"""
A downloader middleware for signing AWS requests just before they get into the
downloader. It is important to sign as close to the downloader as possible
because Amazon Web Service use timestamps for authentication.
"""

import os
import time

from scrapy.utils.httpobj import urlparse_cached
from scrapy.utils.aws import sign_request
from scrapy.conf import settings

class AWSMiddleware(object):
    def __init__(self):
        self.access_key = settings['AWS_ACCESS_KEY_ID'] or \
            os.environ.get('AWS_ACCESS_KEY_ID')
        self.secret_key = settings['AWS_SECRET_ACCESS_KEY'] or \
            os.environ.get('AWS_SECRET_ACCESS_KEY')

    def process_request(self, request, spider):
        hostname = urlparse_cached(request).hostname
        if spider.domain_name == 's3.amazonaws.com' \
                or (hostname and hostname.endswith('s3.amazonaws.com')):
            request.headers['Date'] = time.strftime("%a, %d %b %Y %H:%M:%S GMT", \
                time.gmtime())
            sign_request(request, self.access_key, self.secret_key)