MUTEX=mutex
MUTEX_OWNER=$HOSTNAME
MUTEX_TIMEOUT=600

release_lock() {
  local S3LOCK=$1

  rm -f $MUTEX
  aws s3 rm $S3LOCK
}

# Lock not timed out and we own it: 0
# Lock not timed out and someone else owns it: 1
# Lock timed out: 2
verify_lock() {
  local S3LOCK=$1

  aws s3 cp $S3LOCK $MUTEX
  _host=$(grep "MUTEX_OWNER=" $MUTEX | sed -e 's/MUTEX_OWNER=//')
  _time=$(grep "MUTEX_TIME=" $MUTEX | sed -e 's/MUTEX_TIME=//')

  # Check for timestamp and timeout
  let timepassed=$(date -u +%s)-$_time
  [ $timepassed -gt $MUTEX_TIMEOUT ] && return 2

  [ "$_host" == "$MUTEX_OWNER" ] && return 0
  return 1
}

aquire_lock() {
  local S3LOCK=$1

  echo "MUTEX_OWNER=${MUTEX_OWNER}" > $MUTEX
  echo "MUTEX_TIME=$(date -u +%s)" >> $MUTEX
  aws s3 cp $MUTEX $S3LOCK

  # verify we actually got the lock
  sleep 2
  verify_lock $S3LOCK
}

check_lock() {
  local S3LOCK=$1

  aws s3 ls $S3LOCK && rc=$? || rc=$?

  # No LOCK ? -> get it !
  if [ $rc -ne 0 ]; then
    aquire_lock $S3LOCK

  else
    verify_lock $S3LOCK && rc=$? || rc=$?

    # Lock timeout -> we get it
    if [ $rc -eq 2 ]; then
      aquire_lock $S3LOCK

    # we already own it
    elif [ $rc -eq 0 ]; then
      return 0

    # someone else has a valid lock
    else
      return 1
    fi
  fi
}