refactor: dependency injection for GameSessionStore via composition root

apps/api/src/app.ts

@@ -4,7 +4,8 @@ import { toNodeHandler } from "better-auth/node";
 import cors from "cors";
 import helmet from "helmet";
 import { auth } from "./lib/auth.js";
-import { apiRouter } from "./routes/apiRouter.js";
+import { createApiRouter } from "./routes/apiRouter.js";
+import { InMemoryGameSessionStore } from "./gameSessionStore/index.js";
 import { errorHandler } from "./middleware/errorHandler.js";
 import { authLimiter } from "./middleware/rateLimiters.js";
 
@@ -23,7 +24,10 @@ export function createApp() {
   app.use("/api/auth", authLimiter);
   app.all("/api/auth/*splat", toNodeHandler(auth));
   app.use(express.json());
-  app.use("/api/v1", apiRouter);
+
+  const store = new InMemoryGameSessionStore();
+  app.use("/api/v1", createApiRouter(store));
+  
   app.use(errorHandler);
 
   return app;

apps/api/src/controllers/gameController.ts

@@ -2,41 +2,32 @@ import type { Request, Response, NextFunction } from "express";
 import { GameRequestSchema, AnswerSubmissionSchema } from "@lila/shared";
 import { createGameSession, evaluateAnswer } from "../services/gameService.js";
 import { ValidationError } from "../errors/AppError.js";
+import type { GameSessionStore } from "../gameSessionStore/index.js";
 
-export const createGame = async (
-  req: Request,
-  res: Response,
-  next: NextFunction,
-) => {
-  try {
-    const gameSettings = GameRequestSchema.safeParse(req.body);
-
-    if (!gameSettings.success) {
-      throw new ValidationError(gameSettings.error.message);
+export const createGameController = (store: GameSessionStore) => ({
+  createGame: async (req: Request, res: Response, next: NextFunction) => {
+    try {
+      const gameSettings = GameRequestSchema.safeParse(req.body);
+      if (!gameSettings.success) {
+        throw new ValidationError(gameSettings.error.message);
+      }
+      const gameQuestions = await createGameSession(gameSettings.data, store);
+      res.json({ success: true, data: gameQuestions });
+    } catch (error) {
+      next(error);
     }
+  },
 
-    const gameQuestions = await createGameSession(gameSettings.data);
-    res.json({ success: true, data: gameQuestions });
-  } catch (error) {
-    next(error);
-  }
-};
-
-export const submitAnswer = async (
-  req: Request,
-  res: Response,
-  next: NextFunction,
-) => {
-  try {
-    const submission = AnswerSubmissionSchema.safeParse(req.body);
-
-    if (!submission.success) {
-      throw new ValidationError(submission.error.message);
+  submitAnswer: async (req: Request, res: Response, next: NextFunction) => {
+    try {
+      const submission = AnswerSubmissionSchema.safeParse(req.body);
+      if (!submission.success) {
+        throw new ValidationError(submission.error.message);
+      }
+      const result = await evaluateAnswer(submission.data, store);
+      res.json({ success: true, data: result });
+    } catch (error) {
+      next(error);
     }
-
-    const result = await evaluateAnswer(submission.data);
-    res.json({ success: true, data: result });
-  } catch (error) {
-    next(error);
-  }
-};
+  },
+});

apps/api/src/routes/apiRouter.ts

@@ -1,11 +1,16 @@
 import express from "express";
-import { Router } from "express";
+import type { Router } from "express";
 import { healthRouter } from "./healthRouter.js";
-import { gameRouter } from "./gameRouter.js";
+import { createGameRouter } from "./gameRouter.js";
 import { lobbyRouter } from "./lobbyRouter.js";
+import type { GameSessionStore } from "../gameSessionStore/index.js";
 
-export const apiRouter: Router = express.Router();
+export const createApiRouter = (store: GameSessionStore): Router => {
+  const router = express.Router();
 
