printing-mode

#!/usr/bin/env bash
set -euo pipefail

readonly ENABLED_UNITS=(
  cups.socket
  cups.path
  cups.service
  avahi-daemon.socket
  avahi-daemon.service
  cups-browsed.service
)

readonly STATIC_UNITS=(
  ipp-usb.service
)

ACTION="status"
DRY_RUN=0
MASK_ON_DISABLE=0
UNMASK_ON_ENABLE=1

usage() {
  cat <<'EOF'
Toggle the Linux printing and printer-discovery stack.

Usage:
  printing-mode status
  printing-mode enable [--dry-run] [--no-unmask]
  printing-mode disable [--dry-run] [--mask]
  printing-mode -h|--help

Actions:
  status      Show installed printing/discovery units and their states.
  enable      Enable and start CUPS, printer discovery, Avahi, and USB IPP.
  disable     Stop and disable CUPS, printer discovery, Avahi, and USB IPP.

Options:
  --dry-run     Print the systemctl commands without running them.
  --mask        With disable, also mask units so socket/path activation cannot
                start them again until a later enable unmask runs.
  --no-unmask   With enable, do not unmask previously masked units first.
  -h, --help    Show this help.

Notes:
  - This script targets systemd Linux systems.
  - It skips units that are not installed on the current machine.
  - Disabling Avahi also disables general mDNS/.local discovery, not only
    printer discovery.
EOF
}

log() {
  printf '%s\n' "$*"
}

die() {
  printf 'error: %s\n' "$*" >&2
  exit 1
}

while [[ $# -gt 0 ]]; do
  case "$1" in
    status|enable|disable)
      ACTION="$1"
      shift
      ;;
    --dry-run)
      DRY_RUN=1
      shift
      ;;
    --mask)
      MASK_ON_DISABLE=1
      shift
      ;;
    --no-unmask)
      UNMASK_ON_ENABLE=0
      shift
      ;;
    -h|--help)
      usage
      exit 0
      ;;
    *)
      die "unknown argument: $1"
      ;;
  esac
done

if [[ "$(uname -s)" != "Linux" ]]; then
  die "this script only supports Linux"
fi

command -v systemctl >/dev/null 2>&1 || die "systemctl not found"

SUDO=()
if [[ "${ACTION}" != "status" && "${EUID}" -ne 0 ]]; then
  command -v sudo >/dev/null 2>&1 || die "sudo is required for ${ACTION}"
  SUDO=(sudo)
fi

run_systemctl() {
  if [[ "${DRY_RUN}" -eq 1 ]]; then
    printf '+'
    if [[ "${#SUDO[@]}" -gt 0 ]]; then
      printf ' %q' "${SUDO[@]}"
    fi
    printf ' systemctl'
    printf ' %q' "$@"
    printf '\n'
    return 0
  fi
  "${SUDO[@]}" systemctl "$@"
}

unit_property() {
  local unit="$1"
  local property="$2"
  systemctl show "$unit" --property="$property" --value 2>/dev/null || true
}

unit_exists() {
  local unit="$1"
  local load_state
  load_state="$(unit_property "$unit" LoadState)"
  [[ -n "${load_state}" && "${load_state}" != "not-found" ]]
}

unit_file_state() {
  local unit="$1"
  local state
  state="$(unit_property "$unit" UnitFileState)"
  [[ -n "${state}" ]] || state="unknown"
  printf '%s\n' "$state"
}

enable_capable_units() {
  local unit state
  for unit in "${ENABLED_UNITS[@]}"; do
    unit_exists "$unit" || continue
    state="$(unit_file_state "$unit")"
    if [[ "${state}" == "static" ]]; then
      continue
    fi
    printf '%s\n' "$unit"
  done
}

installed_static_units() {
  local unit
  for unit in "${STATIC_UNITS[@]}"; do
    unit_exists "$unit" || continue
    printf '%s\n' "$unit"
  done
}

print_status() {
  local all_units=("${ENABLED_UNITS[@]}" "${STATIC_UNITS[@]}")
  local unit load enabled active sub

  printf '%-24s %-10s %-12s %-12s %-12s\n' "UNIT" "LOAD" "ENABLED" "ACTIVE" "SUB"
  printf '%-24s %-10s %-12s %-12s %-12s\n' "----" "----" "-------" "------" "---"
  for unit in "${all_units[@]}"; do
    load="$(unit_property "$unit" LoadState)"
    [[ -n "${load}" ]] || load="not-found"
    if [[ "${load}" == "not-found" ]]; then
      printf '%-24s %-10s %-12s %-12s %-12s\n' "$unit" "$load" "-" "-" "-"
      continue
    fi
    enabled="$(unit_file_state "$unit")"
    active="$(unit_property "$unit" ActiveState)"
    sub="$(unit_property "$unit" SubState)"
    printf '%-24s %-10s %-12s %-12s %-12s\n' "$unit" "$load" "$enabled" "$active" "$sub"
  done
}

readarray_or_empty() {
  local array_name="$1"
  local command_name="$2"
  local -n target="$array_name"
  target=()
  while IFS= read -r line; do
    [[ -n "${line}" ]] || continue
    target+=("${line}")
  done < <("$command_name")
}

enable_printing() {
  local enable_units static_units
  readarray_or_empty enable_units enable_capable_units
  readarray_or_empty static_units installed_static_units

  if [[ "${#enable_units[@]}" -eq 0 && "${#static_units[@]}" -eq 0 ]]; then
    log "No known printing units are installed on this machine."
    return 0
  fi

  if [[ "${UNMASK_ON_ENABLE}" -eq 1 && "${#enable_units[@]}" -gt 0 ]]; then
    run_systemctl unmask "${enable_units[@]}"
  fi

  if [[ "${#enable_units[@]}" -gt 0 ]]; then
    run_systemctl enable --now "${enable_units[@]}"
  fi

  if [[ "${#static_units[@]}" -gt 0 ]]; then
    run_systemctl start "${static_units[@]}" || true
  fi
}

disable_printing() {
  local enable_units static_units
  readarray_or_empty enable_units enable_capable_units
  readarray_or_empty static_units installed_static_units

  if [[ "${#static_units[@]}" -gt 0 ]]; then
    run_systemctl stop "${static_units[@]}" || true
  fi

  if [[ "${#enable_units[@]}" -gt 0 ]]; then
    run_systemctl stop "${enable_units[@]}" || true
    run_systemctl disable "${enable_units[@]}"
  fi

  if [[ "${MASK_ON_DISABLE}" -eq 1 && "${#enable_units[@]}" -gt 0 ]]; then
    run_systemctl mask "${enable_units[@]}"
  fi
}

case "${ACTION}" in
  status)
    print_status
    ;;
  enable)
    enable_printing
    ;;
  disable)
    disable_printing
    ;;
  *)
    die "unsupported action: ${ACTION}"
    ;;
esac