package scheduler

import (
	"context"
	"sync"

	"github.com/robfig/cron/v3"
	"go.uber.org/zap"

	"codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/config"
	"codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/pkg/leaderelection"
)

// Task represents a scheduled task
type Task interface {
	Name() string
	Schedule() string
	Execute(ctx context.Context) error
}

// Scheduler manages all scheduled tasks
// Tasks are only executed if this instance is the leader (when leader election is enabled)
type Scheduler struct {
	config          *config.Config
	logger          *zap.Logger
	cron            *cron.Cron
	tasks           []Task
	mu              sync.RWMutex
	ctx             context.Context
	cancel          context.CancelFunc
	leaderElection  leaderelection.LeaderElection // Leader election instance (can be nil if disabled)
}

// ProvideScheduler creates a new Scheduler instance for Wire DI
func ProvideScheduler(
	cfg *config.Config,
	logger *zap.Logger,
	leaderElection leaderelection.LeaderElection,
) *Scheduler {
	ctx, cancel := context.WithCancel(context.Background())

	logger = logger.Named("Scheduler")

	return &Scheduler{
		config:         cfg,
		logger:         logger,
		cron:           cron.New(),
		tasks:          make([]Task, 0),
		ctx:            ctx,
		cancel:         cancel,
		leaderElection: leaderElection,
	}
}

// RegisterTask registers a task to be scheduled
func (s *Scheduler) RegisterTask(task Task) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.logger.Info("Registering scheduled task",
		zap.String("task", task.Name()),
		zap.String("schedule", task.Schedule()))

	// Add task to scheduler
	_, err := s.cron.AddFunc(task.Schedule(), func() {
		s.executeTask(task)
	})

	if err != nil {
		s.logger.Error("Failed to register task",
			zap.String("task", task.Name()),
			zap.Error(err))
		return err
	}

	s.tasks = append(s.tasks, task)
	s.logger.Info("✅ Task registered successfully",
		zap.String("task", task.Name()))

	return nil
}

// executeTask executes a task with error handling and logging
// Tasks are only executed if this instance is the leader (when leader election is enabled)
func (s *Scheduler) executeTask(task Task) {
	// Check if leader election is enabled
	if s.config.LeaderElection.Enabled && s.leaderElection != nil {
		// Only execute if this instance is the leader
		if !s.leaderElection.IsLeader() {
			s.logger.Debug("Skipping task execution - not the leader",
				zap.String("task", task.Name()),
				zap.String("instance_id", s.leaderElection.GetInstanceID()))
			return
		}

		// Log that leader is executing the task
		s.logger.Info("👑 Leader executing scheduled task",
			zap.String("task", task.Name()),
			zap.String("instance_id", s.leaderElection.GetInstanceID()))
	} else {
		// Leader election disabled, execute normally
		s.logger.Info("Executing scheduled task",
			zap.String("task", task.Name()))
	}

	// Create a context for this execution
	ctx := s.ctx

	// Execute the task
	if err := task.Execute(ctx); err != nil {
		s.logger.Error("Task execution failed",
			zap.String("task", task.Name()),
			zap.Error(err))
		return
	}

	s.logger.Info("✅ Task completed successfully",
		zap.String("task", task.Name()))
}

// Start starts the scheduler
func (s *Scheduler) Start() error {
	s.mu.RLock()
	taskCount := len(s.tasks)
	s.mu.RUnlock()

	// Log leader election status
	if s.config.LeaderElection.Enabled && s.leaderElection != nil {
		s.logger.Info("🕐 Starting scheduler with leader election",
			zap.Int("registered_tasks", taskCount),
			zap.Bool("leader_election_enabled", true),
			zap.String("instance_id", s.leaderElection.GetInstanceID()))

		s.logger.Info("ℹ️  Tasks will ONLY execute on the leader instance")
	} else {
		s.logger.Info("🕐 Starting scheduler without leader election",
			zap.Int("registered_tasks", taskCount),
			zap.Bool("leader_election_enabled", false))

		s.logger.Warn("⚠️  Leader election is disabled - tasks will run on ALL instances")
	}

	if taskCount == 0 {
		s.logger.Warn("No tasks registered, scheduler will run but do nothing")
	}

	s.cron.Start()

	s.logger.Info("✅ Scheduler started successfully")
	return nil
}

// Stop stops the scheduler gracefully
func (s *Scheduler) Stop() error {
	s.logger.Info("Stopping scheduler...")

	// Cancel all running tasks
	s.cancel()

	// Stop the cron scheduler
	ctx := s.cron.Stop()
	<-ctx.Done()

	s.logger.Info("✅ Scheduler stopped successfully")
	return nil
}

// GetRegisteredTasks returns a list of registered task names
func (s *Scheduler) GetRegisteredTasks() []string {
	s.mu.RLock()
	defer s.mu.RUnlock()

	taskNames := make([]string, len(s.tasks))
	for i, task := range s.tasks {
		taskNames[i] = task.Name()
	}

	return taskNames
}