// 1. Create a Braintree client instance
braintree.client.create(
  { authorization: "CLIENT_TOKEN_FROM_SERVER" },
  function (clientErr, clientInstance) {
    if (clientErr) { console.error("Error creating client:", clientErr); return; }

    // 2. Create a PayPal Checkout component
    braintree.paypalCheckout.create(
      { client: clientInstance },
      function (paypalCheckoutErr, paypalCheckoutInstance) {
        if (paypalCheckoutErr) { console.error("Error:", paypalCheckoutErr); return; }

        // 3. Load the PayPal JS SDK
        // IMPORTANT: currency and intent must match createPayment() below
        paypalCheckoutInstance.loadPayPalSDK(
          { currency: "USD", intent: "capture" },
          function () {
            // 4. Render PayPal buttons
            paypal.Buttons({
              fundingSource: paypal.FUNDING.PAYPAL,

              createOrder: function () {
                return paypalCheckoutInstance.createPayment({
                  flow: "checkout",           // Required: must be 'checkout'
                  amount: "10.00",            // Order subtotal
                  currency: "USD",            // Must match loadPayPalSDK currency
                  intent: "capture",          // Must match loadPayPalSDK intent
                  enableShippingAddress: true,    // Required: displays shipping in paysheet
                  shippingAddressEditable: true,  // Required: allows address changes
                  shippingCallbackUrl: "https://merchant.example.com/shipping-callback",
                });
              },

              onApprove: function (data, actions) {
                return paypalCheckoutInstance.tokenizePayment(data, function (err, payload) {
                  if (err) { console.error("Error tokenizing:", err); return; }
                  // Send payload.nonce to your server to create a transaction
                  console.log("Payment nonce:", payload.nonce);
                });
              },

              onCancel: function (data) { console.log("Payment cancelled", data); },
              onError: function (err) { console.error("PayPal error:", err); },
            }).render("#paypal-button-container");
          }
        );
      }
    );
  }
);

{
  "id": "2SM98888S4900545P",
  "amount": { "value": "10.00", "currency_code": "USD" },
  "item_total": "10.00",
  "tax_total": "0.00",
  "shipping": "0.00",
  "shipping_address": {
    "admin_area_2": "San Jose",
    "admin_area_1": "CA",
    "postal_code": "95131",
    "country_code": "US"
  }
}

{
  "id": "2SM98888S4900545P",
  "amount": { "value": "15.00", "currency_code": "USD" },
  "item_total": "10.00",
  "tax_total": "2.00",
  "shipping": "3.00",
  "shipping_address": {
    "admin_area_2": "San Jose",
    "admin_area_1": "CA",
    "postal_code": "95131",
    "country_code": "US"
  },
  "shipping_option": {
    "id": "standard",
    "description": "Standard Shipping",
    "type": "SHIPPING",
    "amount": { "value": "3.00", "currency_code": "USD" }
  }
}

{
  "id": "2SM98888S4900545P",
  "amount": {
    "currency_code": "USD",
    "value": "20.00"
  },
  "item_total": "20.00",
  "shipping": "0.00",
  "handling": "0.00",
  "tax_total": "0.00",
  "insurance": "0.00",
  "shipping_discount": "0.00",
  "discount": "0.00",
  "shipping_options": [
    {
      "id": "1",
      "description": "Free Shipping",
      "type": "SHIPPING",
      "selected": true,
      "amount": {
        "currency_code": "USD",
        "value": "0.00"
      }
    },
    {
      "id": "2",
      "description": "USPS Priority Shipping",
      "type": "SHIPPING",
      "selected": false,
      "amount": {
        "currency_code": "USD",
        "value": "7.00"
      }
    },
    {
      "id": "3",
      "description": "1-Day Shipping",
      "type": "SHIPPING",
      "selected": false,
      "amount": {
        "currency_code": "USD",
        "value": "10.00"
      }
    }
  ]
}

const express = require("express");
const app = express();
app.use(express.json());

const SHIPPING_RATES = {
  US: [
    { id: "free",     description: "Free Shipping (5-7 business days)",     amount: "0.00",  type: "SHIPPING" },
    { id: "standard", description: "Standard Shipping (3-5 business days)", amount: "3.00",  type: "SHIPPING" },
    { id: "express",  description: "Express Shipping (1-2 business days)",  amount: "10.00", type: "SHIPPING" },
  ],
  CA: [
    { id: "standard_ca", description: "Standard to Canada (7-10 business days)", amount: "8.00",  type: "SHIPPING" },
    { id: "express_ca",  description: "Express to Canada (3-5 business days)",   amount: "18.00", type: "SHIPPING" },
  ],
};

const BLOCKED_COUNTRIES = ["CU", "IR", "KP", "SY"];

function getTaxRate(state) {
  return { CA: 0.0725, NY: 0.08, TX: 0.0625 }[state] || 0.05;
}

app.post("/shipping-callback", (req, res) => {
  const { id, amount, item_total, shipping_address, shipping_option } = req.body;

  const country = shipping_address.country_code;

  if (BLOCKED_COUNTRIES.includes(country)) {
    return res.status(422).json({ name: "UNPROCESSABLE_ENTITY", details: [{ issue: "COUNTRY_ERROR" }] });
  }

  const options = SHIPPING_RATES[country];
  if (!options) {
    return res.status(422).json({ name: "UNPROCESSABLE_ENTITY", details: [{ issue: "ADDRESS_ERROR" }] });
  }

  // On the first callback, shipping_option is absent — default to first option
  const selectedId = shipping_option?.id || options[0].id;
  const selectedOption = options.find((o) => o.id === selectedId) || options[0];
  const shippingCost = parseFloat(selectedOption.amount);

  const itemTotal = parseFloat(item_total || amount.value);
  const taxTotal = (itemTotal * getTaxRate(shipping_address.admin_area_1)).toFixed(2);
  const total = (itemTotal + shippingCost + parseFloat(taxTotal)).toFixed(2);

  return res.status(200).json({
    id,
    amount: { value: total, currency_code: amount.currency_code },
    item_total: itemTotal.toFixed(2),
    shipping: shippingCost.toFixed(2),
    tax_total: taxTotal,
    shipping_options: options.map((opt) => ({
      id: opt.id,
      description: opt.description,
      selected: opt.id === selectedOption.id,
      type: opt.type,
      amount: { value: opt.amount, currency_code: amount.currency_code },
    })),
  });
});

app.listen(3000);

{
  "name": "UNPROCESSABLE_ENTITY",
  "details": [{ "issue": "ADDRESS_ERROR" }]
}