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README.md

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+# API Billing System
+
+一个基于 Koa.js 的高性能 API 计费系统，支持按月计费和按调用量计费。
+
+## 主要特性
+
+- 支持多种计费模式：
+  - 按月固定额度计费
+  - 按实际使用量计费
+- 高性能设计：
+  - 使用 Redis 进行速率限制和临时数据缓存
+  - MongoDB 用于持久化存储
+  - 异步处理计费记录
+- 完善的错误处理和日志记录
+- RESTful API 设计
+- 实时使用量统计
+- 灵活的计费策略配置
+
+## 系统要求
+
+- Node.js >= 14
+- MongoDB >= 4.4
+- Redis >= 6.0
+
+## 安装
+
+```bash
+# 克隆项目
+git clone [repository-url]
+
+# 安装依赖
+npm install
+
+# 配置环境变量
+cp .env.example .env
+# 编辑 .env 文件配置相关参数
+
+# 启动服务
+npm start
+```
+
+## API 文档
+
+### 认证
+所有 API 请求都需要在 header 中包含 `X-API-Key`
+
+### 计费相关接口
+
+#### 获取月度使用统计
+```
+GET /billing/usage/:year/:month
+```
+
+#### 获取月度账单
+```
+GET /billing/bill/:year/:month
+```
+
+#### 更新计费方案
+```
+PUT /billing/plan
+```
+
+请求体示例：
+```json
+{
+  "billingPlan": "monthly",
+  "monthlyQuota": 10000,
+  "usageRate": 0.01
+}
+```
+
+## 性能优化
+
+1. 使用 Redis 进行速率限制和临时数据缓存
+2. MongoDB 索引优化
+3. 异步处理计费记录
+4. 批量处理和聚合查询
+
+## 安全性考虑
+
+1. API 密钥认证
+2. 速率限制
+3. 输入验证
+4. 错误处理
+5. 敏感信息加密
+
+## 开发计划
+
+- [ ] 支持多种货币
+- [ ] 添加计费预警功能
+- [ ] 支持自定义计费规则
+- [ ] 添加计费报表导出功能
+- [ ] 集成支付网关
+
+## 许可证
+
+MIT

package.json

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+{
+  "name": "api-billing-system",
+  "version": "1.0.0",
+  "description": "A robust API billing system built with Koa.js",
+  "main": "src/app.js",
+  "scripts": {
+    "start": "node src/app.js",
+    "dev": "nodemon src/app.js",
+    "test": "jest"
+  },
+  "dependencies": {
+    "koa": "^2.14.2",
+    "koa-router": "^12.0.1",
+    "koa-bodyparser": "^4.4.1",
+    "mongoose": "^7.5.0",
+    "winston": "^3.10.0",
+    "joi": "^17.10.1",
+    "dotenv": "^16.3.1",
+    "moment": "^2.29.4",
+    "redis": "^4.6.8"
+  },
+  "devDependencies": {
+    "jest": "^29.6.4",
+    "nodemon": "^3.0.1"
+  }
+}

src/app.js

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+require('dotenv').config();
+const Koa = require('koa');
+const Router = require('koa-router');
+const bodyParser = require('koa-bodyparser');
+const mongoose = require('mongoose');
+const { errorHandler } = require('./middleware/errorHandler');
+const { rateLimiter } = require('./middleware/rateLimiter');
+const { logger } = require('./utils/logger');
+const apiRoutes = require('./routes/api');
+const billingRoutes = require('./routes/billing');
+
+const app = new Koa();
+const router = new Router();
+
+// Database connection
+mongoose.connect(process.env.MONGODB_URI)
+  .then(() => logger.info('Connected to MongoDB'))
+  .catch(err => logger.error('MongoDB connection error:', err));
+
+// Middleware
+app.use(errorHandler);
+app.use(bodyParser());
+app.use(rateLimiter);
+
+// Routes
+router.use('/api', apiRoutes.routes());
+router.use('/billing', billingRoutes.routes());
+
+app.use(router.routes());
+app.use(router.allowedMethods());
+
+const PORT = process.env.PORT || 3000;
+app.listen(PORT, () => {
+  logger.info(`Server running on port ${PORT}`);
+});

src/middleware/errorHandler.js

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+const { logger } = require('../utils/logger');
+
+exports.errorHandler = async (ctx, next) => {
+  try {
+    await next();
+  } catch (err) {
+    logger.error('Request error:', err);
+
+    ctx.status = err.status || 500;
+    ctx.body = {
+      error: {
+        message: err.message || 'Internal server error',
+        status: ctx.status,
+        timestamp: new Date().toISOString()
+      }
+    };
+
+    // Emit error for potential monitoring
+    ctx.app.emit('error', err, ctx);
+  }
+};

