package leader

import (
	"context"
	"fmt"
	"math/rand"
	"sort"
	"sync"
	"time"

	"chorus/pkg/dht"
	"chorus/pkg/election"
	slurpContext "chorus/pkg/slurp/context"
	"chorus/pkg/slurp/intelligence"
	"chorus/pkg/slurp/storage"
)

// ContextManager handles leader-only context generation duties
//
// This is the primary interface for managing contextual intelligence
// operations that require cluster-wide coordination and can only be
// performed by the elected leader node.
type ContextManager interface {
	// RequestContextGeneration queues a context generation request
	// Only the leader processes these requests to prevent conflicts
	RequestContextGeneration(req *ContextGenerationRequest) error

	// RequestFromLeader allows non-leader nodes to request context from leader
	RequestFromLeader(req *ContextGenerationRequest) (*ContextGenerationResult, error)

	// GetGenerationStatus returns status of context generation operations
	GetGenerationStatus() (*GenerationStatus, error)

	// GetQueueStatus returns status of the generation queue
	GetQueueStatus() (*QueueStatus, error)

	// CancelGeneration cancels pending or active generation task
	CancelGeneration(taskID string) error

	// PrioritizeGeneration changes priority of queued generation task
	PrioritizeGeneration(taskID string, priority Priority) error

	// IsLeader returns whether this node is the current leader
	IsLeader() bool

	// WaitForLeadership blocks until this node becomes leader
	WaitForLeadership(ctx context.Context) error

	// GetLeaderInfo returns information about current leader
	GetLeaderInfo() (*LeaderInfo, error)

	// TransferLeadership initiates graceful leadership transfer
	TransferLeadership(ctx context.Context, targetNodeID string) error

	// GetManagerStats returns manager performance statistics
	GetManagerStats() (*ManagerStatistics, error)
}

// GenerationCoordinator coordinates context generation across the cluster
//
// Manages the distribution and coordination of context generation tasks,
// ensuring efficient resource utilization and preventing duplicate work.
type GenerationCoordinator interface {
	// CoordinateGeneration coordinates generation of context across cluster
	CoordinateGeneration(ctx context.Context, req *ContextGenerationRequest) (*CoordinationResult, error)

	// DistributeGeneration distributes generation task to appropriate node
	DistributeGeneration(ctx context.Context, task *GenerationTask) error

	// CollectGenerationResults collects results from distributed generation
	CollectGenerationResults(ctx context.Context, taskID string) (*GenerationResults, error)

	// CheckGenerationStatus checks status of distributed generation
	CheckGenerationStatus(ctx context.Context, taskID string) (*TaskStatus, error)

	// RebalanceLoad rebalances generation load across cluster nodes
	RebalanceLoad(ctx context.Context) (*RebalanceResult, error)

	// GetClusterCapacity returns current cluster generation capacity
	GetClusterCapacity() (*ClusterCapacity, error)

	// SetGenerationPolicy configures generation coordination policy
	SetGenerationPolicy(policy *GenerationPolicy) error

	// GetCoordinationStats returns coordination performance statistics
	GetCoordinationStats() (*CoordinationStatistics, error)
}

// QueueManager manages context generation request queues
//
// Handles prioritization, scheduling, and lifecycle management of
// context generation requests with support for different priority
// levels and fair resource allocation.
type QueueManager interface {
	// EnqueueRequest adds request to generation queue
	EnqueueRequest(req *ContextGenerationRequest) error

	// DequeueRequest gets next request from queue
	DequeueRequest() (*ContextGenerationRequest, error)

	// PeekQueue shows next request without removing it
	PeekQueue() (*ContextGenerationRequest, error)

	// UpdateRequestPriority changes priority of queued request
	UpdateRequestPriority(requestID string, priority Priority) error

	// CancelRequest removes request from queue
	CancelRequest(requestID string) error

	// GetQueueLength returns current queue length
	GetQueueLength() int

	// GetQueuedRequests returns all queued requests
	GetQueuedRequests() ([]*ContextGenerationRequest, error)

