/*
 * 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.dataflow.worker;

import static org.apache.beam.runners.core.SplittableParDoViaKeyedWorkItems.ProcessFn;
import static org.apache.beam.vendor.guava.v20_0.com.google.common.base.Preconditions.checkArgument;

import java.util.Collection;
import org.apache.beam.runners.core.DoFnRunner;
import org.apache.beam.runners.core.KeyedWorkItem;
import org.apache.beam.runners.core.StateNamespaces.WindowNamespace;
import org.apache.beam.runners.core.TimerInternals.TimerData;
import org.apache.beam.sdk.state.TimeDomain;
import org.apache.beam.sdk.transforms.DoFn;
import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
import org.apache.beam.sdk.transforms.windowing.GlobalWindow;
import org.apache.beam.sdk.transforms.windowing.PaneInfo;
import org.apache.beam.sdk.util.WindowedValue;
import org.apache.beam.sdk.values.KV;
import org.apache.beam.vendor.guava.v20_0.com.google.common.collect.Iterables;
import org.joda.time.Instant;

/**
 * Runs a {@link ProcessFn} by constructing the appropriate contexts and passing them in.
 *
 * <p>This is the Dataflow-specific version of the runner-agnostic ProcessFnRunner. It's needed
 * because the code for handling pushback on streaming side inputs in Dataflow is also divergent
 * from the runner-agnostic code in runners-core. If that code is ever unified, so can this class.
 */
class DataflowProcessFnRunner<InputT, OutputT, RestrictionT>
    implements DoFnRunner<KeyedWorkItem<byte[], KV<InputT, RestrictionT>>, OutputT> {
  private final DoFnRunner<KeyedWorkItem<byte[], KV<InputT, RestrictionT>>, OutputT> simpleRunner;

  DataflowProcessFnRunner(
      DoFnRunner<KeyedWorkItem<byte[], KV<InputT, RestrictionT>>, OutputT> simpleRunner) {
    this.simpleRunner = simpleRunner;
  }

  @Override
  public void startBundle() {
    simpleRunner.startBundle();
  }

  @Override
  public void processElement(
      WindowedValue<KeyedWorkItem<byte[], KV<InputT, RestrictionT>>> compressedElem) {
    simpleRunner.processElement(placeIntoElementWindow(compressedElem));
  }

  private static <T> WindowedValue<KeyedWorkItem<byte[], T>> placeIntoElementWindow(
      WindowedValue<KeyedWorkItem<byte[], T>> compressedElem) {
    checkTrivialOuterWindows(compressedElem);
    WindowedValue<KeyedWorkItem<byte[], T>> res =
        WindowedValue.of(
            compressedElem.getValue(),
            BoundedWindow.TIMESTAMP_MIN_VALUE,
            getUnderlyingWindow(compressedElem.getValue()),
            PaneInfo.ON_TIME_AND_ONLY_FIRING);
    return res;
  }

  // TODO: move this and the next function into ProcessFn.
  private static <T> void checkTrivialOuterWindows(
      WindowedValue<KeyedWorkItem<byte[], T>> windowedKWI) {
    // In practice it will be in 0 or 1 windows (ValueInEmptyWindows or ValueInGlobalWindow)
    Collection<? extends BoundedWindow> outerWindows = windowedKWI.getWindows();
    if (!outerWindows.isEmpty()) {
      checkArgument(
          outerWindows.size() == 1,
          "The KeyedWorkItem itself must not be in multiple windows, but was in: %s",
          outerWindows);
      BoundedWindow onlyWindow = Iterables.getOnlyElement(outerWindows);
      checkArgument(
          onlyWindow instanceof GlobalWindow,
          "KeyedWorkItem must be in the Global window, but was in: %s",
          onlyWindow);
    }
  }

  private static <T> BoundedWindow getUnderlyingWindow(KeyedWorkItem<byte[], T> kwi) {
    if (Iterables.isEmpty(kwi.elementsIterable())) {
      // ProcessFn sets only a single timer.
      TimerData timer = Iterables.getOnlyElement(kwi.timersIterable());
      return ((WindowNamespace) timer.getNamespace()).getWindow();
    } else {
      // KWI must have a single element in elementsIterable, because it follows a GBK by a
      // uniquely generated key.
      // Additionally, windows must be exploded before GBKIntoKeyedWorkItems, so there's also
      // only a single window.
      WindowedValue<T> value = Iterables.getOnlyElement(kwi.elementsIterable());
      return Iterables.getOnlyElement(value.getWindows());
    }
  }

  @Override
  public void onTimer(
      String timerId, BoundedWindow window, Instant timestamp, TimeDomain timeDomain) {
    throw new UnsupportedOperationException("Unsupported for ProcessFn");
  }

  @Override
  public void finishBundle() {
    simpleRunner.finishBundle();
  }

  @Override
  public DoFn<KeyedWorkItem<byte[], KV<InputT, RestrictionT>>, OutputT> getFn() {
    return simpleRunner.getFn();
  }
}