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/*
 * Copyright (C) 2016 Square, Inc.
 *
 * 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 retrofit2.adapter.java8;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.concurrent.CompletableFuture;
import retrofit2.Call;
import retrofit2.CallAdapter;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;

/**
 * A {@linkplain CallAdapter.Factory call adapter} which creates Java 8 futures.
 * 
 * Adding this class to {@link Retrofit} allows you to return {@link CompletableFuture} from
 * service methods.
 * 

 * interface MyService {
 *   @GET("user/me")
 *   CompletableFuture<User> getUser()
 * }
 * 
 * There are two configurations supported for the {@code CompletableFuture} type parameter:
 * 
 * Direct body (e.g., {@code CompletableFuture}) returns the deserialized body for 2XX
 * responses, sets {@link HttpException} errors for non-2XX responses, and sets {@link IOException}
 * for network errors.
 * Response wrapped body (e.g., {@code CompletableFuture>}) returns a
 * {@link Response} object for all HTTP responses and sets {@link IOException} for network
 * errors
 * 
 */
public final class Java8CallAdapterFactory extends CallAdapter.Factory {
  public static Java8CallAdapterFactory create() {
    return new Java8CallAdapterFactory();
  }

  private Java8CallAdapterFactory() {
  }

  @Override
  public CallAdapter get(Type returnType, Annotation[] annotations, Retrofit retrofit) {
    if (getRawType(returnType) != CompletableFuture.class) {
      return null;
    }
    if (!(returnType instanceof ParameterizedType)) {
      throw new IllegalStateException("CompletableFuture return type must be parameterized"
          + " as CompletableFuture or CompletableFuture");
    }
    Type innerType = getParameterUpperBound(0, (ParameterizedType) returnType);

    if (getRawType(innerType) != Response.class) {
      // Generic type is not Response. Use it for body-only adapter.
      return new BodyCallAdapter(innerType);
    }

    // Generic type is Response. Extract T and create the Response version of the adapter.
    if (!(innerType instanceof ParameterizedType)) {
      throw new IllegalStateException("Response must be parameterized"
          + " as Response or Response");
    }
    Type responseType = getParameterUpperBound(0, (ParameterizedType) innerType);
    return new ResponseCallAdapter(responseType);
  }

  private static class BodyCallAdapter implements CallAdapter> {
    private final Type responseType;

    BodyCallAdapter(Type responseType) {
      this.responseType = responseType;
    }

    @Override public Type responseType() {
      return responseType;
    }

    @Override public  CompletableFuture adapt(final Call call) {
      final CompletableFuture future = new CompletableFuture() {
        @Override public boolean cancel(boolean mayInterruptIfRunning) {
          if (mayInterruptIfRunning) {
            call.cancel();
          }
          return super.cancel(mayInterruptIfRunning);
        }
      };

      call.enqueue(new Callback() {
        @Override public void onResponse(Call call, Response response) {
          if (response.isSuccessful()) {
            future.complete(response.body());
          } else {
            future.completeExceptionally(new HttpException(response));
          }
        }

        @Override public void onFailure(Call call, Throwable t) {
          future.completeExceptionally(t);
        }
      });

      return future;
    }
  }

  private static class ResponseCallAdapter implements CallAdapter> {
    private final Type responseType;

    ResponseCallAdapter(Type responseType) {
      this.responseType = responseType;
    }

    @Override public Type responseType() {
      return responseType;
    }

    @Override public  CompletableFuture> adapt(final Call call) {
      final CompletableFuture> future = new CompletableFuture>() {
        @Override public boolean cancel(boolean mayInterruptIfRunning) {
          if (mayInterruptIfRunning) {
            call.cancel();
          }
          return super.cancel(mayInterruptIfRunning);
        }
      };

      call.enqueue(new Callback() {
        @Override public void onResponse(Call call, Response response) {
          future.complete(response);
        }

        @Override public void onFailure(Call call, Throwable t) {
          future.completeExceptionally(t);
        }
      });

      return future;
    }
  }
}