integration of ChartJS and refactors

src/App.tsx

@@ -1,12 +1,24 @@
 import React, { useState } from 'react';
-import { Header } from './screens';
+import { Header, SpendScreen } from './screens';
+import { type Tab } from './types';
+import { SPEND_SCREEN_ID, SPEND_SCREEN_NAME } from './constants';
+
+const appRender = ({ tab }: { tab: Tab }): JSX.Element => {
+  switch (tab.id) {
+    case SPEND_SCREEN_ID:
+      return <SpendScreen />;
+    default:
+      return <></>;
+  }
+};
 
 function App(): JSX.Element {
-  const [tab, setTab] = useState({});
+  const [tab, setTab] = useState({ id: SPEND_SCREEN_ID, title: SPEND_SCREEN_NAME });
 
   return (
     <div>
       <Header tab={tab} setTab={setTab} />
+      {appRender({ tab })}
     </div>
   );
 }