Merge pull request #2210 from matrix-org/bwindels/resizehandles

Redesign: resizeable/collapsible sections

res/css/_components.scss

@@ -57,6 +57,7 @@
 @import "./views/elements/_MemberEventListSummary.scss";
 @import "./views/elements/_ProgressBar.scss";
 @import "./views/elements/_ReplyThread.scss";
+@import "./views/elements/_ResizeHandle.scss";
 @import "./views/elements/_RichText.scss";
 @import "./views/elements/_RoleButton.scss";
 @import "./views/elements/_Spinner.scss";

res/css/structures/_LeftPanel.scss

@@ -15,32 +15,20 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-.mx_LeftPanel {
-    position: relative;
-
-    display: flex;
-    flex-direction: column;
-
-    border-right: 1px solid $panel-divider-color;
-}
-
 .mx_LeftPanel_container {
     display: flex;
     /* LeftPanel 260px */
-    flex: 0 0 260px;
+    min-width: 260px;
+    flex: 0 0 auto;
 }
 
-.mx_LeftPanel_container.mx_LeftPanel_container_hasTagPanel {
+.mx_LeftPanel_container.collapsed {
-    /* TagPanel 70px + LeftPanel 260px */
+    min-width: unset;
-    flex: 0 0 330px;
-}
-
-.mx_LeftPanel_container_collapsed {
     /* Collapsed LeftPanel 70px */
     flex: 0 0 70px;
 }
 
-.mx_LeftPanel_container_collapsed.mx_LeftPanel_container_hasTagPanel {
+.mx_LeftPanel_container.collapsed.mx_LeftPanel_container_hasTagPanel {
     /* TagPanel 70px + Collapsed LeftPanel 70px */
     flex: 0 0 140px;
 }
@@ -57,6 +45,15 @@ limitations under the License.
 
 }
 
+.mx_LeftPanel {
+    background-color: $secondary-accent-color;
+    flex: 1;
+    position: relative;
+    overflow-x: hidden;
+    display: flex;
+    flex-direction: column;
+}
+
 .mx_LeftPanel .mx_AppTile_mini {
     height: 132px;
 }
@@ -70,7 +67,7 @@ limitations under the License.
     z-index: 6;
 }
 
-.mx_LeftPanel.collapsed .mx_BottomLeftMenu {
+.mx_LeftPanel_container.collapsed .mx_BottomLeftMenu {
    flex: 0 0 160px;
    margin-bottom: 9px;
 }
@@ -93,7 +90,7 @@ limitations under the License.
     pointer-events: none;
 }
 
-.collapsed .mx_RoleButton {
+.mx_LeftPanel_container.collapsed .mx_RoleButton {
     margin-right: 0px ! important;
     padding-top: 3px ! important;
     padding-bottom: 3px ! important;
@@ -117,7 +114,7 @@ limitations under the License.
     margin-right: 0px;
 }
 
-.mx_LeftPanel.collapsed .mx_BottomLeftMenu_settings {
+.mx_LeftPanel_container.collapsed .mx_BottomLeftMenu_settings {
     float: none;
 }
 
@@ -126,7 +123,7 @@ limitations under the License.
         flex: 0 0 50px;
     }
 
-    .mx_LeftPanel.collapsed .mx_BottomLeftMenu {
+    .mx_LeftPanel_container.collapsed .mx_BottomLeftMenu {
         flex: 0 0 160px;
     }
 

res/css/structures/_MatrixChat.scss

@@ -68,19 +68,7 @@ limitations under the License.
     transform: translateX(-50%);
 }
 
-.mx_MatrixChat .mx_LeftPanel {
-    order: 1;
-    background-color: $secondary-accent-color;
-    flex: 0 0 260px;
-}
-
-.mx_MatrixChat .mx_LeftPanel.collapsed {
-    flex: 0 0 60px;
-}
-
 .mx_MatrixChat .mx_MatrixChat_middlePanel {
-    order: 2;
-
     background-color: $primary-bg-color;
 
     flex: 1;
@@ -100,13 +88,3 @@ limitations under the License.
     */
     height: 100%;
 }
-
-.mx_MatrixChat .mx_RightPanel {
-    order: 3;
-
-    flex: 0 0 235px;
-}
-
-.mx_MatrixChat .mx_RightPanel.collapsed {
-    flex: 0 0 122px;
-}

res/css/structures/_RightPanel.scss

@@ -15,8 +15,10 @@ limitations under the License.
 */
 
 .mx_RightPanel {
+    overflow-x: hidden;
+    flex: 0 0 auto;
     position: relative;
-
+    min-width: 250px;
     display: flex;
     flex-direction: column;
 }

res/css/structures/_RoomSubList.scss

@@ -29,7 +29,6 @@ limitations under the License.
 
