#!/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 or /etc/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=512;

# 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 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/.memory_usage_alert.conf" "/etc/memory_usage_alert.conf"

# DO NOT TOUCH BELOW
total=$(free -mt | grep Total | awk '{print $2}')
used=$(free -mt | grep Total | awk '{print $3}')
# shellcheck disable=SC2004
free=$(($total-$used))

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