package scheduler

import (
	"context"
	"fmt"
	"log"
	"sync"
	"time"
)

var (
	budapestLoc     *time.Location
	budapestLocOnce sync.Once
)

func getBudapestLocation() *time.Location {
	budapestLocOnce.Do(func() {
		loc, err := time.LoadLocation("Europe/Budapest")
		if err != nil {
			log.Printf("[ERROR] Cannot load Europe/Budapest timezone: %v — using UTC", err)
			loc = time.UTC
		}
		budapestLoc = loc
	})
	return budapestLoc
}

// JobFunc is the function signature for scheduler jobs.
type JobFunc func(ctx context.Context) error

// Job represents a scheduled task.
type Job struct {
	Name     string
	Fn       JobFunc
	Interval time.Duration // for periodic jobs (every N)
	Schedule string        // for daily jobs ("02:30", "03:00") — mutually exclusive with Interval
	LastRun  time.Time
	LastErr  error
	Running  bool
}

// Scheduler manages periodic and daily jobs.
type Scheduler struct {
	mu     sync.Mutex
	jobs   []*Job
	logger *log.Logger
	ctx    context.Context
	cancel context.CancelFunc
	wg     sync.WaitGroup
}

// New creates a new Scheduler.
func New(logger *log.Logger) *Scheduler {
	return &Scheduler{
		logger: logger,
	}
}

// Every registers a periodic job that runs every interval.
func (s *Scheduler) Every(name string, interval time.Duration, fn JobFunc) {
	if interval <= 0 {
		s.logger.Printf("[ERROR] Periodic job %s has invalid interval %s — job not registered", name, interval)
		return
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	s.jobs = append(s.jobs, &Job{
		Name:     name,
		Fn:       fn,
		Interval: interval,
	})
	s.logger.Printf("[SCHED] Registered periodic job: %s (every %s)", name, interval)
}

// Daily registers a job that runs once per day at the specified time (HH:MM) in Europe/Budapest timezone.
func (s *Scheduler) Daily(name string, timeStr string, fn JobFunc) {
	s.mu.Lock()
	defer s.mu.Unlock()

	// Validate time format
	if _, _, err := parseDailyTime(timeStr); err != nil {
		s.logger.Printf("[ERROR] Daily job %s has invalid schedule %q: %v — job not started", name, timeStr, err)
		return
	}

	s.jobs = append(s.jobs, &Job{
		Name:     name,
		Fn:       fn,
		Schedule: timeStr,
	})

	nextRun := nextDailyRun(timeStr)
	s.logger.Printf("[SCHED] Daily job %s scheduled for %s", name, nextRun.Format("2006-01-02 15:04 MST"))
}

// Start begins running all registered jobs. Safe to call only once.
func (s *Scheduler) Start(ctx context.Context) {
	s.mu.Lock()
	if s.cancel != nil {
		s.mu.Unlock()
		s.logger.Println("[WARN] Scheduler already started — ignoring duplicate Start()")
		return
	}
	s.ctx, s.cancel = context.WithCancel(ctx)

	for _, job := range s.jobs {
		if job.Interval > 0 {
			s.wg.Add(1)
			go s.runPeriodicJob(job)
		} else if job.Schedule != "" {
			s.wg.Add(1)
			go s.runDailyJob(job)
		}
	}

	s.logger.Printf("[SCHED] Scheduler started with %d jobs", len(s.jobs))
	s.mu.Unlock()
}

// Stop cancels all jobs and waits for them to finish (30s timeout).
func (s *Scheduler) Stop() {
	s.mu.Lock()
	cancel := s.cancel
	s.mu.Unlock()
	if cancel != nil {
		cancel()
	}

	done := make(chan struct{})
	go func() {
		s.wg.Wait()
		close(done)
	}()

	select {
	case <-done:
		s.logger.Println("[SCHED] All jobs stopped")
	case <-time.After(30 * time.Second):
		s.logger.Println("[WARN] Scheduler stop timed out after 30s — some jobs may still be running")
	}
}

