package graph

import (
	"context"
	"fmt"

	"github.com/99designs/gqlgen/graphql"
)

func OneOf(ctx context.Context, obj interface{}, next graphql.Resolver) (res interface{}, err error) {
	wasValue := false
	m, ok := obj.(map[string]any)
	if !ok {
		return nil, fmt.Errorf("OneOf error, unknow object type: %T", obj)
	}

	for k, v := range m {
		if v != nil {
			if !wasValue {
				wasValue = true
			} else {
				return nil, fmt.Errorf("OneOf with multiple fields: %s", k)
			}
		}
	}

	return next(ctx)
}