package scheduler

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

	"github.com/Fimeg/RedFlag/aggregator-server/internal/database/queries"
	"github.com/Fimeg/RedFlag/aggregator-server/internal/models"
	"github.com/google/uuid"
)

// Config holds scheduler configuration
type Config struct {
	// CheckInterval is how often to check the queue for due jobs
	CheckInterval time.Duration

	// LookaheadWindow is how far ahead to look for jobs
	// Jobs due within this window will be batched and jittered
	LookaheadWindow time.Duration

	// MaxJitter is the maximum random delay added to job execution
	MaxJitter time.Duration

	// NumWorkers is the number of parallel workers for command creation
	NumWorkers int

	// BackpressureThreshold is max pending commands per agent before skipping
	BackpressureThreshold int

	// RateLimitPerSecond is max commands created per second (0 = unlimited)
	RateLimitPerSecond int
}

// DefaultConfig returns production-ready default configuration
func DefaultConfig() Config {
	return Config{
		CheckInterval:         10 * time.Second,
		LookaheadWindow:       60 * time.Second,
		MaxJitter:             30 * time.Second,
		NumWorkers:            10,
		BackpressureThreshold: 5,
		RateLimitPerSecond:    100,
	}
}

// Scheduler manages subsystem job scheduling with priority queue and worker pool
type Scheduler struct {
	config Config
	queue  *PriorityQueue

	// Database queries
	agentQueries   *queries.AgentQueries
	commandQueries *queries.CommandQueries

	// Worker pool
	jobChan chan *SubsystemJob
	workers []*worker

	// Rate limiting
	rateLimiter chan struct{}

	// Lifecycle management
	ctx      context.Context
	cancel   context.CancelFunc
	wg       sync.WaitGroup
	shutdown chan struct{}

	// Metrics
	mu    sync.RWMutex
	stats Stats
}

// Stats holds scheduler statistics
type Stats struct {
	JobsProcessed       int64
	JobsSkipped         int64
	CommandsCreated     int64
	CommandsFailed      int64
	BackpressureSkips   int64
	LastProcessedAt     time.Time
	QueueSize           int
	WorkerPoolUtilized  int
	AverageProcessingMS int64
}

// NewScheduler creates a new scheduler instance
func NewScheduler(config Config, agentQueries *queries.AgentQueries, commandQueries *queries.CommandQueries) *Scheduler {
	ctx, cancel := context.WithCancel(context.Background())

	s := &Scheduler{
		config:         config,
		queue:          NewPriorityQueue(),
		agentQueries:   agentQueries,
		commandQueries: commandQueries,
		jobChan:        make(chan *SubsystemJob, 1000), // Buffer 1000 jobs
		workers:        make([]*worker, config.NumWorkers),
		shutdown:       make(chan struct{}),
		ctx:            ctx,
		cancel:         cancel,
	}

	// Initialize rate limiter if configured
	if config.RateLimitPerSecond > 0 {
		s.rateLimiter = make(chan struct{}, config.RateLimitPerSecond)
		go s.refillRateLimiter()
	}

	// Initialize workers
	for i := 0; i < config.NumWorkers; i++ {
		s.workers[i] = &worker{
			id:        i,
			scheduler: s,
		}
	}

	return s
}

// LoadSubsystems loads all enabled auto-run subsystems from database into queue
func (s *Scheduler) LoadSubsystems(ctx context.Context) error {
	log.Println("[Scheduler] Loading subsystems from database...")

