(pivotBuilder, pivot, index);
      }
      
      @Override
      protected int comparePivot(int j) {
        final int index = orderedEntries[j];
        setBytesRef(scratch2, scratchBytes2, index);
        return comp.compare(pivot, scratchBytes2);
      }

      private final BytesRef pivot = new BytesRef();
      private final BytesRef scratchBytes1 = new BytesRef();
      private final BytesRef scratchBytes2 = new BytesRef();
      private final BytesRefBuilder pivotBuilder = new BytesRefBuilder();
      private final BytesRefBuilder scratch1 = new BytesRefBuilder();
      private final BytesRefBuilder scratch2 = new BytesRefBuilder();
    }.sort(0, size());
    return orderedEntries;
  }
  
  
sugar for iterator(Comparator<BytesRef>) with a null comparator
/**
   * sugar for {@link #iterator(Comparator)} with a <code>null</code> comparator
   */
  public BytesRefIterator iterator() {
    return iterator(null);
  }
  
  
 Returns a BytesRefIterator with point in time semantics. The iterator provides access to all so far appended BytesRef instances. 

If a non null Comparator is provided the iterator will iterate the byte values in the order specified by the comparator. Otherwise the order is the same as the values were appended. 

This is a non-destructive operation.

/**
   * <p>
   * Returns a {@link BytesRefIterator} with point in time semantics. The
   * iterator provides access to all so far appended {@link BytesRef} instances.
   * </p>
   * <p>
   * If a non <code>null</code> {@link Comparator} is provided the iterator will
   * iterate the byte values in the order specified by the comparator. Otherwise
   * the order is the same as the values were appended.
   * </p>
   * <p>
   * This is a non-destructive operation.
   * </p>
   */
  @Override
  public BytesRefIterator iterator(final Comparator<BytesRef> comp) {
    final BytesRefBuilder spare = new BytesRefBuilder();
    final BytesRef result = new BytesRef();
    final int size = size();
    final int[] indices = comp == null ? null : sort(comp);
    return new BytesRefIterator() {
      int pos = 0;
      @Override
      public BytesRef next() {
        if (pos < size) {
          setBytesRef(spare, result, indices == null ? pos++ : indices[pos++]);
          return result;
        }
        return null;
      }
    };
  }
}