Sprite cache invalidation

background-image: url(images/icons.png);
background-image: url(images/icons.png?a3844c660);

#!/usr/bin/python

import os.path
import re
import hashlib


def file_hash(filename, block_size=2**20):
    md5 = hashlib.md5()
    with open(filename, 'rb') as f:
        for data in iter(lambda: f.read(block_size), ''):
            md5.update(data)
    return md5.hexdigest()


def find_replace(match, basedir):
    match = match.replace("'", '')
    if '?' in match or '#' in match or match.startswith('http://'):
        print 'skipping: ', match
        return None

    filename = os.path.join(basedir, match)
    return '%s?%s' % (match, file_hash(filename)[:10])


def insert_hash(filename, debug=False):
    basedir = os.path.dirname(filename)
    css = open(filename).read()
    matches = re.findall(r"url\((.*?)\)", css)
    replacements = dict([
        (match, find_replace(match, basedir))
        for match in matches
    ])

    if debug:
        for key, value in replacements.iteritems():
            print key, '    =>    ', value
    else:
        for match, repl in replacements.iteritems():
            if repl:
                css = css.replace(match, repl)

        out = open(filename, 'w')
        out.write(css)
        out.close()


if __name__ == '__main__':
    from optparse import OptionParser
    usage = 'usage: %prog filename.css'

    parser = OptionParser(usage=usage)
    parser.add_option("", "--debug", action="store_true", dest="debug", default=False,
                      help="When set, just output list of substitutions.")

    (options, args) = parser.parse_args()

    if len(args) < 1:
        print 'You must provide file name.'

    insert_hash(os.path.realpath(args[0]), options.debug)