# -*- 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.

def build_http_date (when):
	return time.strftime ('%a, %d %b %Y %H:%M:%S GMT', time.gmtime(when))

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