feat: add url shortner

lib/share.ts

@@ -0,0 +1,53 @@
+/**
+ * Short link client — talks to the BFF /share endpoints.
+ *
+ * Used by the text-selection toolbar (`buildShortHighlightUrl`) and the
+ * `/share/[code]` page (`resolveShortLink`).
+ */
+
+import { bff, bffPost } from "@/lib/bff";
+
+// Module-scoped cache: a single user shouldn't generate a fresh code every
+// time they re-click Share on the same selection. Keyed by the relative path
+// (including ?hl=…), this returns the same promise for repeat calls.
+const createCache = new Map<string, Promise<string | null>>();
+
+type CreateResponse = { code: string };
+type ResolveResponse = { url: string };
+
+/**
+ * Create a short code for a same-site relative path (`/books/bg/18/66?hl=…`).
+ * Returns `null` on any failure — caller should fall back to the long URL.
+ */
+export function createShortLink(longPath: string): Promise<string | null> {
+  const cached = createCache.get(longPath);
+  if (cached) return cached;
+
+  const promise = bffPost<CreateResponse>("/share", { url: longPath })
+    .then((r) => r.code)
+    .catch(() => null);
+
+  createCache.set(longPath, promise);
+  // If the request fails, evict so the next click can retry instead of
+  // returning the cached null forever.
+  promise.then((code) => {
+    if (code === null) createCache.delete(longPath);
+  });
+
+  return promise;
+}
+
+/**
+ * Resolve a short code to its full long path. Returns `null` when the code is
+ * not found, expired, disabled, or the BFF is unreachable.
+ */
+export async function resolveShortLink(code: string): Promise<string | null> {
+  try {
+    const r = await bff<ResolveResponse>(`/share/${encodeURIComponent(code)}`, {
+      revalidate: 0,
+    });
+    return r?.url ?? null;
+  } catch {
+    return null;
+  }
+}