import { createTRPCClient, httpBatchLink } from "@trpc/client";
import superjson from "superjson";
import type { AnyTRPCRouter } from "@trpc/server";

// Returns a tRPC client whose fetch is a stub honouring the provided mocks.
// Mocks are keyed by procedure path ("blog.articleBySlug") returning the
// raw response body.
export function createMockTrpcClient<TRouter extends AnyTRPCRouter>(
  mocks: Record<string, unknown> = {},
) {
  const fetchStub: typeof fetch = async (input) => {
    const url = typeof input === "string" ? input : (input as Request).url;
    const path = new URL(url, "http://mock").pathname.replace(
      /^\/api\/trpc\//,
      "",
    );
    // httpBatchLink joins same-tick calls into one request whose path is the
    // comma-separated list of procedure paths; respond with one element per
    // call, in order.
    const paths = path.split(",");
    const body = paths.map((p) =>
      Object.hasOwn(mocks, p)
        ? { result: { data: superjson.serialize(mocks[p]) } }
        : {
            // Error payloads pass through the transformer too — serialize
            // them or the client throws "Unable to transform response".
            error: superjson.serialize({
              code: -32603,
              message: `No mock for ${p}`,
            }),
          },
    );
    return new Response(JSON.stringify(body), { status: 200 });
  };

  // httpBatchLink<TRouter> requires a conditional TransformerOptions<TRouter> that
  // depends on whether the router uses a transformer; making this generic-friendly
  // without parameterizing twice requires <any> here.
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  const link = httpBatchLink<any>({
    url: "http://mock/api/trpc",
    transformer: superjson,
    fetch: fetchStub,
  });

  return createTRPCClient<TRouter>({ links: [link] });
}