// Copyright 2017 The Nomulus Authors. All Rights Reserved.
//
// 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.

package google.registry.mapreduce.inputs;

import com.google.appengine.tools.mapreduce.InputReader;
import com.google.common.collect.ImmutableSet;
import com.googlecode.objectify.Key;
import google.registry.model.EppResource;
import google.registry.model.index.EppResourceIndex;
import google.registry.model.index.EppResourceIndexBucket;
import java.util.NoSuchElementException;

/**
 * Reader that maps over {@link EppResourceIndex} and returns resource keys.
 *
 * <p>When mapping over keys we can't distinguish between Objectify polymorphic types.
 */
class EppResourceKeyReader<R extends EppResource> extends EppResourceBaseReader<Key<R>> {

  private static final long serialVersionUID = -428232054739189774L;

  public EppResourceKeyReader(
      Key<EppResourceIndexBucket> bucketKey, ImmutableSet<Class<? extends R>> resourceClasses) {
    super(
        bucketKey,
        ONE_MB,  // Estimate 1MB of memory for this reader, which is massive overkill.
        varargsToKinds(resourceClasses));
  }

  /**
   * Called for each map invocation.
   *
   * @throws NoSuchElementException if there are no more elements, as specified in the
   *         {@link InputReader#next} Javadoc.
   */
  @Override
  @SuppressWarnings("unchecked")
  public Key<R> next() throws NoSuchElementException {
    // This is a safe cast because we filtered on kind inside the query.
    return (Key<R>) nextEri().getKey();
  }
}