#!/usr/bin/env bash

# usage
usage() {
USAGE=$(cat <<EOF
Usage: memory_usage_alert

Checks available memory and sends out notification via mail. Please see man memory_usage_alert.
EOF
)
	echo "$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 free &> /dev/null || { echo "Requiring 'free' but it's not installed"; exit 1; }
}

MEMORY_USAGE_ALERT_MAIL_ADDRESS="";
MEMORY_USAGE_ALERT_THRESHOLD=512;

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

HOSTNAME=$(hostname)
SUBJECT="[memory $HOSTNAME] memory is low"

# 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