/*
    * Copyright 2020-2023 The OSHI Project Contributors
    * SPDX-License-Identifier: MIT
    */
   package oshi.driver.unix.aix;
   
   import java.time.LocalDateTime;
   import java.time.ZoneId;
   import java.time.format.DateTimeFormatter;
  import java.time.format.DateTimeParseException;
  import java.util.Locale;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  import oshi.annotation.concurrent.ThreadSafe;
  import oshi.util.ExecutingCommand;
  
  /**
   * Utility to query logged in users.
   */
  @ThreadSafe
  public final class Who {
  
      // sample format:
      // system boot 2020-06-16 09:12
      private static final Pattern BOOT_FORMAT_AIX = Pattern.compile("\\D+(\\d{4}-\\d{2}-\\d{2})\\s+(\\d{2}:\\d{2}).*");
      private static final DateTimeFormatter BOOT_DATE_FORMAT_AIX = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm",
              Locale.ROOT);
  
      private Who() {
      }
  
      /**
       * Query {@code who -b} to get boot time
       *
       * @return Boot time in milliseconds since the epoch
       */
      public static long queryBootTime() {
          String s = ExecutingCommand.getFirstAnswer("who -b");
          if (s.isEmpty()) {
              s = ExecutingCommand.getFirstAnswer("/usr/bin/who -b");
          }
          Matcher m = BOOT_FORMAT_AIX.matcher(s);
          if (m.matches()) {
              try {
                  return LocalDateTime.parse(m.group(1) + " " + m.group(2), BOOT_DATE_FORMAT_AIX)
                          .atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
              } catch (DateTimeParseException | NullPointerException e) {
                  // Shouldn't happen with regex matching
              }
          }
          return 0L;
      }
  }