# @wrnexus/router

> File-based router that maps an `app/` directory onto route tables and matches request paths against them.

Part of the **WrNexus** framework — an SSR-first, Bun-native full-stack web framework.

## Overview

`@wrnexus/router` scans an application's `app/` directory once at startup and builds route tables for pages, API endpoints, realtime channels, middleware, server-rendered `.wrn` components, layouts, and validation schemas. It also compiles URL patterns (`/users/[id]`) into RegExps and matches request paths against them. Request input is never turned into a file path, which makes the router immune to path traversal. This is a server-side package used by the WrNexus runtime to resolve incoming requests, plus a codegen helper for compile-time typed links.

## Installation

```bash
bun add @wrnexus/router
```

> Private package — the machine must be authenticated to the `wrnexus` npm org
> (a read token in `~/.npmrc`). Requires **Bun** (Node is not supported).

## Directory conventions

The router maps files under `appDir` onto routes:

```
app/pages/index.tsx        -> GET /
app/pages/about.tsx        -> GET /about
app/pages/users/[id].tsx   -> GET /users/:id
app/api/hello.ts           -> /api/hello
app/realtime/chat.ts       -> /realtime/chat
app/pages/*.wrn  (api)    -> embedded /api/* routes
app/pages/*.wrn  (rt)     -> embedded /realtime/* routes
app/middleware/*.ts        -> global middleware (alphabetical)
app/components/*.wrn      -> server-rendered components (by basename)
app/layouts/*.wrn         -> named page layouts
app/schemas/*.ts           -> validation schemas
```

Allowed route extensions are `.ts`, `.tsx`, and `.wrn`. Dotfiles and underscore-prefixed files are ignored. A trailing `index` segment is dropped from the route. `.wrn` pages may embed `api` and `realtime` blocks, which the router extracts and mounts under `/api/*` and `/realtime/*`.

## API

### `buildRouter(appDir, opts?): Router`

Scan an app directory and build all route tables.

```ts
function buildRouter(appDir: string, opts?: RouterOptions): Router;

interface RouterOptions {
  /** Extra dirs scanned for `.wrn` components (e.g. `@wrnexus/ui`), before
   *  `app/components`, so an app component of the same name wins. */
  componentDirs?: string[];
}
```

The returned `Router` exposes the built tables plus per-kind matchers:

```ts
interface Router {
  pages: Route[];
  api: Route[];
  realtime: Route[];
  /** Absolute paths of middleware modules, in execution order (alphabetical). */
  middlewareFiles: string[];
  /** Server-rendered `.wrn` components, mounted via `data-component`. */
  components: ComponentRef[];
  /** Named page layouts (`app/layouts/<name>.wrn`); a page picks one via `layout`. */
  layouts: ComponentRef[];
  /** Validation schemas (`app/schemas/<name>.ts`) shared by API + forms. */
  schemas: ComponentRef[];
  matchPage(pathname: string): RouteMatch | null;
  matchApi(pathname: string): RouteMatch | null;
  matchRealtime(pathname: string): RouteMatch | null;
}

interface ComponentRef {
  /** Validated component name (matches a `data-component` attribute). */
  name: string;
  /** Absolute path to the component's `.wrn` module. */
  file: string;
}
```

Component, layout, and schema names are validated with `isSafeIslandName` from `@wrnexus/core`; unsafe names are skipped with a warning. Realtime channel names are validated the same way.

### Route matching

| Export                | Signature                                                   | Description                                                                                                         |
| --------------------- | ----------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------- |
| `compileRoutePattern` | `(raw: string) => Pick<Route, "regex" \| "paramNames">`     | Compile a `/users/[id]` pattern into a RegExp (with optional trailing slash) plus ordered param names.              |
| `matchRoute`          | `(routes: Route[], pathname: string) => RouteMatch \| null` | Return the first route whose regex matches; captured params are `decodeURIComponent`-decoded.                       |
| `sortRoutes`          | `(routes: Route[]) => Route[]`                              | Order routes so static routes win over dynamic ones (fewer params first), then longer/more specific patterns first. |

```ts
interface Route {
  raw: string; // e.g. "/users/[id]"
  file: string; // absolute path to the handling module
  regex: RegExp; // compiled matcher
  paramNames: string[]; // ordered dynamic param names
}

interface RouteMatch {
  route: Route;
  params: Record<string, string>;
}
```

### Typed-routes codegen

```ts
function generateRoutesFile(pages: Route[]): string;
```

Emits the source for `app/routes.gen.ts`: a `Routes` map (each page path → its `[param]` types), a `RoutePath` union, and an `href()` builder that fills params and rejects unknown paths at compile time. Entries are de-duplicated and sorted by path.

### Re-exports

`Middleware` (the type from `@wrnexus/core`) is re-exported for callers that load middleware modules themselves.

## Usage

```ts
import { buildRouter } from "@wrnexus/router";

const router = buildRouter("./app", {
  componentDirs: ["./node_modules/@wrnexus/ui/components"],
});

// Resolve an incoming request.
const match = router.matchPage("/users/42");
if (match) {
  console.log(match.route.file); // absolute path to the page module
  console.log(match.params); // { id: "42" }
}

const api = router.matchApi("/api/hello");
const rt = router.matchRealtime("/realtime/chat");
```

Generating the typed-routes file (as `wrnexus dev` does):

```ts
import { generateRoutesFile } from "@wrnexus/router";
import { writeFileSync } from "node:fs";

const router = buildRouter("./app");
writeFileSync("./app/routes.gen.ts", generateRoutesFile(router.pages));
```

```ts
// Then, in app code, links are checked at compile time:
import { href } from "./routes.gen.ts";

href("/users/[id]", { id: "42" }); // "/users/42"
href("/about"); // "/about"
href("/nope"); // type error: unknown path
```

Lower-level pattern matching, if you need it directly:

```ts
import { compileRoutePattern, matchRoute, sortRoutes, type Route } from "@wrnexus/router";

const { regex, paramNames } = compileRoutePattern("/posts/[slug]");
const routes = sortRoutes([{ raw: "/posts/[slug]", file: "…", regex, paramNames }]);
const m = matchRoute(routes, "/posts/hello"); // { route, params: { slug: "hello" } }
```

## Requirements / Notes

- Scanning uses `node:fs` (`existsSync`, `readdirSync`, `statSync`) and `node:path` — runs under Bun.
- Depends on [`@wrnexus/compiler`](../compiler) to `parse` `.wrn` pages and extract embedded `api` / `realtime` blocks.
- Depends on [`@wrnexus/core`](../core) for `isSafeIslandName` (name validation) and the `Middleware` type.
- Missing route directories are tolerated — a route kind you don't use simply yields an empty table.
