#!/usr/bin/env bash

main() {
  while getopts ":l:d:t:x:c:h" opt; do
    case "${opt}" in
      l)
        unset VM_FILTER
        IFS="," read -r -a VM_FILTER <<< "$OPTARG"
        ;;
      d)
        local backup_location="${OPTARG}"
        backup_location="${backup_location%/}"
        ;;
      t)
        declare -g TARGET="$OPTARG"
        ;;
      x)
        declare -g EXTENSION
        if [[ "${OPTARG,,}" == 'none' ]]; then
          EXTENTION=""
        else
          command -v "$OPTARG" >/dev/null 2>&1 || { echo "$OPTARG command not found"; exit 1; }
          EXTENTION="${OPTARG,,}"
        fi

        declare -g COMPRESSION="$OPTARG"
        ;;
      c)
        declare -g run_cleanup=y
        declare -g files_to_keep="${OPTARG}"
        ;;
      h)
        usage
        ;;
      *)
        usage
        ;;
    esac
  done

  backup_location=${backup_location:-$PWD}

  if [[ "${#VM_FILTER[*]}" -gt 0 ]]; then
    backup_vms "$backup_location" "${VM_FILTER[@]}"
  else
    backup_vms "$backup_location"
  fi
}

lxc() {
	local lxc_cmd="${TARGET:-lxc}"
	command "$lxc_cmd" "$@"
}

list_vms() {
	lxc list -c n -f csv
}

usage() {
  cat <<EOF
Usage: ${0##*/} [-l vm[,vm...]] [-d backup_dir] [-t lxc|incus] [-x <compression alogorithm>] [-c <keep 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 keeping a set number (default: 2)
  -h  Show this message

EOF
  exit 1
}

backup_vms() {
  local backup_location="$1"; shift
  local vms=("$@")

  # when no argument use list of all VMs
  if ((${#vms[@]} == 0)); then
    mapfile -t vms < <(list_vms)
  fi

  for vm in "${vms[@]}"; do
    [[ -n $vm ]] || continue
    start_backup "$vm" "$backup_location"
  done
}

start_backup() {
  local vm=$1
  local backup_base="$2"
  local compression="${COMPRESSION:-none}"
  local ext="${EXTENTION}" ; [[ -n "$ext" ]] && ext=".${ext}"
  local destination="${backup_base}/${vm}"
  local backup_name="${vm}_$(date +"%Y-%m-%d_%H-%M-%S").tar${ext}"

  [[ -d "$backup_base" ]] || { echo "${backup_base} is not a directory"; exit 1; }
  [[ -d "$destination" ]] || mkdir "$destination"
  [[ -f "${destination}/${backup_name}" ]] && { echo "Backup already exists"; return 2; }

  lxc export "$vm" --instance-only --compression "${compression}" "${destination}/${backup_name}" || { echo "Error exporting $vm"; return 1; }

  [[ -n "$run_cleanup" ]] && prune_backups "$destination"
}

prune_backups() {
  local backup_directory="$1"
  mapfile -t backup_files < <(find "$backup_directory" -maxdepth 1 -type f -printf '%T@ %p\n' | sort -n | head -n "-${files_to_keep}" | cut -d' ' -f2-)
  
  if [[ ${#backup_files[@]} -gt 0 ]]; then
    echo "Removing ${#qcow2_files[@]} old backup files for $vm (keeping last $total_files_to_keep files)"
    printf '%s\0' "${backup_files[@]}" | xargs -0 rm -fv
  else
    echo "No old backups to remove for $vm"
  fi

}

main "$@"