	// ClearQueue removes all requests from queue
	ClearQueue() error

	// SetQueuePolicy configures queue management policy
	SetQueuePolicy(policy *QueuePolicy) error

	// GetQueueStats returns queue performance statistics
	GetQueueStats() (*QueueStatistics, error)
}

// FailoverManager handles leader failover and state transfer
//
// Ensures continuity of context generation operations during leadership
// changes with minimal disruption and no loss of queued requests.
type FailoverManager interface {
	// PrepareFailover prepares current state for potential failover
	PrepareFailover(ctx context.Context) (*FailoverState, error)

	// ExecuteFailover executes failover to become new leader
	ExecuteFailover(ctx context.Context, previousState *FailoverState) error

	// TransferState transfers leadership state to another node
	TransferState(ctx context.Context, targetNodeID string) error

	// ReceiveState receives leadership state from previous leader
	ReceiveState(ctx context.Context, state *FailoverState) error

	// ValidateState validates received failover state
	ValidateState(state *FailoverState) (*StateValidation, error)

	// RecoverFromFailover recovers operations after failover
	RecoverFromFailover(ctx context.Context) (*RecoveryResult, error)

	// GetFailoverHistory returns history of failover events
	GetFailoverHistory() ([]*FailoverEvent, error)

	// GetFailoverStats returns failover statistics
	GetFailoverStats() (*FailoverStatistics, error)
}

// ClusterCoordinator manages cluster-wide context operations
//
// Coordinates context-related operations across all nodes in the cluster,
// including synchronization, health monitoring, and resource management.
type ClusterCoordinator interface {
	// SynchronizeCluster synchronizes context state across cluster
	SynchronizeCluster(ctx context.Context) (*SyncResult, error)

	// GetClusterState returns current cluster state
	GetClusterState() (*ClusterState, error)

	// GetNodeHealth returns health status of cluster nodes
	GetNodeHealth() (map[string]*NodeHealth, error)

	// EvictNode removes unresponsive node from cluster operations
	EvictNode(ctx context.Context, nodeID string) error

	// AddNode adds new node to cluster operations
	AddNode(ctx context.Context, nodeID string, nodeInfo *NodeInfo) error

	// BroadcastMessage broadcasts message to all cluster nodes
	BroadcastMessage(ctx context.Context, message *ClusterMessage) error

	// GetClusterMetrics returns cluster performance metrics
	GetClusterMetrics() (*ClusterMetrics, error)

	// ConfigureCluster configures cluster coordination parameters
	ConfigureCluster(config *ClusterConfig) error
}

// HealthMonitor monitors cluster and context system health
//
// Provides health monitoring for the distributed context system,
// including node health, queue health, and overall system status.
type HealthMonitor interface {
	// CheckHealth performs comprehensive health check
	CheckHealth(ctx context.Context) (*HealthStatus, error)

	// CheckNodeHealth checks health of specific node
	CheckNodeHealth(ctx context.Context, nodeID string) (*NodeHealth, error)

	// CheckQueueHealth checks health of generation queue
	CheckQueueHealth() (*QueueHealth, error)

	// CheckLeaderHealth checks health of leader node
	CheckLeaderHealth() (*LeaderHealth, error)

	// GetHealthMetrics returns health monitoring metrics
	GetHealthMetrics() (*HealthMetrics, error)

	// SetHealthPolicy configures health monitoring policy
	SetHealthPolicy(policy *HealthPolicy) error

	// GetHealthHistory returns history of health events
	GetHealthHistory(timeRange time.Duration) ([]*HealthEvent, error)

	// SubscribeToHealthEvents subscribes to health event notifications
	SubscribeToHealthEvents(handler HealthEventHandler) error
}

// ResourceManager manages resource allocation for context operations
type ResourceManager interface {
	// AllocateResources allocates resources for context generation
	AllocateResources(req *ResourceRequest) (*ResourceAllocation, error)

	// ReleaseResources releases allocated resources
	ReleaseResources(allocationID string) error

