have piston &&
_piston()
{
  local cur prev commands options command

  COMPREPLY=()
  cur=${COMP_WORDS[COMP_CWORD]}

  commands='update convert help unlock lock import'

  if [[ $COMP_CWORD -eq 1 ]] ; then
    if [[ "$cur" == -* ]]; then
      COMPREPLY=( $( compgen -W '--version' -- $cur ) )
    else
      COMPREPLY=( $( compgen -W "$commands" -- $cur ) )
    fi
  else

    prev=${COMP_WORDS[COMP_CWORD-1]}
    command=${COMP_WORDS[1]}

    if [[ "$cur" == -* ]]; then
      case $command in
        @(update|import))
          options='-r --revision --lock --verbose'
          ;;
      esac
      options="$options --verbose"

      COMPREPLY=( $( compgen -W "$options" -- $cur ) )
    else
      if [[ "$command" == @(help|h|\?) ]]; then
        COMPREPLY=( $( compgen -W "$commands" -- $cur ) )
      else
        _filedir
      fi
    fi
  fi

  return 0
}

[ -n "${have:-}" ] && complete -F _piston $default piston