src/middleware/rateLimiter.js

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+const { RedisClient } = require('../utils/redis');
+const { logger } = require('../utils/logger');
+
+const RATE_LIMIT_WINDOW = 60; // 1 minute window
+const MAX_REQUESTS = 100;     // Maximum requests per window
+
+exports.rateLimiter = async (ctx, next) => {
+  const apiKey = ctx.get('X-API-Key');
+  if (!apiKey) {
+    ctx.status = 401;
+    ctx.body = { error: 'API key required' };
+    return;
+  }
+
+  const key = `ratelimit:${apiKey}`;
+  
+  try {
+    const [requests] = await RedisClient
+      .multi()
+      .incr(key)
+      .expire(key, RATE_LIMIT_WINDOW)
+      .exec();
+
+    const requestCount = requests[1];
+
+    ctx.set('X-RateLimit-Limit', MAX_REQUESTS);
+    ctx.set('X-RateLimit-Remaining', Math.max(0, MAX_REQUESTS - requestCount));
+
+    if (requestCount > MAX_REQUESTS) {
+      ctx.status = 429;
+      ctx.body = { error: 'Rate limit exceeded' };
+      return;
+    }
+
+    await next();
+  } catch (error) {
+    logger.error('Rate limiter error:', error);
+    await next(); // Proceed even if rate limiting fails
+  }
+};

src/models/Usage.js

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+const mongoose = require('mongoose');
+
+const usageSchema = new mongoose.Schema({
+  userId: { 
+    type: mongoose.Schema.Types.ObjectId, 
+    ref: 'User',
+    required: true 
+  },
+  endpoint: { type: String, required: true },
+  requestCount: { type: Number, default: 1 },
+  cost: { type: Number, required: true },
+  timestamp: { type: Date, default: Date.now },
+  billingPeriod: { 
+    year: { type: Number, required: true },
+    month: { type: Number, required: true }
+  }
+});
+
+// Create compound index for efficient querying
+usageSchema.index({ userId: 1, 'billingPeriod.year': 1, 'billingPeriod.month': 1 });
+
+module.exports = mongoose.model('Usage', usageSchema);

src/models/User.js

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+const mongoose = require('mongoose');
+
+const userSchema = new mongoose.Schema({
+  username: { type: String, required: true, unique: true },
+  apiKey: { type: String, required: true, unique: true },
+  billingPlan: {
+    type: String,
+    enum: ['monthly', 'usage'],
+    required: true
+  },
+  monthlyQuota: { type: Number },  // For monthly plan
+  usageRate: { type: Number },     // For usage-based plan
+  balance: { type: Number, default: 0 },
+  isActive: { type: Boolean, default: true },
+  createdAt: { type: Date, default: Date.now },
+  updatedAt: { type: Date, default: Date.now }
+});
+
+module.exports = mongoose.model('User', userSchema);

src/routes/billing.js

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+const Router = require('koa-router');
+const BillingService = require('../services/BillingService');
+const { validateApiKey } = require('../middleware/auth');
+
+const router = new Router();
+
+// Get monthly usage statistics
+router.get('/usage/:year/:month', validateApiKey, async (ctx) => {
+  const { year, month } = ctx.params;
+  const usage = await BillingService.getMonthlyUsage(
+    ctx.state.user._id,
+    parseInt(year),
+    parseInt(month)
+  );
+  ctx.body = { usage };
+});
+
+// Get monthly bill
+router.get('/bill/:year/:month', validateApiKey, async (ctx) => {
+  const { year, month } = ctx.params;
+  const bill = await BillingService.generateMonthlyBill(
+    ctx.state.user._id,
+    parseInt(year),
+    parseInt(month)
+  );
+  ctx.body = { bill };
+});
+
+// Update billing plan
+router.put('/plan', validateApiKey, async (ctx) => {
+  const { billingPlan, monthlyQuota, usageRate } = ctx.request.body;
+  const user = await User.findByIdAndUpdate(
+    ctx.state.user._id,
+    {
+      billingPlan,
+      monthlyQuota,
+      usageRate,
+      updatedAt: new Date()
+    },
+    { new: true }
+  );
+  ctx.body = { user };
+});
+
+module.exports = router;

