"""WSGI middleware
"""

import sys
import logging
import traceback
import time
import calendar

from wsgiref.headers import Headers

try:
	import json
except ImportError:
	import simplejson as json

log = logging.getLogger("muddleware")
RFC_2822_DATE = "%a, %d %b %Y %H:%M:%S +0000"

class StructuredResponse(object):
	def __init__(self, headers):
		self.headers = Headers(headers)
		self.result = "200 OK"
		self.data = None

class JSONWrapper(object):
	"""Wrapper for API request. Takes a function that takes (request,
	response) parameters, and turns it into a WSGI method.
	"""
	def __init__(self, fn):
		self.fn = fn
		
	def __call__(self, environ, start_response):
		# Set up a response
		headers_list = []
		resp = StructuredResponse(headers_list)
		# Call the function
		self.fn(environ, resp)
		# Send the headers
		start_response(resp.result, headers_list)
		# Render it
		resp.headers['Content-type'] = "application/json"
		rv = None
		if resp.data is not None:
			return json.JSONEncoder().iterencode(resp.data)
		else:
			return ""

class ExceptionHandler(object):
	"""Wrapper to handle and report any exceptions that leak out
	"""
	def __init__(self, fn):
		self.fn = fn

	def __call__(self, environ, start_response):
		try:
			return self.fn(environ, start_response)
		except Exception, ex:
			h = []
			headers = Headers(h)
			start_response("500 Infernal Server Error", h)
			log.error("Exception: %s", str(ex))
			for l in traceback.format_exc().split("\n"):
				log.error("Exception: %s", l)
			
			return traceback.format_exc()

def change_test(req, stamp):
	"""Return True if the full content should be returned, False if a
	304 can be returned"""
	try:
		cutoff = time.strptime(req['HTTP_IF_MODIFIED_SINCE'], RFC_2822_DATE)
		cutoff = calendar.timegm(cutoff)
		return stamp >= cutoff
	except KeyError:
		pass
	# Don't catch ValueError, as that's an HTTP problem and deserves a 500

	try:
		cutoff = time.strptime(req['HTTP_IF_UNMODIFIED_SINCE'], RFC_2822_DATE)
		cutoff = calendar.timegm(cutoff)
		return stamp <= cutoff
	except KeyError:
		pass

	return True