/*
 * Copyright 2015 LinkedIn Corp.
 *
 * 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 azkaban.execapp;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

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

import org.apache.log4j.Logger;

import azkaban.executor.Statistics;
import azkaban.utils.JSONUtils;

public class StatisticsServlet extends HttpServlet  {
  private static final long serialVersionUID = 1L;
  private static final int  cacheTimeInMilliseconds = 1000;
  private static final Logger logger = Logger.getLogger(StatisticsServlet.class);
  private static final String noCacheParamName = "nocache";

  protected static Date lastRefreshedTime = null;
  protected static Statistics cachedstats = null;

  /**
   * Handle all get request to Statistics Servlet {@inheritDoc}
   *
   * @see javax.servlet.http.HttpServlet#doGet(javax.servlet.http.HttpServletRequest,
   *      javax.servlet.http.HttpServletResponse)
   */
  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {

    boolean noCache = null!= req && Boolean.getBoolean(req.getParameter(noCacheParamName));

    if (noCache || null == lastRefreshedTime ||
        new Date().getTime() - lastRefreshedTime.getTime() > cacheTimeInMilliseconds){
      this.populateStatistics(noCache);
    }

    JSONUtils.toJSON(cachedstats, resp.getOutputStream(), true);
  }

  /**
   * fill the result set with the percent of the remaining system memory on the server.
   * @param stats reference to the result container which contains all the results, this specific method
   *              will only work work on the property "remainingMemory" and "remainingMemoryPercent".
   *
   * NOTE:
   * a double value will be used to present the remaining memory,
   *         a returning value of '55.6' means 55.6%
   */
  protected void fillRemainingMemoryPercent(Statistics stats){
    if (new File("/bin/bash").exists() &&  new File("/usr/bin/free").exists()) {
      java.lang.ProcessBuilder processBuilder =
          new java.lang.ProcessBuilder("/bin/bash", "-c", "/usr/bin/free -m -s 0.1 -c 5 | grep Mem:");
      try {
        ArrayList<String> output = new ArrayList<String>();
        Process process = processBuilder.start();
        process.waitFor();
        InputStream inputStream = process.getInputStream();
        try {
          java.io.BufferedReader reader =
              new java.io.BufferedReader(new InputStreamReader(inputStream));
          String line = null;
          while ((line = reader.readLine()) != null) {
            output.add(line);
          }
        }finally {
          inputStream.close();
        }
        // process the output from bash call.
        if (output.size() > 0) {
          long totalMemory = 0 ;
          long freeMemory  = 0 ;
          int  sampleCount = 0 ;

          // process all the output, we will do 5 samples.
          for(String line : output){
            String[] splitedresult = line.split("\\s+");
            // expected return format -
            // "Mem:" | total | used | free | shared | buffers | cached
            if (splitedresult.length == 7){
              // create a temp copy of all the readings, if anything goes wrong, we drop the
              // temp reading and move on.
              long tmp_totalMemory = 0 ;
              long tmp_freeMemory  = 0 ;
              try {
                tmp_totalMemory = Long.parseLong(splitedresult[1]);
                tmp_freeMemory = Long.parseLong(splitedresult[3]);

              } catch(NumberFormatException e){
                logger.error("skipping the unprocessable line from the output -" + line);
                continue;
              }

              // add up the result.
              ++sampleCount;
              totalMemory += tmp_totalMemory ;
              freeMemory  += tmp_freeMemory;
            }
          }

          // set the value.
          if (sampleCount > 0){
            freeMemory  = freeMemory  / sampleCount;
            totalMemory = totalMemory / sampleCount;
            logger.info(String.format("total memory - %s , free memory - %s", totalMemory, freeMemory));
            stats.setRemainingMemory(freeMemory);
            stats.setRemainingMemoryPercent(totalMemory == 0? 0 :
              ((double)freeMemory/(double)totalMemory));
          }
        }
      }
      catch (Exception ex){
        logger.error("failed fetch system memory info " +
                     "as exception is captured when fetching result from bash call.");
      }
    } else {
        logger.error("failed fetch system memory info " +
                     "as 'bash' or 'free' command can't be found on the current system.");
    }
  }

  /**
   * call the data providers to fill the returning data container for statistics data.
   * This function refreshes the static cached copy of data in case if necessary.
   * */
  protected synchronized void populateStatistics(boolean noCache){
    //check again before starting the work.
    if (noCache || null == lastRefreshedTime ||
        new Date().getTime() - lastRefreshedTime.getTime() > cacheTimeInMilliseconds){
      final Statistics stats = new Statistics();

