replay

type Apply[S, E any] func(state S, ev Event[E]) S

type Checkpoint[S any] struct {
	Stream StreamKey
	Seq    Seq
	State  S
}

type Event[E any] struct {
	Stream  StreamKey
	Seq     Seq
	Time    time.Time
	Payload E
}

type Log[E any] interface {
	// Append writes an event. The implementation assigns the Seq if
	// the caller passes 0; otherwise the implementation must verify
	// the Seq is the next expected value for the stream.
	Append(ctx context.Context, ev Event[E]) (Seq, error)

	// Read returns up to `limit` events for `stream` starting at Seq
	// >= `from`. Returns an empty slice when there are no more events.
	Read(ctx context.Context, stream StreamKey, from Seq, limit int) ([]Event[E], error)
}

type MemoryLog[E any] struct {
	// contains filtered or unexported fields
}

type MemorySnapshotter[S any] struct {
	// contains filtered or unexported fields
}

type Options struct {
	// BatchSize is the chunk size used when reading from the log.
	// Defaults to 1024.
	BatchSize int
	// Snapshot, when non-nil, will be called after applying every N
	// events with the current state so the caller can persist a
	// checkpoint mid-replay. N == 0 disables.
	SnapshotEvery int
}

type Seq uint64

type Snapshotter[S any] interface {
	Save(ctx context.Context, c Checkpoint[S]) error
	// Load returns the most recent checkpoint with Seq <= atOrBefore.
	// Returns (nil, nil) if no such checkpoint exists.
	Load(ctx context.Context, stream StreamKey, atOrBefore Seq) (*Checkpoint[S], error)
}

type StreamKey string