/*
 * Copyright 2002-2008 the original author or authors.
 *
 * 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 org.springframework.web.servlet.view.document;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.lowagie.text.pdf.PdfReader;
import com.lowagie.text.pdf.PdfStamper;

import org.springframework.web.servlet.view.AbstractUrlBasedView;

/**
 * Abstract superclass for PDF views that operate on an existing
 * document with an AcroForm. Application-specific view classes
 * will extend this class to merge the PDF form with model data.
 *
 * <p>Thanks to Bryant Larsen for the suggestion and the original prototype!
 *
 * @author Juergen Hoeller
 * @since 2.5.4
 * @see AbstractPdfView
 */
public abstract class AbstractPdfStamperView extends AbstractUrlBasedView {

  public AbstractPdfStamperView(){
    setContentType("application/pdf");
  }


	protected boolean generatesDownloadContent() {
		return true;
	}

   protected final void renderMergedOutputModel(
			 Map model, HttpServletRequest request, HttpServletResponse response) throws Exception{

		// IE workaround: write into byte array first.
		ByteArrayOutputStream baos = createTemporaryOutputStream();

    PdfReader reader = readPdfResource();
    PdfStamper stamper = new PdfStamper(reader, baos);
    mergePdfDocument(model, stamper, request, response);
    stamper.close();

		// Flush to HTTP response.
		writeToResponse(response, baos);
  }

	/**
	 * Read the raw PDF resource into an iText PdfReader.
	 * <p>The default implementation resolve the specified "url" property
	 * as ApplicationContext resource.
	 * @return the PdfReader instance
	 * @throws IOException if resource access failed
	 * @see #setUrl
	 */
	protected PdfReader readPdfResource() throws IOException {
		return new PdfReader(getApplicationContext().getResource(getUrl()).getInputStream());
	}

  /**
	 * Subclasses must implement this method to merge the PDF form
	 * with the given model data.
   * <p>This is where you are able to set values on the AcroForm.
   * An example of what can be done at this level is:
	 * <pre class="code">
   * // get the form from the document
   * AcroFields form = stamper.getAcroFields();
   *
   * // set some values on the form
   * form.setField("field1", "value1");
   * form.setField("field2", "Vvlue2");
	 *
   * // set the disposition and filename
   * response.setHeader("Content-disposition", "attachment; FILENAME=someName.pdf");</pre>
	 * <p>Note that the passed-in HTTP response is just supposed to be used
	 * for setting cookies or other HTTP headers. The built PDF document itself
	 * will automatically get written to the response after this method returns.
	 * @param model the model Map
   * @param stamper the PdfStamper instance that will contain the AcroFields.
	 * You may also customize this PdfStamper instance according to your needs,
	 * e.g. setting the "formFlattening" property.
	 * @param request in case we need locale etc. Shouldn't look at attributes.
	 * @param response in case we need to set cookies. Shouldn't write to it.
	 * @throws Exception any exception that occured during document building
   */
  protected abstract void mergePdfDocument(
			Map model, PdfStamper stamper, HttpServletRequest request, HttpServletResponse response)
			throws Exception;

}