import re

from django.utils.text import compress_string

from django.utils.cache import patch_vary_headers

re_accepts_gzip = re.compile(r'\bgzip\b')

class GZipMiddleware(object):

    """

    This middleware compresses content if the browser allows gzip compression.

    It sets the Vary header accordingly, so that caches will base their storage

    on the Accept-Encoding header.

    """

    def process_response(self, request, response):

        # It's not worth compressing non-OK or really short responses.

        if response.status_code != 200 or len(response.content) < 200:

            return response

        patch_vary_headers(response, ('Accept-Encoding',))

        # Avoid gzipping if we've already got a content-encoding.

        if response.has_header('Content-Encoding'):

            return response

        # MSIE have issues with gzipped respones of various content types.

        if "msie" in request.META.get('HTTP_USER_AGENT', '').lower():

            ctype = response.get('Content-Type', '').lower()

            if not ctype.startswith("text/") or "javascript" in ctype:

                return response

        ae = request.META.get('HTTP_ACCEPT_ENCODING', '')

        if not re_accepts_gzip.search(ae):

            return response

        response.content = compress_string(response.content)

        response['Content-Encoding'] = 'gzip'

        response['Content-Length'] = str(len(response.content))

        return response