-apiRouter.use("/health", healthRouter);
-apiRouter.use("/game", gameRouter);
-apiRouter.use("/lobbies", lobbyRouter);
+  router.use("/health", healthRouter);
+  router.use("/game", createGameRouter(store));
+  router.use("/lobbies", lobbyRouter);
+
+  return router;
+};

apps/api/src/routes/gameRouter.ts

@@ -1,13 +1,19 @@
 import express from "express";
 import type { Router } from "express";
-import { createGame, submitAnswer } from "../controllers/gameController.js";
+import { createGameController } from "../controllers/gameController.js";
 import { requireAuth } from "../middleware/authMiddleware.js";
 import { gameLimiter } from "../middleware/rateLimiters.js";
+import type { GameSessionStore } from "../gameSessionStore/index.js";
 
-export const gameRouter: Router = express.Router();
+export const createGameRouter = (store: GameSessionStore): Router => {
+  const router = express.Router();
+  const controller = createGameController(store);
 
-gameRouter.use(requireAuth);
-gameRouter.use(gameLimiter);
+  router.use(requireAuth);
+  router.use(gameLimiter);
 
-gameRouter.post("/start", createGame);
-gameRouter.post("/answer", submitAnswer);
+  router.post("/start", controller.createGame);
+  router.post("/answer", controller.submitAnswer);
+
+  return router;
+};

apps/api/src/services/gameService.test.ts

@@ -5,6 +5,7 @@ vi.mock("@lila/db", () => ({ getGameTerms: vi.fn(), getDistractors: vi.fn() }));
 
 import { getGameTerms, getDistractors } from "@lila/db";
 import { createGameSession, evaluateAnswer } from "./gameService.js";
+import { InMemoryGameSessionStore } from "../gameSessionStore/index.js";
 
 const mockGetGameTerms = vi.mocked(getGameTerms);
 const mockGetDistractors = vi.mocked(getDistractors);
@@ -35,15 +36,22 @@ beforeEach(() => {
 });
 
 describe("createGameSession", () => {
+
+  let store: InMemoryGameSessionStore;
+
+  beforeEach(() => {
+    store = new InMemoryGameSessionStore();
+  });
+
   it("returns a session with the correct number of questions", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
 
     expect(session.sessionId).toBeDefined();
     expect(session.questions).toHaveLength(3);
   });
 
   it("each question has exactly 4 options", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
 
     for (const question of session.questions) {
       expect(question.options).toHaveLength(4);
@@ -51,14 +59,14 @@ describe("createGameSession", () => {
   });
 
   it("each question has a unique questionId", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
     const ids = session.questions.map((q) => q.questionId);
 
     expect(new Set(ids).size).toBe(ids.length);
   });
 
   it("options have sequential optionIds 0-3", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
 
     for (const question of session.questions) {
       const optionIds = question.options.map((o) => o.optionId);
@@ -67,7 +75,7 @@ describe("createGameSession", () => {
   });
 
   it("the correct answer is always among the options", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
 
     for (let i = 0; i < session.questions.length; i++) {
       const question = session.questions[i]!;
@@ -79,7 +87,7 @@ describe("createGameSession", () => {
   });
 
   it("distractors are never the correct answer", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
 
     for (let i = 0; i < session.questions.length; i++) {
       const question = session.questions[i]!;
@@ -95,7 +103,7 @@ describe("createGameSession", () => {
   });
 
   it("sets the prompt from the source text", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
 
     expect(session.questions[0]!.prompt).toBe("dog");
     expect(session.questions[1]!.prompt).toBe("cat");
@@ -103,14 +111,14 @@ describe("createGameSession", () => {
   });
 
   it("passes gloss through (null or string)", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
 
     expect(session.questions[0]!.gloss).toBeNull();
     expect(session.questions[2]!.gloss).toBe("a building for living in");
   });
 
   it("calls getGameTerms with the correct arguments", async () => {
-    await createGameSession(validRequest);
+    await createGameSession(validRequest, store);
 
     expect(mockGetGameTerms).toHaveBeenCalledWith(
       "en",
@@ -122,7 +130,7 @@ describe("createGameSession", () => {
   });
 
   it("calls getDistractors once per question", async () => {
-    await createGameSession(validRequest);
+    await createGameSession(validRequest, store);
 
     expect(mockGetDistractors).toHaveBeenCalledTimes(3);
   });
@@ -130,24 +138,35 @@ describe("createGameSession", () => {
   it("propagates unexpected errors from getGameTerms", async () => {
     mockGetGameTerms.mockRejectedValue(new Error("connection refused"));
 
