refactor: Extract common provider utilities to reduce duplication

- Create shared utilities module for payment providers
- Add webhook response helpers for consistent API responses
- Extract common database operations (find payment, update status)
- Implement shared invoice update logic
- Add consistent error handling and logging utilities
- Refactor Mollie provider to use shared utilities
- Refactor Stripe provider to use shared utilities
- Remove duplicate code between providers

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/providers/utils.ts

@@ -0,0 +1,115 @@
+import type { Payload } from 'payload'
+import type { Payment } from '@/plugin/types/payments'
+import type { BillingPluginConfig } from '@/plugin/config'
+import { defaults } from '@/plugin/config'
+import { extractSlug } from '@/plugin/utils'
+
+/**
+ * Common webhook response utilities
+ */
+export const webhookResponses = {
+  success: () => Response.json({ received: true }, { status: 200 }),
+  error: (message: string, status = 400) => Response.json({ error: message }, { status }),
+  missingBody: () => Response.json({ error: 'Missing request body' }, { status: 400 }),
+  paymentNotFound: () => Response.json({ error: 'Payment not found' }, { status: 404 }),
+  invalidPayload: () => Response.json({ error: 'Invalid webhook payload' }, { status: 400 }),
+}
+
+/**
+ * Find a payment by provider ID
+ */
+export async function findPaymentByProviderId(
+  payload: Payload,
+  providerId: string,
+  pluginConfig: BillingPluginConfig
+): Promise<Payment | null> {
+  const paymentsCollection = extractSlug(pluginConfig.collections?.payments || defaults.paymentsCollection)
+
+  const payments = await payload.find({
+    collection: paymentsCollection,
+    where: {
+      providerId: {
+        equals: providerId
+      }
+    }
+  })
+
+  return payments.docs.length > 0 ? payments.docs[0] as Payment : null
+}
+
+/**
+ * Update payment status and provider data
+ */
+export async function updatePaymentStatus(
+  payload: Payload,
+  paymentId: string | number,
+  status: Payment['status'],
+  providerData: any,
+  pluginConfig: BillingPluginConfig
+): Promise<void> {
+  const paymentsCollection = extractSlug(pluginConfig.collections?.payments || defaults.paymentsCollection)
+
+  await payload.update({
+    collection: paymentsCollection,
+    id: paymentId,
+    data: {
+      status,
+      providerData
+    }
+  })
+}
+
+/**
+ * Update invoice status when payment succeeds
+ */
+export async function updateInvoiceOnPaymentSuccess(
+  payload: Payload,
+  payment: Payment,
+  pluginConfig: BillingPluginConfig
+): Promise<void> {
+  if (!payment.invoice) return
+
+  const invoicesCollection = extractSlug(pluginConfig.collections?.invoices || defaults.invoicesCollection)
+  const invoiceId = typeof payment.invoice === 'object'
+    ? payment.invoice.id
+    : payment.invoice
+
+  await payload.update({
+    collection: invoicesCollection,
+    id: invoiceId,
+    data: {
+      status: 'paid',
+      payment: payment.id
+    }
+  })
+}
+
+/**
+ * Handle webhook errors with consistent logging
+ */
+export function handleWebhookError(
+  provider: string,
+  error: unknown,
+  context?: string
+): Response {
+  const message = error instanceof Error ? error.message : 'Unknown error'
+  const fullContext = context ? `[${provider} Webhook - ${context}]` : `[${provider} Webhook]`
+
+  console.error(`${fullContext} Error:`, error)
+
+  return Response.json({
+    error: 'Webhook processing failed',
+    details: message
+  }, { status: 500 })
+}
+
+/**
+ * Log webhook events
+ */
+export function logWebhookEvent(
+  provider: string,
+  event: string,
+  details?: any
+): void {
+  console.log(`[${provider} Webhook] ${event}`, details ? JSON.stringify(details) : '')
+}