package scheduler

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"log/slog"
	"strings"
	"time"

	"git.mchus.pro/mchus/priceforge/internal/config"
	"git.mchus.pro/mchus/priceforge/internal/models"
	"git.mchus.pro/mchus/priceforge/internal/repository"
	alertsvc "git.mchus.pro/mchus/priceforge/internal/services/alerts"
	pricingsvc "git.mchus.pro/mchus/priceforge/internal/services/pricing"
	"gorm.io/gorm"
)

type Scheduler struct {
	db             *gorm.DB
	alertService   *alertsvc.Service
	pricingService *pricingsvc.Service
	statsRepo      *repository.StatsRepository
	cfg            config.SchedulerConfig
	logger         *slog.Logger
}

type job struct {
	Name     string
	Interval time.Duration
	Run      func(context.Context) error
}

func New(
	db *gorm.DB,
	alertService *alertsvc.Service,
	pricingService *pricingsvc.Service,
	statsRepo *repository.StatsRepository,
	cfg config.SchedulerConfig,
) *Scheduler {
	return &Scheduler{
		db:             db,
		alertService:   alertService,
		pricingService: pricingService,
		statsRepo:      statsRepo,
		cfg:            cfg,
		logger:         slog.Default(),
	}
}

func (s *Scheduler) Start(ctx context.Context) {
	if s == nil || s.db == nil || !s.cfg.Enabled {
		return
	}
	pollInterval := s.cfg.PollInterval
	if pollInterval <= 0 {
		pollInterval = time.Minute
	}
	s.logger.Info("starting embedded scheduler", "poll_interval", pollInterval)
	s.runDueJobs(ctx)
	ticker := time.NewTicker(pollInterval)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			s.logger.Info("embedded scheduler stopped")
			return
		case <-ticker.C:
			s.runDueJobs(ctx)
		}
	}
}

func (s *Scheduler) runDueJobs(ctx context.Context) {
	now := time.Now()
	for _, job := range s.jobs() {
		if job.Interval <= 0 {
			continue
		}
		if err := s.tryRunJob(ctx, job, now); err != nil {
			s.logger.Warn("scheduler job failed", "job", job.Name, "err", err)
		}
	}
}

func (s *Scheduler) jobs() []job {
	return []job{
		{
			Name:     "alerts",
			Interval: s.cfg.AlertsInterval,
			Run: func(ctx context.Context) error {
				if s.alertService == nil {
					return nil
				}
				return s.alertService.CheckAndGenerateAlerts()
			},
		},
		{
			Name:     "update_prices",
			Interval: s.cfg.UpdatePricesInterval,
			Run: func(ctx context.Context) error {
				if s.pricingService == nil {
					return nil
				}
				updated, errs := s.pricingService.RecalculateAllPrices()
				if errs > 0 {
					return fmt.Errorf("recalculation finished with %d errors (updated=%d)", errs, updated)
				}
				return nil
			},
		},
		{
			Name:     "update_popularity",
			Interval: s.cfg.UpdatePopularityInterval,
			Run: func(ctx context.Context) error {
				if s.statsRepo == nil {
					return nil
				}
				return s.statsRepo.UpdatePopularityScores()
			},
		},
		{
			Name:     "reset_weekly_counters",
			Interval: s.cfg.ResetWeeklyCountersInterval,
			Run: func(ctx context.Context) error {
				if s.statsRepo == nil {
					return nil
				}
				return s.statsRepo.ResetWeeklyCounters()
			},
		},
		{
			Name:     "reset_monthly_counters",
			Interval: s.cfg.ResetMonthlyCountersInterval,
			Run: func(ctx context.Context) error {
				if s.statsRepo == nil {
					return nil
				}
				return s.statsRepo.ResetMonthlyCounters()
			},
		},
	}
}

func (s *Scheduler) tryRunJob(ctx context.Context, job job, now time.Time) error {
	acquired, release, err := acquireDBLock(ctx, s.db, "priceforge:scheduler:"+job.Name)
	if err != nil {
		return fmt.Errorf("acquire db lock: %w", err)
	}
	if !acquired {
		return nil
	}
	defer release()

	state, err := s.getRunState(job.Name)
	if err != nil {
		return fmt.Errorf("load run state: %w", err)
	}
	if !jobDue(state.LastFinishedAt, now, job.Interval) {
		return nil
	}

	if err := s.markJobStarted(job.Name, now); err != nil {
		return fmt.Errorf("mark started: %w", err)
	}

	runErr := job.Run(ctx)
	finishedAt := time.Now()
	if err := s.markJobFinished(job.Name, finishedAt, runErr); err != nil {
		return fmt.Errorf("mark finished: %w", err)
	}
	if runErr != nil {
		return runErr
	}
	s.logger.Info("scheduler job completed", "job", job.Name, "finished_at", finishedAt)
	return nil
}

func (s *Scheduler) getRunState(jobName string) (*models.SchedulerRun, error) {
	var run models.SchedulerRun
	err := s.db.Where("job_name = ?", jobName).First(&run).Error
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return &models.SchedulerRun{JobName: jobName}, nil
		}
		return nil, err
	}
	return &run, nil
}

func (s *Scheduler) markJobStarted(jobName string, startedAt time.Time) error {
	run := &models.SchedulerRun{
		JobName:       jobName,
		LastStartedAt: &startedAt,
		LastStatus:    "running",
		LastError:     "",
	}
	return s.db.
		Where("job_name = ?", jobName).
		Assign(run).
		FirstOrCreate(run).
		Error
}

func (s *Scheduler) markJobFinished(jobName string, finishedAt time.Time, runErr error) error {
	status := "success"
	lastError := ""
	if runErr != nil {
		status = "failed"
		lastError = truncateText(runErr.Error(), 2000)
	}
	return s.db.Model(&models.SchedulerRun{}).
		Where("job_name = ?", jobName).
		Updates(map[string]any{
			"last_finished_at": finishedAt,
			"last_status":      status,
			"last_error":       lastError,
		}).Error
}

func acquireDBLock(ctx context.Context, db *gorm.DB, key string) (bool, func(), error) {
	sqlDB, err := db.DB()
	if err != nil {
		return false, nil, err
	}
	conn, err := sqlDB.Conn(ctx)
	if err != nil {
		return false, nil, err
	}
	var acquired sql.NullInt64
	if err := conn.QueryRowContext(ctx, "SELECT GET_LOCK(?, 0)", key).Scan(&acquired); err != nil {
		_ = conn.Close()
		return false, nil, err
	}
	if !acquired.Valid || acquired.Int64 != 1 {
		_ = conn.Close()
		return false, nil, nil
	}
	release := func() {
		var released sql.NullInt64
		if err := conn.QueryRowContext(context.Background(), "SELECT RELEASE_LOCK(?)", key).Scan(&released); err != nil {
			slog.Warn("failed to release scheduler db lock", "key", key, "err", err)
		}
		_ = conn.Close()
	}
	return true, release, nil
}

func jobDue(lastFinishedAt *time.Time, now time.Time, interval time.Duration) bool {
	if interval <= 0 {
		return false
	}
	if lastFinishedAt == nil || lastFinishedAt.IsZero() {
		return true
	}
	return !lastFinishedAt.Add(interval).After(now)
}

func truncateText(v string, limit int) string {
	if limit <= 0 || len(v) <= limit {
		return strings.TrimSpace(v)
	}
	return strings.TrimSpace(v[:limit])
}