/*
    * Copyright 2016-2022 The OSHI Project Contributors
    * SPDX-License-Identifier: MIT
    */
   package oshi.software.common;
   
   import static oshi.software.os.OperatingSystem.ProcessFiltering.ALL_PROCESSES;
   import static oshi.software.os.OperatingSystem.ProcessSorting.NO_SORTING;
   import static oshi.util.Memoizer.memoize;
  
  import java.util.ArrayDeque;
  import java.util.Collection;
  import java.util.Comparator;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.Queue;
  import java.util.Set;
  import java.util.function.Predicate;
  import java.util.function.Supplier;
  import java.util.stream.Collectors;
  
  import com.sun.jna.Platform;
  
  import oshi.software.os.OSProcess;
  import oshi.software.os.OperatingSystem;
  import oshi.util.GlobalConfig;
  import oshi.util.tuples.Pair;
  
  /**
   * Common methods for OperatingSystem implementations
   */
  public abstract class AbstractOperatingSystem implements OperatingSystem {
  
      protected static final boolean USE_WHO_COMMAND = GlobalConfig.get(GlobalConfig.OSHI_OS_UNIX_WHOCOMMAND, false);
  
      private final Supplier<String> manufacturer = memoize(this::queryManufacturer);
      private final Supplier<Pair<String, OSVersionInfo>> familyVersionInfo = memoize(this::queryFamilyVersionInfo);
      private final Supplier<Integer> bitness = memoize(this::queryPlatformBitness);
  
      @Override
      public String getManufacturer() {
          return manufacturer.get();
      }
  
      protected abstract String queryManufacturer();
  
      @Override
      public String getFamily() {
          return familyVersionInfo.get().getA();
      }
  
      @Override
      public OSVersionInfo getVersionInfo() {
          return familyVersionInfo.get().getB();
      }
  
      protected abstract Pair<String, OSVersionInfo> queryFamilyVersionInfo();
  
      @Override
      public int getBitness() {
          return bitness.get();
      }
  
      private int queryPlatformBitness() {
          if (Platform.is64Bit()) {
              return 64;
          }
          // Initialize based on JVM Bitness. Individual OS implementations will test
          // if 32-bit JVM running on 64-bit OS
          int jvmBitness = System.getProperty("os.arch").contains("64") ? 64 : 32;
          return queryBitness(jvmBitness);
      }
  
      /**
       * Backup OS-specific query to determine bitness if previous checks fail
       *
       * @param jvmBitness The bitness of the JVM
       * @return The operating system bitness
       */
      protected abstract int queryBitness(int jvmBitness);
  
      @Override
      public List<OSProcess> getProcesses(Predicate<OSProcess> filter, Comparator<OSProcess> sort, int limit) {
          return queryAllProcesses().stream().filter(filter == null ? ALL_PROCESSES : filter)
                  .sorted(sort == null ? NO_SORTING : sort).limit(limit > 0 ? limit : Long.MAX_VALUE)
                  .collect(Collectors.toList());
      }
  
      protected abstract List<OSProcess> queryAllProcesses();
  
      @Override
      public List<OSProcess> getChildProcesses(int parentPid, Predicate<OSProcess> filter, Comparator<OSProcess> sort,
              int limit) {
          // Get this pid and its children
          List<OSProcess> childProcs = queryChildProcesses(parentPid);
          // Extract the parent from the list
          OSProcess parent = childProcs.stream().filter(p -> p.getProcessID() == parentPid).findAny().orElse(null);
         // Get the parent's start time
         long parentStartTime = parent == null ? 0 : parent.getStartTime();
         // Get children after parent
         return queryChildProcesses(parentPid).stream().filter(filter == null ? ALL_PROCESSES : filter)
                 .filter(p -> p.getProcessID() != parentPid && p.getStartTime() >= parentStartTime)
                 .sorted(sort == null ? NO_SORTING : sort).limit(limit > 0 ? limit : Long.MAX_VALUE)
                 .collect(Collectors.toList());
     }
 
     protected abstract List<OSProcess> queryChildProcesses(int parentPid);
 
     @Override
     public List<OSProcess> getDescendantProcesses(int parentPid, Predicate<OSProcess> filter,
             Comparator<OSProcess> sort, int limit) {
         // Get this pid and its descendants
         List<OSProcess> descendantProcs = queryDescendantProcesses(parentPid);
         // Extract the parent from the list
         OSProcess parent = descendantProcs.stream().filter(p -> p.getProcessID() == parentPid).findAny().orElse(null);
         // Get the parent's start time
         long parentStartTime = parent == null ? 0 : parent.getStartTime();
         // Get descendants after parent
         return queryDescendantProcesses(parentPid).stream().filter(filter == null ? ALL_PROCESSES : filter)
                 .filter(p -> p.getProcessID() != parentPid && p.getStartTime() >= parentStartTime)
                 .sorted(sort == null ? NO_SORTING : sort).limit(limit > 0 ? limit : Long.MAX_VALUE)
                 .collect(Collectors.toList());
     }
 
     protected abstract List<OSProcess> queryDescendantProcesses(int parentPid);
 
     /**
      * Utility method for subclasses to take a full process list as input and return the children or descendants of a
      * particular process. The process itself is also returned to more efficiently extract its start time for filtering
      *
      * @param allProcs       A collection of all processes
      * @param parentPid      The process ID whose children or descendants to return
      * @param allDescendants If false, only gets immediate children of this process. If true, gets all descendants.
      * @return Set of children or descendants of parentPid
      */
     protected static Set<Integer> getChildrenOrDescendants(Collection<OSProcess> allProcs, int parentPid,
             boolean allDescendants) {
         Map<Integer, Integer> parentPidMap = allProcs.stream()
                 .collect(Collectors.toMap(OSProcess::getProcessID, OSProcess::getParentProcessID));
         return getChildrenOrDescendants(parentPidMap, parentPid, allDescendants);
     }
 
     /**
      * Utility method for subclasses to take a map of pid to parent as input and return the children or descendants of a
      * particular process.
      *
      * @param parentPidMap   a map of all processes with processID as key and parentProcessID as value
      * @param parentPid      The process ID whose children or descendants to return
      * @param allDescendants If false, only gets immediate children of this process. If true, gets all descendants.
      * @return Set of children or descendants of parentPid, including the parent
      */
     protected static Set<Integer> getChildrenOrDescendants(Map<Integer, Integer> parentPidMap, int parentPid,
             boolean allDescendants) {
         // Set to hold results
         Set<Integer> descendantPids = new HashSet<>();
         descendantPids.add(parentPid);
         // Queue for BFS algorithm
         Queue<Integer> queue = new ArrayDeque<>();
         queue.add(parentPid);
         // Add children, repeating if recursive
         do {
             for (int pid : getChildren(parentPidMap, queue.poll())) {
                 if (!descendantPids.contains(pid)) {
                     descendantPids.add(pid);
                     queue.add(pid);
                 }
             }
         } while (allDescendants && !queue.isEmpty());
         return descendantPids;
     }
 
     private static Set<Integer> getChildren(Map<Integer, Integer> parentPidMap, int parentPid) {
         return parentPidMap.entrySet().stream()
                 .filter(e -> e.getValue().equals(parentPid) && !e.getKey().equals(parentPid)).map(Entry::getKey)
                 .collect(Collectors.toSet());
     }
 
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();
         sb.append(getManufacturer()).append(' ').append(getFamily()).append(' ').append(getVersionInfo());
         return sb.toString();
     }
 }