import cgi
from typing import Optional

from zerver.lib.url_preview.types import UrlEmbedData


class BaseParser:
    def __init__(self, html_source: bytes, content_type: Optional[str]) -> None:
        # We import BeautifulSoup here, because it's not used by most
        # processes in production, and bs4 is big enough that
        # importing it adds 10s of milliseconds to manage.py startup.
        from bs4 import BeautifulSoup

        charset = None
        if content_type is not None:
            charset = cgi.parse_header(content_type)[1].get("charset")
        self._soup = BeautifulSoup(html_source, "lxml", from_encoding=charset)

    def extract_data(self) -> UrlEmbedData:
        raise NotImplementedError