/*
 * 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.hadoop.yarn.server.webproxy;

import org.apache.hadoop.yarn.webapp.MimeType;
import org.apache.hadoop.yarn.webapp.hamlet.Hamlet;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.EnumSet;

/**
 * Class containing general purpose proxy utilities
 */
public class ProxyUtils {
  private static final Logger LOG = LoggerFactory.getLogger(
      ProxyUtils.class);
  public static final String E_HTTP_HTTPS_ONLY =
      "This filter only works for HTTP/HTTPS";
  public static final String LOCATION = "Location";

  public static class _ implements Hamlet._ {
    //Empty
  }

  public static class Page extends Hamlet {
    Page(PrintWriter out) {
      super(out, 0, false);
    }

    public HTML<ProxyUtils._> html() {
      return new HTML<>("html", null, EnumSet.of(EOpt.ENDTAG));
    }
  }
  
  /**
   * Handle redirects with a status code that can in future support verbs other
   * than GET, thus supporting full REST functionality.
   * <p>
   * The target URL is included in the redirect text returned
   * <p>
   * At the end of this method, the output stream is closed.
   * 
   * @param request request (hence: the verb and any other information
   * relevant to a redirect)
   * @param response the response
   * @param target the target URL -unencoded
   *
   */
  public static void sendRedirect(HttpServletRequest request,
      HttpServletResponse response,
      String target)
      throws IOException {
    if (LOG.isDebugEnabled()) {
      LOG.debug("Redirecting {} {} to {}",
          request.getMethod(), 
          request.getRequestURI(),
          target);
    }
    String location = response.encodeRedirectURL(target);
    response.setStatus(HttpServletResponse.SC_FOUND);
    response.setHeader(LOCATION, location);
    response.setContentType(MimeType.HTML);
    PrintWriter writer = response.getWriter();
    Page p = new Page(writer);
    p.html()
        .head().title("Moved")._()
        .body()
        .h1("Moved")
        .div()
          ._("Content has moved ")
          .a(location, "here")._()
        ._()._();
    writer.close();
  }


  /**
   * Output 404 with appropriate message.
   * @param resp the http response.
   * @param message the message to include on the page.
   * @throws IOException on any error.
   */
  public static void notFound(HttpServletResponse resp, String message)
      throws IOException {
    resp.setStatus(HttpServletResponse.SC_NOT_FOUND);
    resp.setContentType(MimeType.HTML);
    Page p = new Page(resp.getWriter());
    p.html().
        h1(message).
         _();
  }

  /**
   * Reject any request that isn't from an HTTP servlet
   * @param req request
   * @throws ServletException if the request is of the wrong type
   */
  public static void rejectNonHttpRequests(ServletRequest req) throws
      ServletException {
    if (!(req instanceof HttpServletRequest)) {
      throw new ServletException(E_HTTP_HTTPS_ONLY);
    }
  }
}