/*
 * 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.wicket.request.resource;

import java.net.URLConnection;
import java.time.Instant;
import javax.servlet.http.HttpServletResponse;
import org.apache.wicket.request.Response;

/**
 * An abstract resource that can deliver static data - passed to the constructor, or dynamic -
 * returned by {@link #getData(org.apache.wicket.request.resource.IResource.Attributes)}
 *
 * @param <T>
 *            The type of the data this resource can deliver
 */
public abstract class BaseDataResource<T> extends AbstractResource
{
        private static final long serialVersionUID = 1L;

        /** the content type */
        private final String contentType;

        /** the data to deliver */
        private T data;

        /** the time that this resource was last modified; same as construction time. */
        private final Instant lastModified = Instant.now();

        private final String filename;

        /**
         * Creates a {@link org.apache.wicket.request.resource.BaseDataResource} which will provide its
         * data dynamically with
         * {@link #getData(org.apache.wicket.request.resource.IResource.Attributes)}
         *
         * @param contentType
         *            The Content type of the array.
         */
        public BaseDataResource(final String contentType)
        {
                this(contentType, null, null);
        }

        /**
         * Creates a Resource from the given data with its content type
         *
         * @param contentType
         *            The Content type of the array.
         * @param data
         *            The data
         */
        public BaseDataResource(final String contentType, final T data)
        {
                this(contentType, data, null);
        }

        /**
         * Creates a Resource from the given data with its content type and filename
         *
         * @param contentType
         *            The Content type of the array.
         * @param data
         *            The data
         * @param filename
         *            The filename that will be set as the Content-Disposition header.
         */
        public BaseDataResource(final String contentType, final T data, final String filename)
        {
                this.contentType = contentType;
                this.data = data;
                this.filename = filename;
        }

        /**
         * Post-configures the given response, e.g. set/override response headers.
         *
         * @param response
         *            The response to configure
         * @param attributes
         *            The request attributes (web request, web response, parameters)
         */
        protected void configureResponse(final ResourceResponse response, final Attributes attributes)
        {
        }

        @Override
        protected ResourceResponse newResourceResponse(final Attributes attributes)
        {
                final ResourceResponse response = new ResourceResponse();

                String contentType = this.contentType;
                String filename = getFilename();

                if (contentType == null)
                {
                        if (filename != null)
                        {
                                contentType = URLConnection.getFileNameMap().getContentTypeFor(filename);
                        }

                        if (contentType == null)
                        {
                                contentType = "application/octet-stream";
                        }
                }

                response.setContentType(contentType);
                response.setLastModified(lastModified);

                final T data = getData(attributes);
                if (data == null)
                {
                        response.setError(HttpServletResponse.SC_NOT_FOUND);
                }
                else
                {
                        Long length = getLength(data);
                        if (length != null)
                        {
                                response.setContentLength(length);
                        }

                        if (response.dataNeedsToBeWritten(attributes))
                        {
                                if (filename != null)
                                {
                                        response.setFileName(filename);
                                        response.setContentDisposition(ContentDisposition.ATTACHMENT);
                                }
                                else
                                {
                                        response.setContentDisposition(ContentDisposition.INLINE);
                                }

                                response.setWriteCallback(new WriteCallback()
                                {
                                        @Override
                                        public void writeData(final Attributes attributes)
                                        {
                                                BaseDataResource.this.writeData(attributes.getResponse(), data);
                                        }
                                });

                                configureResponse(response, attributes);
                        }
                }

                return response;
        }

        /**
         * Writes the given data to the response
         * 
         * @param response
         *            The response to write to
         * @param data
         *            The data to write
         */
        protected abstract void writeData(Response response, T data);

        /**
         * @param data
         *            The data to be written
         * @return The length of the data to be written. Used to set "Content-Length" response header
         */
        protected abstract Long getLength(T data);

        /**
         * Gets the data for this resource.
         * 
         * @param attributes
         *            the context bringing the request, response and the parameters
         * 
         * @return The data for this resource
         */
        protected T getData(final Attributes attributes)
        {
                return data;
        }

        /**
         * Returns the filename that will be set as the Content-Disposition header.
         *
         * @return the filename
         */
        protected String getFilename()
        {
                return filename;
        }
}