move some files around to confuse everyone

src/App/persistent_state.ts

@@ -0,0 +1,38 @@
+import { Dispatch, SetStateAction, useCallback, useState } from "react";
+
+// like useState, but it is persisted in localStorage
+// important: values must be JSON-(de-)serializable
+export function usePersistentState<T>(key: string, initial: T): [T, Dispatch<SetStateAction<T>>] {
+  const [state, setState] = useState(() => {
+    const recovered = localStorage.getItem(key);
+    let parsed;
+    if (recovered !== null) {
+      try {
+        parsed = JSON.parse(recovered);
+        return parsed;
+      } catch (e) {
+        // console.warn(`failed to recover state for option '${key}'`, e,
+        //  '(this is normal when running the app for the first time)');
+      }
+    }
+    return initial;
+  });
+
+  const setStateWrapped = useCallback((val: SetStateAction<T>) => {
+    setState((oldState: T) => {
+      let newVal;
+      if (typeof val === 'function') {
+        // @ts-ignore: i don't understand why 'val' might not be callable
+        newVal = val(oldState);
+      }
+      else {
+        newVal = val;
+      }
+      const serialized = JSON.stringify(newVal);
+      localStorage.setItem(key, serialized);
+      return newVal;
+    });
+  }, [setState]);
+
+  return [state, setStateWrapped];
+}