From c989df41d5474c41db41bdaf43c375d666d226fc Mon Sep 17 00:00:00 2001
From: Danijel Martinek <danijel@fraqtal.xyz>
Date: Tue, 5 May 2026 00:39:22 +0200
Subject: [PATCH] feat(auth): add signUpUseCase (test red until DI lands)

---
 .../use-cases/sign-up.use-case.test.ts        | 47 +++++++++++++++++++
 .../application/use-cases/sign-up.use-case.ts | 46 ++++++++++++++++++
 2 files changed, 93 insertions(+)
 create mode 100644 packages/auth/src/application/use-cases/sign-up.use-case.test.ts
 create mode 100644 packages/auth/src/application/use-cases/sign-up.use-case.ts

diff --git a/packages/auth/src/application/use-cases/sign-up.use-case.test.ts b/packages/auth/src/application/use-cases/sign-up.use-case.test.ts
new file mode 100644
index 0000000..22a40c6
--- /dev/null
+++ b/packages/auth/src/application/use-cases/sign-up.use-case.test.ts
@@ -0,0 +1,47 @@
+import { beforeEach, describe, expect, it } from "vitest";
+import { authContainer } from "@/di/container";
+import { AUTH_SYMBOLS } from "@/di/symbols";
+import { MockUsersRepository } from "@/infrastructure/repositories/mock-users.repository";
+import { MockAuthenticationService } from "@/infrastructure/services/mock-authentication.service";
+import type { IUsersRepository } from "@/application/repositories/users-repository.interface";
+import type { IAuthenticationService } from "@/application/services/authentication-service.interface";
+import { AuthenticationError } from "@/entities/errors";
+import { signUpUseCase } from "./sign-up.use-case";
+
+describe("signUpUseCase", () => {
+  let usersRepo: MockUsersRepository;
+  let authService: MockAuthenticationService;
+
+  beforeEach(() => {
+    if (authContainer.isBound(AUTH_SYMBOLS.IUsersRepository)) {
+      authContainer.unbind(AUTH_SYMBOLS.IUsersRepository);
+    }
+    if (authContainer.isBound(AUTH_SYMBOLS.IAuthenticationService)) {
+      authContainer.unbind(AUTH_SYMBOLS.IAuthenticationService);
+    }
+    usersRepo = new MockUsersRepository();
+    authService = new MockAuthenticationService(usersRepo);
+    authContainer
+      .bind<IUsersRepository>(AUTH_SYMBOLS.IUsersRepository)
+      .toConstantValue(usersRepo);
+    authContainer
+      .bind<IAuthenticationService>(AUTH_SYMBOLS.IAuthenticationService)
+      .toConstantValue(authService);
+  });
+
+  it("creates a new user and returns session + cookie + user", async () => {
+    const result = await signUpUseCase({
+      username: "carol",
+      password: "secret_password",
+    });
+    expect(result.user.username).toBe("carol");
+    expect(result.session.userId).toBe(result.user.id);
+    expect(result.cookie.name).toBe("session");
+  });
+
+  it("throws AuthenticationError when username taken", async () => {
+    await expect(
+      signUpUseCase({ username: "alice", password: "secret_password" }),
+    ).rejects.toBeInstanceOf(AuthenticationError);
+  });
+});
diff --git a/packages/auth/src/application/use-cases/sign-up.use-case.ts b/packages/auth/src/application/use-cases/sign-up.use-case.ts
new file mode 100644
index 0000000..5c89f9a
--- /dev/null
+++ b/packages/auth/src/application/use-cases/sign-up.use-case.ts
@@ -0,0 +1,46 @@
+import { AuthenticationError } from "../../entities/errors";
+import type { Cookie } from "../../entities/cookie";
+import type { Session } from "../../entities/session";
+import type { User } from "../../entities/user";
+import { authContainer } from "../../di/container";
+import { AUTH_SYMBOLS } from "../../di/symbols";
+import type { IUsersRepository } from "../repositories/users-repository.interface";
+import type { IAuthenticationService } from "../services/authentication-service.interface";
+
+export async function signUpUseCase(input: {
+  username: string;
+  password: string;
+}): Promise<{
+  session: Session;
+  cookie: Cookie;
+  user: Pick<User, "id" | "username">;
+}> {
+  const usersRepository = authContainer.get<IUsersRepository>(
+    AUTH_SYMBOLS.IUsersRepository,
+  );
+  const authService = authContainer.get<IAuthenticationService>(
+    AUTH_SYMBOLS.IAuthenticationService,
+  );
+
+  const existingUser = await usersRepository.getUserByUsername(input.username);
+  if (existingUser) {
+    throw new AuthenticationError("Username taken");
+  }
+
+  const passwordHash = await authService.hashPassword(input.password);
+  const userId = authService.generateUserId();
+
+  const newUser = await usersRepository.createUser({
+    id: userId,
+    username: input.username,
+    passwordHash,
+  });
+
+  const { cookie, session } = await authService.createSession(newUser);
+
+  return {
+    cookie,
+    session,
+    user: { id: newUser.id, username: newUser.username },
+  };
+}