From 45a5b736679db47a3f954fbe3c7f0bdafc589929 Mon Sep 17 00:00:00 2001
From: jimmay5469 <jimmay5469@gmail.com>
Date: Thu, 20 Sep 2018 09:57:09 -0400
Subject: [PATCH] Cleanup and extract prependWithClingBottom to utils

Co-authored-by: Stamates <stamates@hotmail.com>
---
 apps/block_scout_web/assets/js/pages/block.js | 22 +----------
 apps/block_scout_web/assets/js/utils.js       | 38 +++++++++++++++++++
 2 files changed, 40 insertions(+), 20 deletions(-)

diff --git a/apps/block_scout_web/assets/js/pages/block.js b/apps/block_scout_web/assets/js/pages/block.js
index 4a9a9d9a3a..17cf0eec5a 100644
--- a/apps/block_scout_web/assets/js/pages/block.js
+++ b/apps/block_scout_web/assets/js/pages/block.js
@@ -3,7 +3,7 @@ import URI from 'urijs'
 import humps from 'humps'
 import socket from '../socket'
 import { updateAllAges } from '../lib/from_now'
-import { initRedux } from '../utils'
+import { initRedux, prependWithClingBottom } from '../utils'
 
 export const initialState = {
   beyondPageOne: null,
@@ -58,25 +58,7 @@ if ($blockListPage.length) {
 
       if (state.channelDisconnected) $channelDisconnected.show()
       if (oldState.newBlock !== state.newBlock) {
-        const fromBottom = document.body.scrollHeight - window.scrollY
-        let clingBottomAnimationFrame
-        let expectedScrollPosition = window.scrollY
-        function clingBottom () {
-          if (expectedScrollPosition !== window.scrollY) return stopCling()
-
-          expectedScrollPosition = document.body.scrollHeight - fromBottom
-          $(window).scrollTop(expectedScrollPosition)
-          clingBottomAnimationFrame = requestAnimationFrame(clingBottom)
-        }
-        function stopCling () {
-          cancelAnimationFrame(clingBottomAnimationFrame)
-          $blocksList.off('animationend animationcancel', stopCling)
-        }
-        if (window.scrollY > $blocksList.offset().top) {
-          clingBottomAnimationFrame = requestAnimationFrame(clingBottom)
-          $blocksList.on('animationend animationcancel', stopCling)
-        }
-        $blocksList.prepend(state.newBlock)
+        prependWithClingBottom($blocksList, state.newBlock)
         updateAllAges()
       }
     }
diff --git a/apps/block_scout_web/assets/js/utils.js b/apps/block_scout_web/assets/js/utils.js
index 152718aa37..d1212b2e22 100644
--- a/apps/block_scout_web/assets/js/utils.js
+++ b/apps/block_scout_web/assets/js/utils.js
@@ -1,3 +1,4 @@
+import $ from 'jquery'
 import _ from 'lodash'
 import { createStore } from 'redux'
 
@@ -32,3 +33,40 @@ export function initRedux (reducer, { main, render, debug } = {}) {
   }
   if (main) main(store)
 }
+
+export function prependWithClingBottom ($el, content) {
+  function userAtTop () {
+    return window.scrollY < $el.offset().top
+  }
+  if (userAtTop()) return $el.prepend(content)
+
+  let isAnimating
+  function setIsAnimating () {
+    isAnimating = true
+  }
+  $el.on('animationstart', setIsAnimating)
+
+  let expectedScrollPosition = window.scrollY
+  function userIsScrolling () {
+    return expectedScrollPosition !== window.scrollY
+  }
+
+  const clingDistanceFromBottom = document.body.scrollHeight - window.scrollY
+  let clingBottomLoop = window.requestAnimationFrame(function clingBottom () {
+    if (userIsScrolling()) return stopClinging()
+
+    expectedScrollPosition = document.body.scrollHeight - clingDistanceFromBottom
+    $(window).scrollTop(expectedScrollPosition)
+    clingBottomLoop = window.requestAnimationFrame(clingBottom)
+  })
+
+  function stopClinging () {
+    window.cancelAnimationFrame(clingBottomLoop)
+    $el.off('animationstart', setIsAnimating)
+    $el.off('animationend animationcancel', stopClinging)
+  }
+  $el.on('animationend animationcancel', stopClinging)
+  setTimeout(() => !isAnimating && stopClinging(), 100)
+
+  return $el.prepend(content)
+}