package usecase

import (
	"context"

	"apps/backend/internal/module/scout/domain"
)

// StartRun guards queued → running and is idempotent for a retry of the same
// job. A different job can never take over an active or terminal run.
func (s *Service) StartRun(ctx context.Context, ownerUID int64, runID, jobID string) (*domain.Run, error) {
	if s == nil || s.Repo == nil || runID == "" || jobID == "" {
		return nil, domain.ErrValidation
	}
	run, err := s.Repo.GetRun(ctx, ownerUID, runID)
	if err != nil {
		return nil, err
	}
	if run.JobID != jobID {
		return nil, domain.ErrIllegalRunStatus
	}
	if run.Status == domain.RunRunning {
		return run, nil
	}
	if err := run.Transition(domain.RunRunning, domain.NowNano()); err != nil {
		return nil, err
	}
	if err := s.Repo.ReplaceRunGuarded(ctx, ownerUID, runID, []string{domain.RunQueued}, run); err != nil {
		return nil, err
	}
	return run, nil
}