#!/bin/bash -l

set -eE -o pipefail
trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR

base=unison-$(date "+%Y:%m:%d")
for mountp in /mnt/root /mnt/iroot; do
    [[ -e $mountp ]] || continue
    full_base=$mountp/$base
    existing=( $full_base-* )
    if [[ -e ${existing[0]} ]]; then
        snapshot=$full_base-$(( ${#existing[@]} + 1 ))
    else
        snapshot=$full_base-1
    fi
    s btrfs subvolume snapshot -r $mountp $snapshot
    existing=( $mountp/unison-* )
    # keep 10 unison snapshots around
    if (( ${#existing[@]} > 10 )); then
        IFS=$'\n' existing=($(sort -Vr <<<"${existing[*]}"))
        unset IFS
        s btrfs subvolume delete ${existing[@]:10}
    fi
done