#!/bin/bash

function usage {
  echo "Usage:
  -u [UNIT name] (required)
  -t Service is triggered by a timer or is a oneshot service. Is allowed to be inactive
  -d A service is allowed to not be enabled"
}

UNIT_NAME=""
IS_TIMER=false
IS_ALLOWED_DISABLED=false

# Parse command line arguments
while getopts "u:td" opt; do
  case ${opt} in
    u )
      UNIT_NAME=$OPTARG
      ;;
    t )
      IS_TIMER=true
      ;;
    d )
      IS_ALLOWED_DISABLED=true
      ;;
    \? )
      usage
      exit 1
      ;;
    : )
      echo "Invalid option: $OPTARG requires an argument" 1>&2
      exit 1
      ;;
  esac
done
shift $((OPTIND -1))

if [ -z "$UNIT_NAME" ]; then
  echo "Missing unit name."
  usage
  exit -1
fi

# Check if the unit exists
if ! systemctl list-units --full -all 2>/dev/null | grep -Pq "\b$UNIT_NAME\b"; then
    echo "CRITICAL - $UNIT_NAME does not exist"
    exit 2
fi

# Check if the unit is enabled
enabled=$(systemctl is-enabled "$UNIT_NAME")
if [ "$enabled" != "enabled" ] && [ "$IS_ALLOWED_DISABLED" = false ]; then
    echo "CRITICAL - $UNIT_NAME is not enabled"
    exit 2
fi

# Check if the unit is active
active=$(systemctl is-active "$UNIT_NAME")
substate=$(systemctl show "$UNIT_NAME" --property=SubState --value)
exit_code=$(systemctl show "$UNIT_NAME" --property=ExecMainStatus --value)

if [ "$active" = "activating" ]; then
    echo "WARNING - $UNIT_NAME is activating"
    exit 1
elif [ "$active" != "active" ] && [ "$IS_TIMER" = false ]; then
    echo "CRITICAL - $UNIT_NAME is not active"
    exit 2
elif [ "$IS_TIMER" = true ] && [ "$active" = "inactive" ] && [ "$exit_code" != "0" ]; then
    echo "CRITICAL - $UNIT_NAME is inactive with non-zero exit code"
    exit 2
fi

# Get service start time
start_time=$(systemctl show "$UNIT_NAME" --property=ExecMainStartTimestamp --value)
end_time=$(systemctl show "$UNIT_NAME" --property=ExecMainExitTimestamp --value)
current_time=$(date +%s)
start_time_diff_perf=""
end_time_diff_perf=""

start_time_str=""
if [ -n "$start_time" ] && [ "$start_time" != "n/a" ] && [ -z "$start_time" ]; then
  start_time_diff=$((current_time - $(date -d "$start_time" +%s)))
  start_time_diff_perf="| uptime=${start_time_diff}s"
  start_time_str=" Started at $start_time."
fi

end_time_str=""
if [ -n "$end_time" ] && [ "$end_time" != "n/a" ] && [ -z "$end_time" ]; then
  end_time_diff=$((current_time - $(date -d "$end_time" +%s)))
  end_time_diff_perf="| downtime=${end_time_diff}s"
  end_time_str=" Exited at $end_time."
fi

# =============
# Build output

if [ "$IS_TIMER" = true ] && { [ "$substate" = "exited" ] || [ "$active" = "inactive" ]; }; then
    status="exited (returned $exit_code)"
else
    status="active"
fi

if [ "$enabled" = "enabled" ] || [ "$IS_ALLOWED_DISABLED" != true ]; then
    status+=" and enabled"
fi

if [ "$IS_TIMER" = true ] && { [ "$substate" = "exited" ] || [ "$active" = "inactive" ]; }; then
    echo "OK - $UNIT_NAME is $status.$end_time_str $end_time_diff_perf"
else
    echo "OK - $UNIT_NAME is $status.$start_time_str $start_time_diff_perf"
fi

exit 0