/*
 * Copyright (C) 2015 Google Inc.
 *
 * 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.cloud.dataflow.sdk.transforms.windowing;

import org.joda.time.Instant;

import java.util.Arrays;
import java.util.Collection;

/**
 * A {@link WindowFn} that places each value into exactly one window
 * based on its timestamp and never merges windows.
 *
 * @param <T> type of elements being windowed
 * @param <W> window type
 */
public abstract class PartitioningWindowFn<T, W extends BoundedWindow>
    extends NonMergingWindowFn<T, W> {
  private static final long serialVersionUID = 0;

  /**
   * Returns the single window to which elements with this timestamp belong.
   */
  public abstract W assignWindow(Instant timestamp);

  @Override
  public final Collection<W> assignWindows(AssignContext c) {
    return Arrays.asList(assignWindow(c.timestamp()));
  }

  @Override
  public W getSideInputWindow(final BoundedWindow window) {
    if (window instanceof GlobalWindow) {
      throw new IllegalArgumentException(
          "Attempted to get side input window for GlobalWindow from non-global WindowFn");
    }
    return assignWindow(window.maxTimestamp());
  }

  @Override
  public boolean assignsToSingleWindow() {
    return true;
  }
}
