PLT-2672 Refactored posts view with caching (#3054)

* Refactored posts view to use view controller design

* Add post view caching

* Required updates after rebase

* Fixed bug where current channel not set yet was causing breakage

webapp/components/post_view/post_view_cache.jsx

@@ -0,0 +1,85 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information
+
+import PostViewController from './post_view_controller.jsx';
+
+import ChannelStore from 'stores/channel_store.jsx';
+
+import React from 'react';
+
+const MAXIMUM_CACHED_VIEWS = 5;
+
+export default class PostViewCache extends React.Component {
+    constructor(props) {
+        super(props);
+
+        this.onChannelChange = this.onChannelChange.bind(this);
+
+        const channel = ChannelStore.getCurrent();
+
+        this.state = {
+            currentChannelId: channel.id,
+            channels: [channel]
+        };
+    }
+
+    componentDidMount() {
+        ChannelStore.addChangeListener(this.onChannelChange);
+    }
+
+    componentWillUnmount() {
+        ChannelStore.removeChangeListener(this.onChannelChange);
+    }
+
+    onChannelChange() {
+        const channels = Object.assign([], this.state.channels);
+        const currentChannel = ChannelStore.getCurrent();
+
+        if (currentChannel == null) {
+            return;
+        }
+
+        // make sure current channel really changed
+        if (currentChannel.id === this.state.currentChannelId) {
+            return;
+        }
+
+        if (channels.length > MAXIMUM_CACHED_VIEWS) {
+            channels.shift();
+        }
+
+        const index = channels.map((c) => c.id).indexOf(currentChannel.id);
+        if (index !== -1) {
+            channels.splice(index, 1);
+        }
+
+        channels.push(currentChannel);
+
+        this.setState({
+            currentChannelId: currentChannel.id,
+            channels
+        });
+    }
+
+    render() {
+        const channels = this.state.channels;
+        const currentChannelId = this.state.currentChannelId;
+
+        let postViews = [];
+        for (let i = 0; i < channels.length; i++) {
+            postViews.push(
+                <PostViewController
+                    key={'postviewcontroller_' + channels[i].id}
+                    channel={channels[i]}
+                    active={channels[i].id === currentChannelId}
+                />
+            );
+        }
+
+        return (
+            <div id='post-list'>
+                {postViews}
+            </div>
+        );
+    }
+}