# Aether

Distributed actor system with event sourcing for Go, powered by NATS.

## Organization Context

This repo is part of Flowmade. See:
- [Organization manifesto](https://git.flowmade.one/flowmade-one/architecture/src/branch/main/manifesto.md) - who we are, what we believe
- [Repository map](https://git.flowmade.one/flowmade-one/architecture/src/branch/main/repos.md) - how this fits in the bigger picture
- [Vision](./vision.md) - what this specific product does

## Setup

```bash
git clone git@git.flowmade.one:flowmade-one/aether.git
cd aether
go mod download
```

Requires NATS server for integration tests:
```bash
# Install NATS
brew install nats-server

# Run with JetStream enabled
nats-server -js
```

## Project Structure

```
aether/
├── event.go           # Event, ActorSnapshot, EventStore interface
├── eventbus.go        # EventBus, EventBroadcaster interface
├── nats_eventbus.go   # NATSEventBus - cross-node event broadcasting
├── store/
│   ├── memory.go      # InMemoryEventStore (testing)
│   └── jetstream.go   # JetStreamEventStore (production)
├── cluster/
│   ├── manager.go     # ClusterManager
│   ├── discovery.go   # NodeDiscovery
│   ├── hashring.go    # ConsistentHashRing
│   ├── shard.go       # ShardManager
│   ├── leader.go      # LeaderElection
│   └── types.go       # Cluster types
└── model/
    └── model.go       # EventStorming model types
```

## Development

```bash
make build    # Build the library
make test     # Run tests
make lint     # Run linters
```

## Architecture

### Event Sourcing

Events are the source of truth. State is derived by replaying events.

```go
// Create an event
event := &aether.Event{
    ID:        uuid.New().String(),
    EventType: "OrderPlaced",
    ActorID:   "order-123",
    Version:   1,
    Data:      map[string]interface{}{"total": 100.00},
    Timestamp: time.Now(),
}

// Persist to event store
store.SaveEvent(event)

// Replay events to rebuild state
events, _ := store.GetEvents("order-123", 0)
```

### Event Versioning

Events for each actor must have **monotonically increasing versions**. This ensures event stream integrity and enables optimistic concurrency control.

#### Version Semantics

- Each actor has an independent version sequence
- Version must be strictly greater than the current latest version
- For new actors (no events), the first event must have version > 0
- Non-consecutive versions are allowed (gaps are permitted)

#### Optimistic Concurrency Pattern

```go
// 1. Get current version
currentVersion, _ := store.GetLatestVersion("order-123")

// 2. Create event with next version
event := &aether.Event{
    ID:        uuid.New().String(),
    EventType: "OrderUpdated",
    ActorID:   "order-123",
    Version:   currentVersion + 1,
    Data:      map[string]interface{}{"status": "shipped"},
    Timestamp: time.Now(),
}

// 3. Attempt to save
err := store.SaveEvent(event)
if errors.Is(err, aether.ErrVersionConflict) {
    // Another writer won - reload and retry if appropriate
    var versionErr *aether.VersionConflictError
    errors.As(err, &versionErr)
    log.Printf("Conflict: actor %s has version %d, attempted %d",
        versionErr.ActorID, versionErr.CurrentVersion, versionErr.AttemptedVersion)
}
```

#### Error Types

- `ErrVersionConflict` - Sentinel error for version conflicts (use with `errors.Is`)
- `VersionConflictError` - Detailed error with ActorID, CurrentVersion, and AttemptedVersion

### Namespace Isolation

Namespaces provide logical boundaries for events and subscriptions:

```go
// Subscribe to events in a namespace
ch := eventBus.Subscribe("tenant-abc")

// Events are isolated per namespace
eventBus.Publish("tenant-abc", event)  // Only tenant-abc subscribers see this
```

### Clustering

Aether handles node discovery, leader election, and shard distribution:

```go
// Create cluster manager
manager := cluster.NewClusterManager(natsConn, nodeID)

// Join cluster
manager.Start()

// Leader election happens automatically
if manager.IsLeader() {
    // Coordinate shard assignments
}
```

## Key Patterns

- **Events are immutable** - Never modify, only append
- **Versions are monotonic** - Each event must have version > previous for same actor
- **Snapshots for performance** - Periodically snapshot state to avoid full replay
- **Namespaces for isolation** - Not multi-tenancy, just logical boundaries
- **NATS for everything** - Events, pub/sub, clustering all use NATS