	// Get all agents (pass empty strings to get all agents regardless of status/os)
	agents, err := s.agentQueries.ListAgents("", "")
	if err != nil {
		return fmt.Errorf("failed to get agents: %w", err)
	}

	// For now, we'll create default subsystems for each agent
	// In full implementation, this would read from agent_subsystems table
	subsystems := []string{"updates", "storage", "system", "docker"}
	intervals := map[string]int{
		"updates": 15, // 15 minutes
		"storage": 15,
		"system":  30,
		"docker":  15,
	}

	loaded := 0
	for _, agent := range agents {
		// Skip offline agents (haven't checked in for 10+ minutes)
		if time.Since(agent.LastSeen) > 10*time.Minute {
			continue
		}

		for _, subsystem := range subsystems {
			// TODO: Check agent metadata for subsystem enablement
			// For now, assume all subsystems are enabled

			job := &SubsystemJob{
				AgentID:         agent.ID,
				AgentHostname:   agent.Hostname,
				Subsystem:       subsystem,
				IntervalMinutes: intervals[subsystem],
				NextRunAt:       time.Now().Add(time.Duration(intervals[subsystem]) * time.Minute),
				Enabled:         true,
			}

			s.queue.Push(job)
			loaded++
		}
	}

	log.Printf("[Scheduler] Loaded %d subsystem jobs for %d agents\n", loaded, len(agents))
	return nil
}

// Start begins the scheduler main loop and workers
func (s *Scheduler) Start() error {
	log.Printf("[Scheduler] Starting with %d workers, check interval %v\n",
		s.config.NumWorkers, s.config.CheckInterval)

	// Start workers
	for _, w := range s.workers {
		s.wg.Add(1)
		go w.run()
	}

	// Start main loop
	s.wg.Add(1)
	go s.mainLoop()

	log.Println("[Scheduler] Started successfully")
	return nil
}

// Stop gracefully shuts down the scheduler
func (s *Scheduler) Stop() error {
	log.Println("[Scheduler] Shutting down...")

	// Signal shutdown
	s.cancel()
	close(s.shutdown)

	// Close job channel (workers will drain and exit)
	close(s.jobChan)

	// Wait for all goroutines with timeout
	done := make(chan struct{})
	go func() {
		s.wg.Wait()
		close(done)
	}()

	select {
	case <-done:
		log.Println("[Scheduler] Shutdown complete")
		return nil
	case <-time.After(30 * time.Second):
		log.Println("[Scheduler] Shutdown timeout - forcing exit")
		return fmt.Errorf("shutdown timeout")
	}
}

// mainLoop is the scheduler's main processing loop
func (s *Scheduler) mainLoop() {
	defer s.wg.Done()

	ticker := time.NewTicker(s.config.CheckInterval)
	defer ticker.Stop()

	log.Printf("[Scheduler] Main loop started (check every %v)\n", s.config.CheckInterval)

	for {
		select {
		case <-s.shutdown:
			log.Println("[Scheduler] Main loop shutting down")
			return

		case <-ticker.C:
			s.processQueue()
		}
	}
}

// processQueue checks for due jobs and dispatches them to workers
func (s *Scheduler) processQueue() {
	start := time.Now()

	// Get all jobs due within lookahead window
	cutoff := time.Now().Add(s.config.LookaheadWindow)
	dueJobs := s.queue.PopBefore(cutoff, 0) // No limit, get all

	if len(dueJobs) == 0 {
		// No jobs due, just update stats
		s.mu.Lock()
		s.stats.QueueSize = s.queue.Len()
		s.mu.Unlock()
		return
	}

	log.Printf("[Scheduler] Processing %d jobs due before %s\n",
		len(dueJobs), cutoff.Format("15:04:05"))

	// Add jitter to each job and dispatch to workers
	dispatched := 0
	for _, job := range dueJobs {
		// Add random jitter (0 to MaxJitter)
		jitter := time.Duration(rand.Intn(int(s.config.MaxJitter.Seconds()))) * time.Second
		job.NextRunAt = job.NextRunAt.Add(jitter)

