#autoload

## usage: _regex_arguments funcname regex

## configuration key used:

# regex_arguments_path
#  The path to a directory for caching. (default: ~/.zsh/regex_arguments)

##

# _regex_arguments compiles `regex' and emit the result of the state
# machine into the function `funcname'. `funcname' parses a command line
# according to `regex' and evaluate appropriate actions in `regex'. Before
# parsing the command line string is genereted by concatinating `words'
# (before `PREFIX') and `PREFIX' with a separator NUL ($'\0').

# The `regex' is defined as follows.

## regex word definition:

# pattern = "/" ( glob | "[]" ) "/" [ "+" | "-" ]
# lookahead = "%" glob "%"
# guard = "-" zsh-code-to-eval
# action = ":" zsh-code-to-eval

## regex word sequence definition:

# element = pattern [ lookahead ] [ guard ] [ action ]
#
# regex = element 
#	| "(" regex ")"
#	| regex "#"
#	| regex regex
#	| regex "|" regex

# example:

# compdef _tst tst

# _regex_arguments _tst /$'[^\0]#\0'/ /$'[^\0]#\0'/ :'compadd aaa'
#  _tst complete `aaa' for first argument.
#  First $'[^\0]#\0' is required to match with command name.

# _regex_arguments _tst /$'[^\0]#\0'/ \( /$'[^\0]#\0'/ :'compadd aaa' /$'[^\0]#\0'/ :'compadd bbb' \) \#
#  _tst complete `aaa' for (2i+1)th argument and `bbb' for (2i)th argument.

# _regex_arguments _tst /$'[^\0]#\0'/ \( /$'[^\0]#\0'/ :'compadd aaa' \| /$'[^\0]#\0'/ :'compadd bbb' \) \#
#  _tst complete `aaa' or `bbb'.

## Recursive decent regex parser

# return status of parser functions:

# 0 : success
# 1 : parse error
# 2 : fatal parse error

_ra_parse_elt () {
  local state act
  if (( $#regex < index )); then
    return 1
  else
    case "$regex[index]" in
      /*/([-+]|)) state=$index
          first=($state)
	  last=($state)
	  nullable=
	  case "$regex[index]" in 
	    */+) cutoff[$state]=+;;
	    */) cutoff[$state]=/;;
	    */-) cutoff[$state]=-;;
	  esac
          pattern[$state]="${${regex[index++]#/}%/([-+]|)}"
	  if [[ $pattern[$state] != "[]" ]]; then
	    pattern[$state]="(#b)((#B)$pattern[$state])"
	  fi
	  if [[ $index -le $#regex && $regex[index] = %*% ]]; then
	    lookahead[$state]="(#B)${regex[index++][2,-2]}"
	  else
	    lookahead[$state]=""
	  fi
	  if [[ $index -le $#regex && $regex[index] = -* ]]; then
	    guard[$state]="${regex[index++][2,-1]}"
	  else
	    guard[$state]=""
	  fi
	  if [[ $index -le $#regex && $regex[index] = :* ]]; then
	    act="${regex[index++][2,-1]}"
	    action[$state]="$act"
	    : ${actions[$act]::="${actions[$act]} $state"}
	  else
	    action[$state]=""
	  fi
	  ;;
      \() (( index++ ))
          _ra_parse_alt || return $?
	  [[ $index -le $#regex && "$regex[$index]" = \) ]] || return 2
	  (( index++ ))
	  ;;
      *)  return 1
          ;;
    esac
  fi

  return 0
}

_ra_parse_clo () {
  _ra_parse_elt || return $?

  if (( index <= $#regex )) && [[ "$regex[$index]" = \# ]]; then
    (( index++ ))
    nullable=yes

    for i in $last; do tbl[$i]="$tbl[$i] $first"; done
  fi

  return 0
}

_ra_parse_seq () {
  local last_seq
  local first_seq nullable_seq
  first_seq=()
  nullable_seq=yes

  _ra_parse_clo || {
    if (( $? == 2 )); then
      return 2
    else
      first=()
      last=()
      nullable=yes
      return 0
    fi
  }
  first_seq=($first)
  last_seq=($last)
  [[ -n "$nullable" ]] || nullable_seq=

  while :; do
    _ra_parse_clo || {
      if (( $? == 2 )); then
        return 2
      else
        break
      fi
    }
    for i in $last_seq; do tbl[$i]="${tbl[$i]} $first"; done
    [[ -n "$nullable_seq" ]] && first_seq=($first_seq $first)
    [[ -n "$nullable" ]] || { nullable_seq= last_seq=() }
    last_seq=($last_seq $last)
  done

  first=($first_seq)
  nullable=$nullable_seq
  last=($last_seq)
  return 0
}

_ra_parse_alt () {
  local last_alt
  local first_alt nullable_alt 
  first_alt=()
  nullable_alt=

  _ra_parse_seq || return $?
  first_alt=($first_alt $first)
  last_alt=($last_alt $last)
  [[ -n "$nullable" ]] && nullable_alt=yes

  while :; do
    (( index <= $#regex )) || break
    [[ "$regex[$index]" = \| ]] || break
    (( index++ ))

