Only load jinja2 templates once

Instead of every time a new email pusher is created, as loading jinja2
templates is slow.

synapse/push/pusher.py

@@ -26,22 +26,54 @@ logger = logging.getLogger(__name__)
 # process works fine)
 try:
     from synapse.push.emailpusher import EmailPusher
+    from synapse.push.mailer import Mailer, load_jinja2_templates
 except:
     pass
 
 
-def create_pusher(hs, pusherdict):
-    logger.info("trying to create_pusher for %r", pusherdict)
+class PusherFactory(object):
+    def __init__(self, hs):
+        self.hs = hs
 
-    PUSHER_TYPES = {
-        "http": HttpPusher,
-    }
+        self.pusher_types = {
+            "http": HttpPusher,
+        }
 
-    logger.info("email enable notifs: %r", hs.config.email_enable_notifs)
-    if hs.config.email_enable_notifs:
-        PUSHER_TYPES["email"] = EmailPusher
-        logger.info("defined email pusher type")
+        logger.info("email enable notifs: %r", hs.config.email_enable_notifs)
+        if hs.config.email_enable_notifs:
+            self.mailers = {}  # app_name -> Mailer
 
-    if pusherdict['kind'] in PUSHER_TYPES:
-        logger.info("found pusher")
-        return PUSHER_TYPES[pusherdict['kind']](hs, pusherdict)
+            templates = load_jinja2_templates(hs.config)
+            self.notif_template_html, self.notif_template_text = templates
+
+            self.pusher_types["email"] = self._create_email_pusher
+
+            logger.info("defined email pusher type")
+
+    def create_pusher(self, pusherdict):
+        logger.info("trying to create_pusher for %r", pusherdict)
+
+        if pusherdict['kind'] in self.pusher_types:
+            logger.info("found pusher")
+            return self.pusher_types[pusherdict['kind']](self.hs, pusherdict)
+
+    def _create_email_pusher(self, pusherdict):
+        app_name = self._brand_from_pusherdict
+        mailer = self.mailers.get(app_name)
+        if not mailer:
+            mailer = Mailer(
+                hs=self.hs,
+                app_name=app_name,
+                notif_template_html=self.notif_template_html,
+                notif_template_text=self.notif_template_text,
+            )
+            self.mailers[app_name] = mailer
+        return EmailPusher(self.hs, pusherdict, mailer)
+
+    def _app_name_from_pusherdict(self, pusherdict):
+        if 'data' in pusherdict and 'brand' in pusherdict['data']:
+            app_name = pusherdict['data']['brand']
+        else:
+            app_name = self.hs.config.email_app_name
+
+        return app_name