From a13f989ab316b8c5623945d3c27e6b10b58dce0b Mon Sep 17 00:00:00 2001
From: Atul Varma <varmaa@gmail.com>
Date: Fri, 2 Apr 2021 21:17:44 -0400
Subject: [PATCH] Use history.pushState() for internal links.

---
 lib/browser-main.tsx | 34 +++++++++++++++++++++++++++++++---
 lib/page.tsx         | 29 +++++++++++++++++++++++++----
 2 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/lib/browser-main.tsx b/lib/browser-main.tsx
index 5dbd366..608fb1f 100644
--- a/lib/browser-main.tsx
+++ b/lib/browser-main.tsx
@@ -1,4 +1,4 @@
-import React from "react";
+import React, { useEffect, useState } from "react";
 import ReactDOM from "react-dom";
 import { PageContext, PAGE_QUERY_ARG } from "./page";
 import { pageNames, Pages, toPageName, DEFAULT_PAGE } from "./pages";
@@ -11,13 +11,41 @@ if (!appEl) {
   throw new Error(`Unable to find #${APP_ID}!`);
 }
 
+function getWindowSearch(): URLSearchParams {
+  return new URLSearchParams(window.location.search);
+}
+
+/**
+ * Call the given handler whenever a `popstate` event
+ * occurs.
+ *
+ * Return a function that wraps `window.history.pushState()`;
+ * the given handler will be called immediately afterwards.
+ */
+function usePushState(onPushOrPopState: () => void) {
+  useEffect(() => {
+    window.addEventListener("popstate", onPushOrPopState);
+    return () => {
+      window.removeEventListener("popstate", onPushOrPopState);
+    };
+  }, [onPushOrPopState]);
+
+  return function pushState(href: string) {
+    window.history.pushState(null, "", href);
+    onPushOrPopState();
+  };
+}
+
 const App: React.FC<{}> = (props) => {
-  const page = new URLSearchParams(window.location.search);
-  const currPage = toPageName(page.get(PAGE_QUERY_ARG) || "", DEFAULT_PAGE);
+  const [search, setSearch] = useState(getWindowSearch());
+  const updateSearchFromWindow = () => setSearch(getWindowSearch());
+  const currPage = toPageName(search.get(PAGE_QUERY_ARG) || "", DEFAULT_PAGE);
   const PageComponent = Pages[currPage];
+  const pushState = usePushState(updateSearchFromWindow);
   const ctx: PageContext = {
     currPage,
     allPages: pageNames,
+    pushState,
   };
 
   return (
diff --git a/lib/page.tsx b/lib/page.tsx
index a6dbbb2..4caacfe 100644
--- a/lib/page.tsx
+++ b/lib/page.tsx
@@ -1,21 +1,42 @@
-import React, { useContext } from "react";
+import React, { MouseEvent, useContext } from "react";
 import type { PageName } from "./pages";
 
 export type PageContext = {
   currPage: PageName;
   allPages: PageName[];
+  pushState: (href: string) => void;
 };
 
 export const PageContext = React.createContext<PageContext>({
   currPage: "vocabulary",
   allPages: [],
+  pushState: () => {
+    throw new Error("No page context is defined!");
+  },
 });
 
 export const PAGE_QUERY_ARG = "p";
 
-const PageLink: React.FC<{ page: PageName }> = ({ page }) => (
-  <a href={`?${PAGE_QUERY_ARG}=${encodeURIComponent(page)}`}>{page}</a>
-);
+function isNormalLinkClick(e: MouseEvent): boolean {
+  return !e.shiftKey && !e.altKey && !e.metaKey && !e.ctrlKey && e.button === 0;
+}
+
+const PageLink: React.FC<{ page: PageName }> = ({ page }) => {
+  const href = `?${PAGE_QUERY_ARG}=${encodeURIComponent(page)}`;
+  const { pushState } = useContext(PageContext);
+  const handleClick = (e: MouseEvent) => {
+    if (isNormalLinkClick(e)) {
+      pushState(href);
+      e.preventDefault();
+    }
+  };
+
+  return (
+    <a href={href} onClick={handleClick}>
+      {page}
+    </a>
+  );
+};
 
 const Navbar: React.FC<{}> = (props) => {
   const pc = useContext(PageContext);