fname=
lineno=
c=
tok=
tokens=

pgetc()
{
	c="$(dd bs=1 count=1 2>/dev/null; printf '.')"
	c="${c%.}"
}

next()
{
	while :; do
		echo "parsing char '$c'" >&2
		case "${c}" in
			'')
				pgetc
				tok=T_EOF
				return
				;;
			"${LF}")
				pgetc
				lineno=$((${lineno} + 1))
				tok=T_NEWLINE
				return
				;;
			' '|"${HT}")
				pgetc
				continue
				;;
			\\)
				pgetc
				case "${c}" in "${LF}")
					lineno=$((${lineno} + 1))
					pgetc
					continue
					;;
				esac
				next_word
				return
				;;
			'#')
				pgetc
				while :; do
					case "${c}" in "${LF}"|'')
						break
						;;
					esac
					pgetc
				done
				continue
				;;
			'&')
				pgetc
				case "${c}" in '&')
					pgetc
					tok=T_AND_IF
					return
					;;
				esac
				tok=T_AND
				return
				;;
			'|')
				pgetc
				case "${c}" in '|')
					pgetc
					tok=T_OR_IF
					return
					;;
				esac
				tok=T_PIPE
				return
				;;
			';')
				pgetc
				case "${c}" in ';')
					pgetc
					tok=T_DSEMI
					return
					;;
				esac
				tok=T_SEMI
				return
				;;
			'(')
				pgetc
				tok=T_LPAREN
				return
				;;
			')')
				pgetc
				tok=T_RPAREN
				return
				;;
			'<'|'>')
				next_io
				return
				;;
			*)
				next_word
				return
				;;
		esac
		pgetc
	done
}

next_io()
{
	case "${c}" in
		'<')
			pgetc
			case "${c}" in '<')
				pgetc
				case "${c}" in '-')
					pgetc
					tok=T_DLESSDASH
					;;
				esac
				tok=T_DLESS
				;;
			esac
			tok=T_LESS
			;;
		'>')
			pgetc
			case "${c}" in '>')
				pgetc
				tok=T_DGREAT
				;;
			esac
			tok=T_GREAT
			;;
	esac
}

next_word()
{
	local res=
	local lineno_offset=
	local word=

	res="$(scan_word false)"
	lineno_offset=${res%%${RS}*}
	res="${res#*${RS}}"
	c="${res%%${RS}*}"
	res="${res#*${RS}}"
	word="${res%%${RS}*}"

	# We must advance lineno because scan_word() was run in a subshell.
	lineno=$((${lineno} + ${lineno_offset}))
	tok="T_WORD${US}${word}"
}

scan_word()
{
	local in_param="${1}"
	local res=
	local word=
	local quoted=
	local lines=
	local lineno_offset=
	local wordexp=

	word=''
	quoted=false
	lines=0
	while :; do
		echo "parsing word char '$c'" >&2
		case "${c}" in
			'')
				break
				;;
			"${LF}")
				if ! ${in_param} && ! ${quoted}; then
					break
				fi
				lineno=$((${lineno} + 1))
				lines=$((${lines} + 1))
				word="${word}${c}"
				;;
			' '|"${HT}")
				if ! ${in_param} && ! ${quoted}; then
					break
				fi
				word="${word}${c}"
				;;
			'$')
				pgetc
				res=$(scan_wordexp)
				lineno_offset=${res%%${RS}*}
				res="${res#*${RS}}"
				c="${res%%${RS}*}"
				res="${res#*${RS}}"
				wordexp="${res%%${RS}*}"
				# We must advance lineno because scan_wordexp()
				# was run in a subshell.
				lineno=$((${lineno} + ${lineno_offset}))
				word="${word}${wordexp}"
				# scan_wordexp() leaves behind an unused
				# character, so we should skip the pgetc() call
				# below.
				continue
				;;
			\')
				word="${word}${c}"
				while :; do
					pgetc
					word="${word}${c}"
					case "${c}" in \')
						break
						;;
					esac
				done
				;;
			'"')
				word="${word}${c}"
				if ${quoted}; then
					quoted=false
				else
					quoted=true
				fi
				;;
			'}')
				if ${in_param} && ! ${quoted}; then
					break
				fi
				word="${word}${c}"
				;;
			*)
				word="${word}${c}"
				;;
		esac
		pgetc
	done