 .mx_RoomSubList_labelContainer {
     height: 31px; /* mx_RoomSubList_label height including border */
-    width: 235px; /* LHS Panel width */
     position: relative;
 }
 
@@ -39,7 +38,6 @@ limitations under the License.
     color: $roomsublist-label-fg-color;
     font-weight: 700;
     font-size: 12px;
-    width: 203px; /* padding + width = LHS Panel width */
     height: 19px; /* height + padding = 31px = mx_RoomSubList_label height */
     margin-left: 16px;
     padding-left: 16px; /* gutter */
@@ -57,15 +55,6 @@ limitations under the License.
     /* pointer-events: none; */
 }
 
-.collapsed .mx_RoomSubList_label {
-    height: 17px;
-    width: 28px; /* collapsed LHS Panel width */
-}
-
-.collapsed .mx_RoomSubList_labelContainer {
-    width: 28px; /* collapsed LHS Panel width */
-}
-
 .mx_RoomSubList_roomCount {
     display: inline-block;
     font-size: 12px;
@@ -75,10 +64,6 @@ limitations under the License.
     text-transform: none;
 }
 
-.collapsed .mx_RoomSubList_roomCount {
-    display: none;
-}
-
 .mx_RoomSubList_badge {
     display: inline-block;
     min-width: 15px;
@@ -101,12 +86,6 @@ limitations under the License.
     filter: brightness($focus-brightness);
 }
 
-/*
-.collapsed .mx_RoomSubList_badge {
-    display: none;
-}
-*/
-
 .mx_RoomSubList_badgeHighlight {
     background-color: $warning-color;
 }
@@ -123,11 +102,6 @@ limitations under the License.
     border-right: 7px solid transparent;
 }
 
-/* Hide the bottom of speech bubble */
-.collapsed .mx_RoomSubList_badgeHighlight:after {
-    display: none;
-}
-
 .mx_RoomSubList_chevron {
     left: 0px;
     pointer-events: none;
@@ -165,10 +139,6 @@ limitations under the License.
     background-color: $secondary-accent-color;
 }
 
-.collapsed .mx_RoomSubList_ellipsis {
-    height: 20px;
-}
-
 .mx_RoomSubList_line {
     display: inline-block;
     width: 159px;
@@ -176,10 +146,6 @@ limitations under the License.
     vertical-align: middle;
 }
 
-.collapsed .mx_RoomSubList_line {
-    display: none;
-}
-
 .mx_RoomSubList_more {
     display: inline-block;
     text-transform: uppercase;
@@ -193,10 +159,6 @@ limitations under the License.
     vertical-align: middle;
 }
 
-.collapsed .mx_RoomSubList_more {
-    display: none;
-}
-
 .mx_RoomSubList_moreBadge {
     display: inline-block;
     min-width: 15px;
@@ -233,12 +195,6 @@ limitations under the License.
     padding-right: 4px;
 }
 
-.collapsed .mx_RoomSubList_moreBadge {
-    position: static;
-    margin-left: 16px;
-    margin-top: 2px;
-}
-
 .mx_RoomSubList_ellipsis .mx_RoomSubList_chevronDown {
     position: relative;
     top: 4px;
@@ -246,3 +202,40 @@ limitations under the License.
 }
 
 
+.collapsed {
+    .mx_RoomSubList_label {
+        height: 17px;
+        width: 28px; /* collapsed LHS Panel width */
+    }
+
+    .mx_RoomSubList_labelContainer {
+        width: 28px; /* collapsed LHS Panel width */
+    }
+
+    .mx_RoomSubList_roomCount {
+        display: none;
+    }
+
+    /* Hide the bottom of speech bubble */
+    .mx_RoomSubList_badgeHighlight:after {
+        display: none;
+    }
+
+    .mx_RoomSubList_line {
+        display: none;
+    }
+
+    .mx_RoomSubList_moreBadge {
+        position: static;
+        margin-left: 16px;
+        margin-top: 2px;
+    }
+
+    .mx_RoomSubList_ellipsis {
+        height: 20px;
+    }
+
+    .mx_RoomSubList_more {
+        display: none;
+    }
+}

res/css/views/elements/_ResizeHandle.scss

@@ -0,0 +1,32 @@
+/*
+Copyright 2018 New Vector Ltd.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+.mx_ResizeHandle {
+    cursor: row-resize;
+    flex: 0 0 auto;
+    background: $panel-divider-color;
+    padding: 1px
+}
+
+.mx_ResizeHandle.mx_ResizeHandle_horizontal {
+    width: 1px;
+    cursor: col-resize;
+}
+
+.mx_ResizeHandle.mx_ResizeHandle_vertical {
+    height: 1px;
+    cursor: row-resize;
+}

res/css/views/rooms/_RoomTile.scss

@@ -15,12 +15,13 @@ limitations under the License.
 */
 
 .mx_RoomTile {
-    position: relative;
+    display: flex;
+    flex-direction: row;
+    align-items: center;
     cursor: pointer;
-    display: block;
     height: 40px;
-    margin: 0px 9px 0px 9px;
+    margin: 0px 3px;
-
+    position: relative;
     background-color: $secondary-accent-color;
 }
 
