#!/usr/bin/env python3

import lxml.etree as ET

class RssFeed(object):
    """Class for storing an RSS 2.0 feed.

    https://validator.w3.org/feed/docs/rss2.html.

    """

    # pylint: disable=too-many-instance-attributes

    REQUIRED_ELEMENTS = ["title", "link", "description"]
    OPTIONAL_ELEMENTS = ["language", "copyright", "managingEditor", "webMaster",
                         "pubDate", "lastBuildDate", "category", "generator",
                         "docs", "cloud", "ttl", "image", "textInput",
                         "skipHours", "skipDays"]

    def __init__(self):
        """Define available attributes."""
        self.rssurl = None  # the URL of the rss feed
        self.atomlink = None
        for element in self.REQUIRED_ELEMENTS:
            setattr(self, element, None)
        for element in self.OPTIONAL_ELEMENTS:
            setattr(self, element, None)
        self.docs = ET.Element("docs")
        self.docs.text = "https://validator.w3.org/feed/docs/rss2.html"
        self.author_text = None
        self.update_timestamp = None
        self.items = []
        self.rss = None
        self.channel = None

    def assemble_rss(self, FEED_MAX_ENTRIES):
        """Assemble RSS 2.0 feed."""
        self.rss = ET.Element("rss", version="2.0", nsmap={"atom": "http://www.w3.org/2005/Atom"})
        self.channel = ET.SubElement(self.rss, "channel")
        # https://validator.w3.org/feed/docs/warning/MissingAtomSelfLink.html
        self.atomlink = ET.SubElement(self.channel, "{http://www.w3.org/2005/Atom}link",
                                      href=self.rssurl, rel="self", type="application/rss+xml")
        for element in self.REQUIRED_ELEMENTS:
            self.channel.append(getattr(self, element))
        for element in self.OPTIONAL_ELEMENTS:
            attr = getattr(self, element)
            if attr is not None:
                self.channel.append(attr)
        # include at most FEED_MAX_ENTRIES items in the RSS feed
        for item in self.items[:FEED_MAX_ENTRIES]:
            self.channel.append(item.item)

    def dump_rss(self, FEED_MAX_ENTRIES):
        """Dump RSS feed XML."""
        if self.rss is None:
            self.assemble_rss(FEED_MAX_ENTRIES)
        return ET.tostring(self.rss).decode("utf-8")