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
};