/*
    * Copyright 2020-2023 The OSHI Project Contributors
    * SPDX-License-Identifier: MIT
    */
   package oshi.driver.unix;
   
   import java.time.LocalDateTime;
   import java.time.Year;
   import java.time.ZoneId;
  import java.time.format.DateTimeFormatter;
  import java.time.format.DateTimeFormatterBuilder;
  import java.time.format.DateTimeParseException;
  import java.time.temporal.ChronoField;
  import java.time.temporal.ChronoUnit;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Locale;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  import com.sun.jna.Platform;
  
  import oshi.annotation.concurrent.ThreadSafe;
  import oshi.software.os.OSSession;
  import oshi.util.Constants;
  import oshi.util.ExecutingCommand;
  
  /**
   * Utility to query logged in users.
   */
  @ThreadSafe
  public final class Who {
  
      // sample format:
      // oshi pts/0 2020-05-14 21:23 (192.168.1.23)
      private static final Pattern WHO_FORMAT_LINUX = Pattern
              .compile("(\\S+)\\s+(\\S+)\\s+(\\d{4}-\\d{2}-\\d{2})\\s+(\\d{2}:\\d{2})\\s*(?:\\((.+)\\))?");
      private static final DateTimeFormatter WHO_DATE_FORMAT_LINUX = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm",
              Locale.ROOT);
      // oshi ttys000 May 4 23:50 (192.168.1.23)
      // middle 12 characters from Thu Nov 24 18:22:48 1986
      private static final Pattern WHO_FORMAT_UNIX = Pattern
              .compile("(\\S+)\\s+(\\S+)\\s+(\\S+)\\s+(\\d+)\\s+(\\d{2}:\\d{2})\\s*(?:\\((.+)\\))?");
      private static final DateTimeFormatter WHO_DATE_FORMAT_UNIX = new DateTimeFormatterBuilder()
              .appendPattern("MMM d HH:mm").parseDefaulting(ChronoField.YEAR, Year.now(ZoneId.systemDefault()).getValue())
              .toFormatter(Locale.US);
  
      private Who() {
      }
  
      /**
       * Query {@code who} to get logged in users
       *
       * @return A list of logged in user sessions
       */
      public static synchronized List<OSSession> queryWho() {
          List<OSSession> whoList = new ArrayList<>();
          List<String> who = ExecutingCommand.runNative("who");
          for (String s : who) {
              boolean matched = false;
              if (Platform.isLinux()) {
                  matched = matchLinux(whoList, s);
              }
              if (!matched) {
                  matchUnix(whoList, s);
              }
          }
          return whoList;
      }
  
      /**
       * Attempt to match Linux WHO format and add to the list
       *
       * @param whoList the list to add to
       * @param s       the string to match
       * @return true if successful, false otherwise
       */
      private static boolean matchLinux(List<OSSession> whoList, String s) {
          Matcher m = WHO_FORMAT_LINUX.matcher(s);
          if (m.matches()) {
              try {
                  whoList.add(new OSSession(m.group(1), m.group(2),
                          LocalDateTime.parse(m.group(3) + " " + m.group(4), WHO_DATE_FORMAT_LINUX)
                                  .atZone(ZoneId.systemDefault()).toInstant().toEpochMilli(),
                          m.group(5) == null ? Constants.UNKNOWN : m.group(5)));
                  return true;
              } catch (DateTimeParseException | NullPointerException e) {
                  // shouldn't happen if regex matches and OS is producing sensible dates
              }
          }
          return false;
      }
  
      /**
       * Attempt to match Unix WHO format and add to the list
       *
       * @param whoList the list to add to
       * @param s       the string to match
       * @return true if successful, false otherwise
      */
     private static boolean matchUnix(List<OSSession> whoList, String s) {
         Matcher m = WHO_FORMAT_UNIX.matcher(s);
         if (m.matches()) {
             try {
                 // Missing year, parse date time with current year
                 LocalDateTime login = LocalDateTime.parse(m.group(3) + " " + m.group(4) + " " + m.group(5),
                         WHO_DATE_FORMAT_UNIX);
                 // If this date is in the future, subtract a year
                 if (login.isAfter(LocalDateTime.now(ZoneId.systemDefault()))) {
                     login = login.minus(1, ChronoUnit.YEARS);
                 }
                 long millis = login.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
                 whoList.add(new OSSession(m.group(1), m.group(2), millis, m.group(6) == null ? "" : m.group(6)));
                 return true;
             } catch (DateTimeParseException | NullPointerException e) {
                 // shouldn't happen if regex matches and OS is producing sensible dates
             }
         }
         return false;
     }
 }