route.ts

import {
  CopilotRuntime,
  ExperimentalEmptyAdapter,
  copilotRuntimeNextJSAppRouterEndpoint,
} from "@copilotkit/runtime";
import { LangGraphAgent } from "@copilotkit/runtime/langgraph";
import { NextRequest, NextResponse } from "next/server";

// 1. Runtime adapter. Since this starter wires agent responses directly
//    (no OpenAI/Anthropic-compatible chat-completions fallback), we use
//    the empty adapter: it satisfies the runtime interface without
//    dispatching any LLM requests of its own.
const serviceAdapter = new ExperimentalEmptyAdapter();

// 2. LANGGRAPH_DEPLOYMENT_URL handling. In development we fall back to
//    localhost:8125 (the port this starter's LangGraph dev server uses —
//    see apps/agent/package.json) and warn so the developer sees it. In
//    production a missing URL is almost always a misconfiguration — but
//    we defer the hard failure to the first request (see POST below)
//    rather than throwing at module load. `next build` evaluates route
//    modules with NODE_ENV=production during route collection, while
//    runtime-only env vars (Vercel secrets, Railway env, Docker ENV at
//    container start) are NOT injected at build time. Throwing at module
//    load would abort otherwise-valid production builds.
if (
  !process.env.LANGGRAPH_DEPLOYMENT_URL &&
  process.env.NODE_ENV !== "production"
) {
  console.warn(
    "[copilotkit/route] LANGGRAPH_DEPLOYMENT_URL is not set; falling back to http://localhost:8125. Set LANGGRAPH_DEPLOYMENT_URL in production.",
  );
}

// LangSmith is optional; warn once at module load so a missing key
// surfaces in logs. When absent we omit the langsmithApiKey field
// entirely rather than passing "" — omitting the field disables
// LangSmith tracing cleanly; passing an empty string may be forwarded
// to the SDK. Gate the warn on NODE_ENV so it does not fire during
// `next build` in CI (same rationale as the DEPLOYMENT_URL warn above).
if (!process.env.LANGSMITH_API_KEY && process.env.NODE_ENV !== "production") {
  console.warn(
    "[copilotkit/route] LANGSMITH_API_KEY is not set; LangSmith tracing is disabled for this session.",
  );
}

// 3. Lazy runtime construction. We build the LangGraphAgent + runtime +
//    handler on the first request rather than at module load, so that
//    `next build` (which evaluates this file with NODE_ENV=production but
//    without runtime env vars) does not bake the fallback localhost URL
//    into the compiled artifact. The cached closure keeps per-request
//    overhead at the same single-allocation cost as the eager form.
// Matches the signature returned by copilotRuntimeNextJSAppRouterEndpoint:
// `(req: Request) => Response | Promise<Response>`. NextRequest extends
// Request, so the POST handler below can still pass its req through
// without an explicit cast.
let cachedHandleRequest:
  | ((req: Request) => Response | Promise<Response>)
  | null = null;

const getHandleRequest = () => {
  if (cachedHandleRequest) return cachedHandleRequest;

  const deploymentUrl = process.env.LANGGRAPH_DEPLOYMENT_URL;
  if (!deploymentUrl && process.env.NODE_ENV === "production") {
    throw new Error(
      "[copilotkit/route] LANGGRAPH_DEPLOYMENT_URL is required in production. " +
        "Set it to the deployed LangGraph endpoint for this starter.",
    );
  }

  const agent = new LangGraphAgent({
    deploymentUrl: deploymentUrl || "http://localhost:8125",
    graphId: "default",
    // Only pass langsmithApiKey when it's a non-empty string; omitting
    // the field disables LangSmith tracing without asking the SDK to
    // authenticate with an empty key.
    ...(process.env.LANGSMITH_API_KEY
      ? { langsmithApiKey: process.env.LANGSMITH_API_KEY }
      : {}),
  });

  // Register the single LangGraph agent under the `default` name, which
  // matches the <CopilotKit agent="default"> prop in layout.tsx. If you
  // need to expose this agent under an additional id (e.g. when pointing
  // a second frontend at this runtime), add another entry here and
  // update the corresponding <CopilotKit agent="..."> prop.
  const runtime = new CopilotRuntime({
    agents: {
      default: agent,
    },
  });

  const { handleRequest } = copilotRuntimeNextJSAppRouterEndpoint({
    runtime,
    serviceAdapter,
    endpoint: "/api/copilotkit",
  });

  cachedHandleRequest = handleRequest;
  return handleRequest;
};

// 4. POST handler. Resolves the cached handler (building it on first
//    request), then dispatches. Wrap in try/catch so unhandled exceptions
//    surface as a structured 500 rather than a raw Next.js error page,
//    and log the failure for observability. Errors inside the streaming
//    response are handled by the runtime itself.
export const POST = async (req: NextRequest) => {
  // Redact `detail` in production: raw error messages can leak
  // internals (stack-adjacent strings, paths, env-var names). Keep
  // the full detail in non-production builds so developers see the
  // real cause locally.
  const isProd = process.env.NODE_ENV === "production";

  // Split construction vs dispatch into two try/catch regions so
  // logs distinguish runtime-construction failures (bad config / env)
  // from dispatch failures inside handleRequest. Response shape is
  // unchanged between the two.
  let handleRequest: (req: Request) => Response | Promise<Response>;
  try {
    handleRequest = getHandleRequest();
  } catch (err) {
    console.error("[copilotkit/route] runtime construction failed:", err);
    return NextResponse.json(
      {
        error: "Internal error while dispatching CopilotKit request.",
        ...(isProd
          ? {}
          : { detail: err instanceof Error ? err.message : String(err) }),
      },
      { status: 500 },
    );
  }

  try {
    return await handleRequest(req);
  } catch (err) {
    console.error("[copilotkit/route] handleRequest dispatch failed:", err);
    return NextResponse.json(
      {
        error: "Internal error while dispatching CopilotKit request.",
        ...(isProd
          ? {}
          : { detail: err instanceof Error ? err.message : String(err) }),
      },
      { status: 500 },
    );
  }
};