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#!/usr/bin/env bash

valueCharacters=(
	[200]="🫂"
	[50]="💖"
	[10]="✨"
	[5]="🥺"
	[1]=","
	[0]="❤️"
)

separator="👉👈"

fatal() {
	echo "$@" 1>&2
	exit 1
}

main() {
	case "$1" in
	d) decode;;
	*) encode;;
	esac
}

encode() {
	# C is needed to force read to use ASCII codepoints.
	local LANG=C

	# Use a special delimited read to account for NUL characters not being
	# handled properly.
	while IFS= read -d '' -n 1 -r char; do
		printf -v codepoint %d "'$char"

		(( codepoint == 0 )) && {
			echo -n "${valueCharacters[0]}$separator"
			continue
		}

		while (( codepoint > 0 )); do
			for v in 200 50 10 5 1; do
				(( codepoint >= v )) && {
					(( codepoint -= v ))
					echo -n "${valueCharacters[$v]}"
					break
				}
			done
		done

		echo -n "$separator"
	done

	return 0
}

decode() {
	[[ $LANG =~ (UTF|utf)-?8$ ]] || {
		fatal "Error: Locale is not of UTF-8; unable to decode."
	}

	# buf will be used to seek until the section separator.
	buf=""
	# sumChar is used to calculate the summation of bytes so far.
	sumChar=$[0]

	while read -N1 -r char; do
		case "$char" in
		# Check if this is the separator character.
		"${separator:0:1}" | "${separator:1:1}")
			# Append the character and pop the last one out if it's full.
			buf+="$char"
			(( ${#buf} > ${#separator} )) && buf="${buf: -${#separator}}"

			[[ "$buf" == "$separator" ]] && {
				# New section; decode the sum.
				printf -v codepoint "%03o" $[sumChar]

				# We need LANG=C here specifically for this printf because we're
				# outputting possibly partial Unicode bytes, so the terminal
				# must treat it as such.
				LANG=C printf "\\$codepoint"

				# Reset the sum.
				(( sumChar = 0 ))
			}
			;;

		"🫂") (( sumChar += 200 )) ;;
		"💖") (( sumChar += 50  )) ;;
		"✨") (( sumChar += 10  )) ;;
		"🥺") (( sumChar += 5   )) ;;
		"," ) (( sumChar += 1   )) ;;

		$'\u2764') (( sumChar += 0   )) ;;
		$'\uFE0F') ;; # Ignore the trailing special character.

		$'\n') return ;; # Treat a new line as EOF.

		*) fatal "Error: invalid character $char."
		esac
	done

	return 0
}

main "$@"