Merge pull request #20 from gyedongjeon/feature/usage-limits

feat: Usage Limits System (v0.2.0)

Author: gyedongjeon

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "german-api",
-  "version": "0.1.6",
+  "version": "0.2.0",
   "description": "",
   "author": "",
   "private": true,

backend/src/app.module.ts

@@ -21,9 +21,13 @@ import { AuthModule } from './auth/auth.module';
           host: configService.get<string>('POSTGRES_HOST') ?? 'localhost',
           port: configService.get<number>('POSTGRES_PORT') ?? 5432,
           username: configService.get<string>('POSTGRES_USER') ?? 'myuser',
-          password: configService.get<string>('POSTGRES_PASSWORD') ?? 'mypassword',
+          password:
+            configService.get<string>('POSTGRES_PASSWORD') ?? 'mypassword',
           database: configService.get<string>('POSTGRES_DB') ?? 'deutschmock',
-          ssl: configService.get<string>('POSTGRES_HOST') !== 'localhost' ? { rejectUnauthorized: false } : false,
+          ssl:
+            configService.get<string>('POSTGRES_HOST') !== 'localhost'
+              ? { rejectUnauthorized: false }
+              : false,
           autoLoadEntities: true,
           synchronize: true, // Auto-create tables (careful in prod, but ok for MVP)
         };
@@ -37,4 +41,4 @@ import { AuthModule } from './auth/auth.module';
   controllers: [AppController],
   providers: [AppService],
 })
-export class AppModule { }
+export class AppModule {}

backend/src/auth/auth.controller.ts

@@ -13,7 +13,7 @@ import { AuthService } from './auth.service';
 
 @Controller('auth')
 export class AuthController {
-  constructor(private authService: AuthService) { }
+  constructor(private authService: AuthService) {}
 
   @Get('google')
   @UseGuards(AuthGuard('google'))
@@ -40,7 +40,9 @@ export class AuthController {
     });
 
     // Redirect to Frontend (deliver token)
-    const frontendUrls = (process.env.FRONTEND_URL || 'http://localhost:3000').split(',');
+    const frontendUrls = (
+      process.env.FRONTEND_URL || 'http://localhost:3000'
+    ).split(',');
     const primaryUrl = frontendUrls[0].trim();
     res.redirect(`${primaryUrl}/auth/callback?${params.toString()}`);
   }

backend/src/auth/entities/user.entity.ts

@@ -34,6 +34,15 @@ export class User {
   @Column({ default: 'A2' })
   level: string;
 
+  @Column({ default: 0 })
+  usage_count: number;
+
+  @Column({ default: 5 })
+  usage_limit: number;
+
+  @Column({ nullable: true })
+  last_usage_date: Date;
+
   @OneToMany(() => Evaluation, (evaluation) => evaluation.user)
   evaluations: Evaluation[];
 

backend/src/evaluation/evaluation.module.ts

@@ -3,10 +3,11 @@ import { TypeOrmModule } from '@nestjs/typeorm';
 import { EvaluationService } from './evaluation.service';
 import { EvaluationController } from './evaluation.controller';
 import { Evaluation } from './entities/evaluation.entity';
+import { User } from '../auth/entities/user.entity';
 import { AuthModule } from '../auth/auth.module';
 
 @Module({
-  imports: [TypeOrmModule.forFeature([Evaluation]), AuthModule],
+  imports: [TypeOrmModule.forFeature([Evaluation, User]), AuthModule],
   controllers: [EvaluationController],
   providers: [EvaluationService],
 })

backend/src/evaluation/evaluation.service.spec.ts

@@ -6,6 +6,7 @@ import { Evaluation } from './entities/evaluation.entity';
 import { Repository } from 'typeorm';
 import { ConfigService } from '@nestjs/config';
 import { NotFoundException } from '@nestjs/common';
+import { User } from '../auth/entities/user.entity';
 
 const mockEvaluationRepository = () => ({
   create: jest.fn(),
@@ -22,9 +23,17 @@ type MockRepository<T = any> = Partial<
   Record<keyof Repository<any>, jest.Mock>
 >;
 
