/*
 * 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.direct;

import org.apache.beam.sdk.coders.Coder;
import org.apache.beam.sdk.runners.AppliedPTransform;
import org.apache.beam.sdk.util.WindowedValue;
import org.apache.beam.sdk.values.PCollection;

/**
 * Enforcement tools that verify that executing code conforms to the model.
 *
 * <p>ModelEnforcement is performed on a per-element and per-bundle basis. The
 * {@link ModelEnforcement} is provided with the input bundle as part of
 * {@link ModelEnforcementFactory#forBundle(CommittedBundle, AppliedPTransform)} each
 * element before and after that element is provided to an underlying {@link TransformEvaluator},
 * and the output {@link TransformResult} and committed output bundles after the
 * {@link TransformEvaluator} has completed.
 *
 * <p>Typically, {@link ModelEnforcement} will obtain required metadata (such as the {@link Coder}
 * of the input {@link PCollection} on construction, and then enforce per-element behavior
 * (such as the immutability of input elements). When the element is output or the bundle is
 * completed, the required conditions can be enforced across all elements.
 */
interface ModelEnforcement<T> {
  /**
   * Called before a call to {@link TransformEvaluator#processElement(WindowedValue)} on the
   * provided {@link WindowedValue}.
   */
  void beforeElement(WindowedValue<T> element);

  /**
   * Called after a call to {@link TransformEvaluator#processElement(WindowedValue)} on the
   * provided {@link WindowedValue}.
   */
  void afterElement(WindowedValue<T> element);

  /**
   * Called after a bundle has been completed and {@link TransformEvaluator#finishBundle()} has been
   * called, producing the provided {@link TransformResult} and
   * {@link CommittedBundle output bundles}.
   */
  void afterFinish(
      CommittedBundle<T> input,
      TransformResult<T> result,
      Iterable<? extends CommittedBundle<?>> outputs);
}