#!/usr/bin/env bash

# usage
usage() {
SYSTEMD_CHECK_USAGE=$(cat <<EOF
Usage: systemd_check.sh [CONFIG_FILE (absolute path)]

Checks if specific systemd SYSTEMD_CHECK_SERVICES are running and optionally sends a mail.

If no CONFIG_FILE is given, HOME/.systemd_check.conf or /etc/systemd_check.conf is used. This fallback option
has to exist or the script will exit.

Configuration can be done in any file and any pre-defined variable can be overwritten.

The following are at least required for the script to work:
- SYSTEMD_CHECK_LIST_FILE="HOME/.systemd_check.list" // path to file to list services to check, one per line

The following are optional or have reasonable defaults:
- SYSTEMD_CHECK_MAIL_ENABLED=false // send email (SYSTEMD_CHECK_MAIL_ADDRESS has to be set to true)? false|true
- SYSTEMD_CHECK_MAIL_ADDRESS="" // mail.rc has to be configured

You can copy this script to '/usr/local/bin' and use create a custom CONFIG_FILE as user. Examples can be found in '/usr/share/doc/<scriptname>'.
EOF
)
	echo "$SYSTEMD_CHECK_USAGE";
}

set -e;

# vars and defaults
SYSTEMD_CHECK_LIST_FILE="$HOME/.systemd_check.list"
SYSTEMD_CHECK_GLOBAL_LIST_FILE="/etc/systemd_check.list"
SYSTEMD_CHECK_MAIL_ENABLED=fase
SYSTEMD_CHECK_MAIL_ADDRESS=""
SYSTEMD_CHECK_HOSTNAME=$(hostname)
SYSTEMD_CHECK_USER=$(whoami)
SYSTEMD_CHECK_SERVICES=()

# 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;
  source "$config";
  set +a;
}

source_config() {
  local config=$1;
  local configFallback=$2;
  local configGlobalFallback=$3;

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

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

  if [[ -f "$configGlobalFallback" ]]; then
    apply_config "$configGlobalFallback";
    return;
  fi
}
source_config "$1" "$HOME/.systemd_check.conf" "/etc/systemd_check.conf"

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
		if ! $($USER_COMMAND); then
			RESULT=1;
		fi
	else
		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