♻️ set default value on domain picker modal in proxy resource page

src/app/[orgId]/settings/resources/proxy/[niceId]/general/page.tsx

@@ -16,7 +16,7 @@ import {
 import { Input } from "@/components/ui/input";
 import { useResourceContext } from "@app/hooks/useResourceContext";
 import { ListSitesResponse } from "@server/routers/site";
-import { useEffect, useState } from "react";
+import { useEffect, useMemo, useState } from "react";
 import { AxiosResponse } from "axios";
 import { useParams, useRouter } from "next/navigation";
 import { useForm } from "react-hook-form";
@@ -90,6 +90,25 @@ export default function GeneralForm() {
     const [resourceFullDomain, setResourceFullDomain] = useState(
         `${resource.ssl ? "https" : "http"}://${toUnicode(resource.fullDomain || "")}`
     );
+
+    const [defaultSubdomain, defaultBaseDomain] = useMemo(() => {
+        const resourceUrl = new URL(resourceFullDomain);
+        const domain = resourceUrl.hostname;
+
+        const allDomainParts = domain.split(".");
+        let sub = undefined;
+        let base = domain;
+
+        if (allDomainParts.length >= 3) {
+            // 3 parts: [subdomain, domain, tld]
+            const [first, ...rest] = allDomainParts;
+            sub = first;
+            base = rest.join(".");
+        }
+
+        return [sub, base];
+    }, [resourceFullDomain]);
+
     const [selectedDomain, setSelectedDomain] = useState<{
         domainId: string;
         subdomain?: string;
@@ -488,6 +507,8 @@ export default function GeneralForm() {
                             <DomainPicker
                                 orgId={orgId as string}
                                 cols={1}
+                                defaultSubdomain={defaultSubdomain}
+                                defaultBaseDomain={defaultBaseDomain}
                                 onDomainChange={(res) => {
                                     const selected = {
                                         domainId: res.domainId,