/*
 * Copyright 2017 Google LLC
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google LLC nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.google.api.gax.rpc;

import com.google.api.core.AbstractApiFuture;
import com.google.api.core.ApiFuture;

/**
 * A {@link ResponseObserver} that wraps a future. The future will resolved upon receiving the first
 * element or exhausting the streaming.
 *
 * <p>Package-private for internal use.
 *
 * @param <ResponseT> The type of the element in the stream.
 */
class FirstElementResponseObserver<ResponseT> extends StateCheckingResponseObserver<ResponseT> {
  private final MyFuture future = new MyFuture();
  private StreamController controller;

  @Override
  protected void onStartImpl(StreamController controller) {
    // NOTE: the call is started before the future is exposed to the caller
    this.controller = controller;

    controller.disableAutoInboundFlowControl();
    controller.request(1);
  }

  @Override
  protected void onResponseImpl(ResponseT response) {
    future.set(response);
    controller.cancel();
  }

  @Override
  protected void onErrorImpl(Throwable t) {
    future.setException(t);
  }

  @Override
  protected void onCompleteImpl() {
    future.set(null);
  }

  ApiFuture<ResponseT> getFuture() {
    return future;
  }

  /** Simple implementation of a future that allows the receiver to cancel the underlying stream. */
  private class MyFuture extends AbstractApiFuture<ResponseT> {
    @Override
    protected void interruptTask() {
      FirstElementResponseObserver.this.controller.cancel();
    }

    @Override
    protected boolean set(ResponseT value) {
      return super.set(value);
    }

    @Override
    protected boolean setException(Throwable throwable) {
      return super.setException(throwable);
    }
  }
}
