file-date-gen

#! /bin/sh

if [ "$1" = "-f" ]; then
	shift
	DATE_FORMAT="$1"
	shift
fi

: ${FILE:=$1}
: ${DATE_FILE:=$(dirname "$FILE")/.$(basename "${FILE}").date}
: ${DEFAULT_DATE:=$2}
: ${DATE_FORMAT:=%Y-%m-%d}

date=

[ -n "${FILE}" ] || {
	echo >&2 "$0 $(dirname "$0")/file [$(dirname "$0")/file.date [DEFAULT_DATE]]"
	exit 1
}

[ -f "${DATE_FILE}" ] && date="$(cat "${DATE_FILE}")"

[ -n "${date}" ] ||
	date="$(git log -n 1 --format=format:%cD --no-patch "${FILE}")"

[ -n "${date}" ] || year="${DEFAULT_DATE}"

[ -n "${date}" ] || date="$(date -u)"

[ -n "${date}" ] || {
	echo >&2 'Undefined date.'
	exit 1
}

exec printf "%s" $(date "+${DATE_FORMAT}" -d "${date}")