sm2

#!/bin/sh -e

help() {
cat - >&2 <<EOF
sm2 [-f] deck

The deck is a text file that will be modified by the program.

A card is a line of the deck with the form:

front<delimiter>back

Front is the text shown to the user and back is the text the user
intends to remember (e.g. 2+2=4).

The delimiter can be a TAB, =, COMMA, or SPACE (checked in that
order). sm2 will automatically convert each card into a TAB-delimited
format.

The -f flag tells sm2 to show all cards, regardless of when they're
meant to be shown (useful for when you've run out of cards to view
for the day).

For more info on this algorithm, see:
https://www.supermemo.com/en/archives1990-2015/english/ol/sm2
EOF
}


TAB="$(printf '\t')"
BAR='----------------'
EPOCH="$(awk 'BEGIN{srand();print srand()}')"

unset -v force
while getopts 'f' o; do
	case "$o" in
		f) force=1 ;;
		h) help; exit 0 ;;
		*) help; exit 1 ;;
	esac
done
shift $((OPTIND-1))

: "${1:?No deck provided, nothing for me to do!}"

deck=$(shuf < "$1" | grep .)
done=

# --- MADNESS BEGINS --- #

remaining=$(wc -l) <<-EOF
	$deck
EOF
remaining=$((remaining+1))

linedone() {
	done="${done:+$done
}$(printf '%s\t%s\t%s\t%s\t%s\n' "$recalls" "$difficulty" "$date" "$front" "$back")"
}

trap 'trap - EXIT TERM QUIT HUP INT ABRT; done="${done:+$done
}$(tail -n "$remaining")" <<-EOF
	$deck
EOF
printf '"'%s\n'"' "$done" > "$1"' EXIT TERM QUIT HUP INT ABRT

# --- MADNESS ENDS --- #

# If you want to compare to the algorithm in the link above:
# recalls = n, difficulty = EF, days = I, grade = q
while IFS="$TAB" read -r recalls difficulty date front back <&4; do
	remaining=$((remaining-1))

	# handle missing fields
	if [ ! "$back" ]; then
		if [ ! "$difficulty" ]; then
			[ "$recalls" ] || continue # skip blank cards
			case "$recalls" in # handle alternative delimiters
				*=*) difficulty=${recalls#*=}; recalls=${recalls%%=*} ;;
				*,*) difficulty=${recalls#*,}; recalls=${recalls%%,*} ;;
				*' '*) difficulty=${recalls#*\ }; recalls=${recalls%%\ *} ;;
				*) echo "Can't determine delimiter for: $recalls" >&2; exit 1 ;;
			esac

			# correct the fields, set missing fields to default values
			front="$recalls"; back="$difficulty";
			recalls=0; difficulty=2.5; date=0; days=0;
		fi
	fi

	if [ "$date" ]; then
		days=$(bc -l) <<-EOF
			($date - $EPOCH) / 86400
		EOF
	fi

	# skip cards that are too soon to be viewed
	if [ ! "$force" ] && expr "$date" '>' 0 && expr "$date" '<' "$EPOCH"; then
		linedone
		continue
	fi

	printf '%s\n> ' "$front"
	read -r response

	case "$response" in
		"$back") printf "\n$BAR\nCorrect!\n$BAR\n\n" ;;
		*) printf "\n$BAR\nThe correct answer is %s\n$BAR\n\n" "$back" ;;
	esac

	grade() {
		cat - <<-EOF
			Select a grade:
			  (0) Incorrect, complete failure to recall
			  (1) Incorrect, but answer seems familiar
			  (2) Incorrect, but answer seems easy to remember
			  (3) Correct, but difficult to recall
			  (4) Correct, but some hesitation
			  (5) Correct, perfect recall
		EOF
		read -r grade || grade=

		case "$grade" in
			[3-5]) # correct
				case "$recalls" in
					0) days=1 ;; 1) days=6 ;;
					*)
						days=$(bc -l) <<-EOF
							$days*$difficulty
						EOF
						;;
				esac

				if [ "$grade" -ne 4 ]; then
					difficulty=$(bc -l) <<-EOF
						$difficulty-0.8+0.28*$grade-0.02*$grade*$grade
					EOF
				fi

				if expr "$difficulty" '<' 1.3 > /dev/null; then difficulty=1.3; fi
				recalls=$((recalls+1))
				;;
			[0-2]) # incorrect
				recalls=0; days=1
				;;
			*) return 1 ;;
		esac
	}

	while ! grade; do :; done # retries if the user provides bad input

	date=$(bc -l) <<-EOF
		$days * 86400 + $EPOCH
	EOF

	linedone
done 4<<-EOF
	$deck
EOF