# shellcheck shell=bash

delete_subvolume_recursively() {
  IFS=$'\n'
  for i in $(btrfs subvolume list -o "$1" | cut -f 9- -d ' '); do
    delete_subvolume_recursively "/mnt/btrfs/${i}"
  done
  btrfs subvolume delete "$1"
}

mkdir -p /mnt/btrfs
mount "$DEVICE" /mnt/btrfs

if [[ -e /mnt/btrfs/@ ]]; then
  mkdir -p /mnt/btrfs/@.bak
  timestamp=$(date --date="@$(stat -c %Y /mnt/btrfs/@)" "+%Y%m%dT%H%M")
  base="@.$timestamp"

  target="/mnt/btrfs/@.bak/$base"
  if [[ -e "$target" ]]; then
    i=1
    while [[ -e "/mnt/btrfs/@.bak/${base}_$i" ]]; do
      (( i++ ))
    done
    target="/mnt/btrfs/@.bak/${base}_$i"
  fi

  mv /mnt/btrfs/@ "$target"
fi

find /mnt/btrfs/@.bak/ -maxdepth 1 -mtime +7 | while IFS= read -r i; do
  delete_subvolume_recursively "$i"
done

btrfs subvolume create /mnt/btrfs/@

umount /mnt/btrfs
rmdir /mnt/btrfs