package gorm

import (
	"context"
	"errors"
	event2 "github.com/go-saas/kit/pkg/uow/event"

	"github.com/go-saas/kit/event"
	"github.com/go-saas/uow"
	"gorm.io/gorm"
)

var (
	ErrProducerNotFound = errors.New("producer not found")
)

type Agg interface {
	AppendEvent(events ...event.Event)
	ConsumeEventsIfAny(ctx context.Context, fn func(ctx context.Context, events []event.Event) error) (err error)
}

// AggRoot DDD aggregate root. will dispatch events after transaction committed
type AggRoot struct {
	events []event.Event
}

func (a *AggRoot) AppendEvent(events ...event.Event) {
	a.events = append(a.events, events...)
}

func (a *AggRoot) ConsumeEventsIfAny(ctx context.Context, fn func(ctx context.Context, events []event.Event) error) (err error) {
	//TODO lock?
	if len(a.events) > 0 {
		err = fn(ctx, a.events)
		if err == nil {
			//clear events
			a.events = nil
		}
		return err
	}
	return nil
}

func dispatchEvents(db *gorm.DB) {
	if agg, ok := IsModel[Agg](db); ok {
		err := agg.ConsumeEventsIfAny(db.Statement.Context, func(ctx context.Context, events []event.Event) error {
			if uow, ok := uow.FromCurrentUow(ctx); ok {
				// uow manage events
				tdb, err := uow.GetTxDb(ctx, event2.UowKind)
				if err != nil {
					return err
				}
				return tdb.(*event2.Transactional).Send(events...)
			} else {
				//send immediately
				if p, ok := event.FromProducerContext(ctx); ok {
					return p.BatchSend(ctx, events)
				} else {
					return ErrProducerNotFound
				}
			}
			return nil
		})
		if err != nil {
			db.AddError(err)
		}
	}
}

// RegisterAggCallbacks register callback into GORM DB
func RegisterAggCallbacks(db *gorm.DB) {
	callback := db.Callback()
	if callback.Create().Get("agg:create_events") == nil {
		callback.Create().After("gorm:after_create").Register("agg:create_events", dispatchEvents)
	}
	if callback.Update().Get("agg:update_events") == nil {
		callback.Update().After("gorm:after_update").Register("agg:update_events", dispatchEvents)
	}
	if callback.Delete().Get("agg:delete_events") == nil {
		callback.Update().After("gorm:after_delete").Register("agg:delete_events", dispatchEvents)
	}
}