Add get_topic_history_for_stream().

zerver/lib/actions.py

@@ -40,7 +40,7 @@ from zerver.models import Realm, RealmEmoji, Stream, UserProfile, UserActivity,
 from zerver.lib.alert_words import alert_words_in_realm
 from zerver.lib.avatar import get_avatar_url, avatar_url
 
-from django.db import transaction, IntegrityError
+from django.db import transaction, IntegrityError, connection
 from django.db.models import F, Q
 from django.db.models.query import QuerySet
 from django.core.exceptions import ValidationError
@@ -167,6 +167,52 @@ def realm_user_count(realm):
     # type: (Realm) -> int
     return UserProfile.objects.filter(realm=realm, is_active=True, is_bot=False).count()
 
+def get_topic_history_for_stream(user_profile, recipient):
+    # type: (UserProfile, Recipient) -> List[Tuple[str, int]]
+
+    # We tested the below query on some large prod datasets, and we never
+    # saw more than 50ms to execute it, so we think that's acceptable,
+    # but we will monitor it, and we may later optimize it further.
+    query = '''
+        SELECT topic, read, count(*)
+        FROM (
+            SELECT
+                ("zerver_usermessage"."flags" & 1) as read,
+                "zerver_message"."subject" as topic,
+                "zerver_message"."id" as message_id
+            FROM "zerver_usermessage"
+            INNER JOIN "zerver_message" ON (
+                "zerver_usermessage"."message_id" = "zerver_message"."id"
+            ) WHERE (
+                "zerver_usermessage"."user_profile_id" = %s AND
+                "zerver_message"."recipient_id" = %s
+            ) ORDER BY "zerver_usermessage"."message_id" DESC
+        ) messages_for_stream
+        GROUP BY topic, read
+        ORDER BY max(message_id) desc
+    '''
+    cursor = connection.cursor()
+    cursor.execute(query, [user_profile.id, recipient.id])
+    rows = cursor.fetchall()
+    cursor.close()
+
+    topic_names = dict() # type: Dict[str, str]
+    topic_counts = dict() # type: Dict[str, int]
+    topics = []
+    for row in rows:
+        topic_name, read, count = row
+        if topic_name.lower() not in topic_names:
+            topic_names[topic_name.lower()] = topic_name
+        topic_name = topic_names[topic_name.lower()]
+        if topic_name not in topic_counts:
+            topic_counts[topic_name] = 0
+            topics.append(topic_name)
+        if not read:
+            topic_counts[topic_name] += count
+
+    history = [(topic, topic_counts[topic]) for topic in topics]
+    return history
+
 def send_signup_message(sender, signups_stream, user_profile,
                         internal=False, realm=None):
     # type: (UserProfile, text_type, UserProfile, bool, Optional[Realm]) -> None