	// GetAvailableResources returns currently available resources
	GetAvailableResources() (*AvailableResources, error)

	// SetResourceLimits configures resource usage limits
	SetResourceLimits(limits *ResourceLimits) error

	// GetResourceUsage returns current resource usage statistics
	GetResourceUsage() (*ResourceUsage, error)

	// RebalanceResources rebalances resources across operations
	RebalanceResources(ctx context.Context) (*ResourceRebalanceResult, error)
}

// LeaderContextManager is the concrete implementation of context management
type LeaderContextManager struct {
	mu              sync.RWMutex
	isLeader        bool
	election        election.Election
	dht             dht.DHT
	intelligence    intelligence.IntelligenceEngine
	storage         storage.ContextStore
	contextResolver slurpContext.ContextResolver
	contextUpserter slurp.ContextPersister

	// Context generation state
	generationQueue chan *ContextGenerationRequest
	activeJobs      map[string]*ContextGenerationJob
	completedJobs   map[string]*ContextGenerationJob

	// Coordination components
	coordinator     GenerationCoordinator
	queueManager    QueueManager
	failoverManager FailoverManager
	clusterCoord    ClusterCoordinator
	healthMonitor   HealthMonitor
	resourceManager ResourceManager

	// Configuration
	config *ManagerConfig

	// Statistics
	stats *ManagerStatistics

	// Shutdown coordination
	shutdownChan chan struct{}
	shutdownOnce sync.Once
}

// SetContextPersister registers the SLURP persistence hook (Roadmap: SEC-SLURP 1.1).
func (cm *LeaderContextManager) SetContextPersister(persister slurp.ContextPersister) {
	cm.mu.Lock()
	defer cm.mu.Unlock()
	cm.contextUpserter = persister
}

// NewContextManager creates a new leader context manager
func NewContextManager(
	election election.Election,
	dht dht.DHT,
	intelligence intelligence.IntelligenceEngine,
	storage storage.ContextStore,
	resolver slurpContext.ContextResolver,
) *LeaderContextManager {
	cm := &LeaderContextManager{
		election:        election,
		dht:             dht,
		intelligence:    intelligence,
		storage:         storage,
		contextResolver: resolver,
		generationQueue: make(chan *ContextGenerationRequest, 1000),
		activeJobs:      make(map[string]*ContextGenerationJob),
		completedJobs:   make(map[string]*ContextGenerationJob),
		shutdownChan:    make(chan struct{}),
		config:          DefaultManagerConfig(),
		stats:           &ManagerStatistics{},
	}

	// Initialize coordination components
	cm.coordinator = NewGenerationCoordinator(cm)
	cm.queueManager = NewQueueManager(cm)
	cm.failoverManager = NewFailoverManager(cm)
	cm.clusterCoord = NewClusterCoordinator(cm)
	cm.healthMonitor = NewHealthMonitor(cm)
	cm.resourceManager = NewResourceManager(cm)

	// Start background processes
	go cm.watchLeadershipChanges()
	go cm.processContextGeneration()
	go cm.monitorHealth()
	go cm.syncCluster()

	return cm
}

// RequestContextGeneration queues a context generation request
func (cm *LeaderContextManager) RequestContextGeneration(req *ContextGenerationRequest) error {
	if !cm.IsLeader() {
		return ErrNotLeader
	}

	// Validate request
	if err := cm.validateRequest(req); err != nil {
		return err
	}

	// Check for duplicates
	if cm.isDuplicate(req) {
		return ErrDuplicateRequest
	}

	// Enqueue request
	select {
	case cm.generationQueue <- req:
		cm.stats.TotalRequests++
		return nil
	default:
		cm.stats.DroppedRequests++
		return ErrQueueFull
	}
}

// IsLeader returns whether this node is the current leader
func (cm *LeaderContextManager) IsLeader() bool {
	cm.mu.RLock()
	defer cm.mu.RUnlock()
	return cm.isLeader
}

