#!/usr/bin/env bash

main() {
  # Set default options
  local cmd="${CMD:-lxc}"
  local backup_dir="${BACKUP_DIR:-$PWD}"
  local compression="${COMPRESSION:-zstd}"
  local vm_list
  local retention=0

  while getopts ":l:d:t:x:c:h" opt; do
    case "${opt}" in
      l)
        IFS="," read -r -a vm_list <<< "$OPTARG";;
      d)
        backup_dir="${OPTARG%/}";;
      t)
        cmd="$OPTARG";;
      x)
        compression="$OPTARG";;
      c)
        retention="${OPTARG}";;
      h|*)
        usage;;
    esac
  done

  lxc() { command "$cmd" "$@"; }
  list_vms() { lxc list -c n -f csv; }

  if ((${#vm_list[@]} == 0)); then
    mapfile -t vm_list < <(list_vms)
  fi

  for vm in "${vm_list[@]}"; do
    start_backup "$vm" "$backup_dir" "$compression"

    if (( retention > 0 )); then
      prune_backups "$vm" "$backup_dir" "$retention"
    fi
  done

  exit 0
}

usage() {
  cat <<EOF
Usage: ${0##*/} [-l vm[,vm...]] [-d <backup directory>] [-t lxc|incus] [-x <compression alogorithm>] [-c <keep last n backups>] [-h]

Options:
  -l  Comma-separated list of VMs to back up
  -d  Directory where backups will be stored (default: current directory)
  -t  Manager type: lxc or incus (default: lxc)
  -x  Compression algorithm (e.g. gzip, zstd, none)
  -c  Cleanup old backups and keep last <n> (default: keep all)
  -h  Show this message
EOF
  exit 1
}

start_backup() {
  local vm=$1
  local backup_dir="$2"
  local compression="$3"
  local ext=".${compression}"

  if [[ "$compression" == 'none' ]]; then
    ext=""
  else
    command -v "$compression" >/dev/null 2>&1 || { echo "$compression command not found"; exit 1; }
  fi

  local vm_dir="${backup_dir}/${vm}"
  local backup_name
  backup_name="${vm}_$(date +"%Y-%m-%d_%H-%M-%S").tar${ext}"

  [[ -d "$backup_dir" ]] || { echo "${backup_dir} is not a directory"; exit 1; }
  [[ -d "$vm_dir" ]] || mkdir "$vm_dir" || { echo "Cannont create $vm_dir"; exit 1; }
  [[ -f "${vm_dir}/${backup_name}" ]] && { echo "Backup already exists"; return 2; }
  echo "starting $vm"
  lxc export "$vm" --instance-only --compression "${compression}" "${vm_dir}/${backup_name}" || { echo "Error exporting $vm"; return 1; }
}

prune_backups() {
  local vm="$1"
  local backup_dir="$2"
  local retention="$3"
  mapfile -t backup_files < <(find "${backup_dir}/${vm}" -maxdepth 1 -type f -printf '%T@ %p\n' | sort -n | head -n "-${retention}" | cut -d' ' -f2-)

  if [[ ${#backup_files[@]} -gt 0 ]]; then
    echo "Removing ${#backup_files[@]} old backup files for $vm (keeping last $retention files)"
    printf '%s\0' "${backup_files[@]}" | xargs -0 rm -fv > /dev/null
  else
    echo "No old backups to remove for $vm"
  fi

}

main "$@"