scheduled_messages: Rerender send later options at specific time.

Fixes: #25451.

web/src/scheduled_messages.js

@@ -1,6 +1,7 @@
 import $ from "jquery";
 
 import render_success_message_scheduled_banner from "../templates/compose_banner/success_message_scheduled_banner.hbs";
+import render_send_later_modal_options from "../templates/send_later_modal_options.hbs";
 
 import * as channel from "./channel";
 import * as compose from "./compose";
@@ -16,6 +17,8 @@ import * as stream_data from "./stream_data";
 import * as timerender from "./timerender";
 
 export const MINIMUM_SCHEDULED_MESSAGE_DELAY_SECONDS = 5 * 60;
+export const SCHEDULING_MODAL_UPDATE_INTERVAL_IN_MILLISECONDS = 60 * 1000;
+
 export let scheduled_messages_data = [];
 
 function compute_send_times(now = new Date()) {
@@ -322,3 +325,29 @@ export function initialize(scheduled_messages_params) {
         e.stopPropagation();
     });
 }
+
+// This function is exported for unit testing purposes.
+export function should_update_send_later_options(date) {
+    const current_minute = date.getMinutes();
+    const current_hour = date.getHours();
+
+    if (current_hour === 0 && current_minute === 0) {
+        // We need to rerender the available options at midnight,
+        // since Monday could become in range.
+        return true;
+    }
+
+    // Rerender at MINIMUM_SCHEDULED_MESSAGE_DELAY_SECONDS before the
+    // hour, so we don't offer a 4:00PM send time at 3:59 PM.
+    return current_minute === 60 - MINIMUM_SCHEDULED_MESSAGE_DELAY_SECONDS / 60;
+}
+
+export function update_send_later_options() {
+    const now = new Date();
+    if (should_update_send_later_options(now)) {
+        const filtered_send_opts = get_filtered_send_opts(now);
+        $("#send_later_modal .send_later_options").replaceWith(
+            render_send_later_modal_options(filtered_send_opts),
+        );
+    }
+}