# -*- Mode: Python; tab-width: 4 -*-

import re
import string
import time

def concat (*args):
    return ''.join (args)	
    
def join (seq, field=' '):
    return field.join (seq)
    
def group (s):
    return '(' + s + ')'
    
short_days = ['sun','mon','tue','wed','thu','fri','sat']
long_days = ['sunday','monday','tuesday','wednesday','thursday','friday','saturday']

short_day_reg = group (join (short_days, '|'))
long_day_reg = group (join (long_days, '|'))

daymap = {}
for i in range(7):
    daymap[short_days[i]] = i
    daymap[long_days[i]] = i
    
hms_reg = join (3 * [group('[0-9][0-9]')], ':')

months = ['jan','feb','mar','apr','may','jun','jul','aug','sep','oct','nov','dec']

monmap = {}
for i in range(12):
    monmap[months[i]] = i+1
    
months_reg = group (join (months, '|'))

# From draft-ietf-http-v11-spec-07.txt/3.3.1
#       Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
#       Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
#       Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format

# rfc822 format
rfc822_date = join (
        [concat (short_day_reg,','),	# day
         group('[0-9][0-9]?'),			# date
         months_reg,					# month
         group('[0-9]+'),				# year
         hms_reg,						# hour minute second
         'gmt'
         ],
        ' '
        )

rfc822_reg = re.compile (rfc822_date)

def unpack_rfc822 (m):
    g = m.group
    a = string.atoi
    return (
            a(g(4)),	   	# year
            monmap[g(3)],	# month
            a(g(2)),		# day
            a(g(5)),		# hour
            a(g(6)),		# minute
            a(g(7)),		# second
            0,
            0,
            0
            )
    
    # rfc850 format
rfc850_date = join (
        [concat (long_day_reg,','),
         join (
                 [group ('[0-9][0-9]?'),
                  months_reg,
                  group ('[0-9]+')
                  ],
                 '-'
                 ),
         hms_reg,
         'gmt'
         ],
        ' '
        )

rfc850_reg = re.compile (rfc850_date)
# they actually unpack the same way
def unpack_rfc850 (m):
    g = m.group
    a = string.atoi
    return (
            a(g(4)),	   	# year
            monmap[g(3)],	# month
            a(g(2)),		# day
            a(g(5)),		# hour
            a(g(6)),		# minute
            a(g(7)),		# second
            0,
            0,
            0
            )
    
    # parsdate.parsedate	- ~700/sec.
    # parse_http_date    	- ~1333/sec.
    
weekdayname = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
monthname = [None, 'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
             'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']

def build_http_date (when):
    year, month, day, hh, mm, ss, wd, y, z = time.gmtime(when)
    return "%s, %02d %3s %4d %02d:%02d:%02d GMT" % (
            weekdayname[wd],
            day, monthname[month], year,
            hh, mm, ss)

def parse_http_date (d):
    d = string.lower (d)
    tz = time.timezone
    m = rfc850_reg.match (d)
    if m and m.end() == len(d):
        retval = int (time.mktime (unpack_rfc850(m)) - tz)
    else:
        m = rfc822_reg.match (d)
        if m and m.end() == len(d):
            retval = int (time.mktime (unpack_rfc822(m)) - tz)
        else:
            return 0
            # Thanks to Craig Silverstein <csilvers@google.com> for pointing
            # out the DST discrepancy
    if time.daylight and time.localtime(retval)[-1] == 1: # DST correction
        retval = retval + (tz - time.altzone)
    return retval
