/*
 * 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.runners.spark.structuredstreaming.translation.helpers;

import java.util.Collection;
import org.apache.beam.runners.spark.structuredstreaming.translation.TranslationContext;
import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
import org.apache.beam.sdk.transforms.windowing.GlobalWindows;
import org.apache.beam.sdk.transforms.windowing.Window;
import org.apache.beam.sdk.transforms.windowing.WindowFn;
import org.apache.beam.sdk.util.WindowedValue;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Iterables;
import org.apache.spark.api.java.function.MapFunction;
import org.joda.time.Instant;

/** Helper functions for working with windows. */
public final class WindowingHelpers {

  /**
   * Checks if the window transformation should be applied or skipped.
   *
   * <p>Avoid running assign windows if both source and destination are global window or if the user
   * has not specified the WindowFn (meaning they are just messing with triggering or allowed
   * lateness).
   */
  @SuppressWarnings("unchecked")
  public static <T, W extends BoundedWindow> boolean skipAssignWindows(
      Window.Assign<T> transform, TranslationContext context) {
    WindowFn<? super T, W> windowFnToApply = (WindowFn<? super T, W>) transform.getWindowFn();
    PCollection<T> input = (PCollection<T>) context.getInput();
    WindowFn<?, ?> windowFnOfInput = input.getWindowingStrategy().getWindowFn();
    return windowFnToApply == null
        || (windowFnOfInput instanceof GlobalWindows && windowFnToApply instanceof GlobalWindows);
  }

  public static <T, W extends BoundedWindow>
      MapFunction<WindowedValue<T>, WindowedValue<T>> assignWindowsMapFunction(
          WindowFn<T, W> windowFn) {
    return (MapFunction<WindowedValue<T>, WindowedValue<T>>)
        windowedValue -> {
          final BoundedWindow boundedWindow = Iterables.getOnlyElement(windowedValue.getWindows());
          final T element = windowedValue.getValue();
          final Instant timestamp = windowedValue.getTimestamp();
          Collection<W> windows =
              windowFn.assignWindows(
                  windowFn.new AssignContext() {

                    @Override
                    public T element() {
                      return element;
                    }

                    @Override
                    public Instant timestamp() {
                      return timestamp;
                    }

                    @Override
                    public BoundedWindow window() {
                      return boundedWindow;
                    }
                  });
          return WindowedValue.of(element, timestamp, windows, windowedValue.getPane());
        };
  }
}
