/*
    * Copyright 2016-2023 The OSHI Project Contributors
    * SPDX-License-Identifier: MIT
    */
   package oshi.software.os;
   
   import java.util.ArrayList;
   import java.util.Collection;
   import java.util.Comparator;
  import java.util.List;
  import java.util.Objects;
  import java.util.function.Predicate;
  import java.util.stream.Collectors;
  
  import oshi.annotation.concurrent.Immutable;
  import oshi.annotation.concurrent.ThreadSafe;
  import oshi.driver.unix.Who;
  import oshi.driver.unix.Xwininfo;
  import oshi.software.os.OSProcess.State;
  import oshi.util.Constants;
  import oshi.util.UserGroupInfo;
  import oshi.util.Util;
  
  /**
   * An operating system (OS) is the software on a computer that manages the way different programs use its hardware, and
   * regulates the ways that a user controls the computer.
   * <p>
   * Considered thread safe, but see remarks for the {@link #getSessions()} method.
   */
  @ThreadSafe
  public interface OperatingSystem {
  
      /**
       * Constants which may be used to filter Process lists in {@link #getProcesses(Predicate, Comparator, int)},
       * {@link #getChildProcesses(int, Predicate, Comparator, int)}, and
       * {@link #getDescendantProcesses(int, Predicate, Comparator, int)}.
       */
      final class ProcessFiltering {
          private ProcessFiltering() {
          }
  
          /**
           * No filtering.
           */
          public static final Predicate<OSProcess> ALL_PROCESSES = p -> true;
          /**
           * Exclude processes with {@link State#INVALID} process state.
           */
          public static final Predicate<OSProcess> VALID_PROCESS = p -> !p.getState().equals(State.INVALID);
          /**
           * Exclude child processes. Only include processes which are their own parent.
           */
          public static final Predicate<OSProcess> NO_PARENT = p -> p.getParentProcessID() == p.getProcessID();
          /**
           * Only incude 64-bit processes.
           */
          public static final Predicate<OSProcess> BITNESS_64 = p -> p.getBitness() == 64;
          /**
           * Only include 32-bit processes.
           */
          public static final Predicate<OSProcess> BITNESS_32 = p -> p.getBitness() == 32;
      }
  
      /**
       * Constants which may be used to sort Process lists in {@link #getProcesses(Predicate, Comparator, int)},
       * {@link #getChildProcesses(int, Predicate, Comparator, int)}, and
       * {@link #getDescendantProcesses(int, Predicate, Comparator, int)}.
       */
      final class ProcessSorting {
          private ProcessSorting() {
          }
  
          /**
           * No sorting
           */
          public static final Comparator<OSProcess> NO_SORTING = (p1, p2) -> 0;
          /**
           * Sort by decreasing cumulative CPU percentage
           */
          public static final Comparator<OSProcess> CPU_DESC = Comparator
                  .comparingDouble(OSProcess::getProcessCpuLoadCumulative).reversed();
          /**
           * Sort by decreasing Resident Set Size (RSS)
           */
          public static final Comparator<OSProcess> RSS_DESC = Comparator.comparingLong(OSProcess::getResidentSetSize)
                  .reversed();
          /**
           * Sort by up time, newest processes first
           */
          public static final Comparator<OSProcess> UPTIME_ASC = Comparator.comparingLong(OSProcess::getUpTime);
          /**
           * Sort by up time, oldest processes first
           */
          public static final Comparator<OSProcess> UPTIME_DESC = UPTIME_ASC.reversed();
          /**
           * Sort by Process Id
           */
          public static final Comparator<OSProcess> PID_ASC = Comparator.comparingInt(OSProcess::getProcessID);
          /**
          * Sort by Parent Process Id
          */
         public static final Comparator<OSProcess> PARENTPID_ASC = Comparator
                 .comparingInt(OSProcess::getParentProcessID);
         /**
          * Sort by Process Name (case insensitive)
          */
         public static final Comparator<OSProcess> NAME_ASC = Comparator.comparing(OSProcess::getName,
                 String.CASE_INSENSITIVE_ORDER);
     }
 
     /**
      * Get the Operating System family.
      *
      * @return the family
      */
     String getFamily();
 
     /**
      * Get the Operating System manufacturer.
      *
      * @return the manufacturer
      */
     String getManufacturer();
 
     /**
      * Get Operating System version information.
      *
      * @return version information
      */
     OSVersionInfo getVersionInfo();
 
     /**
      * Instantiates a {@link oshi.software.os.FileSystem} object.
      *
      * @return A {@link oshi.software.os.FileSystem} object.
      */
     FileSystem getFileSystem();
 
     /**
      * Instantiates a {@link oshi.software.os.InternetProtocolStats} object.
      *
      * @return a {@link oshi.software.os.InternetProtocolStats} object.
      */
     InternetProtocolStats getInternetProtocolStats();
 
