Add link to next file in the export (#10190)

Co-authored-by: grimhilt <grimhilt@users.noreply.github.com>

test/utils/exportUtils/HTMLExport-test.ts

@@ -315,4 +315,45 @@ describe("HTMLExport", () => {
             expect(fileName).not.toMatch(/^files\/hello/);
         }
     });
+
+    it("should add link to next and previous file", async () => {
+        const exporter = new HTMLExporter(
+            room,
+            ExportType.LastNMessages,
+            {
+                attachmentsIncluded: false,
+                maxSize: 1_024 * 1_024,
+            },
+            () => {},
+        );
+
+        // test link to the first page
+        //@ts-ignore private access
+        exporter.wrapHTML("", 0, 3).then((res) => {
+            expect(res).not.toContain("Previous group of messages");
+            expect(res).toContain(
+                '<div style="text-align:center;margin:10px"><a href="./messages2.html" style="font-weight:bold">Next group of messages</a></div>',
+            );
+        });
+
+        // test link for a middle page
+        //@ts-ignore private access
+        exporter.wrapHTML("", 1, 3).then((res) => {
+            expect(res).toContain(
+                '<div style="text-align:center"><a href="./messages.html" style="font-weight:bold">Previous group of messages</a></div>',
+            );
+            expect(res).toContain(
+                '<div style="text-align:center;margin:10px"><a href="./messages3.html" style="font-weight:bold">Next group of messages</a></div>',
+            );
+        });
+
+        // test link for last page
+        //@ts-ignore private access
+        exporter.wrapHTML("", 2, 3).then((res) => {
+            expect(res).toContain(
+                '<div style="text-align:center"><a href="./messages2.html" style="font-weight:bold">Previous group of messages</a></div>',
+            );
+            expect(res).not.toContain("Next group of messages");
+        });
+    });
 });