Sfs 1755 generate middleware in build time (#2540)

## What's the purpose of this pull request?

This task will allow enabling the redirects middleware within
**@faststore/core** during the build process based on a flag.

The idea is to enable this functionality only for projects that have the
flag `ENABLE_REDIRECTS_MIDDLEWARE` saved in the env vars and which are
hosted by homebrew. In the future, we intend to have control of this
feature through webops.

Next steps: 

- Set this flag in a pipeline env var.
- Implements dynamoDB client (Reference:
#2517)

## How it works?

The key is the name of the file: **middleware__DISABLED.ts**

This middleware is disabled by default. Only stores that are in
**homebrew** and want this functionality will be able to enable it via a
feature flag. When the flag is active, the CLI at build time will check
whether the **ENABLE_REDIRECTS_MIDDLEWARE** flag is set or not, if so,
the file name will be changed to **middleware.ts** and nextjs will know
how to automatically deal with it.

## How to test it?
I created a [PR](vtex-sites/starter.store#599)
with the flag enabled, clone the branch and then:

- Run `yarn build`
- check if the **middleware.ts** was created inside **.faststore/src**

### References


https://docs.google.com/document/d/1iC1fLwJbypnvDyp_JilKBfQfaHjFDHYrjS1kC722sB4/edit?tab=t.0#heading=h.tglo77yl0lf5

packages/cli/src/utils/generate.ts

@@ -437,6 +437,40 @@ function validateAndInstallMissingDependencies(basePath: string) {
   })
 }
 
+// TODO: Read the value from an environment variable
+const ENABLE_REDIRECTS_MIDDLEWARE = false
+
+// Enable redirects middleware by renaming the file from middleware__DISABLED.ts to middleware.tsß
+function enableRedirectsMiddleware(basePath: string) {
+  if (!ENABLE_REDIRECTS_MIDDLEWARE) {
+    return
+  }
+
+  try {
+    const { tmpDir } = withBasePath(basePath)
+
+    const disabledMiddlewarePath = path.join(
+      tmpDir,
+      'src',
+      'middleware__DISABLED.ts'
+    )
+
+    /* Rename the file to enable middleware functionality and then remove the disabled middleware file */
+    if (existsSync(disabledMiddlewarePath)) {
+      const enabledMiddlewarePath = path.join(tmpDir, 'src', 'middleware.ts')
+      copyFileSync(disabledMiddlewarePath, enabledMiddlewarePath)
+      removeSync(disabledMiddlewarePath)
+
+      logger.log(
+        `${chalk.green('success')} Redirects middleware has been enabled`
+      )
+    }
+  } catch (error) {
+    logger.error(error)
+    throw error
+  }
+}
+
 export async function generate(options: GenerateOptions) {
   const { basePath, setup = false } = options
 
@@ -461,5 +495,6 @@ export async function generate(options: GenerateOptions) {
     copyTheme(basePath),
     createCmsWebhookUrlsJsonFile(basePath),
     updateNextConfig(basePath),
+    enableRedirectsMiddleware(basePath),
   ])
 }

packages/core/src/middleware__DISABLED.ts

@@ -0,0 +1,65 @@
+/*
+ * This middleware is disabled by default. Only stores that are in
+ * homebrew and want this functionality will be able to enable it via
+ * a feature flag. When the flag is active, the CLI at build time will
+ * check whether the ENABLE_REDIRECTS_MIDDLEWARE flag is set or not,
+ * if so, the file name will be changed to middleware.ts and nextjs
+ * will know how to automatically deal with it.
+ */
+
+import { NextResponse } from 'next/server'
+import type { NextRequest } from 'next/server'
+import storeConfig from 'discovery.config'
+
+type Redirect = {
+  from: string
+  to: string
+  type: 'permanent' | 'temporary'
+}
+interface RedirectsClient {
+  get(from: string): Promise<Redirect | null>
+}
+
+class DynamoRedirectsClient implements RedirectsClient {
+  async get(from: string): Promise<Redirect | null> {
+    // TODO: Implement DynamoDB client. Ensure that the cluster has access to DynamoDB first.
+    return null
+  }
+}
+
+const redirectsClient = new DynamoRedirectsClient()
+
+export async function middleware(request: NextRequest) {
+  const { pathname } = request.nextUrl
+
+  const redirect = await redirectsClient.get(pathname)
+
+  if (redirect) {
+    const redirectUrl = new URL(redirect.to, storeConfig.storeUrl)
+    const redirectStatusCode = redirect.type === 'permanent' ? 301 : 302
+
+    const response = NextResponse.redirect(redirectUrl, redirectStatusCode)
+
+    response.headers.set(
+      'Cache-Control',
+      'public, max-age=300, stale-while-revalidate=31536000'
+    )
+
+    return response
+  }
+
+  return NextResponse.next()
+}
+
+export const config = {
+  matcher: [
+    /*
+     * Match all request paths except for the ones starting with:
+     * - api (API routes)
+     * - _next/static (static files)
+     * - _next/image (image optimization files)
+     * - favicon.ico (favicon file)
+     */
+    '/((?!api|_next/static|_next/image|favicon.ico).*)',
+  ],
+}