#!/bin/sh
# 2025 dtb. public domain
directory="$1"
alias have='command -v >/dev/null 2>&1'
xml_url_prefix='https://www.youtube.com/feeds/videos.xml?channel_id='
if test -z "$2"; then
	printf 'Usage: %s directory channel_id...\n' "$0" >&2
	exit 64 # sysexits(3) EX_USAGE
fi
while test -n "$2"; do
	if   have curl; then curl=curl
	elif have wget; then curl='wget -O -'
	else curl=false
	fi
	filename="$(printf '%s/%s.xml\n' "$directory" "$2")"
	$curl "$xml_url_prefix""$2" >"$filename".new
	if ! grep '<title>' <"$filename".new | head -n 1 \
			| grep 404 >/dev/null 2>&1
	then mv "$filename".new "$filename" \
		&& printf '%s\n' "$filename"
	fi
	rm -f "$filename".new
	shift
done