#!/usr/bin/env sh

if [ $# != 3 ]; then
  echo "usage: $0 <cache-fs> <backing-pool> <percentage>"
  exit 1
fi

CACHE="${1}"
BACKING="${2}"
PERCENTAGE=${3}

set -o errexit
while [ $(df --output=pcent "${CACHE}" | grep -v Use | cut -d'%' -f1) -gt ${PERCENTAGE} ]
do
    FILE=$(find "${CACHE}" -type f -printf '%A@ %P\n' | \
                  sort | \
                  head -n 1 | \
                  cut -d' ' -f2-)
    test -n "${FILE}"
    rsync -axqHAXWESR --preallocate --relative --remove-source-files "${CACHE}/./${FILE}" "${BACKING}/"
done