from functools import lru_cache, partial
from typing import List
from urllib.parse import urlparse

import bleach
import markdown
import pygments
from django.conf import settings
from markdown.extensions.codehilite import CodeHiliteExtension
from pygments.formatters import HtmlFormatter
from pygments.lexers import get_lexer_by_name, get_lexer_for_filename

ALLOWED_TAGS = [
    # Bleach Defaults
    "a",
    "abbr",
    "acronym",
    "b",
    "blockquote",
    "code",
    "em",
    "i",
    "li",
    "ol",
    "strong",
    "ul",
    # Custom Additions
    "br",
    "caption",
    "cite",
    "col",
    "colgroup",
    "dd",
    "del",
    "details",
    "div",
    "dl",
    "dt",
    "h1",
    "h2",
    "h3",
    "h4",
    "h5",
    "h6",
    "hr",
    "img",
    "p",
    "pre",
    "span",
    "sub",
    "summary",
    "sup",
    "table",
    "tbody",
    "td",
    "th",
    "thead",
    "tr",
    "tt",
    "kbd",
    "var",
]

ALLOWED_ATTRIBUTES = {
    # Bleach Defaults
    "a": ["href", "title"],
    "abbr": ["title"],
    "acronym": ["title"],
    # Custom Additions
    "*": ["id"],
    "hr": ["class"],
    "img": ["src", "width", "height", "alt", "align", "class"],
    "span": ["class"],
    "div": ["class"],
    "th": ["align"],
    "td": ["align"],
    "code": ["class"],
    "p": ["align", "class"],
}


def _set_target(attrs, new=False):
    link_text = attrs["_text"]
    if new and not link_text.startswith(("http:", "https:")):
        return None
    try:
        url = urlparse(attrs[(None, "href")])
    except KeyError:
        return attrs
    if url.netloc not in settings.ALLOWED_HOSTS:
        attrs[(None, "target")] = "_blank"
    else:
        attrs.pop((None, "target"), None)
    return attrs


def markdown_to_html(text):
    """This convert markdown text to html, with two things:
    - Uses bleach.clean to remove unsafe things.
    """
    return bleach.sanitizer.Cleaner(
        tags=getattr(settings, "ALLOWED_TAGS", ALLOWED_TAGS),
        attributes=getattr(settings, "ALLOWED_ATTRIBUTES", ALLOWED_ATTRIBUTES),
        filters=[
            partial(
                bleach.linkifier.LinkifyFilter,
                callbacks=[_set_target],
                skip_tags=["pre"],
                parse_email=False,
            ),
        ],
    ).clean(
        markdown.markdown(
            text,
            extensions=[
                "fenced_code",
                CodeHiliteExtension(guess_lang=False, css_class="highlight"),
                "tables",
                "admonition",
            ],
        ),
    )


def pygmentize(filename, filecontents):
    try:
        lexer = get_lexer_for_filename(filename)
    except pygments.util.ClassNotFound:
        lexer = get_lexer_by_name(settings.PASTE["default_language"])
    formatter = HtmlFormatter(style="emacs")
    return pygments.highlight(filecontents, lexer, formatter)