Created a new message indicator component to indicate new messages (#4299)

* Created a new message indicator component to indicate new messages are present
outside the user's view:

 * Created new component with styling

 * Theming and i18n support for new messages indicator

 * Count new unviewed messages and integrate with component

 * Coding style for new message indicator

* Fixed bugs with new message indicator:

 * Fix display issues with new message indicator
 * Update text to deal with plurals in React

* Fix coded style for ticket 'PLT-1917': add new message indicator.

* Use only server generated timestamps for checking new messages at the bottom

* Move transitionend to prop, fix style selectors

6 files changed, 132 insertions, 4 deletions

diff --git a/webapp/components/post_view/components/new_message_indicator.jsx b/webapp/components/post_view/components/new_message_indicator.jsx
new file mode 100644
index 000000000..7407c1024
--- /dev/null
+++ b/webapp/components/post_view/components/new_message_indicator.jsx
@@ -0,0 +1,65 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+import React from 'react';
+import {FormattedMessage} from 'react-intl';
+
+export default class NewMessageIndicator extends React.Component {
+    constructor(props) {
+        super(props);
+        this.state = {
+            visible: false,
+            rendered: false
+        };
+    }
+    componentWillReceiveProps(nextProps) {
+        if (nextProps.newMessages > 0) {
+            this.setState({rendered: true}, () => {
+                this.setState({visible: true});
+            });
+        } else {
+            this.setState({visible: false});
+        }
+    }
+    render() {
+        let className = 'nav-pills__unread-indicator-bottom';
+        if (this.state.visible > 0) {
+            className += ' visible';
+        }
+        if (!this.state.rendered) {
+            className += ' disabled';
+        }
+        return (
+            <div
+                className={className}
+                onClick={this.props.onClick}
+                onTransitionEnd={this.setRendered.bind(this)}
+                ref='indicator'
+            >
+                <span>
+                    <i
+                        className='fa fa-arrow-circle-o-down'
+                    />
+                    <FormattedMessage
+                        id='posts_view_newMsgBelow'
+                        defaultMessage='{count} new {count, plural, one {message} other {messages}} below'
+                        values={{count: this.props.newMessages}}
+                    />
+                </span>
+            </div>
+        );
+    }
+
+    // Sync 'rendered' state with visibility param, only after transitions
+    // have ended
+    setRendered() {
+        this.setState({rendered: this.state.visible});
+    }
+}
+NewMessageIndicator.defaultProps = {
+    newMessages: 0
+};
+
+NewMessageIndicator.propTypes = {
+    onClick: React.PropTypes.func.isRequired,
+    newMessages: React.PropTypes.number
+};
diff --git a/webapp/components/post_view/components/post_list.jsx b/webapp/components/post_view/components/post_list.jsx
index a0cfb208e..157e0dde2 100644
--- a/webapp/components/post_view/components/post_list.jsx
+++ b/webapp/components/post_view/components/post_list.jsx
@@ -6,6 +6,7 @@ import $ from 'jquery';
 import Post from './post.jsx';
 import FloatingTimestamp from './floating_timestamp.jsx';
 import ScrollToBottomArrows from './scroll_to_bottom_arrows.jsx';
+import NewMessageIndicator from './new_message_indicator.jsx';
 
 import * as GlobalActions from 'actions/global_actions.jsx';
 
@@ -56,7 +57,8 @@ export default class PostList extends React.Component {
         this.state = {
             isScrolling: false,
             fullWidthIntro: PreferenceStore.get(Preferences.CATEGORY_DISPLAY_SETTINGS, Preferences.CHANNEL_DISPLAY_MODE, Preferences.CHANNEL_DISPLAY_MODE_DEFAULT) === Preferences.CHANNEL_DISPLAY_MODE_FULL_SCREEN,
-            topPostId: null
+            topPostId: null,
+            unViewedCount: 0
         };
 
