com.google.doubleclick.util.ProtoUtils Maven / Gradle / Ivy

/*
 * Copyright 2014 Google Inc. 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 com.google.doubleclick.util;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Predicate;
import com.google.common.collect.ImmutableList;
import com.google.protobuf.MessageLiteOrBuilder;

import java.util.ArrayList;
import java.util.List;

/**
 * Partial, private copy of the ProtoUtils class in openrtb-core,
 * so we don't need to add a dependency from openrtb-core just for this.
 */
final class ProtoUtils {

  private ProtoUtils() {
  }

  /**
   * Runs a filter through a sequence of objects.
   *
   * @param objs Message-or-builder objects
   * @param filter Function that returns {@code true} to retain an object, {@code false} to discard
   * @return Retained objects. If some elements are retained and others are discarded,
   *     this will be a new, mutable {@link List} that contains only the retained elements.
   *     If all elements are retained, returns the same, unmodified input sequence.
   *     If all elements are discarded, returns an immutable, empty sequence
   */
  public static 
      List filter(List objs, Predicate filter) {
    checkNotNull(filter);

    for (int i = 0; i < objs.size(); ++i) {
      if (!filter.apply(objs.get(i))) {
        // At least one discarded object, go to slow-path.
        return filterFrom(objs, filter, i);
      }
    }

    // Optimized common case: all items filtered, return the input sequence.
    return objs;
  }

  private static  List filterFrom(
      List objs, Predicate filter, int firstDiscarded) {
    List filtered;

    if (firstDiscarded == 0) {
      filtered = null;
    } else {
      filtered = new ArrayList<>(objs.size() - 1);
      for (int i = 0; i < firstDiscarded; ++i) {
        filtered.add(objs.get(i));
      }
    }

    for (int i = firstDiscarded + 1; i < objs.size(); ++i) {
      M obj = objs.get(i);

      if (filter.apply(obj)) {
        if (filtered == null) {
          filtered = new ArrayList<>(objs.size() - i);
        }
        filtered.add(obj);
      }
    }

    return filtered == null ? ImmutableList.of() : filtered;
  }
}