# Restrict the start of the editable line to the region between cursor
# and mark (including the character at the end).  Can be bound used as
# a zle widget, or called as a function from another widget.
#
# Optionally accepts exactly two arguments, which are used instead of
# $CURSOR and $MARK as limits to the range.
#
# Other options:
#   -p pretext   show `pretext' instead of the buffer text before the region.
#   -P posttext  show  `posttext' instead of the buffer text after the region.
# Either or both may be empty.
#   -n           Only replace the text before or after the region with
#                the -p or -P options if the text was not empty.
#   -S statevar
#   -R statevar
# Save or restore the state in/from the parameter named statevar.  In
# either case no recursive editing takes place; this will typically be
# done within the calling function between calls with -S and -R.  The
# statevar may not begin with the prefix _ntr_ which is reserved for
# parameters within narrow-to-region.

emulate -L zsh
setopt extendedglob

local _ntr_lbuffer _ntr_rbuffer 
local _ntr_predisplay=$PREDISPLAY _ntr_postdisplay=$POSTDISPLAY
integer _ntr_start _ntr_end _ntr_swap _ntr_cursor=$CURSOR _ntr_mark=$MARK
integer _ntr_stat

local _ntr_opt _ntr_pretext _ntr_posttext _ntr_usepretext _ntr_useposttext
local _ntr_nonempty _ntr_save _ntr_restore

while getopts "np:P:R:S:" _ntr_opt; do
  case $_ntr_opt in
    (n) _ntr_nonempty=1
	;;
    (p) _ntr_pretext=$OPTARG _ntr_usepretext=1
	;;
    (P) _ntr_posttext=$OPTARG _ntr_useposttext=1
	;;
    (R) _ntr_restore=$OPTARG
        ;;
    (S)	_ntr_save=$OPTARG
	;;
    (*) [[ $_ntr_opt != '?' ]] && print "$0: unhandled option: $_ntr_opt" >&2
	return 1
	;;
  esac
done
(( OPTIND > 1 )) && shift $(( OPTIND - 1 ))

if [[ $_ntr_restore = _ntr_* || $_ntr_save = _ntr_* ]]; then
  zle -M "$0: _ntr_ prefix is reserved" >&2
  return 1
fi

if [[ -n $_ntr_save || -z $_ntr_restore ]]; then

  if (( $# )); then
    if (( $# != 2 )); then
      zle -M "$0: supply zero or two arguments"
      return 1
    fi
    _ntr_start=$1
    _ntr_end=$2
  else
    _ntr_start=$MARK
    _ntr_end=$CURSOR
  fi

  if (( _ntr_start > _ntr_end )); then
    _ntr_swap=_ntr_start
    _ntr_start=_ntr_end
    _ntr_end=_ntr_swap
  fi

  (( _ntr_end++, _ntr_cursor -= _ntr_start, _ntr_mark -= _ntr_start ))
  
  _ntr_lbuffer=${BUFFER[1,_ntr_start]}
  if [[ -z $_ntr_usepretext || ( -n $_ntr_nonempty && -z $_ntr_lbuffer ) ]]
  then
    _ntr_pretext=$_ntr_lbuffer
  fi
  _ntr_rbuffer=${BUFFER[_ntr_end,-1]}
  if [[ -z $_ntr_useposttext || ( -n $_ntr_nonempty && -z $_ntr_rbuffer ) ]]
  then
    _ntr_posttext=$_ntr_rbuffer
  fi
  PREDISPLAY="$_ntr_predisplay$_ntr_pretext"
  POSTDISPLAY="$_ntr_posttext$_ntr_postdisplay"
  BUFFER=${BUFFER[_ntr_start+1,_ntr_end-1]}
  CURSOR=$_ntr_cursor
  MARK=$_ntr_mark

  if [[ -n $_ntr_save ]]; then
    eval "$_ntr_save=(${(qq)_ntr_predisplay} ${(qq)_ntr_postdisplay}
${(qq)_ntr_lbuffer} ${(qq)_ntr_rbuffer})" || return 1
  fi
fi

if [[ -z $_ntr_save && -z $_ntr_restore ]]; then
  zle recursive-edit
  _ntr_stat=$?
fi

if [[ -n $_ntr_restore || -z $_ntr_save ]]; then
  if [[ -n $_ntr_restore ]]; then
    if ! eval "_ntr_predisplay=\${${_ntr_restore}[1]}
_ntr_postdisplay=\${${_ntr_restore}[2]}
_ntr_lbuffer=\${${_ntr_restore}[3]}
_ntr_rbuffer=\${${_ntr_restore}[4]}"; then
      zle -M Failed.
      return 1
    fi
  fi

  PREDISPLAY=$_ntr_predisplay
  POSTDISPLAY=$_ntr_postdisplay
  LBUFFER="$_ntr_lbuffer$LBUFFER"
  RBUFFER="$RBUFFER$_ntr_rbuffer"
fi

return $_ntr_stat