package cluster

import (
	"context"
	"encoding/json"
	"fmt"

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

// DistributedVM manages a cluster of runtime nodes with VM-per-instance architecture
type DistributedVM struct {
	nodeID       string
	cluster      *ClusterManager
	localRuntime Runtime
	sharding     *ShardManager
	discovery    *NodeDiscovery
	natsConn     *nats.Conn
	ctx          context.Context
	cancel       context.CancelFunc
}

// Runtime defines the interface for a local runtime that executes actors.
// This interface decouples the cluster package from specific runtime implementations.
type Runtime interface {
	// Start initializes and starts the runtime
	Start() error
	// LoadModel loads an EventStorming model into the runtime
	LoadModel(model RuntimeModel) error
	// SendMessage sends a message to an actor in the runtime
	SendMessage(message RuntimeMessage) error
}

// DistributedVMRegistry implements VMRegistry using DistributedVM's local runtime and sharding.
// It provides the cluster manager with access to VM information without import cycles.
type DistributedVMRegistry struct {
	vmProvider VMProvider
	sharding   *ShardManager
}

// VMProvider defines an interface for accessing VMs from a runtime.
// This is used by DistributedVMRegistry to get VM information.
type VMProvider interface {
	// GetActiveVMs returns a map of actor IDs to their VirtualMachine instances
	GetActiveVMs() map[string]VirtualMachine
}

// NewDistributedVM creates a distributed VM runtime cluster node
func NewDistributedVM(nodeID string, natsURLs []string, localRuntime Runtime) (*DistributedVM, error) {
	ctx, cancel := context.WithCancel(context.Background())

	// Connect to NATS cluster
	natsURL := natsURLs[0] // Use first URL for simplicity
	natsConn, err := nats.Connect(natsURL,
		nats.Name(fmt.Sprintf("aether-runtime-%s", nodeID)))
	if err != nil {
		cancel()
		return nil, fmt.Errorf("failed to connect to NATS: %w", err)
	}

	// Create cluster components
	discovery := NewNodeDiscovery(nodeID, natsConn, ctx)
	sharding := NewShardManager(1024, 3) // 1024 shards, 3 replicas
	cluster, err := NewClusterManager(nodeID, natsConn, ctx)
	if err != nil {
		cancel()
		natsConn.Close()
		return nil, fmt.Errorf("failed to create cluster manager: %w", err)
	}

	dvm := &DistributedVM{
		nodeID:       nodeID,
		cluster:      cluster,
		localRuntime: localRuntime,
		sharding:     sharding,
		discovery:    discovery,
		natsConn:     natsConn,
		ctx:          ctx,
		cancel:       cancel,
	}

	return dvm, nil
}

// SetVMProvider sets the VM provider for the distributed VM registry.
// This should be called after the runtime is fully initialized.
func (dvm *DistributedVM) SetVMProvider(provider VMProvider) {
	vmRegistry := &DistributedVMRegistry{
		vmProvider: provider,
		sharding:   dvm.sharding,
	}
	dvm.cluster.SetVMRegistry(vmRegistry)
}

// Start begins the distributed VM cluster node
func (dvm *DistributedVM) Start() error {
	// Start local runtime
	if err := dvm.localRuntime.Start(); err != nil {
		return fmt.Errorf("failed to start local runtime: %w", err)
	}

	// Start cluster services
	go dvm.discovery.Start()
	go dvm.cluster.Start()

	// Start message routing
	go dvm.startMessageRouting()

	return nil
}

// Stop gracefully shuts down the distributed VM node
func (dvm *DistributedVM) Stop() {
	dvm.cancel()
	dvm.cluster.Stop()
	dvm.discovery.Stop()
	dvm.natsConn.Close()
}

// LoadModel distributes EventStorming model across the cluster with VM templates
func (dvm *DistributedVM) LoadModel(model RuntimeModel) error {
	// Load model locally first
	if err := dvm.localRuntime.LoadModel(model); err != nil {
		return fmt.Errorf("failed to load model locally: %w", err)
	}

