runtime-config.ts

// Server-side runtime config for the showcase shell.
//
// This module reads URL / analytics env values at REQUEST time. It must
// only be imported from server components (and from middleware via the
// Edge-safe wrapper below). Importing it from a client component would
// cause Next.js to inline `next/cache` into the client bundle (build
// fails) and would freeze the URLs back into the artifact — defeating
// the runtime switch. See Next.js App Router docs on Dynamic Rendering.
//
// This module MUST NOT be imported from client components. The matching
// client-side reader lives in runtime-config.client.ts and reads from
// window.__SHOWCASE_CONFIG__ which the root layout injects.

import { unstable_noStore as noStore } from "next/cache";

export interface RuntimeConfig {
  /** Canonical shell base URL — used for canonical hrefs, OG metadata, etc. */
  baseUrl: string;
  /** PostHog host — middleware ships seo_redirect events here. */
  posthogHost: string;
}

const PROD_INVALID_BASE_URL = "about:blank#shell-base-url-missing";

/**
 * Resolve the runtime config for shell. Called once per request by the
 * root layout and by middleware (via the Edge wrapper below).
 *
 * Fail-loud strategy mirrors shell-dashboard: in production, missing
 * URL env vars produce sentinel URLs (visible breakage) AND a
 * console.error; in dev, we fall back to localhost so iteration is
 * frictionless. Analytics keys (posthogHost) use the dev fallback
 * unconditionally — historic POSTHOG_HOST default is the EU cloud.
 *
 * `opts.noStore` (default `true`) controls whether to call
 * `unstable_noStore()`. The Node.js server runtime needs the opt-out so
 * Next.js does not statically prerender callers and freeze the URLs into
 * the build artifact. The Edge runtime (middleware) MUST pass
 * `{ noStore: false }` — `unstable_noStore()` is unavailable there, and
 * middleware always runs per-request by definition so there is no
 * static cache to opt out of. The thin `getRuntimeConfigForMiddleware()` wrapper
 * below makes this explicit at the call site.
 */
export function getRuntimeConfig(
  opts: { noStore?: boolean } = {},
): RuntimeConfig {
  if (opts.noStore !== false) noStore();
  const isProd = process.env.NODE_ENV === "production";

  const baseUrl = readUrl(
    "BASE_URL",
    isProd ? PROD_INVALID_BASE_URL : "http://localhost:3000",
    isProd,
  );
  // PostHog host: legitimately absent on non-production deploys; never
  // log a FATAL-CONFIG for it. The historic default (`eu.i.posthog.com`)
  // matches the previous middleware behavior.
  const posthogHost = readKey("POSTHOG_HOST", "https://eu.i.posthog.com");

  return { baseUrl, posthogHost };
}

/**
 * Edge-runtime variant. Identical semantics to `getRuntimeConfig()`
 * except `unstable_noStore()` is skipped — `next/cache`'s no-store
 * helper is not available in the Edge runtime, and middleware always
 * runs per-request by definition so there is no static cache to opt
 * out of. Thin wrapper to keep the body single-sourced.
 *
 * Middleware (`src/middleware.ts`) MUST import this rather than
 * `getRuntimeConfig` — otherwise the Edge bundle pulls in `next/cache`
 * and the build fails with "module not found in edge runtime."
 */
export function getRuntimeConfigForMiddleware(): RuntimeConfig {
  return getRuntimeConfig({ noStore: false });
}

// Env-name tolerance: deploy configs in the wild use either the bare
// name (e.g. `BASE_URL`) or the `NEXT_PUBLIC_*`-prefixed name. We accept
// either — the primary (passed-in) name wins, with transparent fallback
// to the alternate so a Railway service variable set under the "wrong"
// name still works without redeploy.
function altEnvName(envKey: string): string {
  return envKey.startsWith("NEXT_PUBLIC_")
    ? envKey.slice("NEXT_PUBLIC_".length)
    : `NEXT_PUBLIC_${envKey}`;
}

// Length-aware env coalesce: a deliberately-empty primary (e.g. an
// operator clearing `BASE_URL=""` on a Railway service) must NOT mask a
// populated alternate. Treat empty-string as "unset" and fall through to
// the alternate.
function readEnvPair(envKey: string): string | undefined {
  const primary = process.env[envKey];
  if (primary && primary.length > 0) return primary;
  const alt = process.env[altEnvName(envKey)];
  if (alt && alt.length > 0) return alt;
  return undefined;
}

function readUrl(envKey: string, fallback: string, isProd: boolean): string {
  const value = readEnvPair(envKey);
  if (value !== undefined) return value.replace(/\/+$/, "");
  if (isProd) {
    // eslint-disable-next-line no-console
    console.error(
      `[shell runtime-config] FATAL-CONFIG: ${envKey} is unset in a production deploy; ` +
        `using sentinel ${fallback}. Set the env var on the Railway service.`,
    );
  } else {
    // eslint-disable-next-line no-console
    console.warn(
      `[shell runtime-config] ${envKey} unset; using dev fallback ${fallback}`,
    );
  }
  return fallback.replace(/\/+$/, "");
}

// Analytics keys (POSTHOG_HOST etc.) are legitimately absent on
// non-production envs; do NOT log a FATAL-CONFIG warning when missing.
function readKey(envKey: string, fallback: string): string {
  const value = readEnvPair(envKey);
  if (value !== undefined) return value.replace(/\/+$/, "");
  return fallback.replace(/\/+$/, "");
}