package database

import (
	"fmt"

	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

// omitAssociationsCallback is the name the association guard is
// registered under on a per-webhook database's create and update
// callback chains.
const omitAssociationsCallback = "webhooker:omit_associations"

// omitAssociations makes every create and update issued against a
// per-webhook database skip GORM's automatic association save.
//
// A per-webhook database holds the event tier only, but Delivery
// declares belongs-to Event and Target and the delivery engine fills
// both in memory before writing. Without this guard GORM upserts those
// parent rows here on the delivery and retry write paths, and the
// target, whose config holds destination URLs and bearer credentials,
// goes to a targets table this file does not have, which fails the
// write. Registering the guard on the connection
// covers every write path, including writes inside a transaction and
// write paths added later. Every event-tier row this file holds is
// written explicitly, so nothing depends on the automatic save.
func omitAssociations(db *gorm.DB) error {
	omit := func(tx *gorm.DB) {
		tx.Statement.Omits = append(
			tx.Statement.Omits, clause.Associations,
		)
	}

	err := db.Callback().Create().
		Before("gorm:save_before_associations").
		Register(omitAssociationsCallback, omit)
	if err != nil {
		return fmt.Errorf(
			"registering create association guard: %w", err,
		)
	}

	err = db.Callback().Update().
		Before("gorm:save_before_associations").
		Register(omitAssociationsCallback, omit)
	if err != nil {
		return fmt.Errorf(
			"registering update association guard: %w", err,
		)
	}

	return nil
}