feat: share collection URL

lib/og.ts

@@ -470,3 +470,39 @@ export function ogForPost(p: {
     },
   };
 }
+
+/** OG metadata for a public collection (`/c/<id>`). */
+export function ogForCollection(c: {
+  id: string;
+  title: string;
+  description?: string | null;
+  itemCount?: number;
+}) {
+  const imageUrl = new URL(
+    `/api/og/collection/${encodeURIComponent(c.id)}`,
+    SITE_URL,
+  ).toString();
+  const title = c.title;
+  const count =
+    typeof c.itemCount === "number"
+      ? `${c.itemCount} post${c.itemCount === 1 ? "" : "s"}`
+      : "A collection";
+  const description =
+    c.description?.trim() || `${count} on Prabhupāda Says`;
+  return {
+    title,
+    description,
+    openGraph: {
+      title,
+      description,
+      images: [{ url: imageUrl, width: 1200, height: 630, alt: title }],
+      siteName: "Prabhupāda Says",
+    },
+    twitter: {
+      card: "summary_large_image" as const,
+      title,
+      description,
+      images: [imageUrl],
+    },
+  };
+}