feat: Add email subscription check before saving

This commit adds a check to ensure that the email being subscribed is not already present in the database. If the email is already subscribed, an error is thrown. This enhancement improves the data integrity and prevents duplicate email subscriptions.

src/pages/api/subscribe.ts

@@ -1,5 +1,5 @@
 import type { APIRoute } from 'astro';
-import { db, Subscribers } from 'astro:db';
+import { db, like, Subscribers } from 'astro:db';
 
 import arcjet, { validateEmail } from "@arcjet/node";
 import type { ArcjetNodeRequest } from "@arcjet/node";
@@ -40,8 +40,6 @@ export const POST: APIRoute = async ({ params, request }) => {
                 email: json.email,
             });
 
-            console.log("Arcjet decision", decision);
-
             if (decision.isDenied()) {
                 return new Response(JSON.stringify({ ok: false, reason: decision.reason }), {
                     status: 400,
@@ -50,6 +48,13 @@ export const POST: APIRoute = async ({ params, request }) => {
                     }
                 });
             } else {
+                // check if the email is already subscribed
+                const existing = await db.select().from(Subscribers).where(like(Subscribers.email, json.email));
+
+                if (existing.length > 0) {
+                    throw new Error("Email already subscribed");
+                }
+
                 // Save the email to the database
                 await db.insert(Subscribers).values({
                     name: json.name,