#!/usr/bin/env bash

# usage
usage() {
USAGE=$(cat <<EOF
Usage: memory_usage_alert [CONFIG_FILE (absolute path)]

If no CONFIG_FILE is given, HOME/.memory_usage_alert.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:
- MEMORY_USAGE_ALERT_MAIL_ADDRESS="" // mail.rc has to be configured

The following are optional or have reasonable defaults:
- MEMORY_USAGE_ALERT_THRESHOLD=128 // threshold to warn about (in megabytes)

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 "$USAGE";
}

set -e;

HOSTNAME=$(hostname)
SUBJECT="[memory $HOSTNAME] memory is low"
MEMORY_USAGE_ALERT_MAIL_ADDRESS="";
MEMORY_USAGE_ALERT_THRESHOLD=128;

# 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/.memory_usage_alert.conf"

# DO NOT TOUCH BELOW
free=$(free -mt | grep Total | awk '{print $4}')

if [[ "$free" -le $MEMORY_USAGE_ALERT_THRESHOLD  ]]; then
        ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head >/tmp/top_proccesses_consuming_memory.txt

        file=/tmp/top_proccesses_consuming_memory.txt
        echo -e "Memory on $HOSTNAME is running low ($MEMORY_USAGE_ALERT_THRESHOLD MB is the remaining threshold)!\n\nFree memory: $free MB" | mailx -a "$file" -s "$SUBJECT" "$MEMORY_USAGE_ALERT_MAIL_ADDRESS"
fi

exit 0