#!/bin/bash -eu
#
# Copyright 2018 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# Script enables swap on VMs with less then 1GB RAM ($memsmall).

swapfile="/.c2d-swap-file"
swapsize=524288 # 512MB

memsmall=1048576 # 1024MB
spacelimit=$(($swapsize*3))

memavail=$(free | awk '/^Mem:/ {print $2}')
spaceavail=$(df -k / | awk 'END {print $4}')

if [[ $# -eq 1 ]]; then
  if [[ $1 == "disable" ]]; then
    if swapon -s | grep -q "$swapfile"; then
      swapoff "$swapfile" && exit 0
      exit 1
    fi
    exit 0
  fi

  if [[ $1 == "remove" ]]; then
    if swapon -s | grep -q "$swapfile"; then
      swapoff "$swapfile" && rm -f "$swapfile"
    fi
    sed -i -e "\!^$swapfile !d" /etc/fstab && exit 0
    exit 1
  fi
fi

if [[ "$memavail" -lt "$memsmall" && "$spaceavail" -gt "$spacelimit" ]]; then
  if ! swapon -s | grep -q $swapfile; then
    dd if=/dev/zero of="$swapfile" bs=1K count="$swapsize" status=none
    chmod 0600 "$swapfile"
    mkswap -L c2dswap "$swapfile"
    swapon "$swapfile"
    if ! grep -q "^$swapfile " /etc/fstab; then
      echo "$swapfile none swap sw 0 0" >> /etc/fstab
    fi
  else
    echo "swapfile: $swapfile already enabled."
  fi
else
  echo "swap not enabled: available memory over $memsmall or not enough free space on disk."
fi