add support for previewing pages

web/src/app/api/preview/disable/route.ts

@@ -0,0 +1,7 @@
+import { cookies, draftMode } from "next/headers";
+
+export async function POST() {
+  (await draftMode()).disable();
+  (await cookies()).delete("preview-token");
+  return new Response(null, { status: 204 });
+}

web/src/app/api/preview/route.ts

@@ -0,0 +1,25 @@
+import { cookies, draftMode } from "next/headers";
+import { redirect } from "next/navigation";
+import { NextRequest } from "next/server";
+
+// Wagtail-headless-preview directs the editor's preview iframe here with
+// ?content_type=app.Model&token=<signed>. We stash the token in a cookie,
+// enable Next.js draft mode, and redirect to the type-dispatching renderer.
+export async function GET(req: NextRequest) {
+  const token = req.nextUrl.searchParams.get("token");
+  const contentType = req.nextUrl.searchParams.get("content_type");
+  if (!token || !contentType) {
+    return new Response("missing token/content_type", { status: 400 });
+  }
+
+  (await draftMode()).enable();
+  (await cookies()).set("preview-token", token, {
+    httpOnly: true,
+    sameSite: "lax",
+    secure: process.env.NODE_ENV === "production",
+    maxAge: 60 * 60 * 24,
+    path: "/",
+  });
+
+  redirect("/preview/render");
+}