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package com.google.api.gax.httpjson;

import com.google.api.gax.rpc.ApiCallContext;
import com.google.api.gax.rpc.ResponseObserver;
import com.google.api.gax.rpc.ServerStreamingCallable;
import com.google.api.gax.rpc.StreamController;
import com.google.common.base.Preconditions;

/**
 * {@code HttpJsonDirectServerStreamingCallable} creates server-streaming REST calls.
 *
 * <p>In a chain of {@link ServerStreamingCallable}s this is the innermost callable. It wraps a
 * {@link HttpJsonClientCall} in a {@link StreamController} and the downstream {@link
 * ResponseObserver} in a {@link HttpJsonClientCall.Listener}. This class is implemented to look and
 * behave as similarly as possible to gRPC variant of it.
 *
 * <p>Package-private for internal use.
 */
class HttpJsonDirectServerStreamingCallable<RequestT, ResponseT>
    extends ServerStreamingCallable<RequestT, ResponseT> {

  private final ApiMethodDescriptor<RequestT, ResponseT> descriptor;

  HttpJsonDirectServerStreamingCallable(ApiMethodDescriptor<RequestT, ResponseT> descriptor) {
    this.descriptor = descriptor;
  }

  @Override
  public void call(
      RequestT request, ResponseObserver<ResponseT> responseObserver, ApiCallContext context) {

    Preconditions.checkNotNull(request);
    Preconditions.checkNotNull(responseObserver);

    HttpJsonClientCall<RequestT, ResponseT> call = HttpJsonClientCalls.newCall(descriptor, context);
    HttpJsonDirectStreamController<RequestT, ResponseT> controller =
        new HttpJsonDirectStreamController<>(call, responseObserver);
    controller.start(request);
  }
}