Example for my iDDD with Go blog article series at https://medium.com/@TonyBologni

AssertUniqueEmailAddresses.go

package customer

import (
    "github.com/AntonStoeckl/go-iddd/service/customeraccounts/application/domain"
    "github.com/AntonStoeckl/go-iddd/service/customeraccounts/application/domain/customer/value"
    "github.com/AntonStoeckl/go-iddd/service/shared/es"
)

const (
    ShouldAddUniqueEmailAddress = iota
    ShouldReplaceUniqueEmailAddress
    ShouldRemoveUniqueEmailAddress
)

type ForBuildingUniqueEmailAddressAssertions func(recordedEvents ...es.DomainEvent) UniqueEmailAddressAssertions

type UniqueEmailAddressAssertion struct {
    desiredAction        int
    customerID           value.CustomerID
    emailAddressToAdd    value.EmailAddress
    emailAddressToRemove value.EmailAddress
}

type UniqueEmailAddressAssertions []UniqueEmailAddressAssertion

func (spec UniqueEmailAddressAssertion) DesiredAction() int {
    return spec.desiredAction
}

func (spec UniqueEmailAddressAssertion) CustomerID() value.CustomerID {
    return spec.customerID
}

func (spec UniqueEmailAddressAssertion) EmailAddressToAdd() value.EmailAddress {
    return spec.emailAddressToAdd
}

func (spec UniqueEmailAddressAssertion) EmailAddressToRemove() value.EmailAddress {
    return spec.emailAddressToRemove
}

func BuildUniqueEmailAddressAssertions(recordedEvents ...es.DomainEvent) UniqueEmailAddressAssertions {
    var specifications UniqueEmailAddressAssertions

    for _, event := range recordedEvents {
        switch actualEvent := event.(type) {
        case domain.CustomerRegistered:
            specifications = append(
                specifications,
                UniqueEmailAddressAssertion{
                    desiredAction:     ShouldAddUniqueEmailAddress,
                    customerID:        actualEvent.CustomerID(),
                    emailAddressToAdd: actualEvent.EmailAddress(),
                },
            )
        case domain.CustomerEmailAddressChanged:
            specifications = append(
                specifications,
                UniqueEmailAddressAssertion{
                    desiredAction:        ShouldReplaceUniqueEmailAddress,
                    emailAddressToAdd:    actualEvent.EmailAddress(),
                    emailAddressToRemove: actualEvent.PreviousEmailAddress(),
                },
            )
        case domain.CustomerDeleted:
            specifications = append(
                specifications,
                UniqueEmailAddressAssertion{
                    desiredAction:        ShouldRemoveUniqueEmailAddress,
                    emailAddressToRemove: actualEvent.EmailAddress(),
                },
            )
        }
    }

    return specifications
}