#compdef basename gbasename

local args variant
_pick_variant -r variant gnu=GNU $OSTYPE --version

case $variant in
  gnu)
    args=( -s -S -A "-*"
      '(2 -a --multiple)'{-a,--multiple}'[support multiple arguments, handling each]'
      '(2 -a --multiple -s --suffix)'{-s+,--suffix=}'[remove a trailing suffix]:suffix'
      '(-z --zero)'{-z,--zero}'[separate output with NUL rather than newline]'
      '(- *)--version[display version information]'
      '(- *)--help[display help information]'
    )
  ;;
  darwin*|dragonfly*|freebsd*)
    args=( -s -S -A "-*"
      '(2)-a[support multiple arguments, handling each]'
      '(-a 2)-s+[remove a trailing suffix]:suffix'
    )
  ;;
esac

_arguments $args \
  '1:file:_files' \
  '(*)2:suffix' \
  '*:file:_files'