refactor: Extract payment link utilities to separate module

- Create paymentLinkUtils.ts with client-safe utility functions
- Move formatAmount, getTimeUntilExpiration, and validation functions
- Update payment link page to use new utility module
- Separate client-side utils from server-side database functions

Author: Adwaitbytes

demo/src/app/pay/[id]/page.tsx

@@ -24,7 +24,7 @@ import {
 } from 'lucide-react';
 import { QRCodeSVG } from 'qrcode.react';
 import { useZkWallet } from '@/hooks/useZkWallet';
-import { formatAmount, getTimeUntilExpiration } from '@/lib/paymentLinks';
+import { formatAmount, getTimeUntilExpiration } from '@/lib/paymentLinkUtils';
 
 interface PaymentLinkData {
   id: string;

demo/src/lib/paymentLinkUtils.ts

@@ -0,0 +1,81 @@
+/**
+ * Payment Link Utility Functions (Client-safe)
+ *
+ * These functions don't require database access and can be used on the client.
+ */
+
+// Format amount for display
+export function formatAmount(amount: string | null, asset: string = 'XLM'): string {
+  if (!amount) return `Any amount (${asset})`;
+  const num = parseFloat(amount);
+  if (isNaN(num)) return amount;
+  return `${num.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 7 })} ${asset}`;
+}
+
+// Check if link is expired
+export function isLinkExpired(expiresAt: string | null): boolean {
+  if (!expiresAt) return false;
+  return new Date(expiresAt) < new Date();
+}
+
+// Get time until expiration
+export function getTimeUntilExpiration(expiresAt: string | null): string | null {
+  if (!expiresAt) return null;
+
+  const now = new Date();
+  const expiry = new Date(expiresAt);
+  const diff = expiry.getTime() - now.getTime();
+
+  if (diff <= 0) return 'Expired';
+
+  const days = Math.floor(diff / (1000 * 60 * 60 * 24));
+  const hours = Math.floor((diff % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
+  const minutes = Math.floor((diff % (1000 * 60 * 60)) / (1000 * 60));
+
+  if (days > 0) return `${days}d ${hours}h`;
+  if (hours > 0) return `${hours}h ${minutes}m`;
+  return `${minutes}m`;
+}
+
+// Validate Stellar address format
+export function isValidStellarAddress(address: string): boolean {
+  if (!address || address.length !== 56) return false;
+  if (!address.startsWith('G')) return false;
+  return /^G[A-Z2-7]{55}$/.test(address);
+}
+
+// Validate amount
+export function isValidAmount(amount: string): boolean {
+  const num = parseFloat(amount);
+  return !isNaN(num) && num > 0 && num <= 100000000000;
+}
+
+// Generate payment link URL
+export function getPaymentLinkUrl(id: string, baseUrl: string): string {
+  return `${baseUrl}/pay/${id}`;
+}
+
+// Generate Stellar URI for wallet apps
+export function getStellarPayUri(
+  recipientAddress: string,
+  amount?: string | null,
+  memo?: string | null,
+  asset?: string
+): string {
+  let uri = `web+stellar:pay?destination=${recipientAddress}`;
+
+  if (amount) {
+    uri += `&amount=${amount}`;
+  }
+
+  if (memo) {
+    uri += `&memo=${encodeURIComponent(memo)}&memo_type=MEMO_TEXT`;
+  }
+
+  if (asset && asset !== 'XLM') {
+    // For non-XLM assets, would need issuer
+    // uri += `&asset_code=${asset}&asset_issuer=...`;
+  }
+
+  return uri;
+}