recent_senders: Add sort by stream message recency.

If both users haven't posted in the current topic, then
as a second order sort, check which user has posted first
in the stream as a whole.

Fixes part of #5956; we still need to sort by sending in the
organization.

frontend_tests/node_tests/recent_senders.js

@@ -5,9 +5,11 @@ var _ = require('node_modules/underscore/underscore.js');
 (function test_process_message_for_senders() {
     var stream1 = 1;
     var stream2 = 2;
+    var stream3 = 3;
 
     var topic1 = "topic-1";
     var topic2 = "topic-2";
+    var topic3 = "topic-3";
 
     var sender1 = 1;
     var sender2 = 2;
@@ -29,14 +31,17 @@ var _ = require('node_modules/underscore/underscore.js');
     rs.process_message_for_senders(message1);
     rs.process_message_for_senders(message2);
 
+    // Users have posted in only one of the streams
     assert.equal(
         rs.compare_by_recency({user_id: sender1}, {user_id: sender2}, stream1, topic1) < 0,
         true);
     assert.equal(
         rs.compare_by_recency({user_id: sender1}, {user_id: sender2}, stream2, topic1) > 0,
         true);
+
+    // Users haven't posted in this stream, return zero
     assert.equal(
-        rs.compare_by_recency({user_id: sender1}, {user_id: sender2}, stream2, undefined) === 0,
+        rs.compare_by_recency({user_id: sender1}, {user_id: sender2}, stream3, undefined) === 0,
         true);
 
     // New topic
@@ -75,5 +80,37 @@ var _ = require('node_modules/underscore/underscore.js');
         rs.compare_by_recency({user_id: sender1}, {user_id: sender2}, stream1, topic1) < 0,
         true);
 
+    // Same stream, but different topics
+    var message6 = {
+        stream_id: stream3,
+        timestamp: _.uniqueId(),
+        subject: topic1,
+        sender_id: sender1,
+    };
+    var message7 = {
+        stream_id: stream3,
+        timestamp: _.uniqueId(),
+        subject: topic2,
+        sender_id: sender2,
+    };
+    var message8 = {
+        stream_id: stream3,
+        timestamp: _.uniqueId(),
+        subject: topic3,
+        sender_id: sender3,
+    };
+
+    rs.process_message_for_senders(message6);
+    rs.process_message_for_senders(message7);
+    rs.process_message_for_senders(message8);
+
+    // topic3 has a message in it, but sender1 nor sender2 have participated, so sort by stream
+    assert.equal(
+        rs.compare_by_recency({user_id: sender1}, {user_id: sender2}, stream3, topic3) > 0,
+        true);
+    assert.equal(
+        rs.compare_by_recency({user_id: sender2}, {user_id: sender1}, stream3, topic3) < 0,
+        true);
+
     assert.equal(rs.compare_by_recency({}, {}, _.uniqueId(), ''), 0);
 }());

static/js/recent_senders.js

@@ -2,11 +2,14 @@ var recent_senders = (function () {
 
 var exports = {};
 
-var senders = new Dict(); // key is stream-id, value is Dict
+var topic_senders = new Dict(); // key is stream-id, value is Dict
+var stream_senders = new Dict(); // key is stream-id, value is Dict
 
 exports.process_message_for_senders = function (message) {
     var stream_id = message.stream_id.toString();
-    var topic_dict = senders.get(stream_id) || new Dict({fold_case: true});
+
+    // Process most recent sender to topic
+    var topic_dict = topic_senders.get(stream_id) || new Dict({fold_case: true});
     var sender_timestamps = topic_dict.get(message.subject) || new Dict();
     var old_timestamp = sender_timestamps.get(message.sender_id);
 
@@ -15,25 +18,48 @@ exports.process_message_for_senders = function (message) {
     }
 
     topic_dict.set(message.subject, sender_timestamps);
-    senders.set(stream_id, topic_dict);
+    topic_senders.set(stream_id, topic_dict);
+
+    // Process most recent sender to whole stream
+    sender_timestamps = stream_senders.get(stream_id) || new Dict();
+    old_timestamp = sender_timestamps.get(message.sender_id);
+
+    if (old_timestamp === undefined || old_timestamp < message.timestamp) {
+        sender_timestamps.set(message.sender_id, message.timestamp);
+    }
+
+    stream_senders.set(stream_id, sender_timestamps);
 };
 
 exports.compare_by_recency = function (user_a, user_b, stream_id, topic) {
     stream_id = stream_id.toString();
 
-    var topic_dict = senders.get(stream_id);
+    var a_timestamp;
+    var b_timestamp;
+
+    var topic_dict = topic_senders.get(stream_id);
     if (topic !== undefined && topic_dict !== undefined) {
         var sender_timestamps = topic_dict.get(topic);
         if (sender_timestamps !== undefined) {
-            var b_timestamp = sender_timestamps.get(user_b.user_id) || Number.NEGATIVE_INFINITY;
-            var a_timestamp = sender_timestamps.get(user_a.user_id) || Number.NEGATIVE_INFINITY;
-            return b_timestamp - a_timestamp;
+            b_timestamp = sender_timestamps.get(user_b.user_id) || Number.NEGATIVE_INFINITY;
+            a_timestamp = sender_timestamps.get(user_a.user_id) || Number.NEGATIVE_INFINITY;
+
+            if (a_timestamp !== b_timestamp) {
+                return b_timestamp - a_timestamp;
+            }
         }
     }
 
-    // TODO: We should also compare by stream (and maybe also by
-    // overall message recency in the realm) in the common case where
-    // there's no traffic on the current topic from this user.
+    // Check recency for whole stream as tiebreaker
+    var stream_dict = stream_senders.get(stream_id);
+    if (stream_dict !== undefined) {
+        b_timestamp = stream_dict.get(user_b.user_id) || Number.NEGATIVE_INFINITY;
+        a_timestamp = stream_dict.get(user_a.user_id) || Number.NEGATIVE_INFINITY;
+
+        if (a_timestamp !== b_timestamp) {
+            return b_timestamp - a_timestamp;
+        }
+    }
 
     return 0;
 };