notifications: Render emoji in desktop notifications.

In desktop notifications, we no longer display an emoji's status
code. Instead, we show the corresponding Unicode emoji to
render it properly in desktop notifications. For custom
emojis, we continue to display their name.

Fixes #30598.

Co-authored-by: Tanmay Kumar <tnmdotkr@gmail.com>
Co-authored-by: Tim Abbott <tabbott@zulip.com>

web/src/message_notifications.ts

@@ -40,7 +40,7 @@ function get_notification_content(message: Message | TestNotificationMessage): s
     let content;
     // Convert the content to plain text, replacing emoji with their alt text
     const $content = $("<div>").html(message.content);
-    ui_util.replace_emoji_with_text($content);
+    ui_util.convert_unicode_eligible_emoji_to_unicode($content);
     ui_util.change_katex_to_raw_latex($content);
     ui_util.potentially_collapse_quotes($content);
     spoilers.hide_spoilers_in_notification($content);

web/src/ui_util.ts

@@ -22,14 +22,62 @@ export function place_caret_at_end(el: HTMLElement): void {
     }
 }
 
-export function replace_emoji_with_text($element: JQuery): void {
+function extract_emoji_code_from_class(emoji_class_string: string | undefined): string | undefined {
+    if (emoji_class_string === undefined) {
+        return undefined;
+    }
+
+    const classes = emoji_class_string.split(/\s+/);
+    const regex = /^emoji-([0-9a-fA-F-]+)$/;
+
+    for (const cls of classes) {
+        const match = regex.exec(cls);
+        if (match) {
+            return match?.[1] ?? undefined;
+        }
+    }
+    return undefined;
+}
+
+export function convert_emoji_element_to_unicode($emoji_elt: JQuery): string {
+    // This is a custom emoji, we do not have corresponding emoji
+    // unicode for these so we return original markdown.
+    if ($emoji_elt.is("img")) {
+        return $emoji_elt.attr("alt") ?? "";
+    }
+
+    const emoji_class_string = $emoji_elt.attr("class");
+    const emoji_code_hex_string = extract_emoji_code_from_class(emoji_class_string);
+    if (emoji_code_hex_string === undefined) {
+        return $emoji_elt.text();
+    }
+
+    const emoji_code_parts = emoji_code_hex_string.split("-");
+    const emoji_unicode = emoji_code_parts
+        .map((emoji_code) => {
+            const emoji_code_int = Number.parseInt(emoji_code, 16);
+            // Validate the parameter passed to String.fromCodePoint() (here, emoji_code_int).
+            // "An integer between 0 and 0x10FFFF (inclusive) representing a Unicode code point."
+            // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fromCodePoint
+            // for details.
+            if (
+                Number.isNaN(emoji_code_int) ||
+                !(emoji_code_int >= 0 && emoji_code_int <= 0x10ffff)
+            ) {
+                blueslip.error("Invalid unicode codepoint for emoji", {emoji_code_int});
+                return $emoji_elt.text();
+            }
+            return String.fromCodePoint(emoji_code_int);
+        })
+        .join("");
+    return emoji_unicode;
+}
+
+export function convert_unicode_eligible_emoji_to_unicode($element: JQuery): void {
     $element
         .find(".emoji")
         .text(function () {
-            if ($(this).is("img")) {
-                return $(this).attr("alt") ?? "";
-            }
-            return $(this).text();
+            return convert_emoji_element_to_unicode($(this));
         })
         .contents()
         .unwrap();

web/tests/ui_util.test.cjs

@@ -67,3 +67,15 @@ run_test("potentially_collapse_quotes", ({override_rewire}) => {
         expected_texts,
     );
 });
+
+run_test("replace_emoji_name_with_emoji_unicode", () => {
+    const $emoji = $.create("span").attr("class", "emoji emoji-1f419");
+    $emoji.is = () => false;
+
+    const octopus_emoji = "🐙";
+    assert.equal(octopus_emoji, ui_util.convert_emoji_element_to_unicode($emoji));
+
+    $emoji.attr("class", "emoji emoji-1f468-200d-1f373");
+    const man_cook_emoji = "👨‍🍳";
+    assert.equal(man_cook_emoji, ui_util.convert_emoji_element_to_unicode($emoji));
+});