// Copyright 2017 The Bazel Authors. All rights reserved.
//
// 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 com.google.devtools.build.lib.authandtls;

import com.google.auth.Credentials;
import com.google.auth.oauth2.GoogleCredentials;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import io.grpc.CallCredentials;
import io.grpc.ClientInterceptor;
import io.grpc.ManagedChannel;
import io.grpc.auth.MoreCallCredentials;
import io.grpc.netty.GrpcSslContexts;
import io.grpc.netty.NegotiationType;
import io.grpc.netty.NettyChannelBuilder;
import io.netty.handler.ssl.SslContext;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import javax.annotation.Nullable;

/** Utility methods for using {@link AuthAndTLSOptions} with Google Cloud. */
public final class GoogleAuthUtils {

  /**
   * Create a new gRPC {@link ManagedChannel}.
   *
   * @throws IOException in case the channel can't be constructed.
   */
  public static ManagedChannel newChannel(String target, AuthAndTLSOptions options,
      ClientInterceptor... interceptors)
      throws IOException {
    Preconditions.checkNotNull(target);
    Preconditions.checkNotNull(options);
    Preconditions.checkNotNull(interceptors);

    final SslContext sslContext =
        isTlsEnabled(target, options) ? createSSlContext(options.tlsCertificate) : null;

    String targetUrl = convertTargetScheme(target);

    try {
      NettyChannelBuilder builder =
          NettyChannelBuilder.forTarget(targetUrl)
              .negotiationType(
                  isTlsEnabled(target, options) ? NegotiationType.TLS : NegotiationType.PLAINTEXT)
              .defaultLoadBalancingPolicy("round_robin")
              .intercept(interceptors);
      if (sslContext != null) {
        builder.sslContext(sslContext);
        if (options.tlsAuthorityOverride != null) {
          builder.overrideAuthority(options.tlsAuthorityOverride);
        }
      }
      return builder.build();
    } catch (RuntimeException e) {
      // gRPC might throw all kinds of RuntimeExceptions: StatusRuntimeException,
      // IllegalStateException, NullPointerException, ...
      String message = "Failed to connect to '%s': %s";
      throw new IOException(String.format(message, targetUrl, e.getMessage()));
    }
  }

  /**
   * Converts 'grpc(s)' into an empty protocol, because 'grpc(s)' is not a widely supported scheme
   * and is interpreted as 'dns' under the hood.
   *
   * @return target URL with converted scheme
   */
  private static String convertTargetScheme(String target) {
    return target.replace("grpcs://", "").replace("grpc://", "");
  }

  // TODO(ishikhman) remove options.tlsEnabled flag usage when an incompatible flag is flipped
  private static boolean isTlsEnabled(String target, AuthAndTLSOptions options) {
    if (options.incompatibleTlsEnabledRemoved && options.tlsEnabled) {
      throw new IllegalArgumentException("flag --tls_enabled was not found");
    }
    if (options.incompatibleTlsEnabledRemoved) {
      // 'grpcs://' or empty prefix => TLS-enabled
      // when no schema prefix is provided in URL, bazel will treat it as a gRPC request with TLS
      // enabled
      return !target.startsWith("grpc://");
    }
    return target.startsWith("grpcs") || options.tlsEnabled;
  }

  private static SslContext createSSlContext(@Nullable String rootCert) throws IOException {
    if (rootCert == null) {
      try {
        return GrpcSslContexts.forClient().build();
      } catch (Exception e) {
        String message = "Failed to init TLS infrastructure: " + e.getMessage();
        throw new IOException(message, e);
      }
    } else {
      try {
        return GrpcSslContexts.forClient().trustManager(new File(rootCert)).build();
      } catch (Exception e) {
        String message = "Failed to init TLS infrastructure using '%s' as root certificate: %s";
        message = String.format(message, rootCert, e.getMessage());
        throw new IOException(message, e);
      }
    }
  }

  /**
   * Create a new {@link CallCredentials} object.
   *
   * @throws IOException in case the call credentials can't be constructed.
   */
  public static CallCredentials newCallCredentials(AuthAndTLSOptions options) throws IOException {
    Credentials creds = newCredentials(options);
    if (creds != null) {
      return MoreCallCredentials.from(creds);
    }
    return null;
  }

  @VisibleForTesting
  public static CallCredentials newCallCredentials(
      @Nullable InputStream credentialsFile, List<String> authScope) throws IOException {
    Credentials creds = newCredentials(credentialsFile, authScope);
    if (creds != null) {
      return MoreCallCredentials.from(creds);
    }
    return null;
  }

  /**
   * Create a new {@link Credentials} object, or {@code null} if no options are provided.
   *
   * @throws IOException in case the credentials can't be constructed.
   */
  @Nullable
  public static Credentials newCredentials(@Nullable AuthAndTLSOptions options) throws IOException {
    if (options == null) {
      return null;
    } else if (options.googleCredentials != null) {
      // Credentials from file
      try (InputStream authFile = new FileInputStream(options.googleCredentials)) {
        return newCredentials(authFile, options.googleAuthScopes);
      } catch (FileNotFoundException e) {
        String message =
            String.format(
                "Could not open auth credentials file '%s': %s",
                options.googleCredentials, e.getMessage());
        throw new IOException(message, e);
      }
    } else if (options.useGoogleDefaultCredentials) {
      return newCredentials(
          null /* Google Application Default Credentials */, options.googleAuthScopes);
    }
    return null;
  }

  private static Credentials newCredentials(
      @Nullable InputStream credentialsFile, List<String> authScopes) throws IOException {
    try {
      GoogleCredentials creds =
          credentialsFile == null
              ? GoogleCredentials.getApplicationDefault()
              : GoogleCredentials.fromStream(credentialsFile);
      if (!authScopes.isEmpty()) {
        creds = creds.createScoped(authScopes);
      }
      return creds;
    } catch (IOException e) {
      String message = "Failed to init auth credentials: " + e.getMessage();
      throw new IOException(message, e);
    }
  }
}