feat: Add rename calls and slug preview to the HQ client

adminsite/lib/slug.ts

@@ -0,0 +1,56 @@
+/*
+ * A TypeScript mirror of shared/provision's slug rules, used ONLY to preview the
+ * host a rename would move an instance to while the customer types.
+ *
+ * It is a second implementation of Slugify, BaseSlug and ReservedSlugs, and it
+ * must change in the same commit as the Go one — the same hazard as
+ * web/lib/targets.ts. The preview is a courtesy; the server's 409 is the
+ * boundary, and the two are allowed to disagree without anything breaking.
+ */
+
+/** Mirrors provision.MinSlugLength / MaxSlugLength. */
+export const MIN_SLUG_LENGTH = 3;
+export const MAX_SLUG_LENGTH = 40;
+
+/** Mirrors provision.ReservedSlugs. */
+const RESERVED = new Set([
+    "www", "api", "app", "admin", "auth",
+    "install", "static", "_next", "default",
+]);
+
+/*
+ * The tenant subdomain namespace. Also hardcoded in InstanceRecord.tsx and the
+ * customer instance page; those predate this file and are left alone rather than
+ * refactored under a rename change.
+ */
+export const INSTANCE_DOMAIN = "vantage.hostxtra.co.uk";
+
+/** Mirrors provision.Slugify. */
+export function slugify(name: string): string {
+    return name
+        .toLowerCase()
+        .replace(/[^a-z0-9]+/g, "-")
+        .replace(/^-+|-+$/g, "");
+}
+
+/** Mirrors provision.BaseSlug's truncation. */
+export function baseSlug(name: string): string {
+    return slugify(name).slice(0, MAX_SLUG_LENGTH);
+}
+
+/** The reason a name cannot become a slug, or undefined when it can. */
+export function slugError(name: string): string | undefined {
+    const base = slugify(name);
+    if (base.length < MIN_SLUG_LENGTH) {
+        return `Needs at least ${MIN_SLUG_LENGTH} letters or digits.`;
+    }
+    if (RESERVED.has(base.slice(0, MAX_SLUG_LENGTH))) {
+        return "That name is reserved.";
+    }
+    return undefined;
+}
+
+/** The host an instance on this slug is reached at. */
+export function hostFor(slug: string): string {
+    return `${slug}.${INSTANCE_DOMAIN}`;
+}