Refactor code and add comments

Fix eslint errors
Move partNumbers object to a json file

index.js

@@ -1,6 +1,11 @@
+// Require npm packages.
 const fetch = require('node-fetch');
-const commandLineArgs = require('command-line-args')
+const commandLineArgs = require('command-line-args');
 
+// Get partNumbers from json file.
+const partNumbers = require('./partNumbers.json');
+
+// Define command line args accepted.
 const optionDefinitions = [
   { name: 'carrier', type: String, defaultValue: 'TMOBILE' },
   { name: 'model', type: String, defaultValue: 'x' },
@@ -10,72 +15,119 @@ const optionDefinitions = [
   { name: 'delay', type: Number, defaultValue: 30 },
 ];
 
+// Parse command line args.
 const options = commandLineArgs(optionDefinitions);
-console.log(options);
-
-const partNumbers = {
-  'x': {
-    'gray': {
-      '64': "",
-      '256': "MQAU2LL/A",
-    },
-    'silver': {
-      '64': "",
-      '256': "",
-    },
-  },
-  '8': {
-    'gray': {
-      '64': "",
-      '256': "MQ932LL/A",
-    },
-    'silver': {
-      '64': "",
-      '256': "",
-    },
-  },
-};
 
+// Get part number for the specified device.
 const partNumber = partNumbers[options.model][options.color][options.storage];
 
+// Construct the endpoint url with the options selected.
 const endpoint = `https://www.apple.com/shop/retail/pickup-message?pl=true&cppart=${options.carrier}/US&parts.0=${partNumber}&location=${options.zip}`;
-// const endpoint = 'https://www.apple.com/shop/retail/pickup-message?pl=true&cppart=TMOBILE/US&parts.0=MQ932LL/A&location=Salem,%20NH';
 
-let requestsMade = 0;
+// Keep track of the last request time.
+let lastRequestTimestamp = null;
 
-makeRequest();
+/**
+ * Update program status display
+ *
+ * @param {String} str The string that will be outputed.
+ */
+function updateStatus() {
+  if (lastRequestTimestamp === null) {
+    return;
+  }
 
-function checkAvailability(data) {
+  const timeDelta = Date.now() - lastRequestTimestamp;
+  const timeInSeconds = Math.floor(timeDelta / 1000);
+  process.stdout.write(`Status: Device not available. Last request made ${timeInSeconds} seconds ago\r`);
+}
+
+/**
+ * Parse the returned data and find stores where the device is available
+ *
+ * @param {Object} data The api response.
+ * @return {Array} The array of stores where the devices is available.
+ */
+function processResponse(data) {
+  // Destructure the stores object out of the body.
   const { stores } = data.body;
 
-  const storesAvailable = stores.filter(store => {
-    const parts = Object.values(store.partsAvailability);
-    const part = parts[0];
-    const pickupDisplay = part.pickupDisplay;
-    const availability = pickupDisplay === 'available';
+  // Filter out stores that do not have the device available.
+  const storesAvailable = stores.filter((store) => {
+    // Select the specified device partNumber.
+    const part = store.partsAvailability[partNumber];
+    // Check that the pickupDisplay property says 'available'.
+    const availability = part.pickupDisplay === 'available';
+    // Return true if the device is available or else false.
     return availability;
   });
 
-  if (storesAvailable.length > 0) {
-    console.log(`Available at ${storesAvailable.length} stores near you:`);
-    console.log(storesAvailable.map(store => `${store.address.address} which is ${store.storeDistanceWithUnit} away`).reduce((msg,store) => `${msg}\n${store}`));
-    process.exit();
-  } else {
-    displayResultInPlace("unavailable");
-    setTimeout(() => {
-      makeRequest();
-      requestsMade++;
-    }, options.delay * 1000);
-  }
+  // Return an array of stores where the device is available.
+  return storesAvailable;
 }
 
-function makeRequest() {
-  fetch(endpoint)
+/**
+ * Make a request to the endpoint and get list of stores available
+ *
+ * @return {Promise} A promise that should resolve to an array of stores available.
+ */
+function getStoresAvailable() {
+  // Update lastRequestTimestamp.
+  lastRequestTimestamp = Date.now();
+
+  return fetch(endpoint)
     .then(stream => stream.json())
-  .then(data => checkAvailability(data))
-  .catch(error => console.log('Fetch Error :-S', error));
+    .catch(error => process.stderr.write('Fetch Error :-S', error))
+    .then(data => processResponse(data));
 }
 
-function displayResultInPlace(data) {
-  process.stdout.write(`${data} --- req: ${requestsMade}\r`);
+/**
+ * Output list of stores where the device is avaliable.
+ *
+ * @param {Array} storesAvailable The array of stores where the device is avaliable.
+ */
+function displayStoresAvailable(storesAvailable) {
+  // Construct the output string by reducing the storesAvailable array into a string.
+  const storesAvailableStr = storesAvailable.reduce(
+    (result, store) =>
+      `${result}\n${store.address.address} which is ${store.storeDistanceWithUnit} away`,
+    '',
+  );
+
+  // Output the message.
+  process.stdout.write(`The device is currently available at ${storesAvailable.length} stores near you:`);
+  process.stdout.write(storesAvailableStr);
+  process.stdout.write('\n');
 }
+
+/**
+ * The main program loop
+ *
+ * Continuously check for the device availability until it is available somewhere.
+ */
+async function requestLoop() {
+  // Fetch the storesAvailable array.
+  const storesAvailable = await getStoresAvailable();
+
+  if (storesAvailable.length === 0) {
+    // If the array is empty, update the status and after the
+    // specified options.delay amount of seconds, try again.
+    setTimeout(() => {
+      requestLoop();
+    }, options.delay * 1000);
+  } else {
+    // The device is available. Show that information to the user and exit the program.
+    displayStoresAvailable(storesAvailable);
+    process.exit();
+  }
+}
+
+// Display program started message.
+process.stdout.write('Starting program with the following settings:\n');
+process.stdout.write(`${JSON.stringify(options, null, 2)}\n`);
+
+// Kick off program.
+setInterval(() => {
+  updateStatus();
+}, 1000);
+requestLoop();

partNumbers.json

@@ -0,0 +1,22 @@
+{
+  "x": {
+    "gray": {
+      "64": "",
+      "256": "MQAU2LL/A"
+    },
+    "silver": {
+      "64": "",
+      "256": ""
+    }
+  },
+  "8": {
+    "gray": {
+      "64": "",
+      "256": "MQ932LL/A"
+    },
+    "silver": {
+      "64": "",
+      "256": ""
+    }
+  }
+}