refac: hardening pass with multiple overhauls

internal/infrastructure/useCases/AcceptInvite.go

@@ -34,6 +34,9 @@ func (a *AcceptInviteUseCase) AcceptInvite(command AcceptInviteCommand) (user.Us
 	}
 
 	if a.emailHasAccount(pending.Email) {
+		if _, err := findUsableInvite(a.inviteRepository, a.hasher, command.Code, now); err != nil {
+			return user.User{}, err
+		}
 		return user.User{}, invite.ErrEmailHasAccount
 	}
 
@@ -46,20 +49,16 @@ func (a *AcceptInviteUseCase) AcceptInvite(command AcceptInviteCommand) (user.Us
 		return user.User{}, err
 	}
 
-	createdUser, err := a.userRepository.Create(user.User{
+	createdUser, err := a.inviteRepository.AcceptWithUser(pending.ID, now, user.User{
 		Username:   command.Username,
 		Password:   hashedPassword,
 		Email:      pending.Email,
 		IsVerified: true,
 	})
-	if err != nil {
-		return user.User{}, err
+	if errors.Is(err, invite.ErrInviteNotFound) {
+		return user.User{}, invite.ErrInviteInvalid
 	}
-
-	if err := a.inviteRepository.MarkAccepted(pending.ID, now); err != nil {
-		if deleteErr := a.userRepository.Delete(createdUser.ID); deleteErr != nil {
-			return user.User{}, errors.Join(err, deleteErr)
-		}
+	if err != nil {
 		return user.User{}, err
 	}