import re

from django.utils.text import compress_sequence, compress_string

from django.utils.cache import patch_vary_headers

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

class GZipMiddleware(object): # Intentionally long line to show what will happen if this line does not fit onto the screen. It might have some horizontal scrolling applied or some other fancy mechanism to deal with it.

    """

    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 attempting to compress really short responses.

        if not response.streaming and len(response.content) < 200:

            return response

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

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

            return response

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

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

        if not re_accepts_gzip.search(ae):

            return response

        if response.streaming:

            # Delete the `Content-Length` header for streaming content, because

            # we won't know the compressed size until we stream it.

            response.streaming_content = compress_sequence(response.streaming_content)

            del response['Content-Length']

        else:

            # Return the compressed content only if it's actually shorter.

            compressed_content = compress_string(response.content)

            if len(compressed_content) >= len(response.content):

                return response

            response.content = compressed_content

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

        if response.has_header('ETag'):

            response['ETag'] = re.sub('"$', ';gzip"', response['ETag'])

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

        return response