Dynamically merge CSSes into a single one

This will make CSS downloading a single request, instead of making
6-7 requests for each page as it is now. It also moves all the definitions
of URLs for CSS into the templates and not in the raw CSS itself, which
will make it possible to enable client side caching in the future.

Fixes #91

pgweb/core/views.py

@@ -1,14 +1,16 @@
-from django.shortcuts import render_to_response, get_object_or_404
+from django.shortcuts import render_to_response
 from django.http import HttpResponse, Http404, HttpResponseRedirect
-from django.template import TemplateDoesNotExist, loader, Context
+from django.http import HttpResponseNotModified
+from django.template import TemplateDoesNotExist, loader
 from django.contrib.auth.decorators import login_required, user_passes_test
 from django.views.decorators.csrf import csrf_exempt
 from django.db.models import Count
 from django.db import connection, transaction
+from django.utils.http import http_date, parse_http_date
 from django.conf import settings
 
 from datetime import date, datetime
-from os import uname
+import os
 import re
 import urllib
 
@@ -155,6 +157,60 @@ def sitemap(request):
 	x.endDocument()
 	return resp
 
+# dynamic CSS serving, meaning we merge a number of different CSS into a
+# single one, making sure it turns into a single http response. We do this
+# dynamically, since the output will be cached (for all non-SSL users, which
+# is the vast majority) anyway.
+_dynamic_cssmap = {
+	'base': ['../media/css/global.css',
+			 '../media/css/layout.css',
+			 '../media/css/text.css',
+			 '../media/css/navigation.css',
+			 '../media/css/table.css',
+			 '../media/css/iefixes.css'],
+	'docs': ['../media/css/global.css',
+			 '../media/css/table.css',
+			 '../media/css/text.css',
+		     '../media/css/docs.css'],
+	}
+@cache(hours=6)
+def dynamic_css(request, css):
+	if not _dynamic_cssmap.has_key(css):
+		raise Http404('CSS not found')
+	files = _dynamic_cssmap[css]
+	resp = HttpResponse(content_type='text/css')
+
+	# We honor if-modified-since headers by looking at the most recently
+	# touched CSS file.
+	latestmod = 0
+	for fn in files:
+		try:
+			stime = os.stat(fn).st_mtime
+			if latestmod < stime:
+				latestmod = stime
+		except OSError:
+			# If we somehow referred to a file that didn't exist, or
+			# one that we couldn't access.
+			raise Http404('CSS (sub) not found')
+	if request.META.has_key('HTTP_IF_MODIFIED_SINCE'):
+		# This code is mostly stolen from django :)
+		matches = re.match(r"^([^;]+)(; length=([0-9]+))?$",
+						   request.META.get('HTTP_IF_MODIFIED_SINCE'),
+						   re.IGNORECASE)
+		header_mtime = parse_http_date(matches.group(1))
+		# We don't do length checking, just the date
+		if int(latestmod) <= header_mtime:
+			return HttpResponseNotModified(mimetype='text/css')
+	resp['Last-Modified'] = http_date(latestmod)
+
+	for fn in files:
+		with open(fn) as f:
+			resp.write("/* %s */\n" % fn)
+			resp.write(f.read())
+			resp.write("\n")
+
+	return resp
+
 @nocache
 def csrf_failure(request, reason=''):
 	resp = render_to_response('errors/csrf_failure.html', {
@@ -167,7 +223,7 @@ def csrf_failure(request, reason=''):
 @cache(seconds=30)
 def system_information(request):
 	return render_to_response('core/system_information.html', {
-			'server': uname()[1],
+			'server': os.uname()[1],
 			'behind_cache': is_behind_cache(request),
 			'cache_server': is_behind_cache(request) and request.META['REMOTE_ADDR'] or None,
 			'client_ip': get_client_ip(request),