#!/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 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="$HOME/.systemd_check.list"
SYSTEMD_CHECK_MAIL_ENABLED=fase
SYSTEMD_CHECK_MAIL_ADDRESS=""
SYSTEMD_CHECK_HOSTNAME=$(hostname)
SYSTEMD_CHECK_USER=$(whoami)
SYSTEMD_CHECK_SERVICES=()

# check for config file
source_config() {
    local config=$1;
    local configFallback=$2;

    if [[ ! -f "$config" ]]; then
        if [[ ! -f "$configFallback" ]]; then
            echo "No config file specified and could not find default in '$configFallback'!";
            echo "";
            usage;
            exit 1;
        else
            config=$configFallback;
        fi
    fi

    set -a;
    source "$config";
    set +a;
}
source_config "$1" "$HOME/.systemd_check.conf"

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

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

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

	if [ "$(id -u)" != "0" ]; then
		local COMMAND="systemctl --user is-active --quiet $SERVICE";
	fi

	if ! $($COMMAND); 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