      List<Thread> workerPool = new ArrayList<Thread>();
      workerPool.add(new Thread(new Runnable(){ public void run() {
        fillRemainingMemoryPercent(stats); }},"RemainingMemoryPercent"));

      workerPool.add(new Thread(new Runnable(){ public void run() {
        fillRemainingFlowCapacityAndLastDispatchedTime(stats); }},"RemainingFlowCapacityAndLastDispatchedTime"));

      workerPool.add(new Thread(new Runnable(){ public void run() {
        fillCpuUsage(stats); }},"CpuUsage"));

      // start all the working threads.
      for (Thread thread : workerPool){thread.start();}

      // wait for all the threads to finish their work.
      // NOTE: the result container itself is not thread safe, we are good as for now no
      //       working thread will modify the same property, nor have any of them
      //       need to compute values based on value(s) of other properties.
      for (Thread thread : workerPool){
        try {
          // we gave maxim 5 seconds to let the thread finish work.
          thread.join(5000);;
        } catch (InterruptedException e) {
          logger.error(String.format("failed to collect information for %s as the working thread is interrupted.",
              thread.getName()));
        }}

      cachedstats = stats;
      lastRefreshedTime =  new Date();
    }
  }

  /**
   * fill the result set with the remaining flow capacity .
   * @param stats reference to the result container which contains all the results, this specific method
   *              will only work on the property "remainingFlowCapacity".
   */
  protected void fillRemainingFlowCapacityAndLastDispatchedTime(Statistics stats){

    AzkabanExecutorServer server = AzkabanExecutorServer.getApp();
    if (server != null){
      FlowRunnerManager runnerMgr =  AzkabanExecutorServer.getApp().getFlowRunnerManager();
      int assignedFlows = runnerMgr.getNumRunningFlows() + runnerMgr.getNumQueuedFlows();
      stats.setRemainingFlowCapacity(runnerMgr.getMaxNumRunningFlows() - assignedFlows);
      stats.setNumberOfAssignedFlows(assignedFlows);
      stats.setLastDispatchedTime(runnerMgr.getLastFlowSubmittedTime());
    }else {
      logger.error("failed to get data for remaining flow capacity or LastDispatchedTime" +
                   " as the AzkabanExecutorServer has yet been initialized.");
    }
  }


  /**
   * fill the result set with the Remaining temp Storage .
   * @param stats reference to the result container which contains all the results, this specific method
   *              will only work on the property "cpuUdage".
   */
  protected void fillCpuUsage(Statistics stats){
    if (new File("/bin/bash").exists() &&  new File("/usr/bin/top").exists()) {
      java.lang.ProcessBuilder processBuilder =
          new java.lang.ProcessBuilder("/bin/bash", "-c", "/usr/bin/top -bn5 -d 0.1 | grep \"Cpu(s)\"");
      try {
        ArrayList<String> output = new ArrayList<String>();
        Process process = processBuilder.start();
        process.waitFor();
        InputStream inputStream = process.getInputStream();
        try {
          java.io.BufferedReader reader =
              new java.io.BufferedReader(new InputStreamReader(inputStream));
          String line = null;
          while ((line = reader.readLine()) != null) {
            output.add(line);
          }
        }finally {
          inputStream.close();
        }

        // process the output from bash call.
        if (output.size() > 0) {
          double us = 0 ; // user
          double sy = 0 ; // system
          double wi = 0 ; // waiting.
          int   sampleCount = 0;

          // process all the output, we will do 5 samples for the cpu and calculate the avarage.
          for(String line : output){
            String[] splitedresult = line.split("\\s+");
            // expected returning format -
            // Cpu(s):  1.4%us,  0.1%sy,  0.0%ni, 98.5%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
            if (splitedresult.length == 9){
              // create a temp copy of all the readings, if anything goes wrong, we drop the
              // temp reading and move on.
              double tmp_us = 0 ; // user
              double tmp_sy = 0 ; // system
              double tmp_wi = 0 ; // waiting.
              try {
              tmp_us = Double.parseDouble(splitedresult[1].split("%")[0]);
              tmp_sy = Double.parseDouble(splitedresult[2].split("%")[0]);
              tmp_wi = Double.parseDouble(splitedresult[5].split("%")[0]);
              } catch(NumberFormatException e){
                logger.error("skipping the unprocessable line from the output -" + line);
                continue;
              }

              // add up the result.
              ++sampleCount;
              us += tmp_us;
              sy += tmp_sy;
              wi += tmp_wi;
            }
          }

          // set the value.
          if (sampleCount > 0){
            double finalResult = (us + sy + wi)/sampleCount;
            logger.info("Cpu usage result  - " + finalResult );
            stats.setCpuUpsage(finalResult);
          }
        }
      }
      catch (Exception ex){
        logger.error("failed fetch system memory info " +
                     "as exception is captured when fetching result from bash call.");
      }
    } else {
        logger.error("failed fetch system memory info " +
                     "as 'bash' or 'top' command can't be found on the current system.");
    }
  }

  // TO-DO - decide if we need to populate the remaining Storage space and priority info.
}
