feat(WHE-21): scaffold grammy webhook bot server

apps/bot/src/server.ts

@@ -0,0 +1,52 @@
+export interface BotWebhookServerOptions {
+  webhookPath: string
+  webhookSecret: string
+  webhookHandler: (request: Request) => Promise<Response> | Response
+}
+
+function json(body: object, status = 200): Response {
+  return new Response(JSON.stringify(body), {
+    status,
+    headers: {
+      'content-type': 'application/json; charset=utf-8'
+    }
+  })
+}
+
+function isAuthorized(request: Request, expectedSecret: string): boolean {
+  const secretHeader = request.headers.get('x-telegram-bot-api-secret-token')
+
+  return secretHeader === expectedSecret
+}
+
+export function createBotWebhookServer(options: BotWebhookServerOptions): {
+  fetch: (request: Request) => Promise<Response>
+} {
+  const normalizedWebhookPath = options.webhookPath.startsWith('/')
+    ? options.webhookPath
+    : `/${options.webhookPath}`
+
+  return {
+    fetch: async (request: Request) => {
+      const url = new URL(request.url)
+
+      if (url.pathname === '/healthz') {
+        return json({ ok: true })
+      }
+
+      if (url.pathname !== normalizedWebhookPath) {
+        return new Response('Not Found', { status: 404 })
+      }
+
+      if (request.method !== 'POST') {
+        return new Response('Method Not Allowed', { status: 405 })
+      }
+
+      if (!isAuthorized(request, options.webhookSecret)) {
+        return new Response('Unauthorized', { status: 401 })
+      }
+
+      return await options.webhookHandler(request)
+    }
+  }
+}