Task: Apply the Humble Object Pattern

// src/controllers/CheckoutController.ts
import { Request, Response } from 'express'
import { db } from '../db'
import { stripe } from '../stripe'

export class CheckoutController {
  async handle(req: Request, res: Response): Promise<void> {
    const { userId, cartId } = req.body

    // Business logic mixed in
    const cart = await db.query('SELECT * FROM carts WHERE id = $1', [cartId])
    if (cart.rows.length === 0) {
      res.status(404).json({ error: 'Cart not found' })
      return
    }

    const items = cart.rows[0].items as Array<{ price: number; quantity: number }>
    const total = items.reduce((sum, item) => sum + item.price * item.quantity, 0)

    if (total <= 0) {
      res.status(400).json({ error: 'Cart is empty or invalid' })
      return
    }

    const charge = await stripe.charges.create({
      amount: Math.round(total * 100),
      currency: 'usd',
      customer: userId,
    })

    await db.query('UPDATE carts SET status = $1 WHERE id = $2', ['checked_out', cartId])
    res.json({ chargeId: charge.id, total })
  }
}