# events - Functional Specification

**Version**: v1.2.3 | **Status**: Active | **Last Updated**: March 2026

## Purpose

Provides an asynchronous event bus for decoupling system components. Implements the Publish-Subscribe pattern.

## Design Principles

- **Decoupling**: Publishers need not know subscribers.
- **Typed Payloads**: Events carry structured data (dicts/pydantic models).

## Functional Requirements

1. **Publishing**: `bus.publish(event)` or `emitter.emit(type, data)`
2. **Subscription**: `bus.subscribe(types, handler)` or `listener.on(type, handler)`
3. **Synchronous Emission**: `emitter.emit_sync(type, data)` for immediate processing

## Interface Contracts

- **Event**: Dataclass with `event_id`, `event_type`, `source`, `timestamp`, and `priority`.
- **Event Bus**: Central routing hub with sync/async support.
- **Event Emitter**: Standard interface for emitting events (`emit()`, `emit_sync()`).
- **Event Listener**: Consistent API for subscriptions (`on()`, `off()`, `once()`). Legacy aliases like `unregister` and `listeners` property have been removed.
- **Event Priority**: Supports `DEBUG` through `CRITICAL`.

## Navigation

- **Human Documentation**: [README.md](README.md)
- **Technical Documentation**: [AGENTS.md](AGENTS.md)
- **Parent**: [../SPEC.md](../SPEC.md)

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## Detailed Architecture and Implementation

### Design Principles

1. **Strict Modularity**: Each component is isolated and communicates via well-defined APIs.
2. **Performance Optimization**: Implementation leverages lazy loading and intelligent caching to minimize resource overhead.
3. **Error Resilience**: Robust exception handling ensures system stability even under unexpected conditions.
4. **Extensibility**: The architecture is designed to accommodate future enhancements without breaking existing contracts.

### Technical Implementation

The codebase utilizes modern Python features (version 3.10+) to provide a clean, type-safe API. Interaction patterns are documented in the corresponding `AGENTS.md` and `SPEC.md` files, ensuring that both human developers and automated agents can effectively utilize these capabilities.

## Testing

```bash
uv run python -m pytest src/codomyrmex/tests/ -k events -v
```