@@ -31,26 +32,18 @@ limitations under the License.
     left: -12px;
 }
 
-
-.mx_RoomTile_nameContainer {
-    display: inline-block;
-    width: 180px;
-    height: 24px;
-}
-
-.mx_RoomTile_avatar_container {
-    position: relative;
-}
-
 .mx_RoomTile_avatar {
-    display: inline-block;
+    flex: 0;
     padding-top: 4px;
     padding-bottom: 4px;
     padding-left: 14px;
     padding-right: 12px;
     width: 32px;
     height: 32px;
-    vertical-align: middle;
+}
+
+.mx_RoomTile_avatar_container {
+    position: relative;
 }
 
 .mx_RoomTile_dm {
@@ -62,19 +55,13 @@ limitations under the License.
 }
 
 .mx_RoomTile_name {
-    display: inline-block;
+    flex: 1 5 auto;
     font-size: 14px;
     font-weight: 600;
-    position: relative;
+    padding: 6px;
-    width: 165px;
-    vertical-align: middle;
-    padding-left: 6px;
-    padding-right: 6px;
-    padding-top: 2px;
-    padding-bottom: 3px;
     color: $roomtile-name-color;
     white-space: nowrap;
-    overflow: hidden;
+    overflow-x: hidden;
     text-overflow: ellipsis;
 }
 
@@ -82,25 +69,30 @@ limitations under the License.
 /*    color: rgba(69, 69, 69, 0.5); */
 }
 
-.collapsed .mx_RoomTile_nameContainer {
+.collapsed {
-    width: 60px; /* colapsed panel width */
+    .mx_RoomTile_name {
-}
+        display: none;
+    }
 
-.collapsed .mx_RoomTile_name {
+    .mx_RoomTile_badge {
-    display: none;
+        min-width: 12px;
-}
+        border-radius: 16px;
+        padding: 0px 4px 0px 4px;
+        z-index: 3;
+    }
 
-.collapsed .mx_RoomTile_badge {
+    /* Hide the bottom of speech bubble */
-    top: 0px;
+    .mx_RoomTile_highlight .mx_RoomTile_badge:after {
-    min-width: 12px;
+        display: none;
-    border-radius: 16px;
+    }
-    padding: 0px 4px 0px 4px;
-    z-index: 3;
-}
 
-/* Hide the bottom of speech bubble */
+    .mx_RoomTile_badge {
-.collapsed .mx_RoomTile_highlight .mx_RoomTile_badge:after {
+        display: block;
-    display: none;
+        position: absolute;
+        height: 15px;
+        right: 5px;
+        top: 2px;
+    }
 }
 
 /* This is the bottom of the speech bubble */
@@ -116,12 +108,8 @@ limitations under the License.
 }
 
 .mx_RoomTile_badge {
-    display: inline-block;
+    flex: 0 1 content;
     min-width: 15px;
-    height: 15px;
-    position: absolute;
-    right: 8px; /*gutter */
-    top: 9px;
     border-radius: 8px;
     color: $accent-fg-color;
     font-weight: 600;

src/Tinter.js

@@ -155,7 +155,7 @@ class Tinter {
 
     tint(primaryColor, secondaryColor, tertiaryColor) {
         return;
-        
+        // eslint-disable-next-line no-unreachable
         this.currentTint[0] = primaryColor;
         this.currentTint[1] = secondaryColor;
         this.currentTint[2] = tertiaryColor;

src/components/structures/LeftPanel.js

@@ -192,20 +192,13 @@ var LeftPanel = React.createClass({
             topBox = <SearchBox collapsed={ this.props.collapsed } onSearch={ this.onSearch } />;
         }
 */
-        const classes = classNames(
-            "mx_LeftPanel",
-            {
-                "collapsed": this.props.collapsed,
-            },
-        );
-
         const tagPanelEnabled = !SettingsStore.getValue("TagPanel.disableTagPanel");
         const tagPanel = tagPanelEnabled ? <TagPanel /> : <div />;
 
