#! /usr/bin/env sh

# This program is free software: you can redistribute it and/or modify it under
# the terms of the GNU Affero General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option) any
# later version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
# details.

main()
{
	# Handle opts
	opts "$@"
	shift "$OPTS"
	unset OPTS

	# Show help
	[ "$OPT_HELP_ONLY" ] && usage && exit 0

	for url in $@
	do
		curl -s "$url" \
			| grep -Eo 'https://www.youtube.com/feeds/videos.xml?[^"]+' \
			| head -n1
	done

	# An alternate solution to grep -E
	# perl -n -e 'm@(https://www.youtube.com/feeds/videos.xml\?[^"]+)@ and print "$1\n"'
}

opts()
{
	OPTS=0

	while getopts ":h" opt
	do
		case "$opt" in
			h) OPT_HELP_ONLY=1 ;;
			*)
				printf "Invalid option passed: %s\n" "$OPTARG" >&2
				;;
		esac
	done

	unset opt
}

usage()
{
	cat <<EOF
Usage:
	$(basename "$0") -h
	$(basename "$0") <url> [ <urls> ... ]

Get the RSS feed URL of a YouTube channel through the channel's page URL.

Options:
	-h  Show this help text and exit.
EOF
}

main "$@"