init commit for iPAL-kit plugin

src/modules/i18n/localeMiddleware.ts

@@ -0,0 +1,98 @@
+import type { I18nConfig } from './types.js'
+
+import { isValidLocale, LOCALE_COOKIE_NAME, negotiateLocale } from '../i18n/index.js'
+
+/**
+ * Minimal request shape the middleware reads. Kept structural so the plugin
+ * doesn't hard-depend on next/server types; a Next.js `NextRequest` satisfies it.
+ */
+type MiddlewareRequest = {
+  cookies: { get: (name: string) => { value: string } | undefined }
+  headers: { get: (name: string) => null | string }
+  nextUrl: { clone: () => URL; pathname: string; search: string }
+  url: string
+}
+
+/**
+ * What the factory returns — the caller (in Next next-middleware.ts) decides how to
+ * act: `redirect` means send a 307 to `location` and set the locale cookie;
+ * `next` means let the request pass through untouched.
+ */
+export type LocaleMiddlewareResult =
+  { cookie: { name: string; value: string }; location: string; type: 'redirect' } | { type: 'next' }
+
+type CreateLocaleMiddlewareArgs = {
+  config: I18nConfig
+  /** Cookie name for the locale choice. Defaults to LOCALE_COOKIE_NAME. */
+  cookieName?: string
+}
+
+/**
+ * First path segment of a URL pathname, or '' for root.
+ * '/pl/o-nas' → 'pl', '/o-nas' → 'o-nas', '/' → ''.
+ */
+function firstSegment(pathname: string): string {
+  return pathname.split('/').filter(Boolean)[0] ?? ''
+}
+
+/**
+ * Builds locale-routing logic for Next.js middleware.
+ *
+ * Behavior:
+ *  - path already starts with a valid locale (/pl/...) → pass through
+ *  - any other path (/, /o-nas) → redirect to /{locale}{path}, where locale
+ *    comes from negotiateLocale (cookie → Accept-Language → default)
+ *  - the chosen locale is written to a cookie so the next visit is stable
+ *
+ * The plugin returns a decision; the thin next-middleware.ts in the client project
+ * turns it into a NextResponse. This keeps all logic in the plugin while
+ * respecting that next-middleware.ts must physically live in the client app.
+ *
+ * @example
+ * // next-middleware.ts (client project) — one wiring file, no logic:
+ * import { NextResponse } from 'next/server'
+ * import { localeMiddleware } from './ipal.middleware' // created from this factory
+ * export function middleware(req) {
+ *   const r = localeMiddleware(req)
+ *   if (r.type === 'next') return NextResponse.next()
+ *   const res = NextResponse.redirect(r.location)
+ *   res.cookies.set(r.cookie.name, r.cookie.value)
+ *   return res
+ * }
+ */
+export function createLocaleMiddleware({
+  config,
+  cookieName = LOCALE_COOKIE_NAME,
+}: CreateLocaleMiddlewareArgs) {
+  return function localeMiddleware(request: MiddlewareRequest): LocaleMiddlewareResult {
+    const { pathname } = request.nextUrl
+
+    // Already locale-prefixed → nothing to do
+    if (isValidLocale(firstSegment(pathname), config)) {
+      return { type: 'next' }
+    }
+
+    // Resolve the locale to use
+    const locale = negotiateLocale({
+      acceptLanguage: request.headers.get('accept-language'),
+      config,
+      cookieLocale: request.cookies.get(cookieName)?.value ?? null,
+    })
+
+    // Redirect to the locale-prefixed path, preserving the rest
+    const url = request.nextUrl.clone()
+    url.pathname = `/${locale}${pathname === '/' ? '' : pathname}`
+
+    return {
+      type: 'redirect',
+      cookie: { name: cookieName, value: locale },
+      location: url.toString(),
+    }
+  }
+}
+
+/**
+ * Default Next.js middleware matcher: run on everything except API routes, the
+ * admin panel, Next internals, and files with an extension (static assets).
+ */
+export const DEFAULT_MIDDLEWARE_MATCHER = ['/((?!api|admin|_next|.*\\..*).*)']