From 10aa098e505e44b6a99238c2a9cd2071fd218e76 Mon Sep 17 00:00:00 2001
From: Benjamin Dauvergne <bdauvergne@entrouvert.com>
Date: Sat, 1 Oct 2016 11:45:03 +0200
Subject: [PATCH] add a layer of cache using x-combo-page-id for remote
 templates

---
 hobo/context_processors.py | 47 +++++++++++++++++++++++++++++++---------------
 1 file changed, 32 insertions(+), 15 deletions(-)

diff --git a/hobo/context_processors.py b/hobo/context_processors.py
index 31bb8ba..563e0b0 100644
--- a/hobo/context_processors.py
+++ b/hobo/context_processors.py
@@ -30,28 +30,39 @@ def template_vars(request):
     template_vars.update({'statics_hash': statics_hash.hexdigest()})
     return template_vars
 
+
 class RemoteTemplate(object):
     def __init__(self, source):
         self.source = source
 
     @property
     def cache_key(self):
-         return hashlib.md5(urlparse.urlunparse(
-             urlparse.urlparse(self.source)[:3] + ('', '', ''))).hexdigest()
+        return hashlib.md5(urlparse.urlunparse(
+            urlparse.urlparse(self.source)[:3] + ('', '', ''))).hexdigest()
 
     def get_template(self):
-        item = cache.get(self.cache_key)
-        if item is None:
+        x_combo_page_id = cache.get(self.cache_key)
+        if x_combo_page_id is None:
             template_body = self.update_content()
             if template_body is None:
                 raise Exception('Failed to retrieve theme')
         else:
-            template_body, expiry_time = item
-            if expiry_time < datetime.datetime.now():
-                # stale value, put it back into the cache for other consumers and
-                # update the content in a different thread
-                self.cache(template_body)
-                threading.Thread(target=self.update_content).start()
+            combo_page_id, combo_page_id_expiry_time = x_combo_page_id
+
+            item = cache.get(self.combo_page_id_cache_key(combo_page_id))
+            if item is None:
+                template_body = self.update_content()
+                if template_body is None:
+                    raise Exception('Failed to retrieve theme')
+            else:
+                template_body, expiry_time = item
+                if max(expiry_time, combo_page_id_expiry_time) < datetime.datetime.now():
+                    # stale value, put it back into the cache for other consumers and
+                    # update the content in a different thread
+                    # we do not put the template body back in the cache as we do not know if this
+                    # page is going to resolve to the same X-Combo-Page-Id for this update round
+                    self.cache(template_body, update_combo_page_id_cache=False)
+                    threading.Thread(target=self.update_content).start()
         return Template(template_body)
 
     def update_content(self):
@@ -59,14 +70,20 @@ class RemoteTemplate(object):
         if r.status_code != 200:
             logger.error('failed to retrieve theme')
             return None
-        self.cache(r.text)
+        self.cache(r.headers['x-combo-page-id'], r.text)
         return r.text
 
-    def cache(self, template_body):
+    def combo_page_id_cache_key(self, combo_page_id):
+        return hashlib.md5('combo-page-id-' + combo_page_id).hexdigest()
+
+    def cache(self, combo_page_id, template_body, update_combo_page_id_cache=True):
         expiry_time = datetime.datetime.now() + datetime.timedelta(seconds=CACHE_REFRESH_TIMEOUT)
-        cache.set(self.cache_key,
-                (template_body, expiry_time),
-                2592000) # bypass cache level expiration time
+        cache.set(self.cache_key, (combo_page_id, expiry_time),
+                  2592000)  # bypass cache level expiration time
+        if update_combo_page_id_cache:
+            cache.set(self.combo_page_id_cache_key(combo_page_id), (template_body, expiry_time),
+                      2592000)  # bypass cache level expiration time
+
 
 def theme_base(request):
     # this context processor adds two variables to context:
-- 
2.1.4