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.wicket.ui.exec;
  
  import java.io.ByteArrayInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.time.Duration;
  
  import org.apache.wicket.request.IRequestHandler;
  import org.apache.wicket.request.handler.resource.ResourceStreamRequestHandler;
  import org.apache.wicket.request.resource.ContentDisposition;
  import org.apache.wicket.util.resource.AbstractResourceStream;
  import org.apache.wicket.util.resource.IResourceStream;
  import org.apache.wicket.util.resource.ResourceStreamNotFoundException;
  import org.apache.wicket.util.resource.StringResourceStream;
  
  import org.apache.causeway.applib.value.Blob;
  import org.apache.causeway.applib.value.Clob;
  import org.apache.causeway.applib.value.NamedWithMimeType;
  import org.apache.causeway.core.metamodel.spec.feature.ObjectAction;
  
  import lombok.experimental.UtilityClass;
  
  @UtilityClass
  final class DownloadHandlerFactory {
  
      public IRequestHandler downloadHandler(
              final ObjectAction action,
              final Object value) {
          if(value instanceof Clob clob) {
              return handlerFor(action, resourceStreamFor(clob), clob);
          }
          if(value instanceof Blob blob) {
              return handlerFor(action, resourceStreamFor(blob), blob);
          }
          return null;
      }
  
      // -- HELPER
  
      private IResourceStream resourceStreamFor(final Blob blob) {
          final IResourceStream resourceStream = new AbstractResourceStream() {
              private static final long serialVersionUID = 1L;
              @Override public InputStream getInputStream() throws ResourceStreamNotFoundException {
                  return new ByteArrayInputStream(blob.bytes());
              }
              @Override public String getContentType() {
                  return blob.mimeType().toString();
              }
              @Override public void close() throws IOException {
              }
          };
          return resourceStream;
      }
  
      private IResourceStream resourceStreamFor(final Clob clob) {
          return new StringResourceStream(clob.chars(), clob.mimeType().toString());
      }
  
      private IRequestHandler handlerFor(
              final ObjectAction action,
              final IResourceStream resourceStream,
              final NamedWithMimeType namedWithMimeType) {
          var handler =
                  new ResourceStreamRequestHandler(resourceStream, namedWithMimeType.name());
          handler.setContentDisposition(ContentDisposition.ATTACHMENT);
  
          //CAUSEWAY-1619, prevent clients from caching the response content
          return action.getSemantics().isIdempotentOrCachable()
                  ? handler
                  : enforceNoCacheOnClientSide(handler);
      }
  
      // -- CLIENT SIDE CACHING ASPECTS ...
  
      private static IRequestHandler enforceNoCacheOnClientSide(final IRequestHandler downloadHandler){
          if(downloadHandler==null) {
              return downloadHandler;
          }
          if(downloadHandler instanceof ResourceStreamRequestHandler)
              ((ResourceStreamRequestHandler) downloadHandler)
              .setCacheDuration(Duration.ZERO);
  
          return downloadHandler;
      }
  
  }
  