Improve and update billing flow

This commit updates various components in the billing flow due to a new schema that supports multiple line items per plan. The added flexibility rendered 'line-items-mapper.ts' redundant, which has been removed. Additionally, webhooks have been created for handling account membership insertions and deletions, as well as handling subscription deletions when an account is deleted. This message also introduces a new service to handle sending out invitation emails. Lastly, the validation of the billing provider has been improved for increased security and stability.

packages/database-webhooks/src/server/services/database-webhook-handler.service.ts

@@ -0,0 +1,43 @@
+import { Logger } from '@kit/shared/logger';
+import { getSupabaseRouteHandlerClient } from '@kit/supabase/route-handler-client';
+
+import { RecordChange, Tables } from '../record-change.type';
+import { DatabaseWebhookRouterService } from './database-webhook-router.service';
+
+export class DatabaseWebhookHandlerService {
+  private readonly namespace = 'database-webhook-handler';
+
+  async handleWebhook(request: Request, webhooksSecret: string) {
+    Logger.info(
+      {
+        name: this.namespace,
+      },
+      'Received webhook from DB. Processing...',
+    );
+
+    // check if the signature is valid
+    this.assertSignatureIsAuthentic(request, webhooksSecret);
+
+    const json = await request.json();
+
+    await this.handleWebhookBody(json);
+  }
+
+  private handleWebhookBody(body: RecordChange<keyof Tables>) {
+    const client = getSupabaseRouteHandlerClient({
+      admin: true,
+    });
+
+    const service = new DatabaseWebhookRouterService(client);
+
+    return service.handleWebhook(body);
+  }
+
+  private assertSignatureIsAuthentic(request: Request, webhooksSecret: string) {
+    const header = request.headers.get('X-Supabase-Event-Signature');
+
+    if (header !== webhooksSecret) {
+      throw new Error('Invalid signature');
+    }
+  }
+}