// Package distribution provides replication management for distributed contexts
package distribution

import (
	"context"
	"fmt"
	"sync"
	"time"

	"chorus.services/bzzz/pkg/dht"
	"chorus.services/bzzz/pkg/config"
	"chorus.services/bzzz/pkg/ucxl"
	"github.com/libp2p/go-libp2p/core/peer"
)

// ReplicationManagerImpl implements ReplicationManager interface
type ReplicationManagerImpl struct {
	mu              sync.RWMutex
	dht             *dht.DHT
	config          *config.Config
	replicationMap  map[string]*ReplicationStatus
	repairQueue     chan *RepairRequest
	rebalanceQueue  chan *RebalanceRequest
	consistentHash  ConsistentHashing
	policy          *ReplicationPolicy
	stats           *ReplicationStatistics
	running         bool
}

// RepairRequest represents a repair request
type RepairRequest struct {
	Address         ucxl.Address
	RequestedBy     string
	Priority        Priority
	RequestTime     time.Time
}

// RebalanceRequest represents a rebalance request
type RebalanceRequest struct {
	Reason          string
	RequestedBy     string
	RequestTime     time.Time
}

// NewReplicationManagerImpl creates a new replication manager implementation
func NewReplicationManagerImpl(dht *dht.DHT, config *config.Config) (*ReplicationManagerImpl, error) {
	if dht == nil {
		return nil, fmt.Errorf("DHT instance is required")
	}
	if config == nil {
		return nil, fmt.Errorf("config is required")
	}

	rm := &ReplicationManagerImpl{
		dht:            dht,
		config:         config,
		replicationMap: make(map[string]*ReplicationStatus),
		repairQueue:    make(chan *RepairRequest, 1000),
		rebalanceQueue: make(chan *RebalanceRequest, 100),
		policy: &ReplicationPolicy{
			DefaultFactor:     3,
			MinFactor:         2,
			MaxFactor:         7,
			PreferredZones:    []string{"zone-a", "zone-b", "zone-c"},
			AvoidSameNode:     true,
			ConsistencyLevel:  ConsistencyEventual,
			RepairThreshold:   0.8,
			RebalanceInterval: 6 * time.Hour,
		},
		stats: &ReplicationStatistics{
			LastUpdated: time.Now(),
		},
	}

	// Initialize consistent hashing
	consistentHash, err := NewConsistentHashingImpl()
	if err != nil {
		return nil, fmt.Errorf("failed to create consistent hashing: %w", err)
	}
	rm.consistentHash = consistentHash

	// Add known peers to consistent hash ring
	peers := dht.GetConnectedPeers()
	for _, peerID := range peers {
		rm.consistentHash.AddNode(peerID.String())
	}

	return rm, nil
}

// Start starts the replication manager
func (rm *ReplicationManagerImpl) Start(ctx context.Context) error {
	rm.mu.Lock()
	if rm.running {
		rm.mu.Unlock()
		return fmt.Errorf("replication manager already running")
	}
	rm.running = true
	rm.mu.Unlock()

	// Start background workers
	go rm.repairWorker(ctx)
	go rm.rebalanceWorker(ctx)
	go rm.healthChecker(ctx)

	return nil
}

// Stop stops the replication manager
func (rm *ReplicationManagerImpl) Stop() error {
	rm.mu.Lock()
	defer rm.mu.Unlock()

	rm.running = false
	close(rm.repairQueue)
	close(rm.rebalanceQueue)

	return nil
}

// EnsureReplication ensures context meets replication requirements
func (rm *ReplicationManagerImpl) EnsureReplication(ctx context.Context, address ucxl.Address, factor int) error {
	if factor < rm.policy.MinFactor {
		factor = rm.policy.MinFactor
	}
	if factor > rm.policy.MaxFactor {
		factor = rm.policy.MaxFactor
	}

	// Get current replication status
	status, err := rm.GetReplicationStatus(ctx, address)
	if err != nil {
		return fmt.Errorf("failed to get replication status: %w", err)
	}

	if status.CurrentReplicas >= factor {
		return nil // Already sufficiently replicated
	}

	// Calculate how many more replicas we need
	needed := factor - status.CurrentReplicas

	// Select target nodes for additional replicas
	targetNodes, err := rm.selectReplicationNodes(address, needed)
	if err != nil {
		return fmt.Errorf("failed to select replication nodes: %w", err)
	}

	// Create replicas on target nodes
	for _, nodeID := range targetNodes {
		if err := rm.createReplica(ctx, address, nodeID); err != nil {
			// Log error but continue with other nodes
			continue
		}
	}

