#!/usr/bin/env python
import urllib2, time, os, datetime, optparse, sys

parser = optparse.OptionParser("""usage: %prog [options] URL filename - compare modification time of file on http server against mtime of file on disk, return exit 0 if it is newer, exit with 1 if not newer.
example:
if [ ! %prog http://hgdownload.soe.ucsc.edu/admin/hgcentral.sql lastUpdateTime.flag ]; then
    echo skip update
    exit
fi
""")

(options, args) = parser.parse_args()

if len(args)==0:
    parser.print_help()
    sys.exit(1)

URL, flagFname = args

# little helper class to download only the http HEAD
class HeadRequest(urllib2.Request):
    def get_method(self):
        return "HEAD"


# get the mtime of the file on the server
response = urllib2.urlopen(HeadRequest(URL))
timeStr = response.headers.getheader("Last-Modified")
serverTime = datetime.datetime.fromtimestamp(time.mktime(time.strptime(timeStr, "%a, %d %b %Y %H:%M:%S GMT")))

# get the mtime of the flag file
localTime = datetime.datetime.fromtimestamp(0)
if os.path.isfile(flagFname):
    t = os.path.getmtime(flagFname)
    localTime = datetime.datetime.fromtimestamp(t)

if serverTime > localTime:
    print "file was updated on server"
    sys.exit(1)
else:
    sys.exit(0)