content: /*
   * 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
   *
   *     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 org.apache.beam.sdk.transforms.windowing;
  
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Objects;
  import org.apache.beam.sdk.coders.Coder;
  import org.apache.beam.sdk.transforms.display.DisplayData;
  import org.apache.beam.sdk.values.TypeDescriptor;
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.joda.time.Duration;
  
  /**
   * A {@link WindowFn} that windows values into sessions separated by periods with no input for at
   * least the duration specified by {@link #getGapDuration()}.
   *
   * <p>For example, in order to window data into session with at least 10 minute gaps in between
   * them:
   *
   * <pre>{@code
   * PCollection<Integer> pc = ...;
   * PCollection<Integer> windowed_pc = pc.apply(
   *   Window.<Integer>into(Sessions.withGapDuration(Duration.standardMinutes(10))));
   * }</pre>
   */
  public class Sessions extends WindowFn<Object, IntervalWindow> {
    /** Duration of the gaps between sessions. */
    private final Duration gapDuration;
  
    /** Creates a {@code Sessions} {@link WindowFn} with the specified gap duration. */
    public static Sessions withGapDuration(Duration gapDuration) {
      return new Sessions(gapDuration);
    }
  
    /** Creates a {@code Sessions} {@link WindowFn} with the specified gap duration. */
    private Sessions(Duration gapDuration) {
      this.gapDuration = gapDuration;
    }
  
    @Override
    public Collection<IntervalWindow> assignWindows(AssignContext c) {
      // Assign each element into a window from its timestamp until gapDuration in the
      // future.  Overlapping windows (representing elements within gapDuration of
      // each other) will be merged.
      return Arrays.asList(new IntervalWindow(c.timestamp(), gapDuration));
    }
  
    @Override
    public void mergeWindows(MergeContext c) throws Exception {
      MergeOverlappingIntervalWindows.mergeWindows(c);
    }
  
    @Override
    public Coder<IntervalWindow> windowCoder() {
      return IntervalWindow.getCoder();
    }
  
    @Override
    public boolean isCompatible(WindowFn<?, ?> other) {
      return other instanceof Sessions;
    }
  
    @Override
    public void verifyCompatibility(WindowFn<?, ?> other) throws IncompatibleWindowException {
      if (!this.isCompatible(other)) {
        throw new IncompatibleWindowException(
            other,
            String.format(
                "%s is only compatible with %s.",
                Sessions.class.getSimpleName(), Sessions.class.getSimpleName()));
      }
    }
  
    @Override
    public TypeDescriptor<IntervalWindow> getWindowTypeDescriptor() {
      return TypeDescriptor.of(IntervalWindow.class);
    }
  
    @Override
    public WindowMappingFn<IntervalWindow> getDefaultWindowMappingFn() {
      throw new UnsupportedOperationException("Sessions is not allowed in side inputs");
    }
  
    public Duration getGapDuration() {
      return gapDuration;
    }
  
    @Override
    public void populateDisplayData(DisplayData.Builder builder) {
      super.populateDisplayData(builder);
      builder.add(DisplayData.item("gapDuration", gapDuration).withLabel("Session Gap Duration"));
    }
  
    @Override
    public boolean equals(@Nullable Object object) {
      if (!(object instanceof Sessions)) {
        return false;
      }
      Sessions other = (Sessions) object;
      return getGapDuration().equals(other.getGapDuration());
    }
  
    @Override
    public int hashCode() {
      return Objects.hash(gapDuration);
    }
  }
  