	printf "%d${RS}%s${RS}%s" ${lines} "${c}" "${word}"
}

scan_wordexp()
{
	local wordexp=
	local lineno_offset=
	local mod=
	local res=
	local word=

	wordexp=''
	lineno_offset=0
	case "${c}" in
		'{')
			# Parameter expansion brace
			pgetc
			case "${c}" in
				'#')
					pgetc
					case "${c}" in
						[@*#?$!A-Za-z0-9_-])
							# String length
							# expansion
							next_param
							;;
						*)
							# Special parameter "#"
							param='#'
							;;
					esac
					;;
				*)
					next_param
					;;
			esac
			wordexp="\${${param}"
			# Check for modifications
			mod=false
			case "${c}" in
				':')
					mod=true
					wordexp="${wordexp}${c}"
					pgetc
					case "${c}" in '-'|'='|'?'|'+')
						wordexp="${wordexp}${c}"
						pgetc
						;;
					esac
					;;
				'-'|'='|'?'|'+')
					mod=true
					wordexp="${wordexp}${c}"
					pgetc
					;;
				'%')
					mod=true
					wordexp="${wordexp}${c}"
					pgetc
					case "${c}" in '%')
						wordexp="${wordexp}${c}"
						pgetc
						;;
					esac
					;;
				'#')
					mod=true
					wordexp="${wordexp}${c}"
					pgetc
					case "${c}" in '#')
						wordexp="${wordexp}${c}"
						pgetc
						;;
					esac
					;;
			esac
			if ${mod}; then
				# Get word.
				res="$(scan_word true)"
				lineno_offset=${res%%${RS}*}
				res="${res#*${RS}}"
				c="${res%%${RS}*}"
				res="${res#*${RS}}"
				word="${res%%${RS}*}"
				# We must advance lineno because scan_word() was
				# run in a subshell.
				lineno=$((${lineno} + ${lineno_offset}))
				wordexp="${wordexp}${word}"
				echo "param mod word: '$word'" >&2
			fi
			# Check for right brace.
			case "${c}" in
				'}')
					wordexp="${wordexp}${c}"
					pgetc
					;;
				*)
					synerr 'Missing "}"'
					;;
			esac
			;;
		'(')
			;;
		[@*#?$!A-Za-z0-9_-])
			next_param
			wordexp="\$${param}"
			;;
	esac

	printf "%d${RS}%s${RS}%s" ${lineno_offset} "${c}" "${wordexp}"

}

next_param()
{
	param=''
	case "${c}" in
		[@*#?$!0-])
			# Special parameter
			param="${c}"
			pgetc
			;;
		[1-9])
			# Positional parameter
			param="${param}${c}"
			pgetc
			while :; do
				case "${c}" in [!0-9])
					break
					;;
				esac
				param="${param}${c}"
				pgetc
			done
			;;
		[A-Za-z_])
			# Parameter name
			param="${param}${c}"
			pgetc
			while :; do
				case "${c}" in [!A-Za-z0-9_])
					break
					;;
				esac
				param="${param}${c}"
				pgetc
			done
			;;
	esac
}

# Check the current token.  If it matches, add it to the syntax array.
accept()
{
	local t="${1}"

	if [ "x${tok%%${US}*}" = "x${t}" ]; then
		echo "accept $t" >&2
		tokens="${tokens}${tok}${RS}"
		next
		return 0
	fi
	return 1
}

error()
{
	local fmt="${1}"
	shift 1

	case "${fname}" in
		'-')
			printf "stdin:%d: ${fmt}\n" ${lineno} "${@}" >&2
			;;
		*)
			printf "%s:%d: ${fmt}\n" "${fname}" ${lineno} "${@}" >&2
			;;
	esac
}

init_lexer()
{
	local fn="${1}"
	shift 1

	fname="${fn}"
	lineno=1
	tokens=''
	pgetc
	next
}

get_tokens()
{
	printf '%s' "${tokens}"
	return 0
}

synexp()
{
	local t="${1}"
	shift 1

	if [ "x${t}" = 'x' ]; then
		synerr '%s unexpected' "$(tokname "${tok}")"
	else
		synerr '%s unexpected (expecting %s)' "$(tokname "${tok}")" \
			"$(tokname "${t}")"
	fi
}

synerr()
{
	local fmt="${1}"
	shift 1

	error "Syntax error: ${fmt}" "${@}"
}