# HtmlResourceHandler.java

    /*
    ** Module   : HtmlResourceHandler.java
    ** Abstract : delivers main page to AJAX clients
    **
    ** Copyright (c) 2013-2023, Golden Code Development Corporation.
    **
    ** -#- -I- --Date-- ----------------------Description--------------------------
    ** 001 MAG 20131105 First version based on jetty 9.1
    ** 002 MAG 20140206 Set Cache-Control header.
    ** 003 SBI 20180405 Changed to use template key and value provider.
    ** 004 SBI 20191120 Changed to specify UTF-8 encoding to read html templates.
    ** 005 GBB 20230512 Logging methods replaced by CentralLogger/ConversionStatus.
    */
    /*
    ** This program is free software: you can redistribute it and/or modify
    ** it under the terms of the GNU Affero General Public License as
    ** published by the Free Software Foundation, either version 3 of the
    ** License, or (at your option) any later version.
    **
    ** This program is distributed in the hope that it will be useful,
    ** but WITHOUT ANY WARRANTY; without even the implied warranty of
    ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    ** GNU Affero General Public License for more details.
    **
    ** You may find a copy of the GNU Affero GPL version 3 at the following
    ** location: https://www.gnu.org/licenses/agpl-3.0.en.html
    **
    ** Additional terms under GNU Affero GPL version 3 section 7:
    **
    **   Under Section 7 of the GNU Affero GPL version 3, the following additional
    **   terms apply to the works covered under the License.  These additional terms
    **   are non-permissive additional terms allowed under Section 7 of the GNU
    **   Affero GPL version 3 and may not be removed by you.
    **
    **   0. Attribution Requirement.
    **
    **     You must preserve all legal notices or author attributions in the covered
    **     work or Appropriate Legal Notices displayed by works containing the covered
    **     work.  You may not remove from the covered work any author or developer
    **     credit already included within the covered work.
    **
    **   1. No License To Use Trademarks.
    **
    **     This license does not grant any license or rights to use the trademarks
    **     Golden Code, FWD, any Golden Code or FWD logo, or any other trademarks
    **     of Golden Code Development Corporation. You are not authorized to use the
    **     name Golden Code, FWD, or the names of any author or contributor, for
    **     publicity purposes without written authorization.
    **
    **   2. No Misrepresentation of Affiliation.
    **
    **     You may not represent yourself as Golden Code Development Corporation or FWD.
    **
    **     You may not represent yourself for publicity purposes as associated with
    **     Golden Code Development Corporation, FWD, or any author or contributor to
    **     the covered work, without written authorization.
    **
    **   3. No Misrepresentation of Source or Origin.
    **
    **     You may not represent the covered work as solely your work.  All modified
    **     versions of the covered work must be marked in a reasonable way to make it
    **     clear that the modified work is not originating from Golden Code Development
    **     Corporation or FWD.  All modified versions must contain the notices of
    **     attribution required in this license.
    */

    package com.goldencode.p2j.web;

    import java.io.*;
    import java.util.HashMap;
    import java.util.Map;
    import java.util.function.Supplier;
    import java.util.logging.*;

    import javax.servlet.*;
    import javax.servlet.http.*;

    import com.goldencode.p2j.util.logging.*;
    import org.eclipse.jetty.http.*;
    import org.eclipse.jetty.server.handler.*;
    import org.eclipse.jetty.server.*;

    import com.goldencode.p2j.util.*;

    /**
     * jetty Handler which delivers HTML resource files.
     * This class provide a method to parse the HTML text and
     * substitute placeholder's.
     */
    public abstract class HtmlResourceHandler
    extends AbstractHandler
    {
       /** Logger. */
       private static final CentralLogger LOG = CentralLogger.get(HtmlResourceHandler.class.getName());

       /** The root portion of the target request name (part of the URL). */
       private String targetRoot = null;

       /** The html skeleton page. */
       private String skeletonPage = null;

       /**
        * Constructor.
        *
        * @param    targetRoot
        *           Prefix for all URLs relating to this page.
        * @param    skeletonPage
        *           Fully qualified resource name of the HTML file which should be used.
        */
       public HtmlResourceHandler(String targetRoot, String skeletonPage)
       {
          this.targetRoot   = targetRoot;
          this.skeletonPage = skeletonPage;
       }

       /**
        * Return the main page for AJAX clients.
        *
        * @param   target
        *          The target of the request - either a URI or a name.
        * @param   base
        *          The base request.
        * @param   request
        *          The object or a wrapper of the request.
        * @param   response
        *          The object or a wrapper of the response.
        */
       public void handle(String              target,
                          Request             base,
                          HttpServletRequest  request,
                          HttpServletResponse response)
       throws IOException,
              ServletException
       {
          if (!base.isHandled() && target.equalsIgnoreCase(targetRoot))
          {
             generateMainPage(base, response);
          }
       }

       /**
        * Use the skeleton main page to generate a response.
        *
        * @param   base
        *          The details and state the request.
        * @param   response
        *          The details and state of the response.
        *
        * @throws  IOException
        *          ServletException
        *          If any error conditions occur.
        */
       private void generateMainPage(Request base, HttpServletResponse response)
       throws IOException,
              ServletException
       {
          // produce the page contents
          response.setContentType(MimeTypes.Type.TEXT_HTML.asString());
          response.setStatus(HttpServletResponse.SC_OK);
          response.setHeader(HttpHeader.CACHE_CONTROL.asString(),
                             "no-cache, no-store, must-revalidate");
          response.setDateHeader(HttpHeader.EXPIRES.asString(), 0); // Proxies.

          PrintWriter writer = response.getWriter();

          Map<String, Supplier<String>> templateKeys = getTemplateKeys(base);

          try
          {
             InputStream is = this.getClass().getResourceAsStream(skeletonPage);

             TemplateHelper.fill(is, templateKeys, writer, "UTF-8");
          }
          catch (IOException ioe)
          {
             LOG.logp(Level.SEVERE,
                      "HtmlResourceHandler.generateMainPage()",
                      "",
                      "IOException!",
                      ioe);
          }
          finally
          {
             // mark the request as handled
             base.setHandled(true);
          }
       }

       /**
        * Generates a map of template keys with their value suppliers in order to fill gaps in
        * the html skeleton template page.
        *
        * @param    base
        *           The request
        *
        * @return   The target map of template keys with their value suppliers
        */
       protected abstract Map<String, Supplier<String>> getTemplateKeys(Request base);

       /**
        * Holds a map of template keys with their value suppliers.
        */
       protected class HtmlTemplateKeysProvider
       {
          /** The map of template keys with their value suppliers */
          private final Map<String, Supplier<String>> templateKeys;

          /** The request */
          private final Request request;

          /**
           * Creates this html template keys provider.
           *
           * @param    request
           *           The request
           */
          public HtmlTemplateKeysProvider(Request request)
          {
             this.request = request;
             this.templateKeys = new HashMap<>();
          }

          /**
           * Returns the request associated with this html template keys provider.
           *
           * @return   The request
           */
          public Request getRequest()
          {
             return request;
          }

          /**
           * Returns the map of template keys with their value suppliers.
           *
           * @return   The map of template keys with their value suppliers
           */
          public Map<String, Supplier<String>> getTemplateKeys()
          {
             return templateKeys;
          }

          /**
           * Add new key and its value provider.
           *
           * @param    key
           *           The key
           * @param    getter
           *           The value provider
           */
          public void add(String key, Supplier<String> getter)
          {
             templateKeys.put(key, getter);
          }
       }
    }