""" html parser to clean up incoming text from unknown sources """
from html.parser import HTMLParser


class InputHtmlParser(HTMLParser):  # pylint: disable=abstract-method
    """ Removes any html that isn't allowed_tagsed from a block """

    def __init__(self):
        HTMLParser.__init__(self)
        self.allowed_tags = [
            "p",
            "blockquote",
            "br",
            "b",
            "i",
            "strong",
            "em",
            "pre",
            "a",
            "span",
            "ul",
            "ol",
            "li",
        ]
        self.tag_stack = []
        self.output = []
        # if the html appears invalid, we just won't allow any at all
        self.allow_html = True

    def handle_starttag(self, tag, attrs):
        """ check if the tag is valid """
        if self.allow_html and tag in self.allowed_tags:
            self.output.append(("tag", self.get_starttag_text()))
            self.tag_stack.append(tag)
        else:
            self.output.append(("data", ""))

    def handle_endtag(self, tag):
        """ keep the close tag """
        if not self.allow_html or tag not in self.allowed_tags:
            self.output.append(("data", ""))
            return

        if not self.tag_stack or self.tag_stack[-1] != tag:
            # the end tag doesn't match the most recent start tag
            self.allow_html = False
            self.output.append(("data", ""))
            return

        self.tag_stack = self.tag_stack[:-1]
        self.output.append(("tag", "</%s>" % tag))

    def handle_data(self, data):
        """ extract the answer, if we're in an answer tag """
        self.output.append(("data", data))

    def get_output(self):
        """ convert the output from a list of tuples to a string """
        if self.tag_stack:
            self.allow_html = False
        if not self.allow_html:
            return "".join(v for (k, v) in self.output if k == "data")
        return "".join(v for (k, v) in self.output)