// Package natsbus manages the embedded NATS JetStream server that provides
// the coordination bus for Wild Central. Cloud and Works connect to this NATS
// to register services, publish events, and maintain presence.
package natsbus

import (
	"context"
	"fmt"
	"log/slog"
	"os"
	"time"

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

const (
	// KV bucket names
	BucketDomains = "wild-domains" // domain registrations
	BucketPresence = "wild-presence" // node liveness (TTL keys)

	// Stream names
	StreamEvents = "wild-events" // events from all sources

	// Presence TTL — keys expire if not renewed within this window
	PresenceTTL = 60 * time.Second
)

// Server wraps an embedded NATS server with JetStream enabled.
type Server struct {
	ns   *natsserver.Server
	nc   *nats.Conn
	js   jetstream.JetStream
	port int
}

// Config for the embedded NATS server.
type Config struct {
	Port    int    // listen port (default 4222)
	DataDir string // JetStream storage directory
}

// Start launches the embedded NATS server with JetStream and creates
// the required KV buckets and streams.
func Start(cfg Config) (*Server, error) {
	if cfg.Port == 0 {
		cfg.Port = 4222
	}

	opts := &natsserver.Options{
		Port:      cfg.Port,
		JetStream: true,
		StoreDir:  cfg.DataDir,
		// Quiet logging — NATS logs at its own level
		NoLog:  true,
		NoSigs: true,
	}

	ns, err := natsserver.NewServer(opts)
	if err != nil {
		return nil, fmt.Errorf("creating NATS server: %w", err)
	}

	// Start server in background
	go ns.Start()

	// Wait for server to be ready. If it fails (stale lock files, corrupt
	// store), clean the data directory and retry once.
	if !ns.ReadyForConnections(10 * time.Second) {
		ns.Shutdown()
		slog.Warn("NATS server failed to start, cleaning store and retrying", "dataDir", cfg.DataDir)
		os.RemoveAll(cfg.DataDir)
		os.MkdirAll(cfg.DataDir, 0755)

		ns, err = natsserver.NewServer(opts)
		if err != nil {
			return nil, fmt.Errorf("creating NATS server (retry): %w", err)
		}
		go ns.Start()
		if !ns.ReadyForConnections(10 * time.Second) {
			ns.Shutdown()
			return nil, fmt.Errorf("NATS server failed to start after retry")
		}
	}

	slog.Info("NATS JetStream server started", "port", cfg.Port, "dataDir", cfg.DataDir)

	// Connect as internal client
	nc, err := nats.Connect(ns.ClientURL())
	if err != nil {
		ns.Shutdown()
		return nil, fmt.Errorf("connecting to embedded NATS: %w", err)
	}

	js, err := jetstream.New(nc)
	if err != nil {
		nc.Close()
		ns.Shutdown()
		return nil, fmt.Errorf("creating JetStream context: %w", err)
	}

	s := &Server{
		ns:   ns,
		nc:   nc,
		js:   js,
		port: cfg.Port,
	}

	if err := s.ensureBuckets(); err != nil {
		s.Shutdown()
		return nil, fmt.Errorf("creating KV buckets: %w", err)
	}

	if err := s.ensureStreams(); err != nil {
		s.Shutdown()
		return nil, fmt.Errorf("creating streams: %w", err)
	}

	return s, nil
}

// ensureBuckets creates the required KV buckets if they don't exist.
func (s *Server) ensureBuckets() error {
	ctx := context.Background()

	// Services bucket — no TTL, entries persist until explicitly deleted
	_, err := s.js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{
		Bucket:      BucketDomains,
		Description: "Service registrations from Wild Cloud, Wild Works, and manual entries",
	})
	if err != nil {
		return fmt.Errorf("services bucket: %w", err)
	}
	slog.Info("NATS KV bucket ready", "bucket", BucketDomains)

	// Presence bucket — TTL-based, keys expire when nodes stop renewing
	_, err = s.js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{
		Bucket:      BucketPresence,
		Description: "Node liveness via TTL-based keys",
		TTL:         PresenceTTL,
	})
	if err != nil {
		return fmt.Errorf("presence bucket: %w", err)
	}
	slog.Info("NATS KV bucket ready", "bucket", BucketPresence, "ttl", PresenceTTL)

	return nil
}

// ensureStreams creates the required streams if they don't exist.
func (s *Server) ensureStreams() error {
	ctx := context.Background()

	_, err := s.js.CreateOrUpdateStream(ctx, jetstream.StreamConfig{
		Name:        StreamEvents,
		Description: "Events from all Wild Central consumers",
		Subjects:    []string{"wild.events.>"},
		MaxAge:      24 * time.Hour, // retain events for 24h
		Storage:     jetstream.FileStorage,
	})
	if err != nil {
		return fmt.Errorf("events stream: %w", err)
	}
	slog.Info("NATS stream ready", "stream", StreamEvents)

	return nil
}

// JetStream returns the JetStream context for internal use.
func (s *Server) JetStream() jetstream.JetStream {
	return s.js
}

// Conn returns the internal NATS connection.
func (s *Server) Conn() *nats.Conn {
	return s.nc
}

// ClientURL returns the URL clients should use to connect.
func (s *Server) ClientURL() string {
	return s.ns.ClientURL()
}

// Port returns the port the server is listening on.
func (s *Server) Port() int {
	return s.port
}

// Shutdown gracefully stops the NATS server.
func (s *Server) Shutdown() {
	if s.nc != nil {
		s.nc.Close()
	}
	if s.ns != nil {
		s.ns.Shutdown()
		s.ns.WaitForShutdown()
	}
	slog.Info("NATS server stopped")
}