package store

import (
	"encoding/json"
	"fmt"
	"strings"
	"sync"
	"time"

	"git.flowmade.one/flowmade-one/aether"
	"github.com/nats-io/nats.go"
)

// Default configuration values for JetStream event store
const (
	DefaultStreamRetention = 365 * 24 * time.Hour // 1 year
	DefaultReplicaCount    = 1
)

// JetStreamConfig holds configuration options for JetStreamEventStore
type JetStreamConfig struct {
	// StreamRetention is how long to keep events (default: 1 year)
	StreamRetention time.Duration
	// ReplicaCount is the number of replicas for high availability (default: 1)
	ReplicaCount int
}

// DefaultJetStreamConfig returns the default configuration
func DefaultJetStreamConfig() JetStreamConfig {
	return JetStreamConfig{
		StreamRetention: DefaultStreamRetention,
		ReplicaCount:    DefaultReplicaCount,
	}
}

// JetStreamEventStore implements EventStore using NATS JetStream for persistence
type JetStreamEventStore struct {
	js         nats.JetStreamContext
	streamName string
	config     JetStreamConfig
	mu         sync.Mutex       // Protects version checks during SaveEvent
	versions   map[string]int64 // actorID -> latest version cache
}

// NewJetStreamEventStore creates a new JetStream-based event store with default configuration
func NewJetStreamEventStore(natsConn *nats.Conn, streamName string) (*JetStreamEventStore, error) {
	return NewJetStreamEventStoreWithConfig(natsConn, streamName, DefaultJetStreamConfig())
}

// NewJetStreamEventStoreWithConfig creates a new JetStream-based event store with custom configuration
func NewJetStreamEventStoreWithConfig(natsConn *nats.Conn, streamName string, config JetStreamConfig) (*JetStreamEventStore, error) {
	js, err := natsConn.JetStream()
	if err != nil {
		return nil, fmt.Errorf("failed to get JetStream context: %w", err)
	}

	// Apply defaults for zero values
	if config.StreamRetention == 0 {
		config.StreamRetention = DefaultStreamRetention
	}
	if config.ReplicaCount == 0 {
		config.ReplicaCount = DefaultReplicaCount
	}

	// Create or update the stream
	stream := &nats.StreamConfig{
		Name:      streamName,
		Subjects:  []string{fmt.Sprintf("%s.events.>", streamName), fmt.Sprintf("%s.snapshots.>", streamName)},
		Storage:   nats.FileStorage,
		Retention: nats.LimitsPolicy,
		MaxAge:    config.StreamRetention,
		Replicas:  config.ReplicaCount,
	}

	_, err = js.AddStream(stream)
	if err != nil && !strings.Contains(err.Error(), "already exists") {
		return nil, fmt.Errorf("failed to create stream: %w", err)
	}

	return &JetStreamEventStore{
		js:         js,
		streamName: streamName,
		config:     config,
		versions:   make(map[string]int64),
	}, nil
}

// SaveEvent persists an event to JetStream.
// Returns VersionConflictError if the event's version is not strictly greater
// than the current latest version for the actor.
func (jes *JetStreamEventStore) SaveEvent(event *aether.Event) error {
	jes.mu.Lock()
	defer jes.mu.Unlock()

	// Get current latest version for this actor
	currentVersion, err := jes.getLatestVersionLocked(event.ActorID)
	if err != nil {
		return fmt.Errorf("failed to get latest version: %w", err)
	}

	// Validate version is strictly greater than current
	if event.Version <= currentVersion {
		return &aether.VersionConflictError{
			ActorID:          event.ActorID,
			AttemptedVersion: event.Version,
			CurrentVersion:   currentVersion,
		}
	}

	// Serialize event to JSON
	data, err := json.Marshal(event)
	if err != nil {
		return fmt.Errorf("failed to marshal event: %w", err)
	}

	// Create subject: stream.events.actorType.actorID
	subject := fmt.Sprintf("%s.events.%s.%s",
		jes.streamName,
		sanitizeSubject(extractActorType(event.ActorID)),
		sanitizeSubject(event.ActorID))

	// Publish with event ID as message ID for deduplication
	_, err = jes.js.Publish(subject, data, nats.MsgId(event.ID))
	if err != nil {
		return fmt.Errorf("failed to publish event to JetStream: %w", err)
	}

	// Update version cache
	jes.versions[event.ActorID] = event.Version

	return nil
}

// getLatestVersionLocked returns the latest version for an actor.
// Caller must hold jes.mu.
func (jes *JetStreamEventStore) getLatestVersionLocked(actorID string) (int64, error) {
	// Check cache first
	if version, ok := jes.versions[actorID]; ok {
		return version, nil
	}

	// Fetch from JetStream
	events, err := jes.getEventsInternal(actorID, 0)
	if err != nil {
		return 0, err
	}

	if len(events) == 0 {
		return 0, nil
	}

	latestVersion := int64(0)
	for _, event := range events {
		if event.Version > latestVersion {
			latestVersion = event.Version
		}
	}

