#  This software code is made available "AS IS" without warranties of any
#  kind.  You may copy, display, modify and redistribute the software
#  code either by itself or as incorporated into your code; provided that
#  you do not remove any proprietary notices.  Your use of this software
#  code is at your own risk and you waive any claim against Amazon
#  Digital Services, Inc. or its affiliates with respect to your use of
#  this software code. (c) 2006 Amazon Digital Services, Inc. or its
#  affiliates.

# generates the aws canonical string for the given parameters
def canonical_string(method, path, headers, expires=None):
    interesting_headers = {}
    for key in headers:
        lk = key.lower()
        if lk in ['content-md5', 'content-type', 'date'] or lk.startswith(AMAZON_HEADER_PREFIX):
            interesting_headers[lk] = headers[key].strip()

    # these keys get empty strings if they don't exist
    if not interesting_headers.has_key('content-type'):
        interesting_headers['content-type'] = ''
    if not interesting_headers.has_key('content-md5'):
        interesting_headers['content-md5'] = ''

    # just in case someone used this.  it's not necessary in this lib.
    if interesting_headers.has_key('x-amz-date'):
        interesting_headers['date'] = ''

    # if you're using expires for query string auth, then it trumps date
    # (and x-amz-date)
    if expires:
        interesting_headers['date'] = str(expires)

    sorted_header_keys = interesting_headers.keys()
    sorted_header_keys.sort()

    buf = "%s\n" % method
    for key in sorted_header_keys:
        if key.startswith(AMAZON_HEADER_PREFIX):
            buf += "%s:%s\n" % (key, interesting_headers[key])
        else:
            buf += "%s\n" % interesting_headers[key]

    # don't include anything after the first ? in the resource...
    buf += "/%s" % path.split('?')[0]

    # ...unless there is an acl or torrent parameter
    if re.search("[&?]acl($|=|&)", path):
        buf += "?acl"
    elif re.search("[&?]torrent($|=|&)", path):
        buf += "?torrent"

    return buf