typeahead: Add recent_senders module.

In recent_senders module, added a data structure to hold timestamps of
users' latest message in a topic. Also added a function to compare 2
users based on above timestamp. Added a function to process messages for
the data structure and a call in add_message_metadata. Also added node
tests for insertion of data into recent_senders.senders.

.eslintrc.json

@@ -136,6 +136,7 @@
         "current_msg_list": true,
         "home_msg_list": false,
         "pm_list": false,
+        "recent_senders": false,
         "unread_ui": false,
         "unread_ops": false,
         "user_events": false,

frontend_tests/node_tests/recent_senders.js

@@ -0,0 +1,74 @@
+var assert = require('assert');
+var rs = require('js/recent_senders.js');
+var _ = require('node_modules/underscore/underscore.js');
+
+(function test_process_message_for_senders() {
+    var stream1 = 1;
+    var stream2 = 2;
+
+    var topic1 = "topic-1";
+    var topic2 = "topic-2";
+
+    var sender1 = 1;
+    var sender2 = 2;
+    var sender3 = 3;
+
+    // New stream
+    var message1 = {
+        stream_id: stream1,
+        timestamp: _.uniqueId(),
+        subject: topic1,
+        sender_id: sender1,
+    };
+    var message2 = {
+        stream_id: stream2,
+        timestamp: _.uniqueId(),
+        subject: topic1,
+        sender_id: sender2,
+    };
+    rs.process_message_for_senders(message1);
+    rs.process_message_for_senders(message2);
+
+    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);
+
+    // New topic
+    var message3 = {
+        stream_id: stream1,
+        timestamp: _.uniqueId(),
+        subject: topic2,
+        sender_id: sender3,
+    };
+    rs.process_message_for_senders(message3);
+    assert.equal(
+        rs.compare_by_recency({user_id: sender3}, {user_id: sender2}, stream1, topic2) < 0,
+        true);
+
+    // New sender
+    var message4 = {
+        stream_id: stream1,
+        timestamp: _.uniqueId(),
+        subject: topic1,
+        sender_id: sender2,
+    };
+    rs.process_message_for_senders(message4);
+    assert.equal(
+        rs.compare_by_recency({user_id: sender1}, {user_id: sender2}, stream1, topic1) > 0,
+        true);
+
+    // More recent message
+    var message5 = {
+        stream_id: stream1,
+        timestamp: _.uniqueId(),
+        subject: topic1,
+        sender_id: sender1,
+    };
+    rs.process_message_for_senders(message5);
+    assert.equal(
+        rs.compare_by_recency({user_id: sender1}, {user_id: sender2}, stream1, topic1) < 0,
+        true);
+}());

static/js/message_store.js

@@ -148,6 +148,8 @@ exports.add_message_metadata = function (message) {
 
         stream_data.process_message_for_recent_topics(message);
         exports.set_topic_edit_properties(message);
+
+        recent_senders.process_message_for_senders(message);
         break;
 
     case 'private':

static/js/recent_senders.js

@@ -0,0 +1,42 @@
+var recent_senders = (function () {
+
+var exports = {};
+
+var 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});
+    var sender_timestamps = topic_dict.get(message.subject) || new Dict();
+    var old_timestamp = sender_timestamps.get(message.sender_id);
+
+    if (old_timestamp === undefined || old_timestamp < message.timestamp) {
+        sender_timestamps.set(message.sender_id, message.timestamp);
+    }
+
+    topic_dict.set(message.subject, sender_timestamps);
+    senders.set(stream_id, topic_dict);
+};
+
+exports.compare_by_recency = function (user_a, user_b, stream_id, topic) {
+    stream_id = stream_id.toString();
+
+    var topic_dict = senders.get(stream_id);
+    if (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;
+        }
+    }
+
+    return 0;
+};
+
+return exports;
+}());
+
+if (typeof module !== 'undefined') {
+    module.exports = recent_senders;
+}

zproject/settings.py

@@ -875,6 +875,7 @@ JS_SPECS = {
             'js/unread.js',
             'js/topic_list.js',
             'js/pm_list.js',
+            'js/recent_senders.js',
             'js/stream_sort.js',
             'js/topic_generator.js',
             'js/stream_list.js',