feat: Add activity logging for pay code registrations

.env.sample

@@ -32,3 +32,7 @@ MDK_MNEMONIC="your_mnemonic_here"
 # LND_PORT="" # ex. 8082
 # LND_MACAROON="" # base64 invoices macaroon
 # LND_TLS_CERT="" # base64
+
+# Activity Logging (optional)
+# Webhook URL for logging pay code registrations (e.g., Discord webhook)
+# ACTIVITY_WEBHOOK_URL=""

src/lib/notifications.ts

@@ -0,0 +1,45 @@
+/**
+ * Activity logging utilities for monitoring pay code registrations.
+ * Supports optional webhook notifications.
+ */
+
+type PayCodeType = "free" | "paid";
+
+interface ActivityLogOptions {
+  type: PayCodeType;
+  domain: string;
+}
+
+/**
+ * Logs pay code registration activity to configured webhook (if set).
+ * Privacy-preserving: only logs type and domain, not usernames.
+ */
+export async function logPayCodeActivity(
+  options: ActivityLogOptions
+): Promise<void> {
+  const webhookUrl = process.env.ACTIVITY_WEBHOOK_URL;
+
+  if (!webhookUrl) {
+    // Webhook not configured, skip silently
+    return;
+  }
+
+  const emoji = options.type === "free" ? "🆓" : "💰";
+  const label = options.type === "free" ? "Free" : "Paid";
+  const message = `${emoji} ${label} PayCode registered on ${options.domain}`;
+
+  try {
+    await fetch(webhookUrl, {
+      method: "POST",
+      headers: {
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({
+        content: message,
+      }),
+    });
+  } catch (error) {
+    // Log error but don't throw - notifications are non-critical
+    console.error("Failed to send activity notification:", error);
+  }
+}

src/server/api/routers/payCode.ts

@@ -14,6 +14,7 @@ import {
   createBip21FromParams,
   createPayCodeParams,
 } from "@/lib/util";
+import { logPayCodeActivity } from "@/lib/notifications";
 import axios from "axios";
 import {
   adjectives,
@@ -196,6 +197,9 @@ export const payCodeRouter = createTRPCRouter({
       });
       // TODO: catch and throw again?
 
+      // Log activity (non-blocking, fire-and-forget)
+      logPayCodeActivity({ type: "free", domain: input.domain });
+
       return payCode;
     }),
 
@@ -481,6 +485,9 @@ export const payCodeRouter = createTRPCRouter({
           });
         });
 
+      // Log activity (non-blocking, fire-and-forget)
+      logPayCodeActivity({ type: "paid", domain: payCode.domain });
+
       return payCode;
     }),