initial commit

src/lib/urls.ts

@@ -0,0 +1,53 @@
+// Cross-subdomain URL helpers.
+//
+// In production, joshbairstow.com (apex), blog., art., and code. are all served from
+// the same Astro build via the reverse proxy mapping host -> path prefix (see
+// docs/planning.md §6.2). Internal navigation between subdomains must use absolute
+// URLs so the browser actually swaps hosts; same-subdomain links can stay relative.
+//
+// In dev (a single localhost), the absolute hostnames don't resolve, so we collapse
+// everything to relative paths against the path-prefix layout.
+
+const PROD_APEX = "https://joshbairstow.com";
+
+const SUBDOMAIN_HOSTS: Record<string, string> = {
+  apex: PROD_APEX,
+  blog: "https://blog.joshbairstow.com",
+  art: "https://art.joshbairstow.com",
+  code: "https://code.joshbairstow.com",
+};
+
+const SUBDOMAIN_PATH_PREFIXES: Record<string, string> = {
+  apex: "/",
+  blog: "/blog/",
+  art: "/art/",
+  code: "/code/",
+};
+
+export type Subdomain = keyof typeof SUBDOMAIN_HOSTS;
+
+const isProd = import.meta.env.PROD;
+
+/**
+ * Build a URL on a given subdomain. Use this for top-nav links and any
+ * cross-subdomain reference so the apex layout works whether viewed at the
+ * apex or at a subdomain.
+ *
+ * In dev, returns a relative path (so localhost works). In prod, returns an
+ * absolute https URL (so the reverse proxy can route by host).
+ */
+export function url(subdomain: Subdomain, path: string = "/"): string {
+  const normalized = path.startsWith("/") ? path : `/${path}`;
+  if (isProd) {
+    return `${SUBDOMAIN_HOSTS[subdomain]}${normalized === "/" ? "" : normalized}`;
+  }
+  const prefix = SUBDOMAIN_PATH_PREFIXES[subdomain];
+  if (normalized === "/") return prefix;
+  return `${prefix.replace(/\/$/, "")}${normalized}`;
+}
+
+// Convenience shortcuts so authors don't memorize the function signature.
+export const home = (path: string = "/") => url("apex", path);
+export const blog = (path: string = "/") => url("blog", path);
+export const art = (path: string = "/") => url("art", path);
+export const code = (path: string = "/") => url("code", path);