/*
 * 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
 *
 *   https://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.accumulo.core.iterators;

import java.io.IOException;
import java.util.Collection;
import java.util.Map;

import org.apache.accumulo.core.data.ByteSequence;
import org.apache.accumulo.core.data.Key;
import org.apache.accumulo.core.data.Range;
import org.apache.accumulo.core.data.Value;

/**
 * A convenience class for implementing iterators that select, but do not modify, entries read from
 * a source iterator. Default implementations exist for all methods, but {@link #deepCopy} will
 * throw an <code>UnsupportedOperationException</code>.
 *
 * This iterator has some checks in place to enforce the iterator contract. Specifically, it
 * verifies that it has a source iterator and that {@link #seek} has been called before any data is
 * read. If either of these conditions does not hold true, an <code>IllegalStateException</code>
 * will be thrown. In particular, this means that <code>getSource().seek</code> and
 * <code>super.seek</code> no longer perform identical actions. Implementors should take note of
 * this and if <code>seek</code> is overridden, ensure that <code>super.seek</code> is called before
 * data is read.
 */
public abstract class WrappingIterator implements SortedKeyValueIterator<Key,Value> {

  private SortedKeyValueIterator<Key,Value> source = null;
  private IteratorEnvironment env = null;
  boolean seenSeek = false;

  protected void setSource(SortedKeyValueIterator<Key,Value> source) {
    this.source = source;
  }

  protected SortedKeyValueIterator<Key,Value> getSource() {
    if (source == null) {
      throw new IllegalStateException("getting null source");
    }
    return source;
  }

  @Override
  public SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env) {
    throw new UnsupportedOperationException();
  }

  @Override
  public Key getTopKey() {
    if (!seenSeek) {
      throw new IllegalStateException("never been seeked");
    }
    return getSource().getTopKey();
  }

  @Override
  public Value getTopValue() {
    if (!seenSeek) {
      throw new IllegalStateException("never been seeked");
    }
    return getSource().getTopValue();
  }

  @Override
  public boolean hasTop() {
    if (!seenSeek) {
      throw new IllegalStateException("never been seeked");
    }
    return getSource().hasTop();
  }

  @Override
  public void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options,
      IteratorEnvironment env) throws IOException {
    this.setSource(source);
    this.env = env;
  }

  @Override
  public void next() throws IOException {
    if (!seenSeek) {
      throw new IllegalStateException("never been seeked");
    }
    getSource().next();
  }

  @Override
  public void seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive)
      throws IOException {
    getSource().seek(range, columnFamilies, inclusive);
    seenSeek = true;
  }

  @Override
  public boolean isRunningLowOnMemory() {
    if (env == null) {
      return SortedKeyValueIterator.super.isRunningLowOnMemory();
    }
    return env.isRunningLowOnMemory();
  }

}