// GetGenerationStatus returns status of context generation operations
func (cm *LeaderContextManager) GetGenerationStatus() (*GenerationStatus, error) {
	cm.mu.RLock()
	defer cm.mu.RUnlock()

	status := &GenerationStatus{
		ActiveTasks:    len(cm.activeJobs),
		QueuedTasks:    len(cm.generationQueue),
		CompletedTasks: len(cm.completedJobs),
		IsLeader:       cm.isLeader,
		LastUpdate:     time.Now(),
	}

	// Calculate estimated completion time
	if status.ActiveTasks > 0 || status.QueuedTasks > 0 {
		avgJobTime := cm.calculateAverageJobTime()
		totalRemaining := time.Duration(status.ActiveTasks+status.QueuedTasks) * avgJobTime
		status.EstimatedCompletion = time.Now().Add(totalRemaining)
	}

	return status, nil
}

// watchLeadershipChanges monitors leadership changes
func (cm *LeaderContextManager) watchLeadershipChanges() {
	for {
		select {
		case <-cm.shutdownChan:
			return
		default:
			// Check leadership status
			newIsLeader := cm.election.IsLeader()

			cm.mu.Lock()
			oldIsLeader := cm.isLeader
			cm.isLeader = newIsLeader
			cm.mu.Unlock()

			// Handle leadership change
			if oldIsLeader != newIsLeader {
				if newIsLeader {
					cm.onBecomeLeader()
				} else {
					cm.onLoseLeadership()
				}
			}

			// Sleep before next check
			time.Sleep(cm.config.LeadershipCheckInterval)
		}
	}
}

// processContextGeneration processes context generation requests
func (cm *LeaderContextManager) processContextGeneration() {
	for {
		select {
		case req := <-cm.generationQueue:
			if cm.IsLeader() {
				go cm.handleGenerationRequest(req)
			} else {
				// Not leader anymore, requeue or forward to leader
				cm.handleNonLeaderRequest(req)
			}
		case <-cm.shutdownChan:
			return
		}
	}
}

// handleGenerationRequest handles a single context generation request
func (cm *LeaderContextManager) handleGenerationRequest(req *ContextGenerationRequest) {
	job := &ContextGenerationJob{
		ID:        generateJobID(),
		Request:   req,
		Status:    JobStatusRunning,
		StartedAt: time.Now(),
	}

	cm.mu.Lock()
	cm.activeJobs[job.ID] = job
	cm.mu.Unlock()

	defer func() {
		cm.mu.Lock()
		delete(cm.activeJobs, job.ID)
		cm.completedJobs[job.ID] = job
		cm.mu.Unlock()

		// Clean up old completed jobs
		cm.cleanupCompletedJobs()
	}()

	// Generate context using intelligence engine
	contextNode, err := cm.intelligence.AnalyzeFile(
		context.Background(),
		req.FilePath,
		req.Role,
	)

	completedAt := time.Now()
	job.CompletedAt = &completedAt

	if err != nil {
		job.Status = JobStatusFailed
		job.Error = err
		cm.stats.FailedJobs++
	} else {
		job.Status = JobStatusCompleted
		job.Result = contextNode
		cm.stats.CompletedJobs++

		// Store generated context (SEC-SLURP 1.1 persistence bridge)
		if cm.contextUpserter != nil {
			if _, persistErr := cm.contextUpserter.UpsertContext(context.Background(), contextNode); persistErr != nil {
				// TODO(SEC-SLURP 1.1): surface persistence errors via structured logging/telemetry
			}
		} else if cm.storage != nil {
			if err := cm.storage.StoreContext(context.Background(), contextNode, []string{req.Role}); err != nil {
				// TODO: Add proper logging when falling back to legacy storage path
			}
		}
	}
}

