From 4eca87e7b6bd5db4422934227d59fca30b68d038 Mon Sep 17 00:00:00 2001
From: Tal Bereznitskey <berzniz@gmail.com>
Date: Fri, 11 May 2018 16:38:45 +0300
Subject: [PATCH] Add Scroll Spy to highlight current visible file

---
 src/js/components/branch.jsx |  7 ++++---
 src/js/components/file.jsx   |  7 +++++--
 src/js/components/tree.jsx   | 35 ++++++++++++++++++++++++++++++++---
 src/js/lib.js                | 31 +++++++++++++++++++++++++++++--
 4 files changed, 70 insertions(+), 10 deletions(-)

diff --git a/src/js/components/branch.jsx b/src/js/components/branch.jsx
index 62b7c67..085ec57 100644
--- a/src/js/components/branch.jsx
+++ b/src/js/components/branch.jsx
@@ -2,16 +2,17 @@ import React from 'react'
 import TreeView from 'react-treeview'
 import File from './file'
 
-const Branch = ({ nodeLabel, list, href, hasComments }) => {
+const Branch = ({ nodeLabel, list, href, hasComments, diffElement, visibleElement }) => {
   if (href) {
-    return <File name={nodeLabel} href={href} hasComments={hasComments} />
+    const isVisible = (diffElement === visibleElement)
+    return <File name={nodeLabel} href={href} hasComments={hasComments} isVisible={isVisible} />
   }
 
   return (
     <TreeView nodeLabel={nodeLabel} defaultCollapsed={false}>
       {list.map(node => (
         <span key={node.nodeLabel}>
-          <Branch {...node} />
+          <Branch {...node} visibleElement={visibleElement} />
         </span>
       ))}
     </TreeView>
diff --git a/src/js/components/file.jsx b/src/js/components/file.jsx
index 02cbdde..55e24a2 100644
--- a/src/js/components/file.jsx
+++ b/src/js/components/file.jsx
@@ -1,10 +1,13 @@
 import React from 'react'
 import fileIcons from 'file-icons-js'
 
-const File = ({ name, href, hasComments }) => {
+const highlightColor = '#ebebeb'
+const transparentColor = 'transparent'
+
+const File = ({ name, href, hasComments, isVisible }) => {
   const className = fileIcons.getClassWithColor(name)
   return (
-    <div className='github-pr-file'>
+    <div className='github-pr-file' style={{ background: isVisible ? highlightColor : transparentColor }}>
       <span className={`icon ${className}`} />
       <a href={href} className='link-gray-dark'>{name}</a> {hasComments ? ' 💬' : ''}
     </div>
diff --git a/src/js/components/tree.jsx b/src/js/components/tree.jsx
index 44b1ad7..6525c08 100644
--- a/src/js/components/tree.jsx
+++ b/src/js/components/tree.jsx
@@ -1,14 +1,43 @@
 import React from 'react'
 import Branch from './branch.jsx'
+import { isElementVisible } from '../lib'
 
 class Tree extends React.Component {
   constructor (props) {
     super(props)
 
     this.onClose = this.onClose.bind(this)
+    this.onScroll = this.onScroll.bind(this)
 
     this.state = {
-      show: true
+      show: true,
+      visibleElement: null
+    }
+  }
+
+  componentDidMount () {
+    window.addEventListener('DOMContentLoaded', this.onScroll, false)
+    window.addEventListener('load', this.onScroll, false)
+    window.addEventListener('scroll', this.onScroll, false)
+    window.addEventListener('resize', this.onScroll, false)
+  }
+
+  componentWillUnmount () {
+    window.removeEventListener('DOMContentLoaded', this.onScroll, false)
+    window.removeEventListener('load', this.onScroll, false)
+    window.removeEventListener('scroll', this.onScroll, false)
+    window.removeEventListener('resize', this.onScroll, false)
+  }
+
+  onScroll () {
+    const { visibleElement } = this.state
+    const { root } = this.props
+    const { diffElements = [] } = root
+    const nextVisibleElement = diffElements.find(isElementVisible)
+    if (nextVisibleElement !== visibleElement) {
+      this.setState({
+        visibleElement: nextVisibleElement
+      })
     }
   }
 
@@ -20,7 +49,7 @@ class Tree extends React.Component {
 
   render () {
     const { root } = this.props
-    const { show } = this.state
+    const { show, visibleElement } = this.state
 
     if (!show) {
       return null
@@ -31,7 +60,7 @@ class Tree extends React.Component {
         <button onClick={this.onClose} className='close_button'>✖</button>
         {root.list.map(node => (
           <span key={node.nodeLabel}>
-            <Branch {...node} />
+            <Branch {...node} visibleElement={visibleElement} />
           </span>
         ))}
       </div>
diff --git a/src/js/lib.js b/src/js/lib.js
index 58178d1..82a6380 100644
--- a/src/js/lib.js
+++ b/src/js/lib.js
@@ -42,7 +42,8 @@ export const createFileTree = () => {
   })
   const tree = {
     nodeLabel: '/',
-    list: []
+    list: [],
+    diffElements: []
   }
 
   files.forEach(({ parts, href }, fileIndex) => {
@@ -51,7 +52,15 @@ export const createFileTree = () => {
       let node = location.list.find(node => node.nodeLabel === part)
       if (!node) {
         const hasComments = (hasCommentsForFileIndex(fileIndex) > 0)
-        node = { nodeLabel: part, list: [], href: (index === parts.length - 1) ? href : null, hasComments }
+        const diffElement = document.getElementById(`diff-${fileIndex}`)
+        tree.diffElements.push(diffElement)
+        node = {
+          nodeLabel: part,
+          list: [],
+          href: (index === parts.length - 1) ? href : null,
+          hasComments,
+          diffElement
+        }
         location.list.push(node)
       }
       location.list = location.list.sort(sorter)
@@ -63,3 +72,21 @@ export const createFileTree = () => {
     count: fileInfo.length
   }
 }
+
+export const isElementVisible = (el) => {
+  if (!el) {
+    return false
+  }
+
+  const GITHUB_HEADER_HEIGHT = 60
+
+  const rect = el.getBoundingClientRect()
+
+  const windowHeight = (window.innerHeight || document.documentElement.clientHeight)
+  const windowWidth = (window.innerWidth || document.documentElement.clientWidth)
+
+  const vertInView = (rect.top <= windowHeight) && ((rect.top + rect.height) >= GITHUB_HEADER_HEIGHT)
+  const horInView = (rect.left <= windowWidth) && ((rect.left + rect.width) >= 0)
+
+  return (vertInView && horInView)
+}