display migration dialog

Display a dialog on startup to inform the user about Google's decision
to discontinue Inbox. The dialog explains which versions work with
Inbox and which with Gmail.

We add a new config setting 'displayMigrationInfo' to allow the user
to forever dismiss the dialog.

app/main/config.js

@@ -18,5 +18,6 @@ module.exports = new ElectronStore({
       period: 2,
     },
     sendAnalytics: true,
+    displayMigrationInfo: true,
   },
 });

app/main/index.js

@@ -1,7 +1,7 @@
 const fs = require('fs');
 const path = require('path');
 const {
-  app, BrowserWindow, Menu, shell, ipcMain, nativeImage, Notification,
+  app, BrowserWindow, Menu, shell, ipcMain, nativeImage, Notification, dialog,
 } = require('electron');
 const log = require('electron-log');
 const isDev = require('electron-is-dev');
@@ -97,6 +97,39 @@ function createMainWindow() {
   return win;
 }
 
+// Inform the user about Google's plan to discontinue Inbox
+function showMigrationDialog() {
+  if (config.get('displayMigrationInfo') === 'no 1.2.x') { // indicates dialog was dismissed from version 1.2.x
+    return;
+  }
+
+  const message = 'This version of Inboxer will stop working after March 2019';
+  const detail = `Google has announced plans to discontinue Inbox at the end of March 2019. \
+See Google's official announcement here:
+https://www.blog.google/products/gmail/inbox-signing-find-your-favorite-features-new-gmail/
+
+Versions >= 1.3.0 have been migrated from Inbox to Gmail to ensure Inboxer continues \
+to work after Google pulls the plug on Inbox.
+Versions 1.2.x will continue working with Inbox until the bitter end.`;
+
+  dialog.showMessageBox(mainWindow, {
+    type: 'info',
+    icon: nativeImage.createFromPath(path.join(__dirname, '..', 'static/Icon.png')),
+    title: 'Important Message',
+    message,
+    detail,
+    checkboxLabel: 'Show this window again',
+    checkboxChecked: true,
+    buttons: ['Ok'],
+    defaultId: 0,
+  }, (response, checkBoxChecked) => {
+    if (!checkBoxChecked) {
+      config.set('displayMigrationInfo', 'no 1.2.x');
+    }
+  });
+}
+
+
 app.on('ready', () => {
   Menu.setApplicationMenu(appMenu);
   mainWindow = createMainWindow();
@@ -114,6 +147,7 @@ app.on('ready', () => {
 
   webContents.on('dom-ready', () => {
     webContents.insertCSS(fs.readFileSync(path.join(__dirname, '../renderer/browser.css'), 'utf8'));
+    showMigrationDialog();
   });
 
   webContents.on('will-navigate', (e, url) => {