import urllib.parse
import re
from bs4 import BeautifulSoup

def update_html(url, prefix, resp):
    '''
    Find and update HTML attributes which may contain external dependencies

    e.g. <a href="example.com"> -> <a href="http://proxy/fetch/example.com>

    :url: url of page from which CSS is included/inline
    :prefix: proxy method to prepend to join()'d resources
    :resp: request.py urllib response object containing data, headers, etc
    '''
    # update href values to point to our proxy
    soup = BeautifulSoup(resp['data'], 'html.parser')

    # remove <script> elements--Javascript is evil
    [s.decompose() for s in soup('script')]

    # remove cookie popup
    [s.decompose() for s in soup.findAll('div', attrs={'class': 'n-messaging-slot'})]

    # remove deprecated, unsupported tags (object, applet, param, embed)
    obsolete = ['object', 'applet', 'param', 'embed']
    [[s.decompose() for s in soup(elem)] for elem in obsolete]

    # find and update src, href, srcset, and background key values
    for elem in soup.findAll(src=True):
        update_tag(url, prefix, elem, 'src')
    for elem in soup.findAll(href=True):
        update_tag(url, prefix, elem, 'href')
    for elem in soup.findAll(srcset=True):
        update_tag(url, prefix, elem, 'srcset')
    for elem in soup.findAll(background=True):
        update_tag(url, prefix, elem, 'background')
    return soup

def update_tag(url, prefix, elem, key):
    '''
    Update value of element's key to prefix proxy method

    :url: url of page from which CSS is included/inline
    :prefix: proxy method to prepend to join()'d resources
    '''
    # an element's key value can be unpopulated, ignore such cases
    if not elem.get(key):
        return

    # urljoin() w/ root url if url is relative/absolute (no scheme specifier)
    url_split = list(urllib.parse.urlsplit(elem[key]))
    if not url_split[0]:
        elem[key] = urllib.parse.urljoin(url, elem[key])

    # strip extraneous values by space, use first defined resource
    elem[key] = elem[key].split()[0]

    # prepend resource url w/ proxy fetch method
    elem[key] = prefix + elem[key]

def update_css(url, prefix, soup=None, data=None):
    '''
    Update inline OR included CSS file to prefix proxy method

    :url: url of page from which CSS is included/inline
    :prefix: proxy method to prepend to join()'d resources
    :soup: bs4 object (optional)
    :data: CSS file contents as str (optional)
    '''
    # regex objects to match url(), src=, and @import CSS directives
    _url    = re.compile(r'(?P<url>url\s*\()(?P<quote_open>\s*["\']?\s*)' +
                         r'(?P<resource>[^"\']+)' +
                         r'(?P<quote_close>\s*["\']?\s*\))',
                         re.MULTILINE | re.IGNORECASE)
    _import = re.compile(r'(?P<import>@import)'+
                         r'(?P<quote_open>\s*["\']\s*)' +
                         r'(?P<resource>[^"\']+)' +
                         r'(?P<quote_close>\s*["\'])',
                         re.MULTILINE | re.IGNORECASE)
    _src    = re.compile(r'(?P<src>src\s*=\s*)(?P<quote_open>\s*["\']?\s*)' +
                         r'(?P<resource>[^"\']+)' +
                         r'(?P<quote_close>\s*["\']?)',
                         re.MULTILINE | re.IGNORECASE)

    css_regexes = [_url, _import, _src]

    # re.sub() aforementioned directives, prepend proxy method to resources
    if data:
        c = data
        for reg in css_regexes:
            c = reg.sub(lambda m: m.group('url') +
                        m.group('quote_open') +
                        prefix +
                        urllib.parse.urljoin(url, m.group('resource')) +
                        m.group('quote_close'), c)
        return c

    elif soup:
        style_tags = soup.findAll('style')
        for css in style_tags:
            c = css.string
            for reg in css_regexes:
                c = reg.sub(lambda m: m.group('url') +
                            m.group('quote_open') +
                            prefix +
                            urllib.parse.urljoin(url, m.group('resource')) +
                            m.group('quote_close'), c)
            css.string = c
        return soup