#!/usr/bin/env python3
# 2025 dtb. public domain
import re, sys, xml.etree.ElementTree as ET
ET.register_namespace("",      "http://www.w3.org/2005/Atom")
ET.register_namespace("media", "http://search.yahoo.com/mrss/")
ET.register_namespace("yt",    "http://www.youtube.com/xml/schemas/2015")
macrofeed = ET.Element('feed')
macrofeed.extend(
    sorted([
            entry
            # Split the input by file. This relies on a typical <XML /> tag
            # starting a file. Theoretically this assumption could be wrong,
            # but in that case the XML parser would break before
            # ytfeed.aggregate could spit malformed output.
            for feed in re.split(r'<\?xml.*?\?>', sys.stdin.read())[1:]
            # Get the entries out of each file.
            for entry
                in ET.fromstring(feed)
                    .findall("{http://www.w3.org/2005/Atom}entry")
        ],
        # Gets the publication date and sorts the entries from old to new.
        key = lambda entry # (this is a text sort but it still works)
           : entry.findall("{http://www.w3.org/2005/Atom}published")[0].text,
    )
)
print(ET.tostring(macrofeed, encoding="unicode"))