    _ra_parse_seq || {
      if (( $? == 2 )); then
        return 2
      else
        break
      fi
    }
    first_alt=($first_alt $first)
    last_alt=($last_alt $last)
    [[ -n "$nullable" ]] && nullable_alt=yes
  done

  first=($first_alt)
  last=($last_alt)
  nullable=$nullable_alt
  return 0
}

## function generator

_ra_gen_func () {
  local old new
  local state index
  local test tmp
  local start="0"

  old=()
  new=($start)

  print -lr - \
    "$funcname () {" \
      'setopt localoptions extendedglob' \
      'local _ra_state _ra_left _ra_right _ra_actions' \
      "_ra_state=$start" \
      '_ra_left=' \
      '_ra_right="${(pj:\0:)${(@)words[1,CURRENT - 1]:Q}}"$'\''\0'\''"$PREFIX"' \
      '_ra_actions=()' \
      'while :; do' \
	'case "$_ra_state" in'

  while (( $#new )); do
    state="$new[1]"
    shift new
    old=("$old[@]" "$state")
    print -lr - \
	"$state)"
    _ra_gen_parse_state
    print -lr - \
	  ';;'
  done

  print -lr - \
	'esac' \
      'done' \
      'while (( $#_ra_actions )); do' \
	'case "$_ra_actions[1]" in'

  for tmp in "${(@k)actions}"; do
    if [[ "$tmp" != '' ]]; then
      print -lr - "${(j:);&:)${=actions[$tmp]}})" $tmp ';;'
    fi
  done

  print -lr - \
	'esac' \
	'shift _ra_actions' \
      'done' \
    '}'
}

_ra_gen_parse_state () {
  local actions i p
  test='if'
  for index in $=tbl[$state]; do
    if [[ "$pattern[$index]" != "[]" ]]; then
      p="$pattern[$index]$lookahead[$index]*"
      if [[ -z "$guard[$index]" ]]; then
	print -lr - \
	  "$test [[ \$_ra_right = \${~:-${(qqqq)p}} ]]"
      else
	print -lr - \
	  "$test [[ \$_ra_right = \${~:-${(qqqq)p}} ]] && {" \
	      "$guard[$index]" \
	    "}"
      fi
      test='elif'
      (( $old[(I)$index] || $new[(I)$index] )) || new=($index "$new[@]")
      print -lr - \
	  "then" \
	    "_ra_state=$index" \
	    '_ra_right="${_ra_right[mend[1] + 1, -1]}"'
      actions=()
      for i in $=tbl[$index]; do
	if [[ -n $action[$i] ]]; then
	  actions=($actions $i)
	fi
      done
      case "$cutoff[$index]" in
	+) print -lr - \
	    '_ra_left="$_ra_left$match[1]"'
	  if (( $#actions )); then
	    print -lr - \
	    "_ra_actions=($actions \$_ra_actions)"
	  fi
          ;;
	/) print -lr - \
	    '_ra_left='
	  print -lr - \
	    'if (( mend[1] )); then' \
	      "_ra_actions=($actions)"
	  if (( $#actions )); then
	    print -lr - \
	    'else' \
	      "_ra_actions=($actions \$_ra_actions)"
	  fi
	  print -lr - \
	    'fi'
	  ;;
	-) print -lr - \
	    '_ra_left=' \
	    "_ra_actions=($actions)"
	  ;;
      esac
    fi
  done

  if [[ $test != 'if' ]]; then
  # Some branchs are exists. But all of them are failed.
    print -lr - \
	  'else' \
	    'if [[ "$_ra_left$_ra_right" = *$'\''\0'\''* ]]; then' \
	      '_message "parse failed before current word"' \
	      '_ra_actions=()' \
	    'else' \
	      'compset -p $(( $#PREFIX - $#_ra_right - $#_ra_left ))' \
	    'fi' \
	    'break' \
	  'fi'
  else
  # There are no branch.
    print -lr - \
	  '_message "no more arguments"' \
	  '_ra_actions=()' \
	  'break'
  fi
}

_regex_arguments () {
  setopt localoptions extendedglob

  local funcname="_regex_arguments_tmp"
  local funcdef

  typeset -A tbl cutoff pattern lookahead guard action actions
  local regex index first last nullable
  local i state next

  local cache_dir="${compconfig[regex_arguments_path]:-$HOME/.zsh/regex_arguments}"
  local cache_file="$cache_dir/$1"
  local cache_test

  if ! [[ -f "$cache_file" ]] || ! source "$cache_file" "$@"; then
    funcname="$1"

    regex=("${(@)argv[2,-1]}")
    index=1
    tbl=()
    pattern=()
    lookahead=()
    guard=()
    action=()
    actions=()
    _ra_parse_alt

    if (( $? == 2 || index != $#regex + 1 )); then
      if (( index != $#regex + 1 )); then
	print "regex parse error at $index: $regex[index]" >&2
      else
	print "regex parse error at $index (end)" >&2
      fi
      return 1
    fi

    tbl[0]=" $first"

    unfunction "$funcname" 2>/dev/null
    funcdef="$(_ra_gen_func)"

    if [[ -d "$cache_dir" && -w "$cache_dir" ]]; then
      print -lr - \
	'if [[ $# -eq '$#' && "$*" = '"${(qqqq)*}"' ]]; then' \
	"$funcdef" \
	'true; else false; fi' > "${cache_file}.$HOST.$$"
      source "${cache_file}.$HOST.$$" "$@"
      mv "${cache_file}.$HOST.$$" "${cache_file}"
    else
      source =(print -lr - "$funcdef")
    fi
  fi
}

_regex_arguments "$@"