+// Mock User Repository
+const mockUserRepository = () => ({
+  findOne: jest.fn(),
+  update: jest.fn(),
+  increment: jest.fn(),
+});
+
 describe('EvaluationService', () => {
   let service: EvaluationService;
   let repository: MockRepository<Evaluation>;
+  let userRepository: MockRepository<User>;
 
   beforeEach(async () => {
     const module: TestingModule = await Test.createTestingModule({
@@ -34,12 +43,17 @@ describe('EvaluationService', () => {
           provide: getRepositoryToken(Evaluation),
           useFactory: mockEvaluationRepository,
         },
+        {
+          provide: getRepositoryToken(User),
+          useFactory: mockUserRepository,
+        },
         { provide: ConfigService, useValue: mockConfigService },
       ],
     }).compile();
 
     service = module.get<EvaluationService>(EvaluationService);
     repository = module.get(getRepositoryToken(Evaluation));
+    userRepository = module.get(getRepositoryToken(User));
   });
 
   it('should be defined', () => {
@@ -92,7 +106,7 @@ describe('EvaluationService', () => {
     it('should create an evaluation by calling AI and saving to DB', async () => {
       // Mock Data
       const createEvaluationDto = {
-        answer: 'My German Text',
+        answer: 'My German Text is now long enough to pass validation',
         level: 'A2',
         part: 1,
         module: 'writing',

backend/src/evaluation/evaluation.service.ts

@@ -1,5 +1,9 @@
 /* eslint-disable @typescript-eslint/no-unsafe-assignment, @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-return, @typescript-eslint/no-unsafe-argument */
-import { Injectable, NotFoundException } from '@nestjs/common';
+import {
+  Injectable,
+  NotFoundException,
+  ForbiddenException,
+} from '@nestjs/common';
 import { InjectRepository } from '@nestjs/typeorm';
 import { Repository } from 'typeorm';
 import { CreateEvaluationDto } from './dto/create-evaluation.dto';
@@ -19,12 +23,48 @@ export class EvaluationService {
   constructor(
     @InjectRepository(Evaluation)
     private evaluationRepository: Repository<Evaluation>,
+    @InjectRepository(User)
+    private userRepository: Repository<User>,
     private configService: ConfigService,
-  ) {}
+  ) {
+    // ...
+  }
 
   async create(createEvaluationDto: CreateEvaluationDto, user?: User) {
+    // 1. Check Usage Limit (if user exists)
+    if (user) {
+      const freshUser = await this.userRepository.findOne({
+        where: { id: user.id },
+      });
+      if (freshUser) {
+        const today = new Date().toDateString();
+        const lastDate = freshUser.last_usage_date
+          ? freshUser.last_usage_date.toDateString()
+          : null;
+
+        // Reset if new day
+        if (lastDate !== today) {
+          freshUser.usage_count = 0;
+          // We don't save immediately here to save a DB call, we trust the check below
+        }
+
+        if (freshUser.usage_count >= freshUser.usage_limit) {
+          throw new ForbiddenException(
+            'Daily trial limit reached (10/10). Please upgrade or try again tomorrow.',
+          );
+        }
+      }
+    }
+
     const { answer, task } = createEvaluationDto;
 
+    // Validation: Minimum Length
+    if (!answer || answer.trim().length < 20) {
+      throw new ForbiddenException(
+        'Answer is too short. Please write at least 20 characters to proceed.',
+      );
+    }
+
     // Use level/part from task or DTO if available, defaults provided
     const level = task?.level || createEvaluationDto.level || 'A2';
     const part = task?.part || createEvaluationDto.part || 1;
@@ -37,6 +77,40 @@ export class EvaluationService {
       level,
     );
 
