Improve MongoDB init

1) Use promises properly because it's 2019 already
2) Get rid of 'Unhandled promise exceptions'
3) Terminate task successfully when all work is done
4) Purge collections before re-adding data (import is now idempotent)

CF/mongo-init/init-db.js

@@ -1,6 +1,7 @@
-/*jshint esversion: 6 */
+/*jshint esversion: 8 */
 
 const mongoClient = require('mongodb').MongoClient;
+const bindingName = 'catalogue_database';
 
 var mongoURL = 'mongodb://mongodb:27017/catalogue';
 
@@ -9,7 +10,7 @@ if (process.env.VCAP_SERVICES) {
 
     for (let [key, value] of Object.entries(JSON.parse(process.env.VCAP_SERVICES))) {
         connectionDetails = value.find(function(binding) {
-            return 'catalogue_database' == binding.binding_name && binding.credentials;
+            return bindingName == binding.binding_name && binding.credentials;
         }).credentials;
 
         if (connectionDetails) {
@@ -25,15 +26,18 @@ if (!mongoURL) {
     throw new Error('MongoDB connection data missing');
 }
 
-mongoClient.connect(mongoURL, (error, db) => {
-    if(error) {
-        console.log('Cannot connect to MongoDB', error);
-        process.exit(42);
-    } else {
+mongoClient.connect(mongoURL)
+    .catch(function(err) {
+        console.log(`Cannot connect to the MongoDB database: ${err}`);
+        process.exit(4242);
+    })
+    .then(function(db) {
         console.log('Creating products collection');
 
         products = db.collection('products');
 
+        // Delete all old product entries before adding new ones
+        products.deleteMany({});
         products.insertMany([
             {sku: 'HAL-1', name: 'HAL', description: 'Sorry Dave, I cant do that', price: 2001, instock: 2, categories: ['AI']},
             {sku: 'PB-1', name: 'Positronic Brain', description: 'Highly advanced sentient processing unit with the laws of robotics burned in', price: 200, instock: 0, categories: ['AI']},
@@ -57,6 +61,8 @@ mongoClient.connect(mongoURL, (error, db) => {
 
         console.log('Starting users import');
 
+        // Delete all old user entries before adding new ones
+        users.deleteMany({});
         users.insertMany([
             {name: 'user', password: 'password', email: 'user@me.com'},
             {name: 'stan', password: 'bigbrain', email: 'stan@instana.com'}
@@ -76,6 +82,8 @@ mongoClient.connect(mongoURL, (error, db) => {
 
         console.log('Starting catalogue import');
 
+        // Delete all old catalogue entries before adding new ones
+        catalogue.deleteMany({});
         catalogue.insertMany([
             {sku: 'HAL-1', name: 'HAL', description: 'Sorry Dave, I cant do that', price: 2001, instock: 2, categories: ['AI']},
             {sku: 'PB-1', name: 'Positronic Brain', description: 'Highly advanced sentient processing unit with the laws of robotics burned in', price: 200, instock: 0, categories: ['AI']},
@@ -103,7 +111,12 @@ mongoClient.connect(mongoURL, (error, db) => {
         );
 
         console.log('Products imported');
-
+    })
+    .then(function() {
         console.log('All done');
-    }
-});
+        process.exit(0);
+    })
+    .catch(function(err) {
+        console.log(`Error while importing data into the MongoDB '${bindingName}' database: ${err}`);
+        process.exit(42);
+    });