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 static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
  
  import java.util.List;
  import java.util.Objects;
  import org.apache.beam.sdk.state.TimeDomain;
  import org.apache.beam.sdk.transforms.windowing.Trigger.OnceTrigger;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.joda.time.Instant;
  
  /**
   * {@code AfterWatermark} triggers fire based on progress of the system watermark. This time is a
   * lower-bound, sometimes heuristically established, on event times that have been fully processed
   * by the pipeline.
   *
   * <p>For sources that provide non-heuristic watermarks (e.g. PubsubIO when using arrival times as
   * event times), the watermark is a strict guarantee that no data with an event time earlier than
   * that watermark will ever be observed in the pipeline. In this case, it's safe to assume that any
   * pane triggered by an {@code AfterWatermark} trigger with a reference point at or beyond the end
   * of the window will be the last pane ever for that window.
   *
   * <p>For sources that provide heuristic watermarks (e.g. PubsubIO when using user-supplied event
   * times), the watermark itself becomes an <i>estimate</i> that no data with an event time earlier
   * than that watermark (i.e. "late data") will ever be observed in the pipeline. These heuristics
   * can often be quite accurate, but the chance of seeing late data for any given window is non-zero.
   * Thus, if absolute correctness over time is important to your use case, you may want to consider
   * using a trigger that accounts for late data. The default trigger, {@code
   * Repeatedly.forever(AfterWatermark.pastEndOfWindow())}, which fires once when the watermark passes
   * the end of the window and then immediately thereafter when any late data arrives, is one such
   * example.
   *
   * <p>The watermark is the clock that defines {@link TimeDomain#EVENT_TIME}.
   *
   * <p>Additionally firings before or after the watermark can be requested by calling {@code
   * AfterWatermark.pastEndOfWindow.withEarlyFirings(OnceTrigger)} or {@code
   * AfterWatermark.pastEndOfWindow.withLateFirings(OnceTrigger)}.
   */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class AfterWatermark {
  
    private static final String TO_STRING = "AfterWatermark.pastEndOfWindow()";
  
    // Static factory class.
    private AfterWatermark() {}
  
    /** Creates a trigger that fires when the watermark passes the end of the window. */
    public static FromEndOfWindow pastEndOfWindow() {
      return new FromEndOfWindow();
    }
  
    /** @see AfterWatermark */
    public static class AfterWatermarkEarlyAndLate extends Trigger {
  
      private final OnceTrigger earlyTrigger;
      private final @Nullable OnceTrigger lateTrigger;
  
      public OnceTrigger getEarlyTrigger() {
        return earlyTrigger;
      }
  
      public OnceTrigger getLateTrigger() {
        return lateTrigger;
      }
  
      @SuppressWarnings("unchecked")
      private AfterWatermarkEarlyAndLate(OnceTrigger earlyTrigger, OnceTrigger lateTrigger) {
        super(
            lateTrigger == null
                ? ImmutableList.of(earlyTrigger)
                : ImmutableList.of(earlyTrigger, lateTrigger));
        this.earlyTrigger = checkNotNull(earlyTrigger, "earlyTrigger should not be null");
        this.lateTrigger = lateTrigger;
      }
  
      public AfterWatermarkEarlyAndLate withEarlyFirings(OnceTrigger earlyTrigger) {
        return new AfterWatermarkEarlyAndLate(earlyTrigger, lateTrigger);
      }
  
      public AfterWatermarkEarlyAndLate withLateFirings(OnceTrigger lateTrigger) {
        return new AfterWatermarkEarlyAndLate(earlyTrigger, lateTrigger);
      }
  
      @Override
      public Trigger getContinuationTrigger() {
        return new AfterWatermarkEarlyAndLate(
            earlyTrigger.getContinuationTrigger(),
            lateTrigger == null ? null : lateTrigger.getContinuationTrigger());
      }
  
      @Override
      protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
        throw new UnsupportedOperationException(
            "Should not call getContinuationTrigger(List<Trigger>)");
      }
  
      @Override
      public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
        // Even without an early or late trigger, we'll still produce a firing at the watermark.
        return window.maxTimestamp();
      }
  
      /** @return true if there is no late firing set up, otherwise false */
      @Override
      public boolean mayFinish() {
        return lateTrigger == null;
      }
  
      @Override
      public String toString() {
        StringBuilder builder = new StringBuilder(TO_STRING);
  
        if (!(earlyTrigger instanceof Never.NeverTrigger)) {
          builder.append(".withEarlyFirings(").append(earlyTrigger).append(")");
        }
  
        if (lateTrigger != null && !(lateTrigger instanceof Never.NeverTrigger)) {
          builder.append(".withLateFirings(").append(lateTrigger).append(")");
        }
  
        return builder.toString();
      }
    }
  
    /** A watermark trigger targeted relative to the end of the window. */
    public static class FromEndOfWindow extends OnceTrigger {
  
      private FromEndOfWindow() {
        super(null);
      }
  
      /**
       * Creates a new {@code Trigger} like the this, except that it fires repeatedly whenever the
       * given {@code Trigger} fires before the watermark has passed the end of the window.
       */
      public AfterWatermarkEarlyAndLate withEarlyFirings(OnceTrigger earlyFirings) {
        checkNotNull(earlyFirings, "Must specify the trigger to use for early firings");
        return new AfterWatermarkEarlyAndLate(earlyFirings, null);
      }
  
      /**
       * Creates a new {@code Trigger} like the this, except that it fires repeatedly whenever the
       * given {@code Trigger} fires after the watermark has passed the end of the window.
       */
      public AfterWatermarkEarlyAndLate withLateFirings(OnceTrigger lateFirings) {
        checkNotNull(lateFirings, "Must specify the trigger to use for late firings");
        return new AfterWatermarkEarlyAndLate(Never.ever(), lateFirings);
      }
  
      @Override
      public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
        return window.maxTimestamp();
      }
  
      @Override
      protected FromEndOfWindow getContinuationTrigger(List<Trigger> continuationTriggers) {
        return this;
      }
  
      @Override
      public String toString() {
        return TO_STRING;
      }
  
      @Override
      public boolean equals(@Nullable Object obj) {
        return obj instanceof FromEndOfWindow;
      }
  
      @Override
      public int hashCode() {
        return Objects.hash(getClass());
      }
    }
  }
  