+    // 2. Increment Usage Count & Update Date (Only on successful AI call)
+    if (user) {
+      // We perform a safe update that handles the reset implicitly by setting the value
+      const freshUser = await this.userRepository.findOne({
+        where: { id: user.id },
+      });
+      if (freshUser) {
+        const today = new Date();
+        const lastDateStr = freshUser.last_usage_date
+          ? freshUser.last_usage_date.toDateString()
+          : null;
+
+        if (lastDateStr !== today.toDateString()) {
+          // First use of the day
+          await this.userRepository.update(
+            { id: user.id },
+            { usage_count: 1, last_usage_date: today },
+          );
+        } else {
+          // Same day, just increment
+          await this.userRepository.increment(
+            { id: user.id },
+            'usage_count',
+            1,
+          );
+          // Ensure date is current (though distinct days are handled above, keeping it fresh is fine)
+          await this.userRepository.update(
+            { id: user.id },
+            { last_usage_date: today },
+          );
+        }
+      }
+    }
+
     // Save to DB
     const evaluation = this.evaluationRepository.create({
       original_text: answer,

backend/src/evaluation/prompts/evaluation.prompt.ts

@@ -97,6 +97,8 @@ export const generateEvaluationPrompt = (
         }
       }
 
-      Important: Provide the feedback (strengths and improvements) in ${languageName}.
+      Important: Provide the feedback (strengths and improvements) in ${languageName} ONLY. Do NOT provide the German translation in parentheses.
+      Example: "This SMS does not cover all points." (Good)
+      Example: "This SMS does not cover all points. (Diese SMS behandelt nicht alle Punkte.)" (BAD - Do not do this)
     `;
 };

backend/src/evaluation/prompts/task.prompt.ts

@@ -94,16 +94,18 @@ export const generateTaskPrompt = (
     
     The task should be realistic and suitable for ${level} proficiency.
     
+    CRITICAL: You MUST include a specific name for the recipient in the 'scenario' or 'instruction' (e.g. 'Ihre Lehrerin Frau Müller', 'Ihr Freund Thomas', 'das Hotel Stern'). Do NOT say just 'your teacher' or 'a friend'. Give them a NAME.
+    
     Return the task in the following JSON format ONLY:
     {
       "title": "Topic Title (German)",
-      "scenario": "A short description of the situation in German (Sie sind ...).",
-      "points": [
-        "First point to cover (German)",
-        "Second point to cover (German)",
-        "Third point to cover (German)"
-      ],
-      "instruction": "Schreiben Sie ca. ${partSpec.length}. Schreiben Sie zu allen Punkten.",
+    "scenario": "A description of the situation in German (Sie sind ...). IMPORTANT: You MUST specify a name for the recipient (e.g. 'Ihre Lehrerin Frau Müller', 'Ihr Freund Thomas', 'das Hotel Stern').",
+    "points": [
+      "First point to cover (German)",
+      "Second point to cover (German)",
+      "Third point to cover (German)"
+    ],
+    "instruction": "Schreiben Sie eine E-Mail/SMS an [Name]. Schreiben Sie ca. ${partSpec.length}. Schreiben Sie zu allen Punkten.",
       "time": "${partSpec.time}"
     }
   `;

backend/src/main.ts

@@ -7,11 +7,20 @@ import { AppModule } from './app.module';
 async function bootstrap() {
   const app = await NestFactory.create(AppModule);
   app.enableCors({
-    origin: (origin: string, callback: (err: Error | null, allow?: boolean) => void) => {
-      const allowedOrigins = (process.env.FRONTEND_URL || '').split(',').map(url => url.trim());
+    origin: (
+      origin: string,
+      callback: (err: Error | null, allow?: boolean) => void,
+    ) => {
+      const allowedOrigins = (process.env.FRONTEND_URL || '')
+        .split(',')
+        .map((url) => url.trim());
       allowedOrigins.push('http://localhost:3000');
 
-      if (!origin || allowedOrigins.includes(origin) || /\.vercel\.app$/.test(origin)) {
+      if (
+        !origin ||
+        allowedOrigins.includes(origin) ||
+        /\.vercel\.app$/.test(origin)
+      ) {
         callback(null, true);
       } else {
         console.warn(`Blocked CORS for origin: ${origin}`);