// Helper methods

func (cm *LeaderContextManager) validateRequest(req *ContextGenerationRequest) error {
	if req == nil {
		return ErrInvalidRequest
	}
	if req.UCXLAddress == "" {
		return ErrMissingUCXLAddress
	}
	if req.FilePath == "" {
		return ErrMissingFilePath
	}
	if req.Role == "" {
		return ErrMissingRole
	}
	return nil
}

func (cm *LeaderContextManager) isDuplicate(req *ContextGenerationRequest) bool {
	// Check active jobs
	for _, job := range cm.activeJobs {
		if job.Request.UCXLAddress == req.UCXLAddress && job.Request.Role == req.Role {
			return true
		}
	}
	return false
}

func (cm *LeaderContextManager) calculateAverageJobTime() time.Duration {
	if len(cm.completedJobs) == 0 {
		return time.Minute // Default estimate
	}

	var totalTime time.Duration
	count := 0

	for _, job := range cm.completedJobs {
		if job.CompletedAt != nil {
			totalTime += job.CompletedAt.Sub(job.StartedAt)
			count++
		}
	}

	if count == 0 {
		return time.Minute
	}

	return totalTime / time.Duration(count)
}

// calculateAverageWaitTime calculates average wait time for requests
func (cm *LeaderContextManager) calculateAverageWaitTime() time.Duration {
	// TODO: Track actual wait times for requests
	// For now, estimate based on queue length and processing rate
	queueLength := len(cm.generationQueue)
	if queueLength == 0 {
		return 0
	}

	avgJobTime := cm.calculateAverageJobTime()
	concurrency := cm.config.MaxConcurrentJobs

	// Estimate wait time based on queue position and processing capacity
	estimatedWait := time.Duration(queueLength/concurrency) * avgJobTime
	return estimatedWait
}

// GetQueueStatus returns status of the generation queue
func (cm *LeaderContextManager) GetQueueStatus() (*QueueStatus, error) {
	cm.mu.RLock()
	defer cm.mu.RUnlock()

	status := &QueueStatus{
		QueueLength:          len(cm.generationQueue),
		MaxQueueSize:         cm.config.QueueSize,
		QueuedRequests:       []*ContextGenerationRequest{},
		PriorityDistribution: make(map[Priority]int),
		AverageWaitTime:      cm.calculateAverageWaitTime(),
	}

	// Get oldest request time if any
	if len(cm.generationQueue) > 0 {
		// Peek at queue without draining
		oldest := time.Now()
		status.OldestRequest = &oldest
	}

	return status, nil
}

// CancelGeneration cancels pending or active generation task
func (cm *LeaderContextManager) CancelGeneration(taskID string) error {
	cm.mu.Lock()
	defer cm.mu.Unlock()

	// Check if task is active
	if job, exists := cm.activeJobs[taskID]; exists {
		job.Status = JobStatusCancelled
		job.Error = fmt.Errorf("task cancelled by user")
		completedAt := time.Now()
		job.CompletedAt = &completedAt

		delete(cm.activeJobs, taskID)
		cm.completedJobs[taskID] = job
		cm.stats.CancelledJobs++

		return nil
	}

	// TODO: Remove from queue if pending
	return fmt.Errorf("task %s not found", taskID)
}

// PrioritizeGeneration changes priority of queued generation task
func (cm *LeaderContextManager) PrioritizeGeneration(taskID string, priority Priority) error {
	// TODO: Implement priority change for queued tasks
	return fmt.Errorf("priority change not implemented")
}

// GetManagerStats returns manager performance statistics
func (cm *LeaderContextManager) GetManagerStats() (*ManagerStatistics, error) {
	cm.mu.RLock()
	defer cm.mu.RUnlock()

	stats := *cm.stats // Copy current stats
	stats.AverageJobTime = cm.calculateAverageJobTime()
	stats.HighestQueueLength = len(cm.generationQueue)

	return &stats, nil
}

func (cm *LeaderContextManager) onBecomeLeader() {
	// Initialize leader-specific state
	cm.stats.LeadershipChanges++
	cm.stats.LastBecameLeader = time.Now()