-    await expect(createGameSession(validRequest)).rejects.toThrow(
+    await expect(createGameSession(validRequest, store)).rejects.toThrow(
       "connection refused",
     );
   });
 });
 
 describe("evaluateAnswer", () => {
+
+  let store: InMemoryGameSessionStore;
+
+  beforeEach(() => {
+    store = new InMemoryGameSessionStore();
+  });
+
+
   it("returns isCorrect: true when the correct option is selected", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
     const question = session.questions[0]!;
     const correctText = fakeTerms[0]!.targetText;
     const correctOption = question.options.find((o) => o.text === correctText)!;
 
-    const result = await evaluateAnswer({
-      sessionId: session.sessionId,
-      questionId: question.questionId,
-      selectedOptionId: correctOption.optionId,
-    });
+    const result = await evaluateAnswer(
+      {
+        sessionId: session.sessionId,
+        questionId: question.questionId,
+        selectedOptionId: correctOption.optionId,
+      },
+      store,
+    );
 
     expect(result.isCorrect).toBe(true);
     expect(result.correctOptionId).toBe(correctOption.optionId);
@@ -155,17 +174,20 @@ describe("evaluateAnswer", () => {
   });
 
   it("returns isCorrect: false when a wrong option is selected", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
     const question = session.questions[0]!;
     const correctText = fakeTerms[0]!.targetText;
     const correctOption = question.options.find((o) => o.text === correctText)!;
     const wrongOption = question.options.find((o) => o.text !== correctText)!;
 
-    const result = await evaluateAnswer({
-      sessionId: session.sessionId,
-      questionId: question.questionId,
-      selectedOptionId: wrongOption.optionId,
-    });
+    const result = await evaluateAnswer(
+      {
+        sessionId: session.sessionId,
+        questionId: question.questionId,
+        selectedOptionId: wrongOption.optionId,
+      },
+      store,
+    );
 
     expect(result.isCorrect).toBe(false);
     expect(result.correctOptionId).toBe(correctOption.optionId);
@@ -179,13 +201,13 @@ describe("evaluateAnswer", () => {
       selectedOptionId: 0,
     };
 
-    await expect(evaluateAnswer(submission)).rejects.toThrow(
+    await expect(evaluateAnswer(submission, store)).rejects.toThrow(
       "Game session not found",
     );
   });
 
   it("throws NotFoundError for a non-existent question", async () => {
-    const session = await createGameSession(validRequest);
+    const session = await createGameSession(validRequest, store);
 
     const submission: AnswerSubmission = {
       sessionId: session.sessionId,
@@ -193,7 +215,7 @@ describe("evaluateAnswer", () => {
       selectedOptionId: 0,
     };
 
-    await expect(evaluateAnswer(submission)).rejects.toThrow(
+    await expect(evaluateAnswer(submission, store)).rejects.toThrow(
       "Question not found",
     );
   });

apps/api/src/services/gameService.ts

@@ -8,14 +8,13 @@ import type {
   AnswerSubmission,
   AnswerResult,
 } from "@lila/shared";
-import { InMemoryGameSessionStore } from "../gameSessionStore/index.js";
+import type { GameSessionStore } from "../gameSessionStore/index.js";
 import { NotFoundError } from "../errors/AppError.js";
 import { shuffleArray } from "../lib/utils.js";
 
-const gameSessionStore = new InMemoryGameSessionStore();
-
 export const createGameSession = async (
   request: GameRequest,
+  store: GameSessionStore,
 ): Promise<GameSession> => {
   const terms = await getGameTerms(
     request.source_language,
@@ -60,15 +59,16 @@ export const createGameSession = async (
   );
 
   const sessionId = randomUUID();
-  await gameSessionStore.create(sessionId, { answers: answerKey });
+  await store.create(sessionId, { answers: answerKey });
 
   return { sessionId, questions };
 };
 
 export const evaluateAnswer = async (
   submission: AnswerSubmission,
+  store: GameSessionStore,
 ): Promise<AnswerResult> => {
-  const session = await gameSessionStore.get(submission.sessionId);
+  const session = await store.get(submission.sessionId);
 
   if (!session) {
     throw new NotFoundError(`Game session not found: ${submission.sessionId}`);