notification: Fix "narrow to..." link present above composebox.

Earlier copy to the link present above the composebox (which
appears when a message is sent outside the current narrow), it
used to provide the link to the home page which is fixed now.
Now, copy to the link gives the link of the narrow where message
is sent.

static/js/notifications.js

@@ -7,6 +7,7 @@ import * as alert_words from "./alert_words";
 import * as blueslip from "./blueslip";
 import * as channel from "./channel";
 import * as favicon from "./favicon";
+import * as hash_util from "./hash_util";
 import {$t} from "./i18n";
 import * as message_lists from "./message_lists";
 import * as message_store from "./message_store";
@@ -154,11 +155,18 @@ export function is_window_focused() {
     return window_focused;
 }
 
-export function notify_above_composebox(note, link_class, link_msg_id, link_text) {
+export function notify_above_composebox(
+    note,
+    link_class,
+    above_composebox_narrow_url,
+    link_msg_id,
+    link_text,
+) {
     const notification_html = $(
         render_compose_notification({
             note,
             link_class,
+            above_composebox_narrow_url,
             link_msg_id,
             link_text,
         }),
@@ -600,10 +608,12 @@ export function notify_local_mixes(messages, need_user_to_scroll) {
 
         let reason = get_local_notify_mix_reason(message);
 
+        const above_composebox_narrow_url = get_above_composebox_narrow_url(message);
+
         if (!reason) {
             if (need_user_to_scroll) {
                 reason = $t({defaultMessage: "Sent! Scroll down to view your message."});
-                notify_above_composebox(reason, "", null, "");
+                notify_above_composebox(reason, "", above_composebox_narrow_url, null, "");
                 setTimeout(() => {
                     $("#out-of-view-notification").hide();
                 }, 3000);
@@ -621,10 +631,29 @@ export function notify_local_mixes(messages, need_user_to_scroll) {
             {message_recipient: get_message_header(message)},
         );
 
-        notify_above_composebox(reason, link_class, link_msg_id, link_text);
+        notify_above_composebox(
+            reason,
+            link_class,
+            above_composebox_narrow_url,
+            link_msg_id,
+            link_text,
+        );
     }
 }
 
+function get_above_composebox_narrow_url(message) {
+    let above_composebox_narrow_url;
+    if (message.type === "stream") {
+        above_composebox_narrow_url = hash_util.by_stream_topic_uri(
+            message.stream_id,
+            message.topic,
+        );
+    } else {
+        above_composebox_narrow_url = message.pm_with_url;
+    }
+    return above_composebox_narrow_url;
+}
+
 // for callback when we have to check with the server if a message should be in
 // the message_lists.current (!can_apply_locally; a.k.a. "a search").
 export function notify_messages_outside_current_search(messages) {
@@ -632,6 +661,7 @@ export function notify_messages_outside_current_search(messages) {
         if (!people.is_current_user(message.sender_email)) {
             continue;
         }
+        const above_composebox_narrow_url = get_above_composebox_narrow_url(message);
         const link_text = $t(
             {defaultMessage: "Narrow to {message_recipient}"},
             {message_recipient: get_message_header(message)},
@@ -639,6 +669,7 @@ export function notify_messages_outside_current_search(messages) {
         notify_above_composebox(
             $t({defaultMessage: "Sent! Your recent message is outside the current search."}),
             "compose_notification_narrow_by_topic",
+            above_composebox_narrow_url,
             message.id,
             link_text,
         );

static/templates/compose_notification.hbs

@@ -1,5 +1,5 @@
 {{! Content of sent-message notifications }}
 <div class="compose-notifications-content">
-    {{note}} {{#if link_class}}<a href="#" class="{{link_class}}" data-message-id="{{link_msg_id}}">{{link_text}}</a>{{/if}}
+    {{note}} {{#if link_class}}<a href="{{above_composebox_narrow_url}}" class="{{link_class}}" data-message-id="{{link_msg_id}}">{{link_text}}</a>{{/if}}
     <button type="button" class="out-of-view-notification-close close">&times;</button>
 </div>