src/services/BillingService.js

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+const moment = require('moment');
+const User = require('../models/User');
+const Usage = require('../models/Usage');
+const { logger } = require('../utils/logger');
+const { RedisClient } = require('../utils/redis');
+
+class BillingService {
+  static async recordUsage(userId, endpoint) {
+    try {
+      const user = await User.findById(userId);
+      if (!user || !user.isActive) {
+        throw new Error('Invalid or inactive user');
+      }
+
+      const now = moment();
+      const year = now.year();
+      const month = now.month() + 1;
+
+      // Calculate cost based on billing plan
+      let cost = 0;
+      if (user.billingPlan === 'usage') {
+        cost = user.usageRate;
+      }
+
+      // Check monthly quota for monthly plan
+      if (user.billingPlan === 'monthly') {
+        const monthlyUsage = await Usage.aggregate([
+          {
+            $match: {
+              userId: user._id,
+              'billingPeriod.year': year,
+              'billingPeriod.month': month
+            }
+          },
+          {
+            $group: {
+              _id: null,
+              total: { $sum: '$requestCount' }
+            }
+          }
+        ]);
+
+        const currentUsage = monthlyUsage[0]?.total || 0;
+        if (currentUsage >= user.monthlyQuota) {
+          throw new Error('Monthly quota exceeded');
+        }
+      }
+
+      // Record usage with Redis for performance
+      const usageKey = `usage:${userId}:${year}:${month}:${endpoint}`;
+      await RedisClient.hincrby(usageKey, 'count', 1);
+      await RedisClient.expire(usageKey, 60 * 60 * 24 * 7); // Expire after 7 days
+
+      // Persist to MongoDB asynchronously
+      const usage = await Usage.findOneAndUpdate(
+        {
+          userId,
+          endpoint,
+          'billingPeriod.year': year,
+          'billingPeriod.month': month
+        },
+        {
+          $inc: { requestCount: 1 },
+          $set: { cost }
+        },
+        { upsert: true, new: true }
+      );
+
+      // Update user balance for usage-based billing
+      if (user.billingPlan === 'usage') {
+        await User.findByIdAndUpdate(userId, {
+          $inc: { balance: -cost }
+        });
+      }
+
+      return usage;
+    } catch (error) {
+      logger.error('Error recording usage:', error);
+      throw error;
+    }
+  }
+
+  static async getMonthlyUsage(userId, year, month) {
+    try {
+      const usage = await Usage.aggregate([
+        {
+          $match: {
+            userId: mongoose.Types.ObjectId(userId),
+            'billingPeriod.year': year,
+            'billingPeriod.month': month
+          }
+        },
+        {
+          $group: {
+            _id: '$endpoint',
+            totalRequests: { $sum: '$requestCount' },
+            totalCost: { $sum: { $multiply: ['$requestCount', '$cost'] } }
+          }
+        }
+      ]);
+
+      return usage;
+    } catch (error) {
+      logger.error('Error getting monthly usage:', error);
+      throw error;
+    }
+  }
+
+  static async generateMonthlyBill(userId, year, month) {
+    try {
+      const user = await User.findById(userId);
+      const usage = await this.getMonthlyUsage(userId, year, month);
+      
+      let totalCost = 0;
+      if (user.billingPlan === 'monthly') {
+        totalCost = user.monthlyQuota > 0 ? user.usageRate : 0;
+      } else {
+        totalCost = usage.reduce((sum, item) => sum + item.totalCost, 0);
+      }
+
+      return {
+        userId,
+        billingPlan: user.billingPlan,
+        year,
+        month,
+        usage,
+        totalCost
+      };
+    } catch (error) {
+      logger.error('Error generating monthly bill:', error);
+      throw error;
+    }
+  }
+}
+
+module.exports = BillingService;

src/utils/logger.js

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+const winston = require('winston');
+
+const logger = winston.createLogger({
+  level: process.env.NODE_ENV === 'production' ? 'info' : 'debug',
+  format: winston.format.combine(
+    winston.format.timestamp(),
+    winston.format.json()
+  ),
+  transports: [
+    new winston.transports.File({ filename: 'error.log', level: 'error' }),
+    new winston.transports.File({ filename: 'combined.log' })
+  ]
+});
+
+if (process.env.NODE_ENV !== 'production') {
+  logger.add(new winston.transports.Console({
+    format: winston.format.combine(
+      winston.format.colorize(),
+      winston.format.simple()
+    )
+  }));
+}
+
+module.exports = { logger };

src/utils/redis.js

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+const Redis = require('redis');
+const { logger } = require('./logger');
+
+class RedisClient {
+  static client = null;
+
+  static async connect() {
+    if (!this.client) {
+      this.client = Redis.createClient({
+        url: process.env.REDIS_URL
+      });
+
+      this.client.on('error', (err) => {
+        logger.error('Redis Client Error:', err);
+      });
+
+      this.client.on('connect', () => {
+        logger.info('Connected to Redis');
+      });
+
+      await this.client.connect();
+    }
+    return this.client;
+  }
+
+  static async get(key) {
+    const client = await this.connect();
+    return client.get(key);
+  }
+
+  static async set(key, value, expireSeconds = null) {
+    const client = await this.connect();
+    if (expireSeconds) {
+      return client.setEx(key, expireSeconds, value);
+    }
+    return client.set(key, value);
+  }
+
+  static async hincrby(key, field, increment) {
+    const client = await this.connect();
+    return client.hIncrBy(key, field, increment);
+  }
+
+  static async expire(key, seconds) {
+    const client = await this.connect();
+    return client.expire(key, seconds);
+  }
+}
+
+module.exports = { RedisClient };