/*
    * Copyright 2019 LINE Corporation
    *
    * LINE Corporation 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:
    *
    *   https://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.linecorp.centraldogma.server.metadata;
  
  import static java.util.Objects.requireNonNull;
  
  import java.util.function.Function;
  
  import com.linecorp.armeria.common.HttpRequest;
  import com.linecorp.armeria.common.HttpResponse;
  import com.linecorp.armeria.server.HttpService;
  import com.linecorp.armeria.server.Service;
  import com.linecorp.armeria.server.ServiceRequestContext;
  import com.linecorp.armeria.server.SimpleDecoratingHttpService;
  
  import io.netty.util.AttributeKey;
  
  /**
   * Injects the {@link MetadataService} instance into the attribute of the {@link ServiceRequestContext}.
   */
  public final class MetadataServiceInjector extends SimpleDecoratingHttpService {
  
      /**
       * Returns a newly created {@link Service} decorator from the specified {@link MetadataService}.
       */
      public static Function<? super HttpService, MetadataServiceInjector> newDecorator(MetadataService mds) {
          requireNonNull(mds, "mds");
          return service -> new MetadataServiceInjector(service, mds);
      }
  
      private static final AttributeKey<MetadataService> METADATA_SERVICE_ATTRIBUTE_KEY =
              AttributeKey.valueOf(MetadataServiceInjector.class, "METADATA");
  
      private final MetadataService mds;
  
      private MetadataServiceInjector(HttpService delegate, MetadataService mds) {
          super(delegate);
          this.mds = requireNonNull(mds, "mds");
      }
  
      @Override
      public HttpResponse serve(ServiceRequestContext ctx, HttpRequest req) throws Exception {
          ctx.setAttr(METADATA_SERVICE_ATTRIBUTE_KEY, mds);
          return unwrap().serve(ctx, req);
      }
  
      /**
       * Returns the {@link MetadataService} instance from the specified {@link ServiceRequestContext}.
       */
      public static MetadataService getMetadataService(ServiceRequestContext ctx) {
          final MetadataService mds = ctx.attr(METADATA_SERVICE_ATTRIBUTE_KEY);
          if (mds != null) {
              return mds;
          }
          throw new IllegalStateException("No metadata service instance exists.");
      }
  }