     /**
      * Gets currently running processes. No order is guaranteed.
      *
      * @return A list of {@link oshi.software.os.OSProcess} objects for the specified number (or all) of currently
      *         running processes, sorted as specified. The list may contain null elements or processes with a state of
      *         {@link OSProcess.State#INVALID} if a process terminates during iteration.
      */
     default List<OSProcess> getProcesses() {
         return getProcesses(null, null, 0);
     }
 
     /**
      * Gets currently running processes, optionally filtering, sorting, and limited to the top "N".
      *
      * @param filter An optional {@link Predicate} limiting the results to the specified filter. Some common predicates
      *               are available in {@link ProcessSorting}. May be {@code null} for no filtering.
      * @param sort   An optional {@link Comparator} specifying the sorting order. Some common comparators are available
      *               in {@link ProcessSorting}. May be {@code null} for no sorting.
      * @param limit  Max number of results to return, or 0 to return all results
      * @return A list of {@link oshi.software.os.OSProcess} objects, optionally filtered, sorted, and limited to the
      *         specified number.
      *         <p>
      *         The list may contain processes with a state of {@link OSProcess.State#INVALID} if a process terminates
      *         during iteration.
      */
     List<OSProcess> getProcesses(Predicate<OSProcess> filter, Comparator<OSProcess> sort, int limit);
 
     /**
      * Gets information on a {@link Collection} of currently running processes. This has potentially improved
      * performance vs. iterating individual processes.
      *
      * @param pids A collection of process IDs
      * @return A list of {@link oshi.software.os.OSProcess} objects for the specified process ids if it is running
      */
     default List<OSProcess> getProcesses(Collection<Integer> pids) {
         return pids.stream().map(this::getProcess).filter(Objects::nonNull).filter(ProcessFiltering.VALID_PROCESS)
                 .collect(Collectors.toList());
     }
 
     /**
      * Gets information on a currently running process
      *
      * @param pid A process ID
      * @return An {@link oshi.software.os.OSProcess} object for the specified process id if it is running; null
      *         otherwise
      */
     OSProcess getProcess(int pid);
 
     /**
      * Gets currently running child processes of provided parent PID, optionally filtering, sorting, and limited to the
      * top "N".
      *
      * @param parentPid The Process ID whose children to list.
      * @param filter    An optional {@link Predicate} limiting the results to the specified filter. Some common
      *                  predicates are available in {@link ProcessSorting}. May be {@code null} for no filtering.
      * @param sort      An optional {@link Comparator} specifying the sorting order. Some common comparators are
      *                  available in {@link ProcessSorting}. May be {@code null} for no sorting.
      * @param limit     Max number of results to return, or 0 to return all results
      * @return A list of {@link oshi.software.os.OSProcess} objects representing the currently running child processes
      *         of the provided PID, optionally filtered, sorted, and limited to the specified number.
      *         <p>
      *         The list may contain processes with a state of {@link OSProcess.State#INVALID} if a process terminates
      *         during iteration.
      */
     List<OSProcess> getChildProcesses(int parentPid, Predicate<OSProcess> filter, Comparator<OSProcess> sort,
             int limit);
 
     /**
      * Gets currently running processes of provided parent PID's descendants, including their children, the children's
      * children, etc., optionally filtering, sorting, and limited to the top "N".
      *
      * @param parentPid The Process ID whose children to list.
      * @param filter    An optional {@link Predicate} limiting the results to the specified filter. Some common
      *                  predicates are available in {@link ProcessSorting}. May be {@code null} for no filtering.
      * @param sort      An optional {@link Comparator} specifying the sorting order. Some common comparators are
      *                  available in {@link ProcessSorting}. May be {@code null} for no sorting.
      * @param limit     Max number of results to return, or 0 to return all results
      * @return A list of {@link oshi.software.os.OSProcess} objects representing the currently running descendant
      *         processes of the provided PID, optionally filtered, sorted, and limited to the specified number.
      *         <p>
      *         The list may contain processes with a state of {@link OSProcess.State#INVALID} if a process terminates
      *         during iteration.
      */
     List<OSProcess> getDescendantProcesses(int parentPid, Predicate<OSProcess> filter, Comparator<OSProcess> sort,
             int limit);
 
     /**
      * Gets the current process ID (PID).
      *
      * @return the Process ID of the current process
      */
     int getProcessId();
 
     /**
      * Gets the current process.
      *
      * @return the current process
      */
     default OSProcess getCurrentProcess() {
         return getProcess(getProcessId());
     }
 
     /**
      * Get the number of processes currently running
      *
      * @return The number of processes running
      */
     int getProcessCount();
 
     /**
      * Makes a best effort to get the current thread ID (TID). May not be useful in a multithreaded environment. The
      * thread ID returned may have been short lived and no longer exist.
      * <p>
      * Thread IDs on macOS are not correlated with any other Operating System output.
      *
      * @return the Thread ID of the current thread if known, 0 otherwise.
      */
     int getThreadId();
 
