test(account): unlink guard + change-email replace/refuse/deeplink

Integration: unlinking a provider keeps the other identities and refuses removing
the last one; change-email replaces the address (freeing the old), refuses a taken
address without merging, and works through the one-tap deeplink token. Unit: the
change-email template renders localised ru/en copy.

backend/internal/account/emailtemplate_test.go

@@ -16,6 +16,8 @@ func TestRenderConfirmationEmail(t *testing.T) {
 		{"login en", purposeLogin, "en", "sign-in"},
 		{"link ru", purposeLink, "ru", "подтвержд"},
 		{"link en", purposeLink, "en", "confirmation"},
+		{"change ru", purposeChange, "ru", "новый"},
+		{"change en", purposeChange, "en", "new"},
 	}
 	for _, c := range cases {
 		t.Run(c.name, func(t *testing.T) {

backend/internal/inttest/link_change_test.go

@@ -0,0 +1,174 @@
+//go:build integration
+
+package inttest
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/google/uuid"
+
+	"scrabble/backend/internal/account"
+)
+
+// emailOf returns the external id of the account's email identity, or "" when it has none.
+func emailOf(t *testing.T, store *account.Store, id uuid.UUID) string {
+	t.Helper()
+	ids, err := store.Identities(context.Background(), id)
+	if err != nil {
+		t.Fatalf("identities %s: %v", id, err)
+	}
+	for _, i := range ids {
+		if i.Kind == account.KindEmail {
+			return i.ExternalID
+		}
+	}
+	return ""
+}
+
+// TestUnlinkProviderKeepsOthers detaches one provider from a multi-identity account and
+// refuses to remove the last remaining identity.
+func TestUnlinkProviderKeepsOthers(t *testing.T) {
+	ctx := context.Background()
+	store := account.NewStore(testDB)
+
+	acc, err := store.ProvisionByIdentity(ctx, account.KindTelegram, "tg-"+uuid.NewString())
+	if err != nil {
+		t.Fatalf("provision telegram: %v", err)
+	}
+	email := "unlink-" + uuid.NewString() + "@example.com"
+	if err := store.AttachIdentity(ctx, acc.ID, account.KindEmail, email, true); err != nil {
+		t.Fatalf("attach email: %v", err)
+	}
+
+	// Removing a kind the account does not hold reports not-found.
+	if err := store.RemoveIdentity(ctx, acc.ID, account.KindVK); !errors.Is(err, account.ErrNotFound) {
+		t.Fatalf("remove absent vk = %v, want ErrNotFound", err)
+	}
+
+	// Detach Telegram: the email identity remains.
+	if err := store.RemoveIdentity(ctx, acc.ID, account.KindTelegram); err != nil {
+		t.Fatalf("remove telegram: %v", err)
+	}
+	ids, err := store.Identities(ctx, acc.ID)
+	if err != nil {
+		t.Fatalf("identities: %v", err)
+	}
+	if len(ids) != 1 || ids[0].Kind != account.KindEmail {
+		t.Fatalf("identities after unlink = %+v, want only email", ids)
+	}
+
+	// The email is now the last identity, so unlinking it is refused.
+	if err := store.RemoveIdentity(ctx, acc.ID, account.KindEmail); !errors.Is(err, account.ErrLastIdentity) {
+		t.Fatalf("remove last email = %v, want ErrLastIdentity", err)
+	}
+}
+
+// TestChangeEmailReplaces switches an account's confirmed email to a free address,
+// freeing the old one.
+func TestChangeEmailReplaces(t *testing.T) {
+	ctx := context.Background()
+	store := account.NewStore(testDB)
+	mailer := &capturingMailer{}
+	svc := account.NewEmailService(store, mailer, "https://erudit-game.ru")
+
+	acc, err := store.ProvisionByIdentity(ctx, account.KindTelegram, "tg-"+uuid.NewString())
+	if err != nil {
+		t.Fatalf("provision: %v", err)
+	}
+	oldAddr := "old-" + uuid.NewString() + "@example.com"
+	if err := store.AttachIdentity(ctx, acc.ID, account.KindEmail, oldAddr, true); err != nil {
+		t.Fatalf("attach old email: %v", err)
+	}
+	newAddr := "new-" + uuid.NewString() + "@example.com"
+
