/*
 * 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.io.UncheckedIOException;
import java.util.Collection;
import java.util.Collections;
import java.util.Map;

import org.apache.accumulo.core.client.IteratorSetting;
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 SortedKeyValueIterator that filters entries from its source iterator.
 *
 * Subclasses must implement an accept method: public boolean accept(Key k, Value v);
 *
 * Key/Value pairs for which the accept method returns true are said to match the filter. By
 * default, this class iterates over entries that match its filter. This iterator takes an optional
 * "negate" boolean parameter that defaults to false. If negate is set to true, this class instead
 * omits entries that match its filter, thus iterating over entries that do not match its filter.
 */
public abstract class Filter extends WrappingIterator implements OptionDescriber {
  @Override
  public SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env) {
    Filter newInstance;
    try {
      newInstance = this.getClass().getDeclaredConstructor().newInstance();
    } catch (ReflectiveOperationException e) {
      throw new IllegalStateException(e);
    }
    newInstance.setSource(getSource().deepCopy(env));
    newInstance.negate = negate;
    return newInstance;
  }

  protected static final String NEGATE = "negate";
  boolean negate = false;

  @Override
  public void next() throws IOException {
    super.next();
    findTop();
  }

  @Override
  public void seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive)
      throws IOException {
    super.seek(range, columnFamilies, inclusive);
    findTop();
  }

  /**
   * Iterates over the source until an acceptable key/value pair is found.
   */
  protected void findTop() {
    SortedKeyValueIterator<Key,Value> source = getSource();
    while (source.hasTop() && !source.getTopKey().isDeleted()
        && (negate == accept(source.getTopKey(), source.getTopValue()))) {
      try {
        source.next();
      } catch (IOException e) {
        throw new UncheckedIOException(e);
      }
    }
  }

  /**
   * @return <code>true</code> if the key/value pair is accepted by the filter.
   */
  public abstract boolean accept(Key k, Value v);

  @Override
  public void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options,
      IteratorEnvironment env) throws IOException {
    super.init(source, options, env);
    negate = false;
    if (options.get(NEGATE) != null) {
      negate = Boolean.parseBoolean(options.get(NEGATE));
    }
  }

  @Override
  public IteratorOptions describeOptions() {
    return new IteratorOptions("filter", "Filter accepts or rejects each Key/Value pair",
        Collections.singletonMap("negate", "default false keeps k/v that pass"
            + " accept method, true rejects k/v that pass accept method"),
        null);
  }

  @Override
  public boolean validateOptions(Map<String,String> options) {
    if (options.get(NEGATE) != null) {
      try {
        Boolean.parseBoolean(options.get(NEGATE));
      } catch (Exception e) {
        throw new IllegalArgumentException("bad boolean " + NEGATE + ":" + options.get(NEGATE));
      }
    }
    return true;
  }

  /**
   * A convenience method for setting the negation option on a filter.
   *
   * @param is IteratorSetting object to configure.
   * @param negate if false, filter accepts k/v for which the accept method returns true; if true,
   *        filter accepts k/v for which the accept method returns false.
   */
  public static void setNegate(IteratorSetting is, boolean negate) {
    is.addOption(NEGATE, Boolean.toString(negate));
  }
}