	// Update replication status
	rm.updateReplicationStatus(address, status.CurrentReplicas+len(targetNodes))

	return nil
}

// RepairReplicas repairs missing or corrupted replicas
func (rm *ReplicationManagerImpl) RepairReplicas(ctx context.Context, address ucxl.Address) (*RepairResult, error) {
	start := time.Now()

	result := &RepairResult{
		Address:          address.String(),
		RepairTime:       0,
		RepairSuccessful: false,
		Errors:           []string{},
		RepairedAt:       time.Now(),
	}

	// Get current replication status
	status, err := rm.GetReplicationStatus(ctx, address)
	if err != nil {
		result.Errors = append(result.Errors, fmt.Sprintf("failed to get replication status: %v", err))
		return result, err
	}

	// Identify unhealthy replicas
	unhealthyNodes := []string{}
	for nodeID, replica := range status.ReplicaDistribution {
		if replica == 0 { // Node should have replica but doesn't
			unhealthyNodes = append(unhealthyNodes, nodeID)
		}
	}

	// Repair missing replicas
	repaired := 0
	for _, nodeID := range unhealthyNodes {
		if err := rm.createReplica(ctx, address, nodeID); err != nil {
			result.Errors = append(result.Errors, fmt.Sprintf("failed to repair replica on node %s: %v", nodeID, err))
		} else {
			repaired++
		}
	}

	result.RepairedReplicas = repaired
	result.RepairTime = time.Since(start)
	result.RepairSuccessful = len(result.Errors) == 0

	rm.mu.Lock()
	rm.stats.RepairRequests++
	if result.RepairSuccessful {
		rm.stats.SuccessfulRepairs++
	} else {
		rm.stats.FailedRepairs++
	}
	rm.stats.AverageRepairTime = (rm.stats.AverageRepairTime + result.RepairTime) / 2
	rm.stats.LastUpdated = time.Now()
	rm.mu.Unlock()

	return result, nil
}

// BalanceReplicas rebalances replicas across cluster nodes
func (rm *ReplicationManagerImpl) BalanceReplicas(ctx context.Context) (*RebalanceResult, error) {
	start := time.Now()

	result := &RebalanceResult{
		RebalanceTime:      0,
		RebalanceSuccessful: false,
		Errors:             []string{},
		RebalancedAt:       time.Now(),
	}

	// Get current cluster topology
	peers := rm.dht.GetConnectedPeers()
	if len(peers) < rm.policy.MinFactor {
		result.Errors = append(result.Errors, "insufficient peers for rebalancing")
		return result, fmt.Errorf("insufficient peers for rebalancing")
	}

	// Calculate ideal distribution
	idealDistribution := rm.calculateIdealDistribution(peers)

	// Get current distribution for all contexts
	currentDistribution := rm.getCurrentDistribution(ctx)

	// Calculate moves needed
	moves := rm.calculateRebalanceMoves(currentDistribution, idealDistribution)

	// Execute moves
	moved := 0
	for _, move := range moves {
		if err := rm.moveReplica(ctx, move); err != nil {
			result.Errors = append(result.Errors, fmt.Sprintf("failed to move replica: %v", err))
		} else {
			moved++
		}
	}

	result.MovedReplicas = moved
	result.RebalanceTime = time.Since(start)
	result.RebalanceSuccessful = len(result.Errors) == 0

	// Calculate load balance improvement
	if len(moves) > 0 {
		result.LoadBalanceImprovement = float64(moved) / float64(len(moves))
	}

	rm.mu.Lock()
	rm.stats.RebalanceOperations++
	rm.stats.LastRebalanceTime = time.Now()
	rm.stats.LastUpdated = time.Now()
	rm.mu.Unlock()

	return result, nil
}

// GetReplicationStatus returns current replication status
func (rm *ReplicationManagerImpl) GetReplicationStatus(ctx context.Context, address ucxl.Address) (*ReplicaHealth, error) {
	rm.mu.RLock()
	status, exists := rm.replicationMap[address.String()]
	rm.mu.RUnlock()

	if !exists {
		// Create new status entry
		status = &ReplicationStatus{
			Address:             address.String(),
			DesiredReplicas:     rm.policy.DefaultFactor,
			CurrentReplicas:     0,
			HealthyReplicas:     0,
			ReplicationHealth:   0.0,
			ReplicaDistribution: make(map[string]int),
			LastReplication:     time.Time{},
			ReplicationErrors:   []string{},
			Status:              "unknown",
		}

		// Try to discover existing replicas
		rm.discoverReplicas(ctx, address, status)

		rm.mu.Lock()
		rm.replicationMap[address.String()] = status
		rm.mu.Unlock()
	}

	// Convert to ReplicaHealth format
	health := &ReplicaHealth{
		Address:         address,
		TotalReplicas:   status.CurrentReplicas,
		HealthyReplicas: status.HealthyReplicas,
		FailedReplicas:  status.CurrentReplicas - status.HealthyReplicas,
		ReplicaNodes:    []*ReplicaNode{},
		OverallHealth:   rm.determineOverallHealth(status),
		LastChecked:     time.Now(),
		RepairNeeded:    status.HealthyReplicas < status.DesiredReplicas,
	}

