package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"fn-registry/functions/core"
	"fn-registry/functions/infra"
)

// ScheduledDAG represents a DAG with a parsed cron schedule.
type ScheduledDAG struct {
	Name     string    `json:"name"`
	Path     string    `json:"path"`
	Schedule string    `json:"schedule"`
	NextRun  time.Time `json:"next_run"`
}

// Scheduler manages cron-triggered DAG execution.
type Scheduler struct {
	mu       sync.Mutex
	running  bool
	cancel   context.CancelFunc
	dagsDir  string
	executor *Executor
	dags     []ScheduledDAG
}

// NewScheduler creates a new scheduler.
func NewScheduler(executor *Executor, dagsDir string) *Scheduler {
	return &Scheduler{
		executor: executor,
		dagsDir:  dagsDir,
	}
}

// Start scans for DAGs with schedules and starts cron tickers for each.
func (s *Scheduler) Start() error {
	s.mu.Lock()
	if s.running {
		s.mu.Unlock()
		return fmt.Errorf("scheduler already running")
	}

	ctx, cancel := context.WithCancel(context.Background())
	s.cancel = cancel
	s.running = true
	s.mu.Unlock()

	scheduled, err := s.scanDAGs()
	if err != nil {
		s.mu.Lock()
		s.running = false
		s.mu.Unlock()
		cancel()
		return err
	}

	s.mu.Lock()
	s.dags = scheduled
	s.mu.Unlock()

	log.Printf("[scheduler] started with %d DAGs", len(scheduled))

	for _, dag := range scheduled {
		dag := dag
		go s.runTicker(ctx, dag)
	}

	return nil
}

// Stop cancels all tickers and stops the scheduler.
func (s *Scheduler) Stop() {
	s.mu.Lock()
	defer s.mu.Unlock()
	if !s.running {
		return
	}
	s.cancel()
	s.running = false
	s.dags = nil
	log.Printf("[scheduler] stopped")
}

// IsRunning returns true if the scheduler is active.
func (s *Scheduler) IsRunning() bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.running
}

// Status returns the list of scheduled DAGs with their next run time.
type SchedulerStatus struct {
	Running bool           `json:"running"`
	DAGs    []ScheduledDAG `json:"dags"`
}

func (s *Scheduler) Status() SchedulerStatus {
	s.mu.Lock()
	defer s.mu.Unlock()
	return SchedulerStatus{
		Running: s.running,
		DAGs:    s.dags,
	}
}

// scanDAGs reads the dags directory and returns DAGs that have cron schedules.
func (s *Scheduler) scanDAGs() ([]ScheduledDAG, error) {
	entries, err := os.ReadDir(s.dagsDir)
	if err != nil {
		return nil, err
	}

	var scheduled []ScheduledDAG
	for _, entry := range entries {
		ext := filepath.Ext(entry.Name())
		if ext != ".yaml" && ext != ".yml" {
			continue
		}

		path := filepath.Join(s.dagsDir, entry.Name())
		data, err := os.ReadFile(path)
		if err != nil {
			continue
		}

		dag, err := core.DagParse(data)
		if err != nil {
			continue
		}

		for _, expr := range dag.Schedule {
			sched, err := core.ParseCronExpr(strings.TrimSpace(expr))
			if err != nil {
				log.Printf("[scheduler] invalid cron %q in %s: %v", expr, dag.Name, err)
				continue
			}
			next := core.NextCronTime(sched, time.Now())
			scheduled = append(scheduled, ScheduledDAG{
				Name:     dag.Name,
				Path:     path,
				Schedule: expr,
				NextRun:  next,
			})
		}
	}

	return scheduled, nil
}

// runTicker starts a cron ticker for a single DAG schedule.
func (s *Scheduler) runTicker(ctx context.Context, dag ScheduledDAG) {
	sched, err := core.ParseCronExpr(strings.TrimSpace(dag.Schedule))
	if err != nil {
		return
	}

	// Convert core.CronSchedule to infra.CronTickerSchedule.
	tickerSched := infra.CronTickerSchedule{
		Minute:     sched.Minute,
		Hour:       sched.Hour,
		DayOfMonth: sched.DayOfMonth,
		Month:      sched.Month,
		DayOfWeek:  sched.DayOfWeek,
	}

	ch := infra.CronTicker(tickerSched, ctx)
	log.Printf("[scheduler] ticker started for %s (%s), next: %s", dag.Name, dag.Schedule, dag.NextRun.Format(time.RFC3339))

	for t := range ch {
		log.Printf("[scheduler] triggered %s at %s", dag.Name, t.Format(time.RFC3339))
		go func() {
			runID, err := s.executor.ExecuteDAG(ctx, dag.Path, "cron")
			if err != nil {
				log.Printf("[scheduler] %s failed: %v (run: %s)", dag.Name, err, runID)
			} else {
				log.Printf("[scheduler] %s completed (run: %s)", dag.Name, runID)
			}
		}()
	}
}