feat: add refund module (TC-4)

CHANGELOG.md

@@ -12,3 +12,5 @@ All notable changes to this project will be documented in this file.
 - Config module: database configuration by environment
 - Production config YAML
 - Watchflow governance rules
+
+tried tc-4

src/payments/refund.js

@@ -0,0 +1,49 @@
+/**
+ * refund.js — Refund processing
+ */
+
+const REFUND_REASONS = ['duplicate', 'fraudulent', 'customer_request', 'product_issue'];
+const REFUND_STATUSES = ['pending', 'approved', 'rejected', 'processed'];
+
+function createRefund({ orderId, amount, reason, requestedBy } = {}) {
+  if (!orderId) throw new TypeError('orderId is required');
+  if (typeof amount !== 'number' || amount <= 0) throw new RangeError('amount must be a positive number');
+  if (!REFUND_REASONS.includes(reason)) throw new RangeError(`reason must be one of: ${REFUND_REASONS.join(', ')}`);
+  if (!requestedBy) throw new TypeError('requestedBy is required');
+
+  return {
+    id: `ref_${Date.now()}`,
+    orderId,
+    amount: parseFloat(amount.toFixed(2)),
+    reason,
+    requestedBy,
+    status: 'pending',
+    createdAt: new Date().toISOString(),
+    updatedAt: new Date().toISOString(),
+  };
+}
+
+function approveRefund(refund, approvedBy) {
+  if (refund.status !== 'pending') throw new Error(`Cannot approve a refund in status: ${refund.status}`);
+  return { ...refund, status: 'approved', approvedBy, updatedAt: new Date().toISOString() };
+}
+
+function rejectRefund(refund, rejectedBy, rejectionNote = '') {
+  if (refund.status !== 'pending') throw new Error(`Cannot reject a refund in status: ${refund.status}`);
+  return { ...refund, status: 'rejected', rejectedBy, rejectionNote, updatedAt: new Date().toISOString() };
+}
+
+function processRefund(refund) {
+  if (refund.status !== 'approved') throw new Error('Only approved refunds can be processed');
+  return { ...refund, status: 'processed', processedAt: new Date().toISOString(), updatedAt: new Date().toISOString() };
+}
+
+function isFullRefund(refund, originalAmount) {
+  return refund.amount >= originalAmount;
+}
+
+function summarize(refund) {
+  return `Refund ${refund.id}: $${refund.amount.toFixed(2)} for order ${refund.orderId} [${refund.status}] — ${refund.reason}`;
+}
+
+module.exports = { createRefund, approveRefund, rejectRefund, processRefund, isFullRefund, summarize, REFUND_REASONS, REFUND_STATUSES };