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backend/middleware/auditLogger.js

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+const AuditLog = require('../models/AuditLog');
+
+/**
+ * Middleware to log data changes to audit_logs table
+ *
+ * Usage:
+ * const { captureAuditLog } = require('../middleware/auditLogger');
+ *
+ * router.put('/endpoint/:id', async (req, res) => {
+ *   const oldData = await Model.getById(id); // Fetch current data before update
+ *
+ *   // Perform update
+ *   const newData = await Model.update(id, req.body);
+ *
+ *   // Log the change
+ *   await captureAuditLog('table_name', id, 'UPDATE', oldData, newData);
+ *
+ *   res.json({ success: true, data: newData });
+ * });
+ */
+
+/**
+ * Capture audit log for a data change
+ * @param {string} tableName - Name of the table being modified
+ * @param {string|number} recordId - ID of the record being modified
+ * @param {string} action - Action type: CREATE, UPDATE, DELETE
+ * @param {Object} oldValues - Previous values (null for CREATE)
+ * @param {Object} newValues - New values (null for DELETE)
+ * @returns {Promise<Object>} Created audit log entry
+ */
+async function captureAuditLog(tableName, recordId, action, oldValues = null, newValues = null) {
+    try {
+        // Determine which fields changed
+        const changedFields = [];
+
+        if (action === 'UPDATE' && oldValues && newValues) {
+            // Compare old and new values to find changed fields
+            for (const key in newValues) {
+                if (oldValues.hasOwnProperty(key)) {
+                    // Handle different types of values
+                    const oldVal = oldValues[key];
+                    const newVal = newValues[key];
+
+                    // Deep comparison for objects/arrays, simple comparison otherwise
+                    if (JSON.stringify(oldVal) !== JSON.stringify(newVal)) {
+                        changedFields.push(key);
+                    }
+                }
+            }
+        }
+
+        // Only log if there are actual changes (for UPDATE) or always for CREATE/DELETE
+        if (action !== 'UPDATE' || changedFields.length > 0) {
+            return await AuditLog.create(
+                tableName,
+                recordId,
+                action,
+                oldValues,
+                newValues,
+                changedFields
+            );
+        }
+
+        return null; // No changes to log
+    } catch (error) {
+        // Log error but don't fail the main operation
+        console.error('Error capturing audit log:', error);
+        return null;
+    }
+}
+
+/**
+ * Helper to extract only relevant fields for logging
+ * (excludes timestamps and internal fields)
+ * @param {Object} data - Data object
+ * @param {string[]} excludeFields - Fields to exclude (default: created_at, updated_at)
+ * @returns {Object} Filtered data object
+ */
+function filterAuditFields(data, excludeFields = ['created_at', 'updated_at']) {
+    if (!data) return null;
+
+    const filtered = { ...data };
+    excludeFields.forEach(field => {
+        delete filtered[field];
+    });
+
+    return filtered;
+}
+
+module.exports = {
+    captureAuditLog,
+    filterAuditFields
+};