	// Broadcast model to other cluster nodes
	msg := ClusterMessage{
		Type:    "load_model",
		From:    dvm.nodeID,
		To:      "broadcast",
		Payload: model,
	}

	return dvm.publishClusterMessage(msg)
}

// SendMessage routes messages across the distributed cluster
func (dvm *DistributedVM) SendMessage(message RuntimeMessage) error {
	// This is a simplified implementation
	// In practice, this would determine the target node based on sharding
	// and route the message appropriately

	return dvm.localRuntime.SendMessage(message)
}

// GetActorNode determines which node should handle a specific actor
func (dvm *DistributedVM) GetActorNode(actorID string) string {
	// Use consistent hashing to determine the target node
	return dvm.cluster.hashRing.GetNode(actorID)
}

// IsLocalActor checks if an actor should be handled by this node
func (dvm *DistributedVM) IsLocalActor(actorID string) bool {
	targetNode := dvm.GetActorNode(actorID)
	return targetNode == dvm.nodeID
}

// GetActorsInShard returns actors that belong to a specific shard on this node
func (dvm *DistributedVM) GetActorsInShard(shardID int) []string {
	return dvm.cluster.GetActorsInShard(shardID)
}

// startMessageRouting begins routing messages between cluster nodes
func (dvm *DistributedVM) startMessageRouting() {
	// Subscribe to cluster messages
	dvm.natsConn.Subscribe("aether.distributed.*", dvm.handleClusterMessage)
}

// handleClusterMessage processes incoming cluster coordination messages
func (dvm *DistributedVM) handleClusterMessage(msg *nats.Msg) {
	var clusterMsg ClusterMessage
	if err := json.Unmarshal(msg.Data, &clusterMsg); err != nil {
		return
	}

	switch clusterMsg.Type {
	case "load_model":
		// Handle model loading from other nodes
		// Note: Payload comes as interface{} from JSON, need type assertion
		// In practice, this would deserialize to the proper model type
		if model, ok := clusterMsg.Payload.(RuntimeModel); ok {
			dvm.localRuntime.LoadModel(model)
		}

	case "route_message":
		// Handle message routing from other nodes
		// Note: Similar type handling needed here
		if message, ok := clusterMsg.Payload.(RuntimeMessage); ok {
			dvm.localRuntime.SendMessage(message)
		}

	case "rebalance":
		// Handle shard rebalancing requests
		dvm.handleRebalanceRequest(clusterMsg)
	}
}

// handleRebalanceRequest processes shard rebalancing requests
func (dvm *DistributedVM) handleRebalanceRequest(msg ClusterMessage) {
	// Simplified rebalancing logic
	// In practice, this would implement complex actor migration
}

// publishClusterMessage sends a message to other cluster nodes
func (dvm *DistributedVM) publishClusterMessage(msg ClusterMessage) error {
	data, err := json.Marshal(msg)
	if err != nil {
		return err
	}

	subject := fmt.Sprintf("aether.distributed.%s", msg.Type)
	return dvm.natsConn.Publish(subject, data)
}

// GetClusterInfo returns information about the cluster state
func (dvm *DistributedVM) GetClusterInfo() map[string]interface{} {
	nodes := dvm.cluster.GetNodes()

	return map[string]interface{}{
		"nodeId":    dvm.nodeID,
		"isLeader":  dvm.cluster.IsLeader(),
		"leader":    dvm.cluster.GetLeader(),
		"nodeCount": len(nodes),
		"nodes":     nodes,
	}
}

// GetActiveVMs returns a map of active VMs from the VM provider
func (dvr *DistributedVMRegistry) GetActiveVMs() map[string]VirtualMachine {
	if dvr.vmProvider == nil {
		return make(map[string]VirtualMachine)
	}
	return dvr.vmProvider.GetActiveVMs()
}

// GetShard returns the shard number for the given actor ID
func (dvr *DistributedVMRegistry) GetShard(actorID string) int {
	return dvr.sharding.GetShard(actorID)
}