//// First, Implement an interface to intercept the HTTP Request before it goes out.
package com.google.java_scratch;

import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.http.HttpBackOffIOExceptionHandler;
import com.google.api.client.http.HttpBackOffUnsuccessfulResponseHandler;
import com.google.api.client.http.HttpBackOffUnsuccessfulResponseHandler.BackOffRequired;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.http.HttpUnsuccessfulResponseHandler;
import com.google.api.client.util.ExponentialBackOff;

import java.io.IOException;

/**
 * Google Java lib only allows for one HTTP Initializer per service.
 * - Wrap credentials initializer
 * - Handle retry
 */
public class ExponentialBackoffRequestInitializer implements HttpRequestInitializer {
  private final Credential googleCredential;
  private static final ExponentialBackOff backoff =
      new ExponentialBackOff.Builder()
          .setInitialIntervalMillis(500)
          .setMaxElapsedTimeMillis(900000)
          .setMaxIntervalMillis(6000)
          .setMultiplier(1.5)
          .setRandomizationFactor(0.5)
          .build();

  public ExponentialBackoffRequestInitializer(Credential googleCredential) {
    this.googleCredential = googleCredential;
  }

  @Override
  public void initialize(HttpRequest request) {
    final HttpBackOffUnsuccessfulResponseHandler backoffHandler =
        new HttpBackOffUnsuccessfulResponseHandler(backoff);

    // Attach credentials to request.
    request.setInterceptor(googleCredential);

    backoffHandler.setBackOffRequired(new BackOffRequired() {
      public boolean isRequired(HttpResponse response) {
        return (response.getStatusCode() / 100 == 5)
            || (response.getStatusCode() == 403);
      }
    });

    // Override unsuccessful response handler.
    request.setUnsuccessfulResponseHandler(new HttpUnsuccessfulResponseHandler() {
      @Override
      public boolean handleResponse(
          HttpRequest request, HttpResponse response, boolean supportsRetry) throws IOException {
        if (googleCredential.handleResponse(request, response, supportsRetry)) {
          // credentials returned success.
          return true;
        } else if (backoffHandler.handleResponse(request, response, supportsRetry)) {
          return true;
        } else {
          return false;
        }
      }
    });
    request.setIOExceptionHandler(new HttpBackOffIOExceptionHandler(backoff));
  }
}