Add network verification

The app doesn't try to get or update the data if the phone is not
online.

mobile/package-lock.json

@@ -274,6 +274,11 @@
             "resolved": "https://registry.npmjs.org/cordova-plugin-device/-/cordova-plugin-device-2.0.3.tgz",
             "integrity": "sha512-Jb3V72btxf3XHpkPQsGdyc8N6tVBYn1vsxSFj43fIz9vonJDUThYPCJJHqk6PX6N4dJw6I4FjxkpfCR4LDYMlw=="
         },
+        "cordova-plugin-network-information": {
+            "version": "2.0.2",
+            "resolved": "https://registry.npmjs.org/cordova-plugin-network-information/-/cordova-plugin-network-information-2.0.2.tgz",
+            "integrity": "sha512-NwO3qDBNL/vJxUxBTPNOA1HvkDf9eTeGH8JSZiwy1jq2W2mJKQEDBwqWkaEQS19Yd/MQTiw0cykxg5D7u4J6cQ=="
+        },
         "cordova-plugin-whitelist": {
             "version": "1.3.4",
             "resolved": "https://registry.npmjs.org/cordova-plugin-whitelist/-/cordova-plugin-whitelist-1.3.4.tgz",

mobile/package.json

@@ -16,7 +16,8 @@
     "cordova-android": "^8.1.0",
     "cordova-browser": "^6.0.0",
     "cordova-ios": "^5.1.1",
-    "cordova-plugin-device": "^2.0.3"
+    "cordova-plugin-device": "^2.0.3",
+    "cordova-plugin-network-information": "^2.0.2"
   },
   "devDependencies": {
     "cordova-plugin-whitelist": "^1.3.4"
@@ -24,7 +25,8 @@
   "cordova": {
     "plugins": {
       "cordova-plugin-whitelist": {},
-      "cordova-plugin-device": {}
+      "cordova-plugin-device": {},
+      "cordova-plugin-network-information": {}
     },
     "platforms": [
       "android",

mobile/www/index.html

@@ -104,13 +104,13 @@
 
 <!-- Your custom app scripts -->
 <script src="js/app.js"></script>
+<script src="js/index.js"></script>
 <script src="js/database.js"></script>
 <script src="js/graph.js"></script>
 <script src="js/feclass.js"></script>
 <script src="js/stats.js"></script>
 <script src="js/feclass-stats.js"></script>
 <script src="js/comparator.js"></script>
-<script src="js/index.js"></script>
 
 </body>
 </html>

mobile/www/js/database.js

@@ -6,6 +6,17 @@ Description : Communicates with the server to ensure that the data is up to date
 const BASE_URL = "http://localhost/";
 let feData = JSON.parse(localStorage.getItem("feData"));
 
+function isOnline() {
+    const networkState = (navigator.connection) ? navigator.connection.type : null;
+
+    if (networkState != null && networkState != "none") {
+        return true;
+    }
+    return false;
+}
+
+// Get the data from the server or update the data in the localstorage if needed
+function getOrUpdateData() {
     if (feData != null) {
         let body = new FormData();
         body.append('version', feData.version);
@@ -44,7 +55,9 @@ if (feData != null) {
                 console.log(err);
             });
     }
+}
 
+// Update the data in the localstorage
 function updateData(data) {
     // If the data received from the server are not empty then we can save them in the local storage
     if (data != null && Object.keys(data).length > 0) {
@@ -55,3 +68,18 @@ function updateData(data) {
     // End of the update process, we can now display the data
     displayCharacters();
 }
+
+// Doesn't try to get or update the data if the user is not connected to the internet
+if (isOnline()) {
+    getOrUpdateData();
+} else {
+    // If the user is not connected to internet but the data are already present in the app, then we display them
+    if (feData != null) {
+        displayCharacters();
+    } else {
+        alert("Please connect to the internet to download the data");
+    }
+
+    // Create an event to get/update the data when the user goes online
+    document.addEventListener("online", getOrUpdateData, false);
+}