Refactor main process and add exception handler for Socket server

atom-lib/main-window.js

@@ -1,4 +1,5 @@
 const electron = require('electron')
+const app = electron.app
 const BrowserWindow = electron.BrowserWindow
 const path = require('path')
 
@@ -20,4 +21,9 @@ mainWindow.webContents.on('new-window', function (e) {
   e.preventDefault()
 })
 
+app.on('activate', function () {
+  if (mainWindow == null) return null
+  mainWindow.show()
+})
+
 module.exports = mainWindow