package schedule

import (
	"context"
	"errors"
	"log"
	"os"
	"os/exec"
	"time"

	"github.com/robfig/cron/v3"
)

type Config struct {
	CronExpr   string
	ScriptPath string
	Logger     *log.Logger
}

type Scheduler struct {
	cron   *cron.Cron
	logger *log.Logger
}

// Start configures and starts the cron scheduler. It runs the given script at the
// specified cron expression (KST). The caller owns the returned scheduler and must
// call Stop on shutdown.
func Start(cfg Config) (*Scheduler, error) {
	if cfg.CronExpr == "" {
		return nil, errors.New("CronExpr is required")
	}
	if cfg.ScriptPath == "" {
		return nil, errors.New("ScriptPath is required")
	}

	if cfg.Logger == nil {
		cfg.Logger = log.Default()
	}

	if _, err := os.Stat(cfg.ScriptPath); err != nil {
		return nil, err
	}

	kst, err := time.LoadLocation("Asia/Seoul")
	if err != nil {
		kst = time.FixedZone("KST", 9*60*60)
	}

	parser := cron.NewParser(cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow)
	spec, err := parser.Parse(cfg.CronExpr)
	if err != nil {
		return nil, err
	}

	c := cron.New(cron.WithLocation(kst), cron.WithParser(parser))
	c.Schedule(spec, cron.FuncJob(func() {
		runScript(cfg.Logger, cfg.ScriptPath)
	}))

	c.Start()

	cfg.Logger.Printf("scheduler started with cron=%s script=%s tz=%s", cfg.CronExpr, cfg.ScriptPath, kst)

	return &Scheduler{
		cron:   c,
		logger: cfg.Logger,
	}, nil
}

// Stop halts the scheduler. It does not cancel a currently running job.
func (s *Scheduler) Stop() context.Context {
	if s == nil || s.cron == nil {
		return context.Background()
	}
	return s.cron.Stop()
}

func runScript(logger *log.Logger, script string) {
	start := time.Now()
	logger.Printf("scheduler: running %s", script)

	cmd := exec.Command("/bin/bash", script)
	cmd.Env = os.Environ()
	out, err := cmd.CombinedOutput()
	duration := time.Since(start)

	if len(out) > 0 {
		logger.Printf("scheduler: output:\n%s", string(out))
	}
	if err != nil {
		logger.Printf("scheduler: %s failed after %s: %v", script, duration, err)
		return
	}
	logger.Printf("scheduler: %s completed in %s", script, duration)
}