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observer-pattern

README.md

Observer Pattern Example

This example demonstrates the Observer pattern implementation in the Modular framework. It shows how to:

  • Use ObservableApplication for automatic event emission
  • Create modules that implement the Observer interface
  • Register observers for specific event types
  • Emit custom events from modules
  • Use the EventLogger module for structured event logging
  • Handle errors gracefully in observers

Features Demonstrated

1. ObservableApplication

  • Automatically emits events for module/service registration and application lifecycle
  • Thread-safe observer management
  • Event filtering by type

2. EventLogger Module

  • Multiple output targets (console, file, syslog)
  • Configurable log levels and formats
  • Event type filtering
  • Async processing with buffering

3. Custom Observable Modules

  • UserModule: Emits custom events for user operations
  • NotificationModule: Observes user events and sends notifications
  • AuditModule: Observes all events for compliance logging

4. Event Types

  • Framework events: module.registered, service.registered, application.started
  • Custom events: user.created, user.login

Running the Example

Basic Usage

go run .

Generate Sample Configuration

go run . --generate-config yaml config-sample.yaml

Environment Variables

You can override configuration using environment variables:

EVENTLOGGER_LOGLEVEL=DEBUG go run .
USERMODULE_MAXUSERS=50 go run .

Expected Output

When you run the example, you'll see:

  1. Application startup events logged by EventLogger
  2. Module registration events for each registered module
  3. Service registration events for registered services
  4. Custom user events when users are created and log in
  5. Notification handling by the NotificationModule
  6. Audit logging of all events by the AuditModule
  7. Application shutdown events during graceful shutdown

Configuration

The example uses a comprehensive configuration that demonstrates:

  • EventLogger with console output and optional file logging
  • Configurable log levels and formats
  • Event type filtering options
  • User module configuration

Observer Pattern Flow

  1. ObservableApplication emits framework lifecycle events
  2. EventLogger observes all events and logs them to configured outputs
  3. UserModule emits custom events for business operations
  4. NotificationModule observes user events and sends notifications
  5. AuditModule observes all events for compliance and security

Code Structure

  • main.go - Application setup and coordination
  • user_module.go - Demonstrates event emission and observation
  • notification_module.go - Demonstrates event-driven notifications
  • audit_module.go - Demonstrates comprehensive event auditing
  • config.yaml - Configuration with event logging setup

Key Learning Points

  1. Observer Registration: How to register observers for specific event types
  2. Event Emission: How modules can emit custom events
  3. Error Handling: How observer errors are handled gracefully
  4. Configuration: How to configure event logging and filtering
  5. Integration: How the Observer pattern integrates with the existing framework

Testing

Run the example and observe the detailed event logging that shows the Observer pattern in action. The output demonstrates:

  • Real-time event processing
  • Event filtering and routing
  • Error handling and recovery
  • Performance with async processing