#!/bin/sh

set -e

. /etc/default/swapfile

# check defaults
[ -n "$SIZE" ] || exit 0
[ -n "$FILE" ] || exit 0

create_swapfile() {
  local FILE=$1
  local SIZE=$2
  fallocate -l $((1024*1024*SIZE)) "$FILE"
  mkswap "$FILE" >/dev/null 2>&1
  chmod 0600 "$FILE"
}

delete_swapfile() {
  if grep -q "$FILE" /proc/swaps; then
    swapoff "$1"
  fi
  rm -f "$1"
}

# SIZE is zero (or smaller), drop out
# (and delete possibly existing file)
if [ "$SIZE" -le "0" ]; then
    [ -e "$FILE" ] && delete_swapfile "$FILE"
    exit 0
fi

# file does not exist, create it
if [ ! -e "$FILE" ]; then
  create_swapfile "$FILE" "$SIZE"
fi

# file exists but has the wrong size
if [ "$(stat -c %s "$FILE")" -ne "$((1024*1024*SIZE))" ]; then
  delete_swapfile "$FILE"
  create_swapfile "$FILE" "$SIZE"
fi

# swap on if we aren't already
grep -q "$FILE" /proc/swaps || swapon "$FILE"