     /**
      * Makes a best effort to get the current thread. May not be useful in a multithreaded environment. The thread
      * returned may have been short lived and no longer exist.
      * <p>
      * On macOS, returns the oldest thread in the calling process.
      *
      * @return the current thread if known; an invalid thread otherwise.
      */
     OSThread getCurrentThread();
 
     /**
      * Get the number of threads currently running
      *
      * @return The number of threads running
      */
     int getThreadCount();
 
     /**
      * Gets the bitness (32 or 64) of the operating system.
      *
      * @return The number of bits supported by the operating system.
      */
     int getBitness();
 
     /**
      * Get the System up time (time since boot).
      *
      * @return Number of seconds since boot.
      */
     long getSystemUptime();
 
     /**
      * Get Unix time of boot.
      *
      * @return The approximate time at which the system booted, in seconds since the Unix epoch.
      */
     long getSystemBootTime();
 
     /**
      * Determine whether the current process has elevated permissions such as sudo / Administrator
      *
      * @return True if this process has elevated permissions
      */
     default boolean isElevated() {
         return UserGroupInfo.isElevated();
     }
 
     /**
      * Instantiates a {@link oshi.software.os.NetworkParams} object.
      *
      * @return A {@link oshi.software.os.NetworkParams} object.
      */
     NetworkParams getNetworkParams();
 
     /**
      * Gets the all services on the system. The definition of what is a service is platform-dependent.
      *
      * @return An array of {@link OSService} objects
      */
     default List<OSService> getServices() {
         return new ArrayList<>();
     }
 
     /**
      * Gets currently logged in users.
      * <p>
      * On macOS, Linux, and Unix systems, the default implementation uses native code (see {@code man getutxent}) that
      * is not thread safe. OSHI's use of this code is synchronized and may be used in a multi-threaded environment
      * without introducing any additional conflicts. Users should note, however, that other operating system code may
      * access the same native code.
      * <p>
      * The {@link oshi.driver.unix.Who#queryWho()} method produces similar output parsing the output of the
      * Posix-standard {@code who} command, and may internally employ reentrant code on some platforms. Users may opt to
      * use this command-line variant by default using the {@code oshi.os.unix.whoCommand} configuration property.
      *
      * @return A list of {@link oshi.software.os.OSSession} objects representing logged-in users
      */
     default List<OSSession> getSessions() {
         return Who.queryWho();
     }
 
     /**
      * Gets windows on the operating system's GUI desktop.
      * <p>
      * On Unix-like systems, reports X11 windows only, which may be limited to the current display and will not report
      * windows used by other window managers.
      * <p>
      * While not a guarantee, a best effort is made to return windows in foreground-to-background order. This ordering
      * may be used along with {@link OSDesktopWindow#getOrder()} to (probably) determine the frontmost window.
      *
      * @param visibleOnly Whether to restrict the list to only windows visible to the user.
      *                    <p>
      *                    This is a best effort attempt at a reasonable definition of visibility. Visible windows may be
      *                    completely transparent.
      * @return A list of {@link oshi.software.os.OSDesktopWindow} objects representing the desktop windows.
      */
     default List<OSDesktopWindow> getDesktopWindows(boolean visibleOnly) {
         // Default X11 implementation for Unix-like operating systems.
         // Overridden on Windows and macOS
         return Xwininfo.queryXWindows(visibleOnly);
     }
 
     /**
      * A class representing the Operating System version details.
      */
     @Immutable
     class OSVersionInfo {
         private final String version;
         private final String codeName;
         private final String buildNumber;
         private final String versionStr;
 
         public OSVersionInfo(String version, String codeName, String buildNumber) {
             this.version = version;
             this.codeName = codeName;
             this.buildNumber = buildNumber;
 
             StringBuilder sb = new StringBuilder(getVersion() != null ? getVersion() : Constants.UNKNOWN);
             if (!Util.isBlank(getCodeName())) {
                 sb.append(" (").append(getCodeName()).append(')');
             }
             if (!Util.isBlank(getBuildNumber())) {
                 sb.append(" build ").append(getBuildNumber());
             }
             this.versionStr = sb.toString();
         }
 
         /**
          * Gets the operating system version.
          *
          * @return The version, if any. May be {@code null}.
          */
         public String getVersion() {
             return version;
         }
 
         /**
          * Gets the operating system codename.
          *
          * @return The code name, if any. May be {@code null}.
          */
         public String getCodeName() {
             return codeName;
         }
 
         /**
          * Gets the operating system build number.
          *
          * @return The build number, if any. May be {@code null}.
          */
         public String getBuildNumber() {
             return buildNumber;
         }
 
         @Override
         public String toString() {
             return this.versionStr;
         }
     }
 }