/*
 * 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.beam.runners.dataflow.worker.status;

import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import java.io.File;
import java.io.IOException;
import javax.management.InstanceNotFoundException;
import javax.management.MBeanException;
import javax.management.MalformedObjectNameException;
import javax.management.ReflectionException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.beam.runners.dataflow.worker.util.MemoryMonitor;
import org.apache.beam.vendor.guava.v20_0.com.google.common.io.Files;

/**
 * Respond to /heapz with a page allowing downloading of the heap dumps.
 *
 * <p>Respond to /heapz?action=download with a download of the actual heap dump.
 *
 * <p><b>Not actually serializable</b>. Its superclass is serializable but this subclass is not.
 */
@SuppressFBWarnings("SE_BAD_FIELD") // not serializable
public class HeapzServlet extends BaseStatusServlet {

  private final MemoryMonitor memoryMonitor;

  public HeapzServlet(MemoryMonitor memoryMonitor) {
    super("heapz");
    this.memoryMonitor = memoryMonitor;
  }

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    String action = req.getParameter("action");
    if (action == null || action.isEmpty()) {
      resp.setContentType("text/html;charset=utf-8");
      resp.setStatus(HttpServletResponse.SC_OK);

      ServletOutputStream writer = resp.getOutputStream();
      writer.println("<html>");
      writer.println(
          String.format(
              "Click <a href=\"%s\">here to download heap dump</a>", getPath("action=download")));
      writer.println("</html>");
      return;
    } else if ("download".equals(action)) {
      doDownload(resp);
    }
  }

  private void doDownload(HttpServletResponse resp) throws IOException {
    File file;

    try {
      file = memoryMonitor.dumpHeap();
    } catch (MalformedObjectNameException
        | InstanceNotFoundException
        | ReflectionException
        | MBeanException e) {
      resp.setContentType("text/html;charset=utf-8");
      resp.setStatus(HttpServletResponse.SC_OK);

      ServletOutputStream writer = resp.getOutputStream();
      writer.println("<html>\nFailed to dump heap: <br>\n<pre>");
      writer.println(e.toString());
      writer.println("</pre>\n</html>");
      return;
    }

    resp.setContentType("application/octet-stream");
    resp.setContentLength((int) file.length());
    resp.setHeader(
        "Content-Disposition", String.format("attachment; filename=\"%s\"", file.getName()));

    try {
      Files.copy(file, resp.getOutputStream());
      resp.setStatus(HttpServletResponse.SC_OK);
    } catch (IOException e) {
      resp.reset();
      resp.setContentType("text/html;charset=utf-8");
      ServletOutputStream writer = resp.getOutputStream();
      writer.println("<html>\nFailed to dump heap: <br>\n<pre>\n");
      writer.println(e.toString());
      writer.println("</pre>\n</html>");
      resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
    }
  }
}