#!/usr/local/bin/zsh
#

local option
local -i argpos
local -i counter

read -cn argpos

#echo 
#echo $1_$2($argpos)

if [[ "$1" = *[bCfFgKLNTVX]* ]]
then
  # option with parameter present, before cursor.  
  option=$1
  # check that the option with parameter is at the end of the string.
  if [[ $option[(i)[bCfFgKLNTVX]] = $#option ]]
  then
    # accept it, put a space after it.
    reply=($1$2\ )
  else
    # Very little we can do - best to disable completion.
    reply=( )
  fi
  return
else
  # let $option contain the stripped-off options.
  option="$1${2%%[bCfFgKLNTVX]*}"
  #echo "{$option}"
  if [[ "$option" = *[Acdrtux]*[Acdrtux]* ]]
  then
    # multiple mandatory options; only one allowed - no completions.
    reply=( )
  elif [[ $argpos -gt 2 || "$option" = *[Acdrtux]* ]]
  then
    # single mandatory option already given; don't prompt for others.
    if [[ -n "$2" ]]
    then
      # not at end of string - only permit simple options.
      reply=(B G h i k l m M o O p P R s S v w W z Z)
    else
      # at end of string - permit options taking values.
      reply=(b C f F g K L N T V X B G h i k l m M o O p P R s S v w W z Z)
    fi
  else
    # prompt for mandatory option before allowing others.
    reply=(A c d r t u x)
  fi
fi

reply=($1${^reply}$2)

#echo "($reply)"