# Email Notification System - Robustness Documentation

## Overview
Sistem email notification yang sangat robust dengan error handling yang komprehensif, retry mechanism, dan transaction safety untuk memastikan tidak ada data yang rusak.

## Fitur Robustness yang Diimplementasikan

### 1. **Email Validation**
- ✅ Validasi format email dengan regex sebelum mengirim
- ✅ Filter email yang tidak valid dari recipients
- ✅ Error handling jika tidak ada valid recipients

### 2. **Retry Mechanism dengan Exponential Backoff**
- ✅ Retry hingga 3 kali (configurable)
- ✅ Exponential backoff: delay meningkat dengan setiap retry (5s, 10s, 20s)
- ✅ Smart retry: hanya retry untuk error yang retryable (network, timeout, server errors)
- ✅ Non-retryable errors: invalid email, authentication errors langsung stop

### 3. **Timeout Handling**
- ✅ Connection timeout: 30 detik
- ✅ Greeting timeout: 30 detik
- ✅ Socket timeout: 30 detik
- ✅ Email send timeout: 30 detik dengan Promise.race

### 4. **Transaction Safety**
- ✅ Email notification tidak memblokir workflow transaction
- ✅ Error handling di workflow service dengan try-catch terpisah
- ✅ Transaction rollback hanya untuk validation errors, bukan email failures
- ✅ History email tetap tercatat meskipun email gagal

### 5. **Error Handling**
- ✅ Comprehensive error handling di setiap layer
- ✅ Error logging yang detail untuk debugging
- ✅ Error messages yang informatif
- ✅ Graceful degradation: sistem tetap berjalan meskipun email gagal

### 6. **Data Validation**
- ✅ Parameter validation sebelum processing
- ✅ Email template validation
- ✅ HTML content validation
- ✅ Subject length validation (max 255 chars)
- ✅ Body length truncation untuk database compatibility

### 7. **Attachment Handling**
- ✅ File existence check sebelum attach
- ✅ Error handling jika file tidak ditemukan
- ✅ Continue tanpa attachment jika file access fails

### 8. **History Tracking**
- ✅ History email untuk setiap recipient (to, cc, bcc)
- ✅ Status tracking: sent, failed, pending
- ✅ Error message tracking (truncated to 255 chars)
- ✅ Robust error handling untuk history creation

### 9. **Email Account Configuration**
- ✅ Validation sebelum create transporter
- ✅ Error handling jika email account tidak ditemukan
- ✅ Configurable per company

### 10. **Template Safety**
- ✅ Template loading dengan error handling
- ✅ Template output validation
- ✅ Fallback values untuk missing data
- ✅ Safe date formatting dengan error handling

## Modul yang Didukung

### 1. **PKWT Notifications**
- ✅ Email expiration reminder
- ✅ Additional recipients support
- ✅ Template email professional

### 2. **Absence Clarification**
- ✅ Need Approval email
- ✅ Approved email
- ✅ Rejected email
- ✅ Revised email
- ✅ Cancelled email

### 3. **Permit Ease**
- ✅ Need Approval email
- ✅ Approved email
- ✅ Rejected email
- ✅ Revised email
- ✅ Cancelled email

### 4. **Attendance Request** (Existing)
- ✅ Need Approval email
- ✅ Approved email
- ✅ Rejected email
- ✅ Revised email
- ✅ Cancelled email

### 5. **Leave Application** (Existing)
- ✅ Need Approval email
- ✅ Approved email
- ✅ Rejected email
- ✅ Revised email
- ✅ Cancelled email

## Error Scenarios yang Ditangani

### 1. **Network Errors**
- ✅ Connection refused
- ✅ Connection timeout
- ✅ Host not found
- ✅ Network unreachable
- ✅ **Handling**: Retry dengan exponential backoff

### 2. **SMTP Server Errors**
- ✅ Server timeout
- ✅ Temporary failures (451, 452, 552)
- ✅ **Handling**: Retry dengan exponential backoff

### 3. **Invalid Data Errors**
- ✅ Invalid email address
- ✅ Missing required fields
- ✅ Invalid template
- ✅ **Handling**: Stop retry, return error immediately

### 4. **Authentication Errors**
- ✅ Invalid credentials
- ✅ Unauthorized access
- ✅ **Handling**: Stop retry, return error immediately

### 5. **File System Errors**
- ✅ Attachment file not found
- ✅ File access denied
- ✅ **Handling**: Continue without attachment, log warning

### 6. **Database Errors**
- ✅ Transaction errors
- ✅ History email creation errors
- ✅ **Handling**: Rollback transaction, log error, continue

## Best Practices yang Diterapkan

1. **Separation of Concerns**
   - Email sending logic terpisah dari business logic
   - Reusable email service untuk semua modul

2. **Fail-Safe Design**
   - Email failure tidak memblokir workflow
   - History tetap tercatat meskipun email gagal
   - Transaction safety terjamin

3. **Comprehensive Logging**
   - Log setiap attempt email sending
   - Log errors dengan detail
   - Log retry attempts

4. **Data Integrity**
   - Transaction rollback untuk validation errors
   - History email untuk audit trail
   - Error messages untuk debugging

5. **Performance Optimization**
   - Exponential backoff untuk mengurangi server load
   - Timeout handling untuk menghindari hanging
   - Efficient email validation

## Testing Recommendations

### 1. **Unit Tests**
- Test email validation
- Test retry mechanism
- Test error handling
- Test template generation

### 2. **Integration Tests**
- Test email sending dengan mock SMTP server
- Test transaction safety
- Test history tracking

### 3. **Error Scenario Tests**
- Test network failures
- Test invalid email addresses
- Test missing email account
- Test attachment failures

## Monitoring & Maintenance

### 1. **Monitoring**
- Monitor email success rate
- Monitor retry attempts
- Monitor error patterns
- Monitor history email records

### 2. **Maintenance**
- Regular review of error logs
- Update email templates as needed
- Adjust retry settings based on SMTP server behavior
- Review and update timeout values

## Configuration

### Email Service Configuration
```javascript
{
  maxRetries: 3,        // Maximum retry attempts
  retryDelay: 5000,     // Base retry delay in ms
  connectionTimeout: 30000,  // Connection timeout in ms
  greetingTimeout: 30000,   // Greeting timeout in ms
  socketTimeout: 30000       // Socket timeout in ms
}
```

### SMTP Configuration (per company)
- SMTP server
- SMTP port
- SSL/TLS settings
- Authentication credentials

## Future Improvements

1. **Queue System**: Implement email queue untuk high-volume scenarios
2. **Rate Limiting**: Add rate limiting untuk prevent SMTP server overload
3. **Email Templates Caching**: Cache compiled templates untuk performance
4. **Monitoring Dashboard**: Real-time monitoring dashboard untuk email status
5. **Email Analytics**: Track email open rates, click rates, etc.

## Conclusion

Sistem email notification ini telah dirancang dengan sangat robust dengan:
- ✅ Comprehensive error handling
- ✅ Retry mechanism dengan exponential backoff
- ✅ Transaction safety
- ✅ Data validation
- ✅ History tracking
- ✅ Graceful degradation

Sistem ini siap untuk production use dan dapat diandalkan untuk mengirim email notification tanpa merusak data atau memblokir workflow transactions.
