#!/bin/sh
set -eu

usage() {
	cat <<-'EOF'
		Usage:
		  feed FILENAME
		  feed -h
	EOF
}

help() {
	cat <<-'EOF'


		Options:
		  -h, --help    show this message

		  FILENAME      the target feed to be generated


		Generate FILENAME as an Atom feed.  The collection type and
		language are inferred by the name of FILENAME.


		Examples:

		  Generate a feed for TILs:

		    $ feed src/en/feeds/til.xml
	EOF
}


for flag in "$@"; do
	case "$flag" in
		--)
			break
			;;
		--help)
			usage
			help
			exit
			;;
		*)
			;;
	esac
done

while getopts 'h' flag; do
	case "$flag" in
		h)
			usage
			help
			exit
			;;
		*)
			usage >&2
			exit 2
			;;
	esac
done
shift $((OPTIND - 1))

. src/lib.sh

FILENAME="${1:-}"
eval "$(assert_arg "$FILENAME" 'FILENAME')"


COLLECTION="$(basename "$FILENAME" '.xml')"
LANGUAGE="$(lang-for "$FILENAME")"
DIR="$(dirname "$(dirname "$FILENAME")")/$COLLECTION"


. src/lib/base.conf
# shellcheck source=/dev/null
. src/lib/base."$LANGUAGE".conf

now="$(date -uIs)"
url="$(url-for "${FILENAME#"$CONTENT_PREFIX"}" | absolute)"
site_name_html="$(htmlesc "${site_name:?}")"
export now url site_name_html


mkdir -p "$(dirname "$FILENAME")"
{
	envsubst < src/lib/feed.xml
	find "$DIR"/*.sortdata 2>/dev/null | sort -nr | xargs cat | xargs cat
	printf '</feed>\n'
} > "$FILENAME"