import re
from html.entities import name2codepoint
from html.parser import HTMLParser

from mezzanine.utils.deprecation import mark_safe

SELF_CLOSING_TAGS = ["br", "img"]
NON_SELF_CLOSING_TAGS = ["script", "iframe"]
ABSOLUTE_URL_TAGS = {"img": "src", "a": "href", "iframe": "src"}

# Tags and attributes added to richtext filtering whitelist when the
# RICHTEXT_FILTER_LEVEL is set to low. General use-case for these is
# allowing embedded video, but we will add to this fixed list over
# time as more use-cases come up. We won't ever add script tags or
# events (onclick etc) to this list. To enable those, filtering can
# be turned off in the settings admin.
LOW_FILTER_TAGS = ("iframe", "embed", "video", "param", "source", "object")
LOW_FILTER_ATTRS = (
    "allowfullscreen",
    "autostart",
    "loop",
    "hidden",
    "playcount",
    "volume",
    "controls",
    "data",
    "classid",
)


def absolute_urls(html):
    """
    Converts relative URLs into absolute URLs. Used for RSS feeds to
    provide more complete HTML for item descriptions, but could also
    be used as a general richtext filter.
    """

    from bs4 import BeautifulSoup

    from mezzanine.core.request import current_request

    request = current_request()
    if request is not None:
        dom = BeautifulSoup(html, "html.parser")
        for tag, attr in ABSOLUTE_URL_TAGS.items():
            for node in dom.findAll(tag):
                url = node.get(attr, "")
                if url:
                    node[attr] = request.build_absolute_uri(url)
        html = str(dom)
    return html


def decode_entities(html):
    """
    Remove HTML entities from a string.
    Adapted from http://effbot.org/zone/re-sub.htm#unescape-html
    """

    def decode(m):
        html = m.group(0)
        if html[:2] == "&#":
            try:
                if html[:3] == "&#x":
                    return chr(int(html[3:-1], 16))
                else:
                    return chr(int(html[2:-1]))
            except ValueError:
                pass
        else:
            try:
                html = chr(name2codepoint[html[1:-1]])
            except KeyError:
                pass
        return html

    return re.sub(r"&#?\w+;", decode, html.replace("&amp;", "&"))


@mark_safe
def escape(html):
    """
    Escapes HTML according to the rules defined by the settings
    ``RICHTEXT_FILTER_LEVEL``, ``RICHTEXT_ALLOWED_TAGS``,
    ``RICHTEXT_ALLOWED_ATTRIBUTES``, ``RICHTEXT_ALLOWED_STYLES``.
    """
    from bleach import ALLOWED_PROTOCOLS, clean
    from bleach.css_sanitizer import CSSSanitizer

    from mezzanine.conf import settings
    from mezzanine.core import defaults

    if settings.RICHTEXT_FILTER_LEVEL == defaults.RICHTEXT_FILTER_LEVEL_NONE:
        return html
    tags = settings.RICHTEXT_ALLOWED_TAGS
    attrs = settings.RICHTEXT_ALLOWED_ATTRIBUTES
    css_sanitizer = CSSSanitizer(
        allowed_css_properties=settings.RICHTEXT_ALLOWED_STYLES
    )
    if settings.RICHTEXT_FILTER_LEVEL == defaults.RICHTEXT_FILTER_LEVEL_LOW:
        tags += LOW_FILTER_TAGS
        attrs += LOW_FILTER_ATTRS
    if isinstance(attrs, tuple):
        attrs = list(attrs)
    return clean(
        html,
        tags=tags,
        attributes=attrs,
        strip=True,
        strip_comments=False,
        css_sanitizer=css_sanitizer,
        protocols=ALLOWED_PROTOCOLS.union(["tel"]),
    )


@mark_safe
def thumbnails(html):
    """
    Given a HTML string, converts paths in img tags to thumbnail
    paths, using Mezzanine's ``thumbnail`` template tag. Used as
    one of the default values in the ``RICHTEXT_FILTERS`` setting.
    """
    from bs4 import BeautifulSoup
    from django.conf import settings

    from mezzanine.core.templatetags.mezzanine_tags import thumbnail

    # If MEDIA_URL isn't in the HTML string, there aren't any
    # images to replace, so bail early.
    if settings.MEDIA_URL.lower() not in html.lower():
        return html

    dom = BeautifulSoup(html, "html.parser")
    for img in dom.findAll("img"):
        src = img.get("src", "")
        src_in_media = src.lower().startswith(settings.MEDIA_URL.lower())
        width = img.get("width")
        height = img.get("height")
        if src_in_media and str(width).isdigit() and str(height).isdigit():
            img["src"] = settings.MEDIA_URL + thumbnail(src, width, height)
    # BS adds closing br tags, which the browser interprets as br tags.
    return str(dom).replace("</br>", "")


class TagCloser(HTMLParser):
    """
    HTMLParser that closes open tags. Takes a HTML string as its first
    arg, and populate a ``html`` attribute on the parser with the
    original HTML arg and any required closing tags.
    """

    def __init__(self, html):
        HTMLParser.__init__(self)
        self.html = html
        self.tags = []
        self.feed(self.html)
        self.html += "".join("</%s>" % tag for tag in self.tags)

    def handle_starttag(self, tag, attrs):
        if tag not in SELF_CLOSING_TAGS:
            self.tags.insert(0, tag)

    def handle_endtag(self, tag):
        try:
            self.tags.remove(tag)
        except ValueError:
            pass
