Hacky lookahead / peek with `read -N1`

lookahead.sh

# shellcheck shell=bash

# Caveat: Only one start_peek can be ran for any particular case block
start_peek() {
	if [ "$peek_status" = not_peeking ]; then
		peek_status='currently_peeking'
		peek_current=0
		peek_total="$1"
		REPLY_PEEKED_CHARACTERS="$2"

		# Return true, so the conditional after 'lookahead_char' is ran.
		# The conditional must have 'continue'
		return 0
	elif [ "$peek_status" = currently_peeking ]; then
		# This shouldn't fire due to the 'continue' statement
		:
	elif [ "$peek_status" = done_peeking ]; then
		REPLY_PEEKED_CHARACTERS="${REPLY_PEEKED_CHARACTERS#?}"
		peek_status='not_peeking'
		return 1
	fi
}

# Use separate variable 'REPLY_LOOKAHEAD' since 'REPLY' could be clobbered by something else
peek_status='not_peeking'
peek_total=
peek_current=

parse_char() {
	local char="$1"

	echo "current char: '$char'"

	case "$char" in
	\ )
		if start_peek 3 \ ; then
			return
		fi

		# remember output is correct. two occurenced of current char: ' '
		# Since lookaheads don't gobble the input stream, one print is when we do
		# the lookahead, and the second one is here, where we finish the peek
		echo "start_peek 3 result: '$REPLY_PEEKED_CHARACTERS'"
		;;
	\{)
		:
		;;
	esac
}

string1="key =fourd"

echo "original string: '$string1"

# shellcheck disable=SC2059
while IFS= read -rN1 char; do
	if [ "$peek_status" = currently_peeking ] ; then
		if ((peek_current < peek_total)); then
			REPLY_PEEKED_CHARACTERS+="$char"
			peek_current=$((peek_current+1))
			continue
		elif ((peek_current == peek_total)); then
			REPLY_PEEKED_CHARACTERS+="$char"
			peek_current=$((peek_current+1))
		fi

		peek_status='done_peeking'

		while IFS= read -rN1 char; do
			parse_char "$char"
		done < <(printf "$REPLY_PEEKED_CHARACTERS")

		continue
	fi

	parse_char "$char"
done < <(printf "$string1")