+	if err := svc.RequestChangeCode(ctx, acc.ID, newAddr); err != nil {
+		t.Fatalf("request change: %v", err)
+	}
+	code := sixDigit.FindString(mailer.lastBody)
+	if _, err := svc.ConfirmChange(ctx, acc.ID, newAddr, code); err != nil {
+		t.Fatalf("confirm change: %v", err)
+	}
+	if got := emailOf(t, store, acc.ID); got != newAddr {
+		t.Fatalf("email after change = %q, want %q", got, newAddr)
+	}
+	if !identityConfirmed(t, account.KindEmail, newAddr) {
+		t.Error("the new email identity must be confirmed")
+	}
+	// The old address is freed: another account can now claim it.
+	other, err := store.ProvisionByIdentity(ctx, account.KindTelegram, "tg-"+uuid.NewString())
+	if err != nil {
+		t.Fatalf("provision other: %v", err)
+	}
+	if err := store.AttachIdentity(ctx, other.ID, account.KindEmail, oldAddr, true); err != nil {
+		t.Fatalf("old address should be free after change, got: %v", err)
+	}
+}
+
+// TestChangeEmailRefusesTaken refuses (without merging) a new address already confirmed by
+// another account, leaving the caller's email untouched.
+func TestChangeEmailRefusesTaken(t *testing.T) {
+	ctx := context.Background()
+	store := account.NewStore(testDB)
+	mailer := &capturingMailer{}
+	svc := account.NewEmailService(store, mailer, "https://erudit-game.ru")
+
+	acc, err := store.ProvisionByIdentity(ctx, account.KindTelegram, "tg-"+uuid.NewString())
+	if err != nil {
+		t.Fatalf("provision caller: %v", err)
+	}
+	mine := "mine-" + uuid.NewString() + "@example.com"
+	if err := store.AttachIdentity(ctx, acc.ID, account.KindEmail, mine, true); err != nil {
+		t.Fatalf("attach caller email: %v", err)
+	}
+	other, err := store.ProvisionByIdentity(ctx, account.KindTelegram, "tg-"+uuid.NewString())
+	if err != nil {
+		t.Fatalf("provision other: %v", err)
+	}
+	taken := "taken-" + uuid.NewString() + "@example.com"
+	if err := store.AttachIdentity(ctx, other.ID, account.KindEmail, taken, true); err != nil {
+		t.Fatalf("attach other email: %v", err)
+	}
+
+	if err := svc.RequestChangeCode(ctx, acc.ID, taken); err != nil {
+		t.Fatalf("request change: %v", err)
+	}
+	code := sixDigit.FindString(mailer.lastBody)
+	if _, err := svc.ConfirmChange(ctx, acc.ID, taken, code); !errors.Is(err, account.ErrEmailTaken) {
+		t.Fatalf("confirm change to taken = %v, want ErrEmailTaken", err)
+	}
+	if got := emailOf(t, store, acc.ID); got != mine {
+		t.Errorf("caller email after refused change = %q, want unchanged %q", got, mine)
+	}
+}
+
+// TestChangeEmailViaDeeplink switches the email through the one-tap confirm token.
+func TestChangeEmailViaDeeplink(t *testing.T) {
+	ctx := context.Background()
+	store := account.NewStore(testDB)
+	mailer := &capturingMailer{}
+	svc := account.NewEmailService(store, mailer, "https://erudit-game.ru")
+
+	acc, err := store.ProvisionByIdentity(ctx, account.KindTelegram, "tg-"+uuid.NewString())
+	if err != nil {
+		t.Fatalf("provision: %v", err)
+	}
+	if err := store.AttachIdentity(ctx, acc.ID, account.KindEmail, "old-"+uuid.NewString()+"@example.com", true); err != nil {
+		t.Fatalf("attach old email: %v", err)
+	}
+	newAddr := "dl-" + uuid.NewString() + "@example.com"
+	if err := svc.RequestChangeCode(ctx, acc.ID, newAddr); err != nil {
+		t.Fatalf("request change: %v", err)
+	}
+	res, err := svc.ConfirmByToken(ctx, tokenFromMail(t, mailer.lastBody))
+	if err != nil {
+		t.Fatalf("confirm by token: %v", err)
+	}
+	if res.IsLogin() || res.NeedsMerge || res.Account != acc.ID {
+		t.Fatalf("deeplink change result = %+v, want a plain change for %s", res, acc.ID)
+	}
+	if got := emailOf(t, store, acc.ID); got != newAddr {
+		t.Fatalf("email after deeplink change = %q, want %q", got, newAddr)
+	}
+}