From 4fdf7d1cb50c3dd8ea8e96f7fb4cf8f655152dcc Mon Sep 17 00:00:00 2001
From: crupest <crupest@outlook.com>
Date: Sun, 24 Apr 2022 19:50:26 +0800
Subject: ...

---
 FrontEnd/src/utilities/url.ts                      |  9 +++-
 .../utilities/useReverseScrollPositionRemember.ts  | 56 ++++++++++++++++++++++
 2 files changed, 64 insertions(+), 1 deletion(-)
 create mode 100644 FrontEnd/src/utilities/useReverseScrollPositionRemember.ts

(limited to 'FrontEnd/src/utilities')

diff --git a/FrontEnd/src/utilities/url.ts b/FrontEnd/src/utilities/url.ts
index 4f2a6ecd..45ad0ab7 100644
--- a/FrontEnd/src/utilities/url.ts
+++ b/FrontEnd/src/utilities/url.ts
@@ -13,5 +13,12 @@ export function applyQueryParameters<T>(url: string, query: T): string {
       console.error("Unknown query parameter type. Param: ", value);
     }
   }
-  return url + "?" + params.toString();
+
+  const p = params.toString();
+
+  if (p == "") {
+    return url;
+  }
+
+  return url + "?" + p;
 }
diff --git a/FrontEnd/src/utilities/useReverseScrollPositionRemember.ts b/FrontEnd/src/utilities/useReverseScrollPositionRemember.ts
new file mode 100644
index 00000000..6fdd4b43
--- /dev/null
+++ b/FrontEnd/src/utilities/useReverseScrollPositionRemember.ts
@@ -0,0 +1,56 @@
+import React from "react";
+
+let on = false;
+
+let rememberedReversePosition = getReverseScrollPosition();
+
+export function getReverseScrollPosition(): number {
+  if (document.documentElement.scrollHeight <= window.innerHeight) {
+    return 0;
+  } else {
+    return (
+      document.documentElement.scrollHeight -
+      document.documentElement.scrollTop -
+      window.innerHeight
+    );
+  }
+}
+
+export function scrollToReverseScrollPosition(reversePosition: number): void {
+  if (document.documentElement.scrollHeight <= window.innerHeight) return;
+
+  const old = document.documentElement.style.scrollBehavior;
+  document.documentElement.style.scrollBehavior = "auto";
+
+  const newPosition =
+    document.documentElement.scrollHeight -
+    window.innerHeight -
+    reversePosition;
+
+  window.scrollTo(0, newPosition);
+
+  document.documentElement.style.scrollBehavior = old;
+}
+
+const scrollListener = (): void => {
+  rememberedReversePosition = getReverseScrollPosition();
+};
+
+const resizeObserver = new ResizeObserver(() => {
+  scrollToReverseScrollPosition(rememberedReversePosition);
+});
+
+export default function useReverseScrollPositionRemember(): void {
+  React.useEffect(() => {
+    if (on) return;
+    on = true;
+    window.addEventListener("scroll", scrollListener);
+    resizeObserver.observe(document.documentElement);
+
+    return () => {
+      resizeObserver.disconnect();
+      window.removeEventListener("scroll", scrollListener);
+      on = false;
+    };
+  }, []);
+}
-- 
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