Artifact [b7c4803994]

Artifact b7c480399404f73f1470b0697c716282ca3a7589aa5e24bc235c07a8ad3d4e40:

• File internal/events/events.go — part of check-in [14b0c96b83] at 2026-08-15 20:36:39 on branch trunk — events: work-queue retention on ZITEVT; migrate old streams

  Acked events leave the stream, so disk tracks the in-flight backlog, not store history (was 5.6GB beside sqlite's 218MB). Old-config streams are dropped with their cursors; the census republishes and idempotent folds converge. (user: dmestas, size: 3930) [annotate] [blame] [check-ins using]

// Package events is the event plane (0001 §1): embedded NATS with
// JetStream, the dagnats/notify operational shape. Everything here lives
// under --data and is never truth — the stream is rederivable from the
// stores, which is what lets the disposability harness wipe it freely.
package events

import (
	"fmt"
	"time"

	"github.com/nats-io/nats-server/v2/server"
	"github.com/nats-io/nats.go"
)

const (
	// StreamName holds every store event; subjects follow the 0001 §4
	// shape zit.evt.<project_code>.<kind>.
	StreamName = "ZITEVT"
	// CursorBucket is the KV bucket for watcher cursors (advisory —
	// a lost cursor re-reads from zero).
	CursorBucket = "cursors"
)

// Server is an embedded NATS server plus an in-process client.
type Server struct {
	srv *server.Server
	nc  *nats.Conn
	js  nats.JetStreamContext
}

// Start runs an embedded server with JetStream storage under dir. The
// listen port is disabled — phase 1 is one process; the external-NATS
// URL is the scale-out flag (0003 §2).
func Start(dir string) (*Server, error) {
	srv, err := server.NewServer(&server.Options{
		DontListen: true,
		JetStream:  true,
		StoreDir:   dir,
		// Parsed artifacts ride the stream whole; large stores (sqlite's
		// baseline manifests, big clusters) blow the 1MB default.
		MaxPayload: 8 << 20,
	})
	if err != nil {
		return nil, err
	}
	go srv.Start()
	if !srv.ReadyForConnections(10 * time.Second) {
		return nil, fmt.Errorf("events: embedded NATS not ready")
	}
	nc, err := nats.Connect("", nats.InProcessServer(srv))
	if err != nil {
		srv.Shutdown()
		return nil, err
	}
	js, err := nc.JetStream()
	if err != nil {
		nc.Close()
		srv.Shutdown()
		return nil, err
	}
	// Work-queue retention: an event is deleted the moment its indexer
	// acks it, so the stream's disk footprint is the in-flight backlog,
	// not the store's history (the store is truth; replay is republish).
	// Retention can't be changed on a live stream — an older-config
	// stream is dropped along with the cursors, which forces the census
	// to republish; idempotent folds converge.
	if info, ierr := js.StreamInfo(StreamName); ierr == nil && info.Config.Retention != nats.WorkQueuePolicy {
		if derr := js.DeleteStream(StreamName); derr != nil {
			nc.Close()
			srv.Shutdown()
			return nil, fmt.Errorf("events: migrate stream: %w", derr)
		}
		_ = js.DeleteKeyValue(CursorBucket)
	}
	if _, err := js.AddStream(&nats.StreamConfig{
		Name:      StreamName,
		Subjects:  []string{"zit.evt.>"},
		Retention: nats.WorkQueuePolicy,
	}); err != nil && err != nats.ErrStreamNameAlreadyInUse {
		nc.Close()
		srv.Shutdown()
		return nil, fmt.Errorf("events: stream: %w", err)
	}
	if _, err := js.CreateKeyValue(&nats.KeyValueConfig{Bucket: CursorBucket}); err != nil {
		if _, kerr := js.KeyValue(CursorBucket); kerr != nil {
			nc.Close()
			srv.Shutdown()
			return nil, fmt.Errorf("events: kv: %w", err)
		}
	}
	return &Server{srv: srv, nc: nc, js: js}, nil
}

// JS exposes the JetStream context for publishers and consumers.
func (s *Server) JS() nats.JetStreamContext { return s.js }

// Cursors returns the advisory cursor KV bucket.
func (s *Server) Cursors() (nats.KeyValue, error) {
	return s.js.KeyValue(CursorBucket)
}

// Watch returns a channel that ticks when anything happens on one
// repo's subjects — the change signal live pages coalesce on. The
// channel never blocks the publisher (capacity 1, drop-if-full: a tick
// means "something changed", not "N things changed"). cancel stops the
// subscription.
func (s *Server) Watch(code string) (<-chan struct{}, func()) {
	ch := make(chan struct{}, 1)
	sub, err := s.nc.Subscribe("zit.evt."+code+".>", func(*nats.Msg) {
		select {
		case ch <- struct{}{}:
		default:
		}
	})
	if err != nil {
		close(ch)
		return ch, func() {}
	}
	return ch, func() { sub.Unsubscribe() }
}

func (s *Server) Close() {
	s.nc.Close()
	s.srv.Shutdown()
	s.srv.WaitForShutdown()
}