dns

#!/usr/bin/env bash

set -euo pipefail

assert_command() {
  if ! type "${1}" >/dev/null 2>&1; then
    echo "${2:-"command not found: ${1}"}"
    exit 1
  fi
}

assert_val() {
  if [[ -z "${1}" ]]; then
    echo "${2}"
    exit 1
  fi
}

assert_func() {
  if ! declare -F "${1}" >/dev/null; then
    echo "${2}"
    exit 1
  fi
}

_darwin_flush() {
  sudo dscacheutil -flushcache
}

_darwin_restart() {
  sudo killall -HUP mDNSResponder
}

_linux_flush() {
  sudo resolvectl flush-caches
}

_linux_restart() {
  sudo systemctl restart systemd-resolved
}

declare OS=""
case "${OSTYPE}" in
  darwin*)
    OS="darwin"
    ;;
  linux*)
    OS="linux"
    ;;
  *)
    echo "Unsupported OS!"
    exit 1;;
esac

declare -r cmd="${1:-"help"}"
shift || true

case "${cmd}" in
  help)
    cat << HELP
USAGE:
  dns flush
  dns restart
HELP
    exit 0
esac

declare -r func="_${OS}_${cmd}"
assert_func "${func}" "invalid command: ${cmd}"

$func $@