content: /*
   *  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.causeway.viewer.restfulobjects.rendering.service;
  
  import java.util.List;
  import java.util.function.Function;
  import java.util.stream.Collectors;
  
  import jakarta.annotation.Priority;
  import jakarta.inject.Inject;
  import jakarta.inject.Named;
  import jakarta.ws.rs.core.Response;
  
  import org.springframework.stereotype.Service;
  
  import org.apache.causeway.applib.annotation.PriorityPrecedence;
  import org.apache.causeway.core.metamodel.interactions.managed.ManagedAction;
  import org.apache.causeway.core.metamodel.interactions.managed.ManagedCollection;
  import org.apache.causeway.core.metamodel.interactions.managed.ManagedProperty;
  import org.apache.causeway.core.metamodel.object.ManagedObject;
  import org.apache.causeway.viewer.restfulobjects.applib.CausewayModuleViewerRestfulObjectsApplib;
  import org.apache.causeway.viewer.restfulobjects.rendering.IResourceContext;
  import org.apache.causeway.viewer.restfulobjects.rendering.domainobjects.ObjectAndActionInvocation;
  import org.apache.causeway.viewer.restfulobjects.rendering.service.conneg.ContentNegotiationService;
  import org.apache.causeway.viewer.restfulobjects.rendering.service.conneg.ContentNegotiationServiceForRestfulObjectsV1_0;
  
  import lombok.extern.log4j.Log4j2;
  
  /**
   * Configures the Restful Objects viewer to emit custom representations (rather than the
   * standard representations defined in the RO spec).
   *
   * <p>
   *     The default implementations ultimately generate representations according
   *     to the <a href="http://restfulobjects.org">Restful Objects spec</a> v1.0.
   *     It does this through a level of abstraction by delegating to
   *     implementations of the
   *     {@link org.apache.causeway.viewer.restfulobjects.rendering.service.conneg.ContentNegotiationService}
   *     SPI.  This provides a mechanism for altering representations according
   *     to the HTTP `Accept` header.
   * </p>
   *
   * <p>
   * This interface is EXPERIMENTAL and may change in the future.
   * </p>
   *
   * @since 1.x {@index}
   */
  @Service
  @Named(CausewayModuleViewerRestfulObjectsApplib.NAMESPACE + ".RepresentationService")
  @Priority(PriorityPrecedence.EARLY)
  @Log4j2
  public class RepresentationService {
  
      private final List<ContentNegotiationService> contentNegotiationServices;
  
      @Inject
      public RepresentationService(List<ContentNegotiationService> contentNegotiationServices) {
          this.contentNegotiationServices = contentNegotiationServices;
      }
  
      /**
       * As returned by {@link IResourceContext#getIntent()}, applies only to the representation of
       * domain objects.
       */
      public enum Intent {
          /**
           * object just created, ie return a 201
           */
          JUST_CREATED,
          /**
           * object already persistent, ie return a 200
           */
          ALREADY_PERSISTENT,
          /**
           * representation is not of a domain object, so does not apply.
           */
          NOT_APPLICABLE
      }
  
      /**
       * Returns a representation of a single object.
       *
       * <p>
       *     By default this representation is as per section 14.4 of the
       *     RO spec, v1.0.
       * </p>
       */
      public Response objectRepresentation(
              final IResourceContext resourceContext,
              final ManagedObject objectAdapter) {
  
          final Response.ResponseBuilder responseBuilder = buildResponse(
                  connegService -> connegService.buildResponse(resourceContext, objectAdapter));
  
          assertContentNegotiationServiceHandled(responseBuilder);
          return buildResponse(responseBuilder);
      }
  
      /**
       * Returns a representation of a single property of an object.
       *
       * <p>
       *     By default this representation is as per section 16.4 of the
       *     RO spec, v1.0.
       * </p>
       */
      public Response propertyDetails(
              final IResourceContext resourceContext,
              final ManagedProperty objectAndProperty) {
  
          final Response.ResponseBuilder responseBuilder = buildResponse(
                  connegService -> connegService.buildResponse(resourceContext, objectAndProperty));
  
          assertContentNegotiationServiceHandled(responseBuilder);
          return buildResponse(responseBuilder);
      }
  
      /**
       * Returns a representation of a single collection of an object.
       *
       * <p>
       *     By default this representation is as per section 17.5 of the
       *     RO spec, v1.0.
       * </p>
       */
      public Response collectionDetails(
              final IResourceContext resourceContext,
              final ManagedCollection objectAndCollection) {
  
          final Response.ResponseBuilder responseBuilder = buildResponse(
                  connegService -> connegService.buildResponse(resourceContext, objectAndCollection));
  
          assertContentNegotiationServiceHandled(responseBuilder);
          return buildResponse(responseBuilder);
      }
  
      /**
       * Returns a representation of a single action (prompt) of an object.
       *
       * <p>
       *     By default this representation is as per section 18.2 of the
       *     RO spec, v1.0.
       * </p>
       */
      public Response actionPrompt(
              final IResourceContext resourceContext,
              final ManagedAction objectAndAction) {
  
          final Response.ResponseBuilder responseBuilder = buildResponse(
                  connegService -> connegService.buildResponse(resourceContext, objectAndAction));
  
          assertContentNegotiationServiceHandled(responseBuilder);
          return buildResponse(responseBuilder);
      }
  
      /**
       * Returns a representation of a single action invocation of an object.
       *
       * <p>
       *     By default this representation is as per section 19.5 of the
       *     RO spec, v1.0.
       * </p>
       */
      public Response actionResult(
              final IResourceContext resourceContext,
              final ObjectAndActionInvocation objectAndActionInvocation) {
  
          final Response.ResponseBuilder responseBuilder = buildResponse(
                  connegService -> connegService.buildResponse(resourceContext, objectAndActionInvocation));
  
          assertContentNegotiationServiceHandled(responseBuilder);
          return buildResponse(responseBuilder);
      }
  
      void assertContentNegotiationServiceHandled(final Response.ResponseBuilder responseBuilder) {
          if (responseBuilder == null) {
              throw new IllegalStateException("Could not locate " + ContentNegotiationService.class.getSimpleName() + " to handle request");
          }
      }
  
      /**
       * Iterates over all {@link #contentNegotiationServices injected} {@link ContentNegotiationService}s to find one
       * that returns a {@link Response.ResponseBuilder} using the provided function.
       *
       * <p>
       *     There will always be at least one such service, namely the
       *     {@link ContentNegotiationServiceForRestfulObjectsV1_0}.
       * </p>
       *
       * @param connegServiceBuildResponse - the function to ask of the {@link ContentNegotiationService}.
       */
      Response.ResponseBuilder buildResponse(
              Function<ContentNegotiationService, Response.ResponseBuilder> connegServiceBuildResponse) {
  
          log.debug("ContentNegotiationServices:\n{}", ()->contentNegotiationServices.stream()
                  .map(Object::getClass)
                  .map(Class::getSimpleName)
                  .map(s->" - "+s)
                  .collect(Collectors.joining("\n")));
  
          for (var contentNegotiationService : contentNegotiationServices) {
              var responseBuilder = connegServiceBuildResponse.apply(contentNegotiationService);
              if(responseBuilder != null) {
  
                  log.debug("--> winner: {}", ()->contentNegotiationService.getClass().getSimpleName());
                  return responseBuilder;
              }
          }
          return null;
      }
  
      /**
       * Override to allow further customization.
       */
      protected Response buildResponse(final Response.ResponseBuilder responseBuilder) {
          return responseBuilder.build();
      }
  
  }
  