From 208d788672e92a2f3a6d352fb1bc265ab5951be4 Mon Sep 17 00:00:00 2001
From: Hariharan Sampath <gowtham2095@gmail.com>
Date: Wed, 14 Apr 2021 08:05:50 +0530
Subject: [PATCH] Fix feed navigation shortcuts when first article is not 100%
 visible (#11874)

Co-authored-by: Nick Taylor <nick@iamdeveloper.com>
Co-authored-by: Hariharan <hariharan.s@samsung.com>
---
 .../shared/components/useListNavigation.js    | 22 ++++++++---
 app/javascript/utilities/viewport.js          | 39 +++++++++++++++----
 2 files changed, 48 insertions(+), 13 deletions(-)

diff --git a/app/javascript/shared/components/useListNavigation.js b/app/javascript/shared/components/useListNavigation.js
index ebc280c73..97478a996 100644
--- a/app/javascript/shared/components/useListNavigation.js
+++ b/app/javascript/shared/components/useListNavigation.js
@@ -152,7 +152,7 @@ function navigate(
   const nextFocusable = nextContainer?.querySelector(focusableSelector);
   if (nextFocusable) {
     nextFocusable.focus();
-    if (!isInViewport(nextFocusable, 64)) {
+    if (!isInViewport({ element: nextFocusable, offsetTop: 64 })) {
       window.scrollTo({ top: nextContainer.offsetTop - 64 });
     }
   }
@@ -211,15 +211,27 @@ function getPreviousElement(
 }
 
 /**
- * Gets the first visible element that matches a selector
+ * Checks if the first completely visible element is present that matches a selector and returns if it is available
+ * If that isn't visible, it looks for the partially visible element that is present and returns that
+ * If no elements visible(like the banner case which could cover the entire viewport), we select the first element from the list
  *
  * @param {string} selector - The CSS selector
  *
  * @returns {object} The first visible element
  */
 function getFirstVisibleElement(selector) {
-  const elements = document.querySelectorAll(selector);
-  return Array.prototype.find.call(elements, (element) =>
-    isInViewport(element),
+  const elements = [...document.querySelectorAll(selector)];
+  const completelyVisibleFirstElement = elements.find((element) =>
+    isInViewport({ element }),
   );
+  if (completelyVisibleFirstElement) {
+    return completelyVisibleFirstElement;
+  }
+  const partiallyVisibleFirstElement = elements.find((element) =>
+    isInViewport({ element, allowPartialVisibility: true }),
+  );
+  if (partiallyVisibleFirstElement) {
+    return partiallyVisibleFirstElement;
+  }
+  return elements[0];
 }
diff --git a/app/javascript/utilities/viewport.js b/app/javascript/utilities/viewport.js
index 920a190ad..c3eb5489e 100644
--- a/app/javascript/utilities/viewport.js
+++ b/app/javascript/utilities/viewport.js
@@ -3,22 +3,45 @@
  *
  * @example
  * const element = document.getElementById('element');
- * isInViewport(element); // true or false
+ * isInViewport({element, allowPartialVisibility = true}); // true or false
  *
- * @param {object} element - The HTML element to check
+ * @param {HTMLElement} element - The HTML element to check
  * @param {number} [offsetTop=0] - Part of the screen to ignore counting from the top
- *
+ * @param {boolean} [allowPartialVisibility=false] - A boolean to flip the check between partial or completely visible in the viewport
  * @returns {boolean} isInViewport - true if the element is visible in the viewport
  */
-export function isInViewport(element, offsetTop = 0) {
+export function isInViewport({
+  element,
+  offsetTop = 0,
+  allowPartialVisibility = false,
+}) {
   const boundingRect = element.getBoundingClientRect();
   const clientHeight =
     window.innerHeight || document.documentElement.clientHeight;
   const clientWidth = window.innerWidth || document.documentElement.clientWidth;
+  const topIsInViewport =
+    boundingRect.top <= clientHeight && boundingRect.top >= offsetTop;
+  const rightIsInViewport =
+    boundingRect.right >= 0 && boundingRect.right <= clientWidth;
+  const bottomIsInViewport =
+    boundingRect.bottom >= offsetTop && boundingRect.bottom <= clientHeight;
+  const leftIsInViewport =
+    boundingRect.left <= clientWidth && boundingRect.left >= 0;
+  const topIsOutOfViewport = boundingRect.top <= offsetTop;
+  const bottomIsOutOfViewport = boundingRect.bottom >= clientHeight;
+  const elementSpansEntireViewport =
+    topIsOutOfViewport && bottomIsOutOfViewport;
+
+  if (allowPartialVisibility) {
+    return (
+      (topIsInViewport || bottomIsInViewport || elementSpansEntireViewport) &&
+      (leftIsInViewport || rightIsInViewport)
+    );
+  }
   return (
-    boundingRect.top >= offsetTop &&
-    boundingRect.left >= 0 &&
-    boundingRect.bottom <= clientHeight &&
-    boundingRect.right <= clientWidth
+    topIsInViewport &&
+    bottomIsInViewport &&
+    leftIsInViewport &&
+    rightIsInViewport
   );
 }