#!/usr/bin/env bash

# usage
usage() {
SYSTEMD_CHECK_USAGE=$(cat <<EOF
Usage: systemd_check.sh

Checks a set of systemd services, targets, mounts of timers, and notifies if their state is not up and running. Please see man systemd_check.

EOF
)
	echo "$SYSTEMD_CHECK_USAGE";
}

set -e;

# check for config file
apply_config() {
  local config=$1;

  if [[ ! -f "$config" ]]; then
      echo "No config file specified";
      echo "";
      usage;
      exit 1;
  fi

  set -a;
  # shellcheck disable=SC1090
  source "$config";
  set +a;
}

source_config() {
  local configFallback=$1;
  local configGlobalFallback=$2;

  if [[ -f "$configFallback" ]]; then
    apply_config "$configFallback";
    return;
  fi

  if [[ -f "$configGlobalFallback" ]]; then
    apply_config "$configGlobalFallback";
    return;
  fi
}

check_required() {
  type hostname &> /dev/null || { echo "Requiring 'hostname' but it's not installed"; exit 1; }
  type mailx &> /dev/null || { echo "Requiring 'mailx' but it's not installed"; exit 1; }
  type whoami &> /dev/null || { echo "Requiring 'whoami' but it's not installed"; exit 1; }
  type systemctl &> /dev/null || { echo "Requiring 'systemctl' but it's not installed"; exit 1; }
}

SYSTEMD_CHECK_LIST_FILE="$HOME/.systemd_check.list"
SYSTEMD_CHECK_GLOBAL_LIST_FILE="/etc/systemd_check.list"
SYSTEMD_CHECK_MAIL_ENABLED=fase
SYSTEMD_CHECK_MAIL_ADDRESS=""
SYSTEMD_CHECK_SERVICES=()

source_config "$HOME/.systemd_check.conf" "/etc/systemd_check.conf"
check_required

SYSTEMD_CHECK_HOSTNAME=$(hostname)
SYSTEMD_CHECK_USER=$(whoami)

listFileToUse=""
if [[ -f "$SYSTEMD_CHECK_LIST_FILE" ]]; then
	listFileToUse="$SYSTEMD_CHECK_LIST_FILE"
else
	listFileToUse="$SYSTEMD_CHECK_GLOBAL_LIST_FILE"
fi

if [[ ! -f $listFileToUse ]]; then
	echo "$listFileToUse doesn't exist. Add a file which holds one systemd service or timer per line.";
	echo "";
	usage;
	exit 1;
fi

echo "Scanning $listFileToUse for services...";
while IFS='' read -r line || [[ -n "$line" ]]; do
    SYSTEMD_CHECK_SERVICES+=("$line")
	echo "-> Found $line";
done < "$listFileToUse"

# get status for a service
function checkService() {
	local SERVICE=$1;
	local MESSAGE="$SERVICE is not running for user $SYSTEMD_CHECK_USER";

	local ROOT_COMMAND="systemctl is-active --quiet $SERVICE";
	local USER_COMMAND="systemctl --user is-active --quiet $SERVICE";

	local RESULT=0;

	if [ "$(id -u)" != "0" ]; then
		# shellcheck disable=SC2091
		if ! $($USER_COMMAND); then
			RESULT=1;
		fi
	else
		# shellcheck disable=SC2091
		if ! $($ROOT_COMMAND) && ! $($USER_COMMAND); then
			RESULT=1;
		fi
	fi

	if [ "$RESULT" -gt 0 ]; then
		local SUBJECT="[systemd $SYSTEMD_CHECK_HOSTNAME for $SYSTEMD_CHECK_USER] CRITICAL $SERVICE";
		echo "-> $SUBJECT: $MESSAGE";

		if [ "$SYSTEMD_CHECK_MAIL_ENABLED" = true ]; then
	        echo "$MESSAGE"|mailx -Ssendwait -s "$SUBJECT" "$SYSTEMD_CHECK_MAIL_ADDRESS";
	    fi
	fi

	return;
}

# execute check for defined SYSTEMD_CHECK_SERVICES
for service in "${SYSTEMD_CHECK_SERVICES[@]}"; do
	echo "Checking $service...";
	checkService "$service"
done