From 9d1f8b9d6af1d384a4dd68bc6353a2fde5735b33 Mon Sep 17 00:00:00 2001
From: Akihiko Odaki <akihiko.odaki.4i@stu.hosei.ac.jp>
Date: Sat, 5 Aug 2017 01:57:46 +0900
Subject: [PATCH] Scroll columns area to right when children property is
 changed (#4517)

The feature to pin column could hide the rightmost column, which is
specified with children property of ColumnsArea.

The user is likely to see the column when the property changed, so scroll
the area in such cases.
---
 app/javascript/mastodon/components/column.js       |  2 +-
 .../mastodon/features/ui/components/column.js      |  2 +-
 .../features/ui/components/columns_area.js         | 14 ++++++++++++--
 app/javascript/mastodon/scroll.js                  | 11 ++++++-----
 4 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/app/javascript/mastodon/components/column.js b/app/javascript/mastodon/components/column.js
index 93f1d6260b..05a7c14369 100644
--- a/app/javascript/mastodon/components/column.js
+++ b/app/javascript/mastodon/components/column.js
@@ -1,7 +1,7 @@
 import React from 'react';
 import PropTypes from 'prop-types';
 import detectPassiveEvents from 'detect-passive-events';
-import scrollTop from '../scroll';
+import { scrollTop } from '../scroll';
 
 export default class Column extends React.PureComponent {
 
diff --git a/app/javascript/mastodon/features/ui/components/column.js b/app/javascript/mastodon/features/ui/components/column.js
index aea102aac5..9031c16fc2 100644
--- a/app/javascript/mastodon/features/ui/components/column.js
+++ b/app/javascript/mastodon/features/ui/components/column.js
@@ -2,7 +2,7 @@ import React from 'react';
 import ColumnHeader from './column_header';
 import PropTypes from 'prop-types';
 import { debounce } from 'lodash';
-import scrollTop from '../../../scroll';
+import { scrollTop } from '../../../scroll';
 import { isMobile } from '../../../is_mobile';
 
 export default class Column extends React.PureComponent {
diff --git a/app/javascript/mastodon/features/ui/components/columns_area.js b/app/javascript/mastodon/features/ui/components/columns_area.js
index 63bd1b0212..7652d67a08 100644
--- a/app/javascript/mastodon/features/ui/components/columns_area.js
+++ b/app/javascript/mastodon/features/ui/components/columns_area.js
@@ -12,6 +12,8 @@ import ColumnLoading from './column_loading';
 import BundleColumnError from './bundle_column_error';
 import { Compose, Notifications, HomeTimeline, CommunityTimeline, PublicTimeline, HashtagTimeline, FavouritedStatuses } from '../../ui/util/async-components';
 
+import { scrollRight } from '../../../scroll';
+
 const componentMap = {
   'COMPOSE': Compose,
   'HOME': HomeTimeline,
@@ -49,9 +51,13 @@ export default class ColumnsArea extends ImmutablePureComponent {
     this.setState({ shouldAnimate: true });
   }
 
-  componentDidUpdate() {
+  componentDidUpdate(prevProps) {
     this.lastIndex = getIndex(this.context.router.history.location.pathname);
     this.setState({ shouldAnimate: true });
+
+    if (this.props.children !== prevProps.children) {
+      scrollRight(this.node);
+    }
   }
 
   handleSwipe = (index) => {
@@ -74,6 +80,10 @@ export default class ColumnsArea extends ImmutablePureComponent {
     }
   }
 
+  setRef = (node) => {
+    this.node = node;
+  }
+
   renderView = (link, index) => {
     const columnIndex = getIndex(this.context.router.history.location.pathname);
     const title = this.props.intl.formatMessage({ id: link.props['data-preview-title-id'] });
@@ -114,7 +124,7 @@ export default class ColumnsArea extends ImmutablePureComponent {
     }
 
     return (
-      <div className='columns-area'>
+      <div className='columns-area' ref={this.setRef}>
         {columns.map(column => {
           const params = column.get('params', null) === null ? null : column.get('params').toJS();
 
diff --git a/app/javascript/mastodon/scroll.js b/app/javascript/mastodon/scroll.js
index c089d37db8..44f95b17f0 100644
--- a/app/javascript/mastodon/scroll.js
+++ b/app/javascript/mastodon/scroll.js
@@ -1,9 +1,9 @@
 const easingOutQuint = (x, t, b, c, d) => c * ((t = t / d - 1) * t * t * t * t + 1) + b;
 
-const scrollTop = (node) => {
+const scroll = (node, key, target) => {
   const startTime = Date.now();
-  const offset    = node.scrollTop;
-  const targetY   = -offset;
+  const offset    = node[key];
+  const gap       = target - offset;
   const duration  = 1000;
   let interrupt   = false;
 
@@ -15,7 +15,7 @@ const scrollTop = (node) => {
       return;
     }
 
-    node.scrollTop = easingOutQuint(0, elapsed, offset, targetY, duration);
+    node[key] = easingOutQuint(0, elapsed, offset, gap, duration);
     requestAnimationFrame(step);
   };
 
@@ -26,4 +26,5 @@ const scrollTop = (node) => {
   };
 };
 
-export default scrollTop;
+export const scrollRight = (node) => scroll(node, 'scrollLeft', node.scrollWidth);
+export const scrollTop = (node) => scroll(node, 'scrollTop', 0);