         if (props.channel) {
@@ -74,6 +76,23 @@ export default class PostList extends React.Component {
                 this.introText = createChannelIntroMessage(this.props.channel, this.state.fullWidthIntro);
             }
         }
+
+        const posts = nextProps.postList.posts;
+        const order = nextProps.postList.order;
+        let unViewedCount = 0;
+
+        // Only count if we're  not at the bottom, not in highlight view,
+        // or anything else
+        if (nextProps.scrollType === Constants.ScrollTypes.FREE) {
+            for (let i = order.length - 1; i >= 0; i--) {
+                const post = posts[order[i]];
+                if (post.create_at > nextProps.lastViewedBottom &&
+                    post.user_id !== nextProps.currentUser.id) {
+                    unViewedCount++;
+                }
+            }
+        }
+        this.setState({unViewedCount});
     }
 
     handleKeyDown(e) {
@@ -553,6 +572,10 @@ export default class PostList extends React.Component {
                     atBottom={this.wasAtBottom}
                     onClick={this.scrollToBottomAnimated}
                 />
+                <NewMessageIndicator
+                    newMessages={this.state.unViewedCount}
+                    onClick={this.scrollToBottomAnimated}
+                />
                 <div
                     ref='postlist'
                     className='post-list-holder-by-time'
@@ -576,6 +599,7 @@ export default class PostList extends React.Component {
 
 PostList.defaultProps = {
     lastViewed: 0,
+    lastViewedBottom: Number.MAX_VALUE,
     ownNewMessage: false
 };
 
@@ -590,6 +614,7 @@ PostList.propTypes = {
     showMoreMessagesTop: React.PropTypes.bool,
     showMoreMessagesBottom: React.PropTypes.bool,
     lastViewed: React.PropTypes.number,
+    lastViewedBottom: React.PropTypes.number,
     ownNewMessage: React.PropTypes.bool,
     postsToHighlight: React.PropTypes.object,
     displayNameType: React.PropTypes.string,
diff --git a/webapp/components/post_view/post_view_controller.jsx b/webapp/components/post_view/post_view_controller.jsx
index 53cd0b28c..e053db118 100644
--- a/webapp/components/post_view/post_view_controller.jsx
+++ b/webapp/components/post_view/post_view_controller.jsx
@@ -37,9 +37,11 @@ export default class PostViewController extends React.Component {
         const profiles = UserStore.getProfiles();
 
         let lastViewed = Number.MAX_VALUE;
+        let lastViewedBottom = Number.MAX_VALUE;
         const member = ChannelStore.getMyMember(channel.id);
         if (member != null) {
             lastViewed = member.last_viewed_at;
+            lastViewedBottom = member.last_viewed_at;
         }
 
         const joinLeaveEnabled = PreferenceStore.getBool(Constants.Preferences.CATEGORY_ADVANCED_SETTINGS, 'join_leave', true);
@@ -58,6 +60,7 @@ export default class PostViewController extends React.Component {
             statuses,
             atTop: PostStore.getVisibilityAtTop(channel.id),
             lastViewed,
+            lastViewedBottom,
             ownNewMessage: false,
             loading,
             scrollType: ScrollTypes.NEW_MESSAGE,
@@ -187,9 +190,11 @@ export default class PostViewController extends React.Component {
 
     onPostsViewJumpRequest(type, postId) {
         switch (type) {
-        case Constants.PostsViewJumpTypes.BOTTOM:
-            this.setState({scrollType: ScrollTypes.BOTTOM});
+        case Constants.PostsViewJumpTypes.BOTTOM: {
+            const lastPost = PostStore.getLatestPost(this.state.channel.id);
+            this.setState({scrollType: ScrollTypes.BOTTOM, lastViewedBottom: lastPost.create_at || new Date().getTime()});
             break;
+        }
         case Constants.PostsViewJumpTypes.POST:
             this.setState({
                 scrollType: ScrollTypes.POST,
@@ -213,7 +218,8 @@ export default class PostViewController extends React.Component {
 
