/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.beam.sdk.extensions.gcp.auth;

import com.google.auth.Credentials;
import com.google.auth.oauth2.GoogleCredentials;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import org.apache.beam.sdk.options.PipelineOptions;

/**
 * Construct an oauth credential to be used by the SDK and the SDK workers.
 * Returns a GCP credential.
 */
public class GcpCredentialFactory implements CredentialFactory {
  /**
   * The scope cloud-platform provides access to all Cloud Platform resources.
   * cloud-platform isn't sufficient yet for talking to datastore so we request
   * those resources separately.
   *
   * <p>Note that trusted scope relationships don't apply to OAuth tokens, so for
   * services we access directly (GCS) as opposed to through the backend
   * (BigQuery, GCE), we need to explicitly request that scope.
   */
  private static final List<String> SCOPES = Arrays.asList(
      "https://www.googleapis.com/auth/cloud-platform",
      "https://www.googleapis.com/auth/devstorage.full_control",
      "https://www.googleapis.com/auth/userinfo.email",
      "https://www.googleapis.com/auth/datastore",
      "https://www.googleapis.com/auth/pubsub");

  private static final GcpCredentialFactory INSTANCE = new GcpCredentialFactory();

  public static GcpCredentialFactory fromOptions(PipelineOptions options) {
    return INSTANCE;
  }

  /**
   * Returns a default GCP {@link Credentials} or null when it fails.
   */
  @Override
  public Credentials getCredential() {
    try {
      return GoogleCredentials.getApplicationDefault().createScoped(SCOPES);
    } catch (IOException e) {
      // Ignore the exception
      // Pipelines that only access to public data should be able to run without credentials.
      return null;
    }
  }
}