From db88a7699ce75a738458710de3018f87d3a6ee23 Mon Sep 17 00:00:00 2001
From: William Tran <william.tran1@uwaterloo.ca>
Date: Mon, 5 Jul 2021 13:02:04 -0400
Subject: [PATCH] Make burger disappear when off screen

---
 components/OrganizedContent.tsx | 50 +++++++++++++++++++++++++--------
 1 file changed, 39 insertions(+), 11 deletions(-)

diff --git a/components/OrganizedContent.tsx b/components/OrganizedContent.tsx
index fc3dd357..528e2689 100644
--- a/components/OrganizedContent.tsx
+++ b/components/OrganizedContent.tsx
@@ -49,8 +49,11 @@ export function OrganizedContent(props: Props) {
       : (document.body.style.overflow = "visible");
   }, [open]);
 
+  const ref = useRef<HTMLDivElement>(null);
+  const isVisible = useOnScreen(ref);
+
   return (
-    <div className={styles.wrapper}>
+    <div className={styles.wrapper} ref={ref}>
       <Nav sections={sections} currentIndex={currentIndex} link={props.link} />
       <div className={styles.content}>
         {isReadAll ? (
@@ -76,6 +79,7 @@ export function OrganizedContent(props: Props) {
         currentIndex={currentIndex}
         link={props.link}
         pageTitle={props.pageTitle}
+        componentIsVisible={isVisible}
       />
     </div>
   );
@@ -166,6 +170,7 @@ interface MobileProps {
   currentIndex: number;
   link: Link;
   pageTitle: string;
+  componentIsVisible: boolean;
 }
 
 function MobileWrapper(mobileProps: MobileProps) {
@@ -174,7 +179,7 @@ function MobileWrapper(mobileProps: MobileProps) {
 
   return (
     <div ref={wrapperRef}>
-      <Burger open={mobileProps.open} setOpen={mobileProps.setOpen} />
+      <Burger {...mobileProps} />
       <Menu {...mobileProps} />
     </div>
   );
@@ -183,23 +188,24 @@ function MobileWrapper(mobileProps: MobileProps) {
 interface BurgerProps {
   open: boolean;
   setOpen: React.Dispatch<React.SetStateAction<boolean>>;
+  componentIsVisible: boolean;
 }
 
-const Burger = ({ open, setOpen }: BurgerProps) => {
+const Burger = ({ open, setOpen, componentIsVisible }: BurgerProps) => {
   const [prevScrollPos, setPrevScrollPos] = useState(0);
-  const [visible, setVisible] = useState(true);
+  const [burgerVisible, setBurgerVisible] = useState(true);
   const debouncedPrevScrollPos = useDebounce<number>(prevScrollPos, 100);
 
   useEffect(() => {
     const handleScroll = () => {
       // find current scroll position
       const currentScrollPos = window.pageYOffset;
-
       // set state based on location info (explained in more detail below)
-      setVisible(
-        (debouncedPrevScrollPos > currentScrollPos &&
-          debouncedPrevScrollPos - currentScrollPos > 70) ||
-          currentScrollPos < 10
+      setBurgerVisible(
+        componentIsVisible &&
+          ((debouncedPrevScrollPos > currentScrollPos &&
+            debouncedPrevScrollPos - currentScrollPos > 70) ||
+            currentScrollPos < 10)
       );
 
       // set state to new scroll position
@@ -208,11 +214,13 @@ const Burger = ({ open, setOpen }: BurgerProps) => {
     window.addEventListener("scroll", handleScroll);
 
     return () => window.removeEventListener("scroll", handleScroll);
-  }, [debouncedPrevScrollPos, visible]);
+  }, [componentIsVisible, debouncedPrevScrollPos, burgerVisible]);
 
   return (
     <div
-      className={styles.burger + " " + (visible ? "" : styles.hiddenBurger)}
+      className={
+        styles.burger + " " + (burgerVisible ? "" : styles.hiddenBurger)
+      }
       onClick={() => setOpen(!open)}
     >
       <div>
@@ -317,3 +325,23 @@ function Arrow({ direction }: { direction: "left" | "right" }) {
     </svg>
   );
 }
+
+function useOnScreen(ref: React.RefObject<HTMLDivElement>) {
+  const [isIntersecting, setIntersecting] = useState(false);
+
+  useEffect(() => {
+    const observer = new IntersectionObserver(([entry]) =>
+      setIntersecting(entry.isIntersecting)
+    );
+
+    if (ref.current) {
+      observer.observe(ref.current);
+    }
+    // Remove the observer as soon as the component is unmounted
+    return () => {
+      observer.disconnect();
+    };
+  }, [ref]);
+
+  return isIntersecting;
+}