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/*
 * Copyright 2014 The gRPC Authors
 *
 * 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.grpc;

import com.google.common.base.Preconditions;
import io.grpc.MethodDescriptor.Marshaller;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
 * Utility methods for working with {@link ClientInterceptor}s.
 */
public class ClientInterceptors {

  // Prevent instantiation
  private ClientInterceptors() {}

  /**
   * Create a new {@link Channel} that will call {@code interceptors} before starting a call on the
   * given channel. The first interceptor will have its {@link ClientInterceptor#interceptCall}
   * called first.
   *
   * @param channel the underlying channel to intercept.
   * @param interceptors array of interceptors to bind to {@code channel}.
   * @return a new channel instance with the interceptors applied.
   */
  public static Channel interceptForward(Channel channel, ClientInterceptor... interceptors) {
    return interceptForward(channel, Arrays.asList(interceptors));
  }

  /**
   * Create a new {@link Channel} that will call {@code interceptors} before starting a call on the
   * given channel. The first interceptor will have its {@link ClientInterceptor#interceptCall}
   * called first.
   *
   * @param channel the underlying channel to intercept.
   * @param interceptors a list of interceptors to bind to {@code channel}.
   * @return a new channel instance with the interceptors applied.
   */
  public static Channel interceptForward(Channel channel,
                                         List interceptors) {
    List copy = new ArrayList<>(interceptors);
    Collections.reverse(copy);
    return intercept(channel, copy);
  }

  /**
   * Create a new {@link Channel} that will call {@code interceptors} before starting a call on the
   * given channel. The last interceptor will have its {@link ClientInterceptor#interceptCall}
   * called first.
   *
   * @param channel the underlying channel to intercept.
   * @param interceptors array of interceptors to bind to {@code channel}.
   * @return a new channel instance with the interceptors applied.
   */
  public static Channel intercept(Channel channel, ClientInterceptor... interceptors) {
    return intercept(channel, Arrays.asList(interceptors));
  }

  /**
   * Create a new {@link Channel} that will call {@code interceptors} before starting a call on the
   * given channel. The last interceptor will have its {@link ClientInterceptor#interceptCall}
   * called first.
   *
   * @param channel the underlying channel to intercept.
   * @param interceptors a list of interceptors to bind to {@code channel}.
   * @return a new channel instance with the interceptors applied.
   */
  public static Channel intercept(Channel channel, List interceptors) {
    Preconditions.checkNotNull(channel, "channel");
    for (ClientInterceptor interceptor : interceptors) {
      channel = new InterceptorChannel(channel, interceptor);
    }
    return channel;
  }

  /**
   * Creates a new ClientInterceptor that transforms requests into {@code WReqT} and responses into
   * {@code WRespT} before passing them into the {@code interceptor}.
   */
  static  ClientInterceptor wrapClientInterceptor(
      final ClientInterceptor interceptor,
      final Marshaller reqMarshaller,
      final Marshaller respMarshaller) {
    return new ClientInterceptor() {
      @Override
      public  ClientCall interceptCall(
          final MethodDescriptor method, CallOptions callOptions, Channel next) {
        final MethodDescriptor wrappedMethod =
            method.toBuilder(reqMarshaller, respMarshaller).build();
        final ClientCall wrappedCall =
            interceptor.interceptCall(wrappedMethod, callOptions, next);
        return new PartialForwardingClientCall() {
          @Override
          public void start(final Listener responseListener, Metadata headers) {
            wrappedCall.start(new PartialForwardingClientCallListener() {
              @Override
              public void onMessage(WRespT wMessage) {
                InputStream bytes = respMarshaller.stream(wMessage);
                RespT message = method.getResponseMarshaller().parse(bytes);
                responseListener.onMessage(message);
              }

              @Override
              protected Listener delegate() {
                return responseListener;
              }
            }, headers);
          }

          @Override
          public void sendMessage(ReqT message) {
            InputStream bytes = method.getRequestMarshaller().stream(message);
            WReqT wReq = reqMarshaller.parse(bytes);
            wrappedCall.sendMessage(wReq);
          }

          @Override
          protected ClientCall delegate() {
            return wrappedCall;
          }
        };
      }
    };
  }

  private static class InterceptorChannel extends Channel {
    private final Channel channel;
    private final ClientInterceptor interceptor;

    private InterceptorChannel(Channel channel, ClientInterceptor interceptor) {
      this.channel = channel;
      this.interceptor = Preconditions.checkNotNull(interceptor, "interceptor");
    }

    @Override
    public  ClientCall newCall(
        MethodDescriptor method, CallOptions callOptions) {
      return interceptor.interceptCall(method, callOptions, channel);
    }

    @Override
    public String authority() {
      return channel.authority();
    }
  }

  private static final ClientCall NOOP_CALL = new ClientCall() {
    @Override
    public void start(Listener