// GetJobs returns a snapshot of all jobs (copies, not pointers).
func (s *Scheduler) GetJobs() []Job {
	s.mu.Lock()
	defer s.mu.Unlock()

	result := make([]Job, len(s.jobs))
	for i, j := range s.jobs {
		result[i] = *j
	}
	return result
}

func (s *Scheduler) runPeriodicJob(job *Job) {
	defer s.wg.Done()

	// Quiet mode: jobs with interval <= 30s only log failures
	quiet := job.Interval <= 30*time.Second

	ticker := time.NewTicker(job.Interval)
	defer ticker.Stop()

	for {
		select {
		case <-s.ctx.Done():
			return
		case <-ticker.C:
			s.executeJob(job, quiet)
		}
	}
}

func (s *Scheduler) runDailyJob(job *Job) {
	defer s.wg.Done()

	for {
		nextRun := nextDailyRun(job.Schedule)
		waitDuration := time.Until(nextRun)

		if waitDuration < 0 {
			waitDuration = 0
		}

		timer := time.NewTimer(waitDuration)
		select {
		case <-s.ctx.Done():
			timer.Stop()
			return
		case <-timer.C:
			s.executeJob(job, false)
		}
	}
}

func (s *Scheduler) executeJob(job *Job, quiet bool) {
	s.mu.Lock()
	if job.Running {
		s.mu.Unlock()
		s.logger.Printf("[WARN] Job %s still running, skipping", job.Name)
		return
	}
	job.Running = true
	s.mu.Unlock()

	defer func() {
		s.mu.Lock()
		job.Running = false
		s.mu.Unlock()
	}()

	// Panic recovery
	defer func() {
		if r := recover(); r != nil {
			s.mu.Lock()
			job.LastErr = fmt.Errorf("panic: %v", r)
			job.LastRun = time.Now()
			s.mu.Unlock()
			s.logger.Printf("[ERROR] Job %s panicked: %v", job.Name, r)
		}
	}()

	if !quiet {
		s.logger.Printf("[SCHED] Running job: %s", job.Name)
	}

	start := time.Now()
	err := job.Fn(s.ctx)
	elapsed := time.Since(start)

	s.mu.Lock()
	job.LastRun = time.Now()
	job.LastErr = err
	s.mu.Unlock()

	if err != nil {
		s.logger.Printf("[WARN] Job %s failed: %v (took %s)", job.Name, err, elapsed.Round(time.Millisecond))
	} else if !quiet {
		s.logger.Printf("[SCHED] Job %s completed (took %s)", job.Name, elapsed.Round(time.Millisecond))
	}
}

// parseDailyTime parses "HH:MM" and returns hour and minute.
func parseDailyTime(timeStr string) (int, int, error) {
	var hour, min int
	n, err := fmt.Sscanf(timeStr, "%d:%d", &hour, &min)
	if err != nil || n != 2 {
		return 0, 0, fmt.Errorf("expected HH:MM format, got %q", timeStr)
	}
	if hour < 0 || hour > 23 || min < 0 || min > 59 {
		return 0, 0, fmt.Errorf("invalid time %q: hour must be 0-23, minute 0-59", timeStr)
	}
	return hour, min, nil
}

// NextDailyRun is the exported version of nextDailyRun for external callers.
func NextDailyRun(timeStr string) time.Time {
	return nextDailyRun(timeStr)
}

// nextDailyRun calculates the next occurrence of the daily schedule in Europe/Budapest timezone.
func nextDailyRun(timeStr string) time.Time {
	hour, min, err := parseDailyTime(timeStr)
	if err != nil {
		// Should not happen — validated at registration
		return time.Now().Add(24 * time.Hour)
	}

	loc := getBudapestLocation()

	now := time.Now().In(loc)
	next := time.Date(now.Year(), now.Month(), now.Day(), hour, min, 0, 0, loc)

	// If the time has already passed today, schedule for tomorrow.
	// Use time.Date with day+1 instead of Add(24h) to correctly handle DST transitions
	// (spring forward/fall back in Europe/Budapest would shift by 1 hour with Add(24h)).
	if !next.After(now) {
		next = time.Date(now.Year(), now.Month(), now.Day()+1, hour, min, 0, 0, loc)
	}

	return next
}