     onPostListScroll(atBottom) {
         if (atBottom) {
-            this.setState({scrollType: ScrollTypes.BOTTOM});
+            const lastPost = PostStore.getLatestPost(this.state.channel.id);
+            this.setState({scrollType: ScrollTypes.BOTTOM, lastViewedBottom: lastPost.create_at || new Date().getTime()});
         } else {
             this.setState({scrollType: ScrollTypes.FREE});
         }
@@ -334,6 +340,7 @@ export default class PostViewController extends React.Component {
                     useMilitaryTime={this.state.useMilitaryTime}
                     flaggedPosts={this.state.flaggedPosts}
                     lastViewed={this.state.lastViewed}
+                    lastViewedBottom={this.state.lastViewedBottom}
                     ownNewMessage={this.state.ownNewMessage}
                     statuses={this.state.statuses}
                     isBusy={this.state.isBusy}
diff --git a/webapp/i18n/en.json b/webapp/i18n/en.json
index e6650fe22..55768d7c6 100644
--- a/webapp/i18n/en.json
+++ b/webapp/i18n/en.json
@@ -1624,6 +1624,7 @@
   "post_info.reply": "Reply",
   "posts_view.loadMore": "Load more messages",
   "posts_view.newMsg": "New Messages",
+  "posts_view.newMsgBelow": "{count} new {count, plural, one {message} other {messages}} below",
   "reaction.clickToAdd": "(click to add)",
   "reaction.clickToRemove": "(click to remove)",
   "reaction.multipleReacted": "<b>{users} and {lastUser}</b> reacted with <b>:{emojiName}:</b>",
diff --git a/webapp/sass/layout/_post.scss b/webapp/sass/layout/_post.scss
index 7a119b7af..9c93c09d7 100644
--- a/webapp/sass/layout/_post.scss
+++ b/webapp/sass/layout/_post.scss
@@ -258,6 +258,33 @@
         outline: none;
         text-align: center;
     }
+    .nav-pills__unread-indicator-bottom {
+      position: absolute;
+      bottom: -30px;
+      left: 0;
+      right: 0;
+
+      @include border-radius(50px);
+      font-size: 13.5px;
+      margin: 0 auto;
+      padding: 3px 0 4px;
+      text-align: center;
+      max-width: 250px;
+      z-index: 1;
+      cursor: pointer;
+      transition: bottom 0.2s ease-out;
+
+      .fa {
+        margin-right: 0.5rem;
+      }
+
+      &.visible {
+        bottom: 0;
+      }
+      &.disabled {
+        display: none;
+      }
+    }
 }
 
 .post-list__timestamp {
diff --git a/webapp/utils/utils.jsx b/webapp/utils/utils.jsx
index 00b7f53f8..7d7cc3583 100644
--- a/webapp/utils/utils.jsx
+++ b/webapp/utils/utils.jsx
@@ -560,6 +560,7 @@ export function applyTheme(theme) {
         changeCss('body.app__body', 'scrollbar-face-color:' + theme.centerChannelBg);
         changeCss('body.app__body', 'scrollbar-track-color:' + theme.centerChannelBg);
         changeCss('.app__body .post-list__new-messages-below', 'color:' + theme.centerChannelBg);
+        changeCss('.app__body .nav-pills__unread-indicator-bottom', 'color:' + theme.centerChannelBg);
     }
 
     if (theme.centerChannelColor) {
@@ -642,6 +643,8 @@ export function applyTheme(theme) {
         changeCss('.app__body a, .app__body a:focus, .app__body a:hover, .app__body .btn, .app__body .btn:focus, .app__body .btn:hover', 'color:' + theme.linkColor);
         changeCss('.app__body .attachment .attachment__container', 'border-left-color:' + changeOpacity(theme.linkColor, 0.5));
         changeCss('.app__body .channel-header__links .icon:hover, .app__body .post .flag-icon__container.visible, .app__body .post .comment-icon__container, .app__body .post .post__reply', 'fill:' + theme.linkColor);
+        changeCss('.app__body .nav-pills__unread-indicator-bottom', 'background:' + theme.linkColor);
+        changeCss('.app__body .nav-pills__unread-indicator-bottom:hover', 'background:' + changeColor(theme.linkColor, 0.1));
     }
 
     if (theme.buttonBg) {