promiseChainAsynch.js

const store = {
  sunglasses: {
    inventory: 817,
    cost: 9.99,
  },
  pants: {
    inventory: 236,
    cost: 7.99,
  },
  bags: {
    inventory: 17,
    cost: 12.99,
  },
};

const checkInventory = (order) => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      const itemsArr = order.items;
      let inStock = itemsArr.every(
        (item) => store[item[0]].inventory >= item[1]
      );

      if (inStock) {
        let total = 0;
        itemsArr.forEach((item) => {
          total += item[1] * store[item[0]].cost;
        });
        console.log(
          `All of the items are in stock. The total cost of the order is ${total}.`
        );
        resolve([order, total]);
      } else {
        reject(
          `The order could not be completed because some items are sold out.`
        );
      }
    }, generateRandomDelay());
  });
};

const processPayment = (responseArray) => {
  const order = responseArray[0];
  const total = responseArray[1];
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      let hasEnoughMoney = order.giftcardBalance >= total;
      // For simplicity we've omited a lot of functionality
      // If we were making more realistic code, we would want to update the giftcardBalance and the inventory
      if (hasEnoughMoney) {
        console.log(
          `Payment processed with giftcard. Generating shipping label.`
        );
        let trackingNum = generateTrackingNumber();
        resolve([order, trackingNum]);
      } else {
        reject(`Cannot process order: giftcard balance was insufficient.`);
      }
    }, generateRandomDelay());
  });
};

const shipOrder = (responseArray) => {
  const order = responseArray[0];
  const trackingNum = responseArray[1];
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(
        `The order has been shipped. The tracking number is: ${trackingNum}.`
      );
    }, generateRandomDelay());
  });
};

// This function generates a random number to serve as a "tracking number" on the shipping label. In real life this wouldn't be a random number
function generateTrackingNumber() {
  return Math.floor(Math.random() * 1000000);
}

// This function generates a random number to serve as delay in a setTimeout() since real asynchrnous operations take variable amounts of time
function generateRandomDelay() {
  return Math.floor(Math.random() * 2000);
}

module.exports = { checkInventory, processPayment, shipOrder };