/*
    * Copyright 2020-2022 The OSHI Project Contributors
    * SPDX-License-Identifier: MIT
    */
   package oshi.driver.windows.wmi;
   
   import static oshi.util.Memoizer.memoize;
   
   import java.util.HashMap;
  import java.util.Map;
  import java.util.concurrent.locks.ReentrantLock;
  import java.util.function.Supplier;
  
  import com.sun.jna.platform.win32.COM.WbemcliUtil.WmiResult;
  
  import oshi.annotation.concurrent.GuardedBy;
  import oshi.annotation.concurrent.ThreadSafe;
  import oshi.driver.windows.wmi.Win32Process.CommandLineProperty;
  import oshi.util.platform.windows.WmiUtil;
  import oshi.util.tuples.Pair;
  
  /**
   * Utility to query WMI class {@code Win32_Process} using cache
   */
  @ThreadSafe
  public final class Win32ProcessCached {
  
      private static final Supplier<Win32ProcessCached> INSTANCE = memoize(Win32ProcessCached::createInstance);
  
      // Use a map to cache command line queries
      @GuardedBy("commandLineCacheLock")
      private final Map<Integer, Pair<Long, String>> commandLineCache = new HashMap<>();
      private final ReentrantLock commandLineCacheLock = new ReentrantLock();
  
      private Win32ProcessCached() {
      }
  
      /**
       * Get the singleton instance of this class, instantiating the map which caches command lines.
       *
       * @return the singleton instance
       */
      public static Win32ProcessCached getInstance() {
          return INSTANCE.get();
      }
  
      private static Win32ProcessCached createInstance() {
          return new Win32ProcessCached();
      }
  
      /**
       * Gets the process command line, while also querying and caching command lines for all running processes if the
       * specified process is not in the cache.
       * <p>
       * When iterating over a process list, the WMI overhead of querying each single command line can quickly exceed the
       * time it takes to query all command lines. This method permits access to cached queries from a previous call,
       * significantly improving aggregate performance.
       *
       * @param processId The process ID for which to return the command line.
       * @param startTime The start time of the process, in milliseconds since the 1970 epoch. If this start time is after
       *                  the time this process was previously queried, the prior entry will be deemed invalid and the
       *                  cache refreshed.
       * @return The command line of the specified process. If the command line is cached from a previous call and the
       *         start time is prior to the time it was cached, this method will quickly return the cached value.
       *         Otherwise, will refresh the cache with all running processes prior to returning, which may incur some
       *         latency.
       *         <p>
       *         May return a command line from the cache even after a process has terminated. Otherwise will return the
       *         empty string.
       */
      public String getCommandLine(int processId, long startTime) {
          // We could use synchronized method but this is more clear
          commandLineCacheLock.lock();
          try {
              // See if this process is in the cache already
              Pair<Long, String> pair = commandLineCache.get(processId);
              // Valid process must have been started before map insertion
              if (pair != null && startTime < pair.getA()) {
                  // Entry is valid, return it!
                  return pair.getB();
              } else {
                  // Invalid entry, rebuild cache
                  // Processes started after this time will be invalid
                  long now = System.currentTimeMillis();
                  // Gets all processes. Takes ~200ms
                  WmiResult<CommandLineProperty> commandLineAllProcs = Win32Process.queryCommandLines(null);
                  // Stale processes use resources. Periodically clear before building
                  // Use a threshold of map size > 2x # of processes
                  if (commandLineCache.size() > commandLineAllProcs.getResultCount() * 2) {
                      commandLineCache.clear();
                  }
                  // Iterate results and put in map. Save value for current PID along the way
                  String result = "";
                  for (int i = 0; i < commandLineAllProcs.getResultCount(); i++) {
                      int pid = WmiUtil.getUint32(commandLineAllProcs, CommandLineProperty.PROCESSID, i);
                      String cl = WmiUtil.getString(commandLineAllProcs, CommandLineProperty.COMMANDLINE, i);
                      commandLineCache.put(pid, new Pair<>(now, cl));
                      if (pid == processId) {
                          result = cl;
                     }
                 }
                 return result;
             }
         } finally {
             commandLineCacheLock.unlock();
         }
     }
 }