simple undo/redo of application state

src/App.tsx

@@ -82,25 +82,64 @@ const tripleFunctionCallEditorState: EditorState = {
 }
 
 export function App() {
-  // const [state, setState] = useState<EditorState>(initialEditorState);
-  // const [state, setState] = useState<EditorState>(nonEmptyEditorState);
-  const [state, setState] = useState<EditorState>(tripleFunctionCallEditorState);
+  const [history, setHistory] = useState([initialEditorState]);
+  // const [history, setHistory] = useState([nonEmptyEditorState]);
+  // const [history, setHistory] = useState([tripleFunctionCallEditorState]);
+
+  const [future, setFuture] = useState<EditorState[]>([]);
+
+  const pushHistory = (s: EditorState) => {
+    console.log('pushHistory');
+    setHistory(history.concat([s]));
+    setFuture([]);
+  };
+
+  const onUndo = () => {
+    setFuture(future.concat(history.at(-1)!)); // add
+    setHistory(history.slice(0,-1)); // remove
+  };
+  const onRedo = () => {
+    setHistory(history.concat(future.at(-1)!)); // add
+    setFuture(future.slice(0,-1)); // remove
+  };
+
+  const onKeyDown = (e) => {
+    if (e.key === "Z" && e.ctrlKey) {
+      if (e.shiftKey) {
+        if (future.length > 0) {
+          onRedo();
+        }
+      }
+      else {
+        if (history.length > 1) {
+          onUndo();
+        }
+      }
+      e.preventDefault();
+    }
+  };
+
 
   useEffect(() => {
-    window['APP_STATE'] = state;
+    window['APP_STATE'] = history;
     // console.log("EDITOR STATE:", state);
-  }, [state]);
+  }, [history]);
+
+  useEffect(() => {
+    window.onkeydown = onKeyDown;
+  }, []);
 
   return (
     <>
       <header>
-        {/* Header content */}
+        <button disabled={history.length===1} onClick={onUndo}>Undo ({history.length-1}) [Ctrl+Z]</button>
+        <button disabled={future.length===0} onClick={onRedo}>Redo ({future.length})  [Ctrl+Shift+Z]</button>
       </header>
 
       <main>
         <Editor
-          state={state}
-          setState={setState}
+          state={history.at(-1)!}
+          setState={pushHistory}
           onResolve={() => {console.log("toplevel resolved")}}
           onCancel={() => {console.log("toplevel canceled")}}
         />