AIが迷わない疎結合設計へリファクタ！
コードレビュー道場 #2：凝集度/結合度

class PaymentService {
  constructor(http) {
    this.http = http;
  }

  async pay(order) {
    console.log('PAYMENT START', new Date(), order.id);

    const result = await this.http.post('/payments', { orderId: order.id });

    console.log('PAYMENT END', new Date(), order.id, result.status);

    return result;
  }
}

function connectDb() {
  const client = new DbClient({
    host: 'db.example.internal',
    port: 5432,
    user: 'app_user',
    password: 'secret'
  });
  return client;
}

function renderList(items, showHeader, showFooter, highlightActive, allowDelete) {
  // たくさんの条件分岐で描画を切り替える
}

class ReportGenerator {
  generate() {
    const config = JSON.parse(localStorage.getItem('report-config') || '{}');
    // config をもとにレポートを生成
  }
}

function createReport(params) {
  // params = {
  //   userId, userName, userAge,
  //   projectId, projectName,
  //   startDate, endDate,
  //   includePrivate, includeDeleted,
  //   ...
  // }
  // 複雑なレポート生成処理
}

function formatUserAddress(user) {
  return `${user.postalCode} ${user.pref} ${user.city} ${user.street}`;
}

function formatShippingLabel(order) {
  const user = order.user;
  return `${user.postalCode} ${user.pref} ${user.city} ${user.street}`;
}

function updateUserName(user) {
  const input = document.getElementById('user-name-input');
  user.name = input.value;
}

function completeTask(task, user, project) {
  task.completed = true;
  task.completedAt = new Date();

  user.completedTaskCount++;

  project.lastActivityAt = new Date();
}

function calculateDiscount(user, now = new Date()) {
  if (user.isPremium && now.getDay() === 5) {
    return 0.2;
  }
  return 0;
}

class UserManager {
  constructor(db) {
    this.db = db;
  }

  async findById(id) {
    return this.db.query('SELECT * FROM users WHERE id = ?', [id]);
  }

  async changeEmail(id, newEmail) {
    const user = await this.findById(id);
    // ドメインルールのチェック（省略）
    await this.db.execute('UPDATE users SET email = ? WHERE id = ?', [newEmail, id]);
  }
}