from __future__ import absolute_import
import html.parser as HTMLParser
import re
import unicodedata


def ensure_unicode(s):
    """
    Ensure string is a unicode string. If it isn't it assumed it is
    utf-8 and decodes it to a unicode string.
    """
    if isinstance(s, bytes):
        s = s.decode('utf-8', 'replace')
    return s


def decode_html_entities(s):
    """
    Replaces html entities with the character they represent.

        >>> print(decode_html_entities("<3 &"))
        <3 &
    """
    parser = HTMLParser.HTMLParser()

    def unesc(m):
        return parser.unescape(m.group())
    return re.sub(r'(&[^;]+;)', unesc, ensure_unicode(s))


def filenamify(title):
    """
    Convert a string to something suitable as a file name. E.g.

     Matlagning del 1 av 10 - Räksmörgås | SVT Play
       ->  matlagning.del.1.av.10.-.raksmorgas.svt.play
    """
    # ensure it is unicode
    title = ensure_unicode(title)

    # NFD decomposes chars into base char and diacritical mark, which
    # means that we will get base char when we strip out non-ascii.
    title = unicodedata.normalize('NFD', title)

    # Convert to lowercase
    # Drop any non ascii letters/digits
    # Drop any leading/trailing whitespace that may have appeared
    title = re.sub(r'[^a-z0-9 .-]', '', title.lower().strip())

    # Replace whitespace with dot
    title = re.sub(r'\s+', '.', title)
    title = re.sub(r'\.-\.', '-', title)

    return title