stream_topic_history: Update topic last msg_id after msg deletion.

Fixes #15992.
If the last message of the topic was deleted, we update the stored
message_id in the topic history so that the topic order in topic_list
is updated correctly.

frontend_tests/node_tests/dispatch.js

@@ -813,6 +813,7 @@ run_test("delete_message", (override) => {
         assert_same(args.opts.stream_id, 99);
         assert_same(args.opts.topic_name, "topic1");
         assert_same(args.opts.num_messages, 1);
+        assert_same(args.opts.max_removed_msg_id, 1337);
     });
 });
 

frontend_tests/node_tests/stream_topic_history.js

@@ -41,11 +41,40 @@ run_test("basics", () => {
     assert.deepEqual(history, ["topic2", "Topic1"]);
     assert.deepEqual(max_message_id, 103);
 
+    stream_topic_history.add_message({
+        stream_id,
+        message_id: 104,
+        topic_name: "Topic1",
+    });
+    history = stream_topic_history.get_recent_topic_names(stream_id);
+    max_message_id = stream_topic_history.get_max_message_id(stream_id);
+    assert.deepEqual(history, ["Topic1", "topic2"]);
+    assert.deepEqual(max_message_id, 104);
+
+    set_global("message_util", {
+        get_messages_in_topic: () => [{id: 101}, {id: 102}],
+    });
+    // Removing the last msg in topic1 changes the order
+    stream_topic_history.remove_messages({
+        stream_id,
+        topic_name: "Topic1",
+        num_messages: 1,
+        max_removed_msg_id: 104,
+    });
+    history = stream_topic_history.get_recent_topic_names(stream_id);
+    assert.deepEqual(history, ["topic2", "Topic1"]);
+    max_message_id = stream_topic_history.get_max_message_id(stream_id);
+    assert.deepEqual(max_message_id, 104);
+
+    set_global("message_util", {
+        get_messages_in_topic: () => [{id: 102}],
+    });
     // Removing first topic1 message has no effect.
     stream_topic_history.remove_messages({
         stream_id,
         topic_name: "toPic1",
         num_messages: 1,
+        max_removed_msg_id: 101,
     });
     history = stream_topic_history.get_recent_topic_names(stream_id);
     assert.deepEqual(history, ["topic2", "Topic1"]);
@@ -58,6 +87,7 @@ run_test("basics", () => {
         stream_id,
         topic_name: "Topic1",
         num_messages: 1,
+        max_removed_msg_id: 102,
     });
     history = stream_topic_history.get_recent_topic_names(stream_id);
     assert.deepEqual(history, ["topic2"]);
@@ -67,6 +97,7 @@ run_test("basics", () => {
         stream_id,
         topic_name: "Topic1",
         num_messages: 1,
+        max_removed_msg_id: 0,
     });
     history = stream_topic_history.get_recent_topic_names(stream_id);
     assert.deepEqual(history, ["topic2"]);

static/js/echo.js

@@ -202,6 +202,7 @@ exports.edit_locally = function (message, request) {
             stream_id: message.stream_id,
             topic_name: message.topic,
             num_messages: 1,
+            max_removed_msg_id: message.id,
         });
 
         if (new_stream_id !== undefined) {

static/js/message_events.js

@@ -196,6 +196,7 @@ exports.update_messages = function update_messages(events) {
                     stream_id: msg.stream_id,
                     topic_name: msg.topic,
                     num_messages: 1,
+                    max_removed_msg_id: msg.id,
                 });
 
                 // Update the unread counts; again, this must be called

static/js/server_events_dispatch.js

@@ -33,17 +33,20 @@ exports.dispatch_normal_event = function dispatch_normal_event(event) {
             // which returns all the unread messages out of a given list.
             // So double marking something as read would not occur
             unread_ops.process_read_messages_event(msg_ids);
+            // This methods updates message_list too and since stream_topic_history relies on it
+            // this method should be called first.
+            ui.remove_messages(msg_ids);
 
             if (event.message_type === "stream") {
                 stream_topic_history.remove_messages({
                     stream_id: event.stream_id,
                     topic_name: event.topic,
                     num_messages: msg_ids.length,
+                    max_removed_msg_id: Math.max(...msg_ids),
                 });
                 stream_list.update_streams_sidebar();
             }
 
-            ui.remove_messages(msg_ids);
             break;
         }
 

static/js/stream_topic_history.js

@@ -202,6 +202,7 @@ exports.remove_messages = function (opts) {
     const stream_id = opts.stream_id;
     const topic_name = opts.topic_name;
     const num_messages = opts.num_messages;
+    const max_removed_msg_id = opts.max_removed_msg_id;
     const history = stream_dict.get(stream_id);
 
     // This is the special case of "removing" a message from
@@ -213,6 +214,23 @@ exports.remove_messages = function (opts) {
 
     // This is the normal case of an incoming message.
     history.maybe_remove(topic_name, num_messages);
+
+    const existing_topic = history.topics.get(topic_name);
+    if (!existing_topic) {
+        return;
+    }
+
+    // Update max_message_id in topic
+    if (existing_topic.message_id <= max_removed_msg_id) {
+        const msgs_in_topic = message_util.get_messages_in_topic(stream_id, topic_name);
+        let max_message_id = 0;
+        for (const msg of msgs_in_topic) {
+            if (msg.id > max_message_id) {
+                max_message_id = msg.id;
+            }
+        }
+        existing_topic.message_id = max_message_id;
+    }
 };
 
 exports.find_or_create = function (stream_id) {