content: /*
   * Copyright (C) 2020 ActiveJ LLC.
   *
   * Licensed 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 io.activej.datastream.consumer;
  
  import io.activej.async.process.AsyncCloseable;
  import io.activej.datastream.processor.transformer.StreamConsumerTransformer;
  import io.activej.datastream.supplier.StreamDataAcceptor;
  import io.activej.datastream.supplier.StreamSupplier;
  import io.activej.promise.Promise;
  import org.jetbrains.annotations.Nullable;
  
  import java.util.function.UnaryOperator;
  
  /**
   * This interface represents an object that can asynchronously receive streams of data.
   * <p>
   * Implementors of this interface might want to extend {@link AbstractStreamConsumer}
   * instead of this interface, since it makes the threading and state management easier.
   */
  public interface StreamConsumer<T> extends AsyncCloseable {
  	/**
  	 * Begins streaming data from the given supplier into this consumer.
  	 * This method may not be called directly, use {@link StreamSupplier#streamTo} instead.
  	 * <p>
  	 * This method must have no effect after {@link #getAcknowledgement() the acknowledgement} is set.
  	 */
  	void consume(StreamSupplier<T> streamSupplier);
  
  	@Nullable StreamDataAcceptor<T> getDataAcceptor();
  
  	/**
  	 * A signal promise of the <i>acknowledgement</i> state of this consumer - its completion means that
  	 * this consumer changed to that state and is now <b>closed</b>.
  	 * <p>
  	 * When the consumer is in this state nobody must send any more data to any of its related acceptors.
  	 * <p>
  	 * If promise completes with an error then this consumer closes with that error.
  	 */
  	Promise<Void> getAcknowledgement();
  
  	default boolean isComplete() {
  		return getAcknowledgement().isComplete();
  	}
  
  	default boolean isResult() {
  		return getAcknowledgement().isResult();
  	}
  
  	default boolean isException() {
  		return getAcknowledgement().isException();
  	}
  
  	/**
  	 * Transforms this supplier with a given transformer.
  	 */
  	default <R> R transformWith(StreamConsumerTransformer<T, R> fn) {
  		return fn.transform(this);
  	}
  
  	/**
  	 * Creates a consumer from this one with its <i>acknowledge</i> signal modified by the given function.
  	 */
  	default StreamConsumer<T> withAcknowledgement(UnaryOperator<Promise<Void>> fn) {
  		Promise<Void> acknowledgement = getAcknowledgement();
  		Promise<Void> newAcknowledgement = fn.apply(acknowledgement);
  		if (acknowledgement == newAcknowledgement) return this;
  		return new ForwardingStreamConsumer<>(this) {
  			@Override
  			public Promise<Void> getAcknowledgement() {
  				return newAcknowledgement;
  			}
  		};
  	}
  }
  