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;
  
  import java.io.Serializable;
  import org.apache.beam.sdk.values.PCollectionView;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.MoreObjects;
  
  /** Pair of a bit of user code (a "closure") and the {@link Requirements} needed to run it. */
  public final class Contextful<ClosureT> implements Serializable {
    private final ClosureT closure;
    private final Requirements requirements;
  
    private Contextful(ClosureT closure, Requirements requirements) {
      this.closure = closure;
      this.requirements = requirements;
    }
  
    /** Returns the closure. */
    public ClosureT getClosure() {
      return closure;
    }
  
    /** Returns the requirements needed to run the closure. */
    public Requirements getRequirements() {
      return requirements;
    }
  
    /** Constructs a pair of the given closure and its requirements. */
    public static <ClosureT> Contextful<ClosureT> of(ClosureT closure, Requirements requirements) {
      return new Contextful<>(closure, requirements);
    }
  
    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this)
          .add("closure", closure)
          .add("requirements", requirements)
          .toString();
    }
  
    /**
     * A function from an input to an output that may additionally access {@link Context} when
     * computing the result.
     */
    public interface Fn<InputT, OutputT> extends Serializable {
      /**
       * Invokes the function on the given input with the given context. The function may use the
       * context only for the capabilities declared in the {@link Contextful#getRequirements} of the
       * enclosing {@link Contextful}.
       */
      OutputT apply(InputT element, Context c) throws Exception;
  
      /** An accessor for additional capabilities available in {@link #apply}. */
      abstract class Context {
        /**
         * Accesses the given side input. The window in which it is accessed is unspecified, depends
         * on usage by the enclosing {@link PTransform}, and must be documented by that transform.
         */
        public <T> T sideInput(PCollectionView<T> view) {
          throw new UnsupportedOperationException();
        }
  
        /**
         * Convenience wrapper for creating a {@link Context} from a {@link DoFn.ProcessContext}, to
         * support the common case when a {@link PTransform} is invoking the {@link
         * Contextful#getClosure() closure} from inside a {@link DoFn}.
         */
        public static <InputT> Context wrapProcessContext(final DoFn<InputT, ?>.ProcessContext c) {
          return new ContextFromProcessContext<>(c);
        }
  
        private static class ContextFromProcessContext<InputT> extends Context {
          private final DoFn<InputT, ?>.ProcessContext c;
  
          ContextFromProcessContext(DoFn<InputT, ?>.ProcessContext c) {
            this.c = c;
          }
  
          @Override
          public <T> T sideInput(PCollectionView<T> view) {
            return c.sideInput(view);
          }
        }
      }
    }
  
    /**
     * Wraps a {@link ProcessFunction} as a {@link Contextful} of {@link Fn} with empty {@link
     * Requirements}.
     */
    public static <InputT, OutputT> Contextful<Fn<InputT, OutputT>> fn(
        final ProcessFunction<InputT, OutputT> fn) {
      return new Contextful<>((element, c) -> fn.apply(element), Requirements.empty());
    }
  
    /** Binary compatibility adapter for {@link #fn(ProcessFunction)}. */
    public static <InputT, OutputT> Contextful<Fn<InputT, OutputT>> fn(
        final SerializableFunction<InputT, OutputT> fn) {
      return fn((ProcessFunction<InputT, OutputT>) fn);
    }
  
    /** Same with {@link #of} but with better type inference behavior for the case of {@link Fn}. */
    public static <InputT, OutputT> Contextful<Fn<InputT, OutputT>> fn(
        final Fn<InputT, OutputT> fn, Requirements requirements) {
      return of(fn, requirements);
    }
  }
  