	// Populate replica nodes
	for nodeID, count := range status.ReplicaDistribution {
		if count > 0 {
			health.ReplicaNodes = append(health.ReplicaNodes, &ReplicaNode{
				NodeID:         nodeID,
				Status:         rm.getNodeReplicaStatus(nodeID),
				LastSeen:       time.Now(),
				Version:        1,
				Checksum:       "",
				Latency:        0,
				NetworkAddress: nodeID,
			})
		}
	}

	return health, nil
}

// SetReplicationFactor sets the desired replication factor
func (rm *ReplicationManagerImpl) SetReplicationFactor(factor int) error {
	if factor < 1 {
		return fmt.Errorf("replication factor must be at least 1")
	}
	if factor > 10 {
		return fmt.Errorf("replication factor cannot exceed 10")
	}

	rm.mu.Lock()
	rm.policy.DefaultFactor = factor
	rm.mu.Unlock()

	return nil
}

// GetReplicationStats returns replication statistics
func (rm *ReplicationManagerImpl) GetReplicationStats() (*ReplicationStatistics, error) {
	rm.mu.RLock()
	defer rm.mu.RUnlock()

	// Update calculated fields
	rm.stats.AverageReplicationFactor = rm.calculateAverageReplicationFactor()
	rm.stats.ReplicationEfficiency = rm.calculateReplicationEfficiency()

	return rm.stats, nil
}

// Background workers

func (rm *ReplicationManagerImpl) repairWorker(ctx context.Context) {
	for {
		select {
		case <-ctx.Done():
			return
		case req := <-rm.repairQueue:
			if req == nil {
				return // Channel closed
			}
			rm.RepairReplicas(ctx, req.Address)
		}
	}
}

func (rm *ReplicationManagerImpl) rebalanceWorker(ctx context.Context) {
	ticker := time.NewTicker(rm.policy.RebalanceInterval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			rm.BalanceReplicas(ctx)
		case req := <-rm.rebalanceQueue:
			if req == nil {
				return // Channel closed
			}
			rm.BalanceReplicas(ctx)
		}
	}
}

func (rm *ReplicationManagerImpl) healthChecker(ctx context.Context) {
	ticker := time.NewTicker(5 * time.Minute)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			rm.checkReplicaHealth(ctx)
		}
	}
}

// Helper methods

func (rm *ReplicationManagerImpl) selectReplicationNodes(address ucxl.Address, count int) ([]string, error) {
	// Use consistent hashing to select nodes
	candidates, err := rm.consistentHash.GetNodes(address.String(), count*2) // Get more candidates than needed
	if err != nil {
		return nil, err
	}

	// Filter out nodes that already have replicas and apply placement policies
	selectedNodes := []string{}
	for _, nodeID := range candidates {
		if len(selectedNodes) >= count {
			break
		}

		// Check if node already has this replica
		if rm.hasReplica(address, nodeID) {
			continue
		}

		// Check placement policies
		if rm.policy.AvoidSameNode && rm.isNodeOverloaded(nodeID) {
			continue
		}

		selectedNodes = append(selectedNodes, nodeID)
	}

	return selectedNodes, nil
}

func (rm *ReplicationManagerImpl) createReplica(ctx context.Context, address ucxl.Address, nodeID string) error {
	// In a real implementation, this would:
	// 1. Connect to the target node
	// 2. Transfer the context data
	// 3. Verify successful storage
	// For now, we'll simulate success
	return nil
}

func (rm *ReplicationManagerImpl) updateReplicationStatus(address ucxl.Address, currentReplicas int) {
	rm.mu.Lock()
	defer rm.mu.Unlock()

	addressStr := address.String()
	if status, exists := rm.replicationMap[addressStr]; exists {
		status.CurrentReplicas = currentReplicas
		status.LastReplication = time.Now()
	}
}

func (rm *ReplicationManagerImpl) discoverReplicas(ctx context.Context, address ucxl.Address, status *ReplicationStatus) {
	// In a real implementation, this would query the DHT to discover existing replicas
	// For now, we'll simulate some replicas
	peers := rm.dht.GetConnectedPeers()
	if len(peers) > 0 {
		status.CurrentReplicas = min(len(peers), rm.policy.DefaultFactor)
		status.HealthyReplicas = status.CurrentReplicas
		
		for i, peer := range peers {
			if i >= status.CurrentReplicas {
				break
			}
			status.ReplicaDistribution[peer.String()] = 1
		}
	}
}

func (rm *ReplicationManagerImpl) determineOverallHealth(status *ReplicationStatus) HealthStatus {
	if status.HealthyReplicas == 0 {
		return HealthFailed
	}
	
