# shellcheck shell=bash

_memory_file="${XDG_CONFIG_HOME:-$HOME/.config}/bash/memory.tsv"
_memory_state_dir="${XDG_STATE_HOME:-$HOME/.local/state}/bash"
_memory_state_file="$_memory_state_dir/memory-question"
_memory_question_color='\033[38;5;11m'
_memory_names=()
_memory_questions=()
_memory_answers=()
declare -A _memory_seen=()
_memory_invalid=0
_memory_line_number=0

if [[ -r "$_memory_file" ]]; then
	while IFS=$'\t' read -r _memory_name _memory_question _memory_answer _memory_extra; do
		((_memory_line_number++))

		if [[ -z "$_memory_name$_memory_question$_memory_answer$_memory_extra" ]]; then
			continue
		fi

		if [[ -z "$_memory_name" || -z "$_memory_question" || -z "$_memory_answer" || -n "$_memory_extra" ]]; then
			printf 'Invalid memory question on line %d.\n' "$_memory_line_number" >&2
			_memory_invalid=1
			continue
		fi

		if [[ -n ${_memory_seen[$_memory_name]:-} ]]; then
			printf 'Duplicate memory question for %s on line %d.\n' "$_memory_name" "$_memory_line_number" >&2
			_memory_invalid=1
			continue
		fi

		_memory_seen[$_memory_name]=1
		_memory_names+=("$_memory_name")
		_memory_questions+=("$_memory_question")
		_memory_answers+=("$_memory_answer")
	done < "$_memory_file"
else
	printf 'Memory question file is unavailable: %s\n' "$_memory_file" >&2
	_memory_invalid=1
fi

if [[ $_memory_invalid -eq 0 && ${#_memory_names[@]} -gt 0 ]]; then
	_memory_load_state() {
		local -a fields=() state_deck=()
		local state_date state_index item
		local -A state_seen=()

		[[ -r "$_memory_state_file" ]] || return 1
		IFS=$'\t' read -r -a fields < "$_memory_state_file"
		[[ ${#fields[@]} -eq $((${#_memory_names[@]} + 2)) ]] || return 1

		state_date=${fields[0]}
		state_index=${fields[1]}
		state_deck=("${fields[@]:2}")
		[[ $state_index =~ ^[0-9]+$ && $state_index -lt ${#state_deck[@]} ]] || return 1

		for item in "${state_deck[@]}"; do
			[[ -n ${_memory_seen[$item]:-} && -z ${state_seen[$item]:-} ]] || return 1
			state_seen[$item]=1
		done

		_memory_state_date=$state_date
		_memory_index=$state_index
		_memory_deck=("${state_deck[@]}")
	}

	_memory_shuffle_deck() {
		local previous_name=$1
		local i j swap

		_memory_deck=("${_memory_names[@]}")
		for ((i = ${#_memory_deck[@]} - 1; i > 0; i--)); do
			j=$((RANDOM % (i + 1)))
			swap=${_memory_deck[$i]}
			_memory_deck[i]=${_memory_deck[j]}
			_memory_deck[j]=$swap
		done

		if [[ ${#_memory_deck[@]} -gt 1 && ${_memory_deck[0]} == "$previous_name" ]]; then
			swap=${_memory_deck[0]}
			_memory_deck[0]=${_memory_deck[1]}
			_memory_deck[1]=$swap
		fi

		_memory_index=0
	}

	_memory_save_state() {
		local state_tmp="${_memory_state_file}.$$"
		local item

		mkdir -p "$_memory_state_dir" || return 1
		{
			printf '%s\t%s' "$_memory_state_date" "$_memory_index"
			for item in "${_memory_deck[@]}"; do
				printf '\t%s' "$item"
			done
			printf '\n'
		} > "$state_tmp" || return 1
		mv -f -- "$state_tmp" "$_memory_state_file"
	}

	_memory_select_current() {
		local current_name=${_memory_deck[$_memory_index]}
		local i

		for ((i = 0; i < ${#_memory_names[@]}; i++)); do
			if [[ ${_memory_names[$i]} == "$current_name" ]]; then
				_MEMORY_ANSWER=${_memory_answers[$i]}
				_MEMORY_QUESTION=${_memory_questions[$i]}
				return
			fi
		done

		return 1
	}

	_memory_advance() {
		local previous_name=${_memory_deck[$_memory_index]}

		((_memory_index++))
		if [[ $_memory_index -ge ${#_memory_deck[@]} ]]; then
			_memory_shuffle_deck "$previous_name"
		fi

		_memory_select_current
		_memory_save_state
	}

	_memory_sync_day() {
		local today

		today=$(date +%F)
		[[ $_memory_state_date != "$today" ]] || return 0

		_memory_state_date=$today
		_memory_advance
	}

	_memory_print_question() {
		printf '%b%s%b (answerpls, refreshpls)\n\n' \
			"$_memory_question_color" "$_MEMORY_QUESTION" "$_NC"
	}

	_memory_today=$(date +%F)
	if _memory_load_state; then
		_memory_select_current
		_memory_sync_day
	else
		_memory_state_date=$_memory_today
		_memory_shuffle_deck ''
		_memory_select_current
		_memory_save_state
	fi

	answerpls() {
		printf '%s\n' "$_MEMORY_ANSWER"
	}

	refreshpls() {
		if _memory_load_state; then
			_memory_select_current
		else
			_memory_state_date=$(date +%F)
			_memory_shuffle_deck "${_memory_deck[$_memory_index]:-}"
			_memory_select_current
			_memory_save_state
		fi

		_memory_sync_day
		_memory_advance
		_memory_print_question
	}

	_memory_print_question
fi

unset _memory_file
unset _memory_invalid _memory_line_number _memory_name _memory_question
unset _memory_answer _memory_extra _memory_today