use display name function

src/lib/getUserDisplayName.ts

@@ -0,0 +1,36 @@
+import { GetUserResponse } from "@server/routers/user";
+
+type UserDisplayNameInput =
+    | {
+          user: GetUserResponse;
+      }
+    | {
+          email?: string | null;
+          name?: string | null;
+          username?: string | null;
+      };
+
+/**
+ * Gets the display name for a user.
+ * Priority: email > name > username
+ *
+ * @param input - Either a user object or individual email, name, username properties
+ * @returns The display name string
+ */
+export function getUserDisplayName(input: UserDisplayNameInput): string {
+    let email: string | null | undefined;
+    let name: string | null | undefined;
+    let username: string | null | undefined;
+
+    if ("user" in input) {
+        email = input.user.email;
+        name = input.user.name;
+        username = input.user.username;
+    } else {
+        email = input.email;
+        name = input.name;
+        username = input.username;
+    }
+
+    return email || name || username || "";
+}