	healthRatio := float64(status.HealthyReplicas) / float64(status.DesiredReplicas)
	
	if healthRatio >= 1.0 {
		return HealthHealthy
	} else if healthRatio >= 0.7 {
		return HealthDegraded
	} else if healthRatio >= 0.3 {
		return HealthCritical
	} else {
		return HealthFailed
	}
}

func (rm *ReplicationManagerImpl) getNodeReplicaStatus(nodeID string) ReplicaStatus {
	// In a real implementation, this would check the actual status of the replica on the node
	// For now, assume healthy
	return ReplicaHealthy
}

func (rm *ReplicationManagerImpl) calculateAverageReplicationFactor() float64 {
	rm.mu.RLock()
	defer rm.mu.RUnlock()

	if len(rm.replicationMap) == 0 {
		return 0
	}

	total := 0
	for _, status := range rm.replicationMap {
		total += status.CurrentReplicas
	}

	return float64(total) / float64(len(rm.replicationMap))
}

func (rm *ReplicationManagerImpl) calculateReplicationEfficiency() float64 {
	rm.mu.RLock()
	defer rm.mu.RUnlock()

	if len(rm.replicationMap) == 0 {
		return 1.0
	}

	efficient := 0
	for _, status := range rm.replicationMap {
		if status.HealthyReplicas >= status.DesiredReplicas {
			efficient++
		}
	}

	return float64(efficient) / float64(len(rm.replicationMap))
}

func (rm *ReplicationManagerImpl) checkReplicaHealth(ctx context.Context) {
	rm.mu.RLock()
	addresses := make([]string, 0, len(rm.replicationMap))
	for addr := range rm.replicationMap {
		addresses = append(addresses, addr)
	}
	rm.mu.RUnlock()

	for _, addrStr := range addresses {
		addr, err := ucxl.ParseAddress(addrStr)
		if err != nil {
			continue
		}

		// Check if repair is needed
		status, err := rm.GetReplicationStatus(ctx, addr)
		if err != nil {
			continue
		}

		if status.RepairNeeded {
			select {
			case rm.repairQueue <- &RepairRequest{
				Address:     addr,
				RequestedBy: "health_checker",
				Priority:    PriorityNormal,
				RequestTime: time.Now(),
			}:
			default:
				// Queue is full, skip this repair
			}
		}
	}
}

func (rm *ReplicationManagerImpl) calculateIdealDistribution(peers []peer.ID) map[string]int {
	// Simple ideal distribution - equal replicas per node
	distribution := make(map[string]int)
	for _, peer := range peers {
		distribution[peer.String()] = 0
	}
	return distribution
}

func (rm *ReplicationManagerImpl) getCurrentDistribution(ctx context.Context) map[string]map[string]int {
	// Returns current distribution: address -> node -> replica count
	distribution := make(map[string]map[string]int)
	
	rm.mu.RLock()
	for addr, status := range rm.replicationMap {
		distribution[addr] = make(map[string]int)
		for nodeID, count := range status.ReplicaDistribution {
			distribution[addr][nodeID] = count
		}
	}
	rm.mu.RUnlock()
	
	return distribution
}

func (rm *ReplicationManagerImpl) calculateRebalanceMoves(current, ideal map[string]map[string]int) []*RebalanceMove {
	moves := []*RebalanceMove{}
	// Simplified implementation - in production would use sophisticated algorithms
	return moves
}

func (rm *ReplicationManagerImpl) moveReplica(ctx context.Context, move *RebalanceMove) error {
	// Implementation would move replica from source to target node
	return nil
}

func (rm *ReplicationManagerImpl) hasReplica(address ucxl.Address, nodeID string) bool {
	rm.mu.RLock()
	defer rm.mu.RUnlock()

	if status, exists := rm.replicationMap[address.String()]; exists {
		return status.ReplicaDistribution[nodeID] > 0
	}
	return false
}

func (rm *ReplicationManagerImpl) isNodeOverloaded(nodeID string) bool {
	// Simple implementation - check if node has too many replicas
	rm.mu.RLock()
	defer rm.mu.RUnlock()

	totalReplicas := 0
	for _, status := range rm.replicationMap {
		totalReplicas += status.ReplicaDistribution[nodeID]
	}

	// Consider overloaded if more than average + 50%
	averageLoad := rm.calculateAverageReplicationFactor()
	return float64(totalReplicas) > averageLoad*1.5
}

// RebalanceMove represents a replica move operation
type RebalanceMove struct {
	Address     ucxl.Address `json:"address"`
	FromNode    string       `json:"from_node"`
	ToNode      string       `json:"to_node"`
	Priority    Priority     `json:"priority"`
	Reason      string       `json:"reason"`
}

// Utility functions
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}