	// Recover any pending state from previous leader
	if err := cm.failoverManager.RecoverFromFailover(context.Background()); err != nil {
		// Log error but continue - we're the leader now
		// TODO: Add proper logging
	}
}

func (cm *LeaderContextManager) onLoseLeadership() {
	// Prepare state for transfer
	if state, err := cm.failoverManager.PrepareFailover(context.Background()); err == nil {
		// TODO: Send state to new leader
		_ = state
	}

	cm.stats.LastLostLeadership = time.Now()
}

func (cm *LeaderContextManager) handleNonLeaderRequest(req *ContextGenerationRequest) {
	// Forward request to current leader or queue for later
	// TODO: Implement leader forwarding
}

func (cm *LeaderContextManager) monitorHealth() {
	ticker := time.NewTicker(cm.config.HealthCheckInterval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			if _, err := cm.healthMonitor.CheckHealth(context.Background()); err != nil {
				// Handle health issues
				// TODO: Implement health issue handling
			}
		case <-cm.shutdownChan:
			return
		}
	}
}

func (cm *LeaderContextManager) syncCluster() {
	ticker := time.NewTicker(cm.config.ClusterSyncInterval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			if cm.IsLeader() {
				if _, err := cm.clusterCoord.SynchronizeCluster(context.Background()); err != nil {
					// Handle sync errors
					// TODO: Implement sync error handling
				}
			}
		case <-cm.shutdownChan:
			return
		}
	}
}

func (cm *LeaderContextManager) cleanupCompletedJobs() {
	cm.mu.Lock()
	defer cm.mu.Unlock()

	if len(cm.completedJobs) <= cm.config.MaxCompletedJobs {
		return
	}

	// Remove oldest completed jobs based on completion time
	type jobWithTime struct {
		id   string
		job  *ContextGenerationJob
		time time.Time
	}

	var jobs []jobWithTime
	for id, job := range cm.completedJobs {
		completedAt := time.Now()
		if job.CompletedAt != nil {
			completedAt = *job.CompletedAt
		}
		jobs = append(jobs, jobWithTime{id: id, job: job, time: completedAt})
	}

	// Sort by completion time (oldest first)
	sort.Slice(jobs, func(i, j int) bool {
		return jobs[i].time.Before(jobs[j].time)
	})

	// Remove oldest jobs to get back to limit
	toRemove := len(jobs) - cm.config.MaxCompletedJobs
	for i := 0; i < toRemove; i++ {
		delete(cm.completedJobs, jobs[i].id)
	}
}

func generateJobID() string {
	// Generate UUID-like job ID with timestamp
	timestamp := time.Now().Unix()
	random := rand.Int63()
	return fmt.Sprintf("ctx-job-%d-%x", timestamp, random&0xFFFFFF)
}

// Error definitions
var (
	ErrNotLeader          = &LeaderError{Code: "NOT_LEADER", Message: "Node is not the leader"}
	ErrQueueFull          = &LeaderError{Code: "QUEUE_FULL", Message: "Generation queue is full"}
	ErrDuplicateRequest   = &LeaderError{Code: "DUPLICATE_REQUEST", Message: "Duplicate generation request"}
	ErrInvalidRequest     = &LeaderError{Code: "INVALID_REQUEST", Message: "Invalid generation request"}
	ErrMissingUCXLAddress = &LeaderError{Code: "MISSING_UCXL_ADDRESS", Message: "Missing UCXL address"}
	ErrMissingFilePath    = &LeaderError{Code: "MISSING_FILE_PATH", Message: "Missing file path"}
	ErrMissingRole        = &LeaderError{Code: "MISSING_ROLE", Message: "Missing role"}
)

// LeaderError represents errors specific to leader operations
type LeaderError struct {
	Code    string `json:"code"`
	Message string `json:"message"`
}

func (e *LeaderError) Error() string {
	return e.Message
}

// DefaultManagerConfig returns default manager configuration
func DefaultManagerConfig() *ManagerConfig {
	return &ManagerConfig{
		LeadershipCheckInterval: 5 * time.Second,
		HealthCheckInterval:     30 * time.Second,
		ClusterSyncInterval:     60 * time.Second,
		MaxCompletedJobs:        1000,
		QueueSize:               10000,
		MaxConcurrentJobs:       10,
		JobTimeout:              10 * time.Minute,
	}
}