		// Dispatch to worker pool (non-blocking)
		select {
		case s.jobChan <- job:
			dispatched++
		default:
			// Worker pool full, re-queue job
			log.Printf("[Scheduler] Worker pool full, re-queueing %s\n", job.String())
			s.queue.Push(job)

			s.mu.Lock()
			s.stats.JobsSkipped++
			s.mu.Unlock()
		}
	}

	// Update stats
	duration := time.Since(start)
	s.mu.Lock()
	s.stats.JobsProcessed += int64(dispatched)
	s.stats.LastProcessedAt = time.Now()
	s.stats.QueueSize = s.queue.Len()
	s.stats.WorkerPoolUtilized = len(s.jobChan)
	s.stats.AverageProcessingMS = duration.Milliseconds()
	s.mu.Unlock()

	log.Printf("[Scheduler] Dispatched %d jobs in %v (queue: %d remaining)\n",
		dispatched, duration, s.queue.Len())
}

// refillRateLimiter continuously refills the rate limiter token bucket
func (s *Scheduler) refillRateLimiter() {
	ticker := time.NewTicker(time.Second / time.Duration(s.config.RateLimitPerSecond))
	defer ticker.Stop()

	for {
		select {
		case <-s.shutdown:
			return
		case <-ticker.C:
			// Try to add token (non-blocking)
			select {
			case s.rateLimiter <- struct{}{}:
			default:
				// Bucket full, skip
			}
		}
	}
}

// GetStats returns current scheduler statistics (thread-safe)
func (s *Scheduler) GetStats() Stats {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.stats
}

// GetQueueStats returns current queue statistics
func (s *Scheduler) GetQueueStats() QueueStats {
	return s.queue.GetStats()
}

// worker processes jobs from the job channel
type worker struct {
	id        int
	scheduler *Scheduler
}

func (w *worker) run() {
	defer w.scheduler.wg.Done()

	log.Printf("[Worker %d] Started\n", w.id)

	for job := range w.scheduler.jobChan {
		if err := w.processJob(job); err != nil {
			log.Printf("[Worker %d] Failed to process %s: %v\n", w.id, job.String(), err)

			w.scheduler.mu.Lock()
			w.scheduler.stats.CommandsFailed++
			w.scheduler.mu.Unlock()
		} else {
			w.scheduler.mu.Lock()
			w.scheduler.stats.CommandsCreated++
			w.scheduler.mu.Unlock()
		}

		// Re-queue job for next execution
		job.NextRunAt = time.Now().Add(time.Duration(job.IntervalMinutes) * time.Minute)
		w.scheduler.queue.Push(job)
	}

	log.Printf("[Worker %d] Stopped\n", w.id)
}

func (w *worker) processJob(job *SubsystemJob) error {
	// Apply rate limiting if configured
	if w.scheduler.rateLimiter != nil {
		select {
		case <-w.scheduler.rateLimiter:
			// Token acquired
		case <-w.scheduler.shutdown:
			return fmt.Errorf("shutdown during rate limit wait")
		}
	}

	// Check backpressure: skip if agent has too many pending commands
	pendingCount, err := w.scheduler.commandQueries.CountPendingCommandsForAgent(job.AgentID)
	if err != nil {
		return fmt.Errorf("failed to check pending commands: %w", err)
	}

	if pendingCount >= w.scheduler.config.BackpressureThreshold {
		log.Printf("[Worker %d] Backpressure: agent %s has %d pending commands, skipping %s\n",
			w.id, job.AgentHostname, pendingCount, job.Subsystem)

		w.scheduler.mu.Lock()
		w.scheduler.stats.BackpressureSkips++
		w.scheduler.mu.Unlock()

		return nil // Not an error, just skipped
	}

	// Create command
	cmd := &models.AgentCommand{
		ID:          uuid.New(),
		AgentID:     job.AgentID,
		CommandType: fmt.Sprintf("scan_%s", job.Subsystem),
		Params:      models.JSONB{},
		Status:      models.CommandStatusPending,
		Source:      models.CommandSourceSystem,
		CreatedAt:   time.Now(),
	}

	if err := w.scheduler.commandQueries.CreateCommand(cmd); err != nil {
		return fmt.Errorf("failed to create command: %w", err)
	}

	log.Printf("[Worker %d] Created %s command for %s\n",
		w.id, job.Subsystem, job.AgentHostname)

	return nil
}