	// Update cache
	jes.versions[actorID] = latestVersion

	return latestVersion, nil
}

// GetEvents retrieves all events for an actor since a version
func (jes *JetStreamEventStore) GetEvents(actorID string, fromVersion int64) ([]*aether.Event, error) {
	return jes.getEventsInternal(actorID, fromVersion)
}

// getEventsInternal is the internal implementation of GetEvents
func (jes *JetStreamEventStore) getEventsInternal(actorID string, fromVersion int64) ([]*aether.Event, error) {
	// Create subject filter for this actor
	subject := fmt.Sprintf("%s.events.%s.%s",
		jes.streamName,
		sanitizeSubject(extractActorType(actorID)),
		sanitizeSubject(actorID))

	// Create consumer to read events
	consumer, err := jes.js.PullSubscribe(subject, "")
	if err != nil {
		return nil, fmt.Errorf("failed to create consumer: %w", err)
	}
	defer consumer.Unsubscribe()

	var events []*aether.Event

	// Fetch messages in batches
	for {
		msgs, err := consumer.Fetch(100, nats.MaxWait(time.Second))
		if err != nil {
			if err == nats.ErrTimeout {
				break // No more messages
			}
			return nil, fmt.Errorf("failed to fetch messages: %w", err)
		}

		for _, msg := range msgs {
			var event aether.Event
			if err := json.Unmarshal(msg.Data, &event); err != nil {
				continue // Skip malformed events
			}

			// Filter by version
			if event.Version > fromVersion {
				events = append(events, &event)
			}

			msg.Ack()
		}

		if len(msgs) < 100 {
			break // No more messages
		}
	}

	return events, nil
}

// GetLatestVersion returns the latest version for an actor
func (jes *JetStreamEventStore) GetLatestVersion(actorID string) (int64, error) {
	events, err := jes.GetEvents(actorID, 0)
	if err != nil {
		return 0, err
	}

	if len(events) == 0 {
		return 0, nil
	}

	latestVersion := int64(0)
	for _, event := range events {
		if event.Version > latestVersion {
			latestVersion = event.Version
		}
	}

	return latestVersion, nil
}

// GetLatestSnapshot gets the most recent snapshot for an actor
func (jes *JetStreamEventStore) GetLatestSnapshot(actorID string) (*aether.ActorSnapshot, error) {
	// Create subject for snapshots
	subject := fmt.Sprintf("%s.snapshots.%s.%s",
		jes.streamName,
		sanitizeSubject(extractActorType(actorID)),
		sanitizeSubject(actorID))

	// Try to get the latest snapshot
	consumer, err := jes.js.PullSubscribe(subject, "", nats.DeliverLast())
	if err != nil {
		return nil, fmt.Errorf("failed to create snapshot consumer: %w", err)
	}
	defer consumer.Unsubscribe()

	msgs, err := consumer.Fetch(1, nats.MaxWait(time.Second))
	if err != nil {
		if err == nats.ErrTimeout {
			return nil, fmt.Errorf("no snapshot found for actor %s", actorID)
		}
		return nil, fmt.Errorf("failed to fetch snapshot: %w", err)
	}

	if len(msgs) == 0 {
		return nil, fmt.Errorf("no snapshot found for actor %s", actorID)
	}

	var snapshot aether.ActorSnapshot
	if err := json.Unmarshal(msgs[0].Data, &snapshot); err != nil {
		return nil, fmt.Errorf("failed to unmarshal snapshot: %w", err)
	}

	msgs[0].Ack()
	return &snapshot, nil
}

// SaveSnapshot saves a snapshot of actor state
func (jes *JetStreamEventStore) SaveSnapshot(snapshot *aether.ActorSnapshot) error {
	// Serialize snapshot to JSON
	data, err := json.Marshal(snapshot)
	if err != nil {
		return fmt.Errorf("failed to marshal snapshot: %w", err)
	}

	// Create subject for snapshots
	subject := fmt.Sprintf("%s.snapshots.%s.%s",
		jes.streamName,
		sanitizeSubject(extractActorType(snapshot.ActorID)),
		sanitizeSubject(snapshot.ActorID))

	// Publish snapshot
	_, err = jes.js.Publish(subject, data)
	if err != nil {
		return fmt.Errorf("failed to publish snapshot to JetStream: %w", err)
	}

	return nil
}

// Helper functions

// extractActorType extracts the actor type from an actor ID
func extractActorType(actorID string) string {
	for i, c := range actorID {
		if c == '-' && i > 0 {
			return actorID[:i]
		}
	}
	return "unknown"
}

// sanitizeSubject sanitizes a string for use in NATS subjects
func sanitizeSubject(s string) string {
	s = strings.ReplaceAll(s, " ", "_")
	s = strings.ReplaceAll(s, ".", "_")
	s = strings.ReplaceAll(s, "*", "_")
	s = strings.ReplaceAll(s, ">", "_")
	return s
}