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
	// Namespace is an optional prefix for stream names to provide storage isolation.
	// When set, the actual stream name becomes "{namespace}_{streamName}".
	// Events in namespaced stores are completely isolated from other namespaces.
	// Leave empty for backward-compatible non-namespaced behavior.
	Namespace string
}

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

// JetStreamEventStore implements EventStore using NATS JetStream for persistence.
// It also implements EventStoreWithErrors to report malformed events during replay.
//
// ## Version Cache Invalidation Strategy
//
// JetStreamEventStore maintains an in-memory cache of actor versions for optimistic
// concurrency control. The cache is invalidated on any miss (GetLatestVersion call
// that finds a newer version in JetStream) to ensure consistency even when external
// processes write to the same JetStream stream.
//
// If only Aether owns the stream (single-writer assumption), the cache provides
// excellent performance for repeated version checks. If external writers modify
// the stream, the cache will remain consistent because:
//
// 1. On SaveEvent: getLatestVersionLocked() checks JetStream on cache miss
// 2. On GetLatestVersion: If actual version > cached version, cache is invalidated
// 3. Subsequent checks for that actor will fetch fresh data from JetStream
//
// This strategy prevents data corruption from stale cache while maintaining
// performance for the single-writer case.
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())
}

// NewJetStreamEventStoreWithNamespace creates a new JetStream-based event store with namespace isolation.
// The namespace is prefixed to the stream name to ensure complete isolation at the storage level.
// This is a convenience function; the same can be achieved by setting Namespace in JetStreamConfig.
func NewJetStreamEventStoreWithNamespace(natsConn *nats.Conn, streamName string, namespace string) (*JetStreamEventStore, error) {
	config := DefaultJetStreamConfig()
	config.Namespace = namespace
	return NewJetStreamEventStoreWithConfig(natsConn, streamName, config)
}

// 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
	}

	// Apply namespace prefix to stream name if provided
	effectiveStreamName := streamName
	if config.Namespace != "" {
		effectiveStreamName = fmt.Sprintf("%s_%s", sanitizeSubject(config.Namespace), streamName)
	}

	// Create or update the stream
	stream := &nats.StreamConfig{
		Name:      effectiveStreamName,
		Subjects:  []string{fmt.Sprintf("%s.events.>", effectiveStreamName), fmt.Sprintf("%s.snapshots.>", effectiveStreamName)},
		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: effectiveStreamName,
		config:     config,
		versions:   make(map[string]int64),
	}, nil
}

// GetNamespace returns the namespace configured for this store, or empty string if not namespaced.
func (jes *JetStreamEventStore) GetNamespace() string {
	return jes.config.Namespace
}

// GetStreamName returns the effective stream name (including namespace prefix if applicable).
func (jes *JetStreamEventStore) GetStreamName() string {
	return jes.streamName
}

// 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 - use internal method that returns result
	result, err := jes.getEventsWithErrorsInternal(actorID, 0)
	if err != nil {
		return 0, err
	}

	if len(result.Events) == 0 {
		return 0, nil
	}

	latestVersion := int64(0)
	for _, event := range result.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.
// Note: This method silently skips malformed events for backward compatibility.
// Use GetEventsWithErrors to receive information about malformed events.
func (jes *JetStreamEventStore) GetEvents(actorID string, fromVersion int64) ([]*aether.Event, error) {
	result, err := jes.getEventsWithErrorsInternal(actorID, fromVersion)
	if err != nil {
		return nil, err
	}
	return result.Events, nil
}

// GetEventsWithErrors retrieves events for an actor and reports any malformed
// events encountered. This method allows callers to decide how to handle
// corrupted data rather than silently skipping it.
func (jes *JetStreamEventStore) GetEventsWithErrors(actorID string, fromVersion int64) (*aether.ReplayResult, error) {
	return jes.getEventsWithErrorsInternal(actorID, fromVersion)
}

// getEventsWithErrorsInternal is the internal implementation that tracks both
// successfully parsed events and errors for malformed events.
func (jes *JetStreamEventStore) getEventsWithErrorsInternal(actorID string, fromVersion int64) (*aether.ReplayResult, 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()

	result := &aether.ReplayResult{
		Events: make([]*aether.Event, 0),
		Errors: make([]aether.ReplayError, 0),
	}

	// 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 {
				// Record the error with context instead of silently skipping
				metadata, _ := msg.Metadata()
				seqNum := uint64(0)
				if metadata != nil {
					seqNum = metadata.Sequence.Stream
				}
				result.Errors = append(result.Errors, aether.ReplayError{
					SequenceNumber: seqNum,
					RawData:        msg.Data,
					Err:            err,
				})
				msg.Ack() // Still ack to prevent redelivery
				continue
			}

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

			msg.Ack()
		}

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

	return result, nil
}

// GetLatestVersion returns the latest version for an actor, repopulating cache
// with fresh data to ensure consistency even if external processes write to
// the same JetStream stream.
func (jes *JetStreamEventStore) GetLatestVersion(actorID string) (int64, error) {
	// Hold lock during fetch to prevent race condition with SaveEvent
	jes.mu.Lock()
	defer jes.mu.Unlock()

	events, err := jes.GetEvents(actorID, 0)
	if err != nil {
		return 0, err
	}

	if len(events) == 0 {
		// No events for this actor - ensure cache is cleared
		delete(jes.versions, actorID)
		return 0, nil
	}

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

	// Always repopulate cache with the fresh data just fetched
	// This ensures cache is in sync with actual state, whether from local writes
	// or external writes detected by version comparison
	jes.versions[actorID] = latestVersion

	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
}

// Compile-time check that JetStreamEventStore implements EventStoreWithErrors
var _ aether.EventStoreWithErrors = (*JetStreamEventStore)(nil)