         const containerClasses = classNames(
             "mx_LeftPanel_container", "mx_fadable",
             {
-                "mx_LeftPanel_container_collapsed": this.props.collapsed,
+                "collapsed": this.props.collapsed,
                 "mx_LeftPanel_container_hasTagPanel": tagPanelEnabled,
                 "mx_fadable_faded": this.props.disabled,
             },
@@ -214,7 +207,7 @@ var LeftPanel = React.createClass({
         return (
             <div className={containerClasses}>
                 { tagPanel }
-                <aside className={classes} onKeyDown={ this._onKeyDown } onFocus={ this._onFocus } onBlur={ this._onBlur }>
+                <aside className={"mx_LeftPanel"} onKeyDown={ this._onKeyDown } onFocus={ this._onFocus } onBlur={ this._onBlur }>
                     { topBox }
                     <CallPreview ConferenceHandler={VectorConferenceHandler} />
                     <RoomList

src/components/structures/LoggedInView.js

@@ -34,7 +34,8 @@ import RoomListStore from "../../stores/RoomListStore";
 
 import TagOrderActions from '../../actions/TagOrderActions';
 import RoomListActions from '../../actions/RoomListActions';
-
+import ResizeHandle from '../views/elements/ResizeHandle';
+import {Resizer, CollapseDistributor} from '../../resizer'
 // We need to fetch each pinned message individually (if we don't already have it)
 // so each pinned message may trigger a request. Limit the number per room for sanity.
 // NB. this is just for server notices rather than pinned messages in general.
@@ -91,6 +92,12 @@ const LoggedInView = React.createClass({
         };
     },
 
+    componentDidMount: function() {
+        this.resizer = this._createResizer();
+        this.resizer.attach();
+        this._loadResizerPreferences();
+    },
+
     componentWillMount: function() {
         // stash the MatrixClient in case we log out before we are unmounted
         this._matrixClient = this.props.matrixClient;
@@ -120,6 +127,7 @@ const LoggedInView = React.createClass({
         if (this._sessionStoreToken) {
             this._sessionStoreToken.remove();
         }
+        this.resizer.detach();
     },
 
     // Child components assume that the client peg will not be null, so give them some
@@ -145,6 +153,49 @@ const LoggedInView = React.createClass({
         });
     },
 
+    _createResizer() {
+        const classNames = {
+            handle: "mx_ResizeHandle",
+            vertical: "mx_ResizeHandle_vertical",
+            reverse: "mx_ResizeHandle_reverse"
+        };
+        const collapseConfig = {
+            toggleSize: 260 - 50,
+            onCollapsed: (collapsed, item) => {
+                if (item.classList.contains("mx_LeftPanel_container")) {
+                    this.setState({collapseLhs: collapsed});
+                    if (collapsed) {
+                        window.localStorage.setItem("mx_lhs_size", '0');
+                    }
+                }
+            },
+            onResized: (size, item) => {
+                if (item.classList.contains("mx_LeftPanel_container")) {
+                    window.localStorage.setItem("mx_lhs_size", '' + size);
+                } else if(item.classList.contains("mx_RightPanel")) {
+                    window.localStorage.setItem("mx_rhs_size", '' + size);
+                }
+            },
+        };
+        const resizer = new Resizer(
+            this.resizeContainer,
+            CollapseDistributor,
+            collapseConfig);
+        resizer.setClassNames(classNames);
+        return resizer;
+    },
+
+    _loadResizerPreferences() {
+        const lhsSize = window.localStorage.getItem("mx_lhs_size");
+        if (lhsSize !== null) {
+            this.resizer.forHandleAt(0).resize(parseInt(lhsSize, 10));
+        }
+        const rhsSize = window.localStorage.getItem("mx_rhs_size");
+        if (rhsSize !== null) {
+            this.resizer.forHandleAt(1).resize(parseInt(rhsSize, 10));
+        }
+    },
+
     onAccountData: function(event) {
         if (event.getType() === "im.vector.web.settings") {
             this.setState({
@@ -361,6 +412,10 @@ const LoggedInView = React.createClass({
         this.setState({mouseDown: null});
     },
 
+    _setResizeContainerRef(div) {
+        this.resizeContainer = div;
+    },
+
     render: function() {
         const LeftPanel = sdk.getComponent('structures.LeftPanel');
         const RightPanel = sdk.getComponent('structures.RightPanel');
@@ -507,14 +562,16 @@ const LoggedInView = React.createClass({
             <div className='mx_MatrixChat_wrapper' aria-hidden={this.props.hideToSRUsers} onMouseDown={this._onMouseDown} onMouseUp={this._onMouseUp}>
                 { topBar }
                 <DragDropContext onDragEnd={this._onDragEnd}>
-                    <div className={bodyClasses}>
+                    <div ref={this._setResizeContainerRef} className={bodyClasses}>
                         <LeftPanel
-                            collapsed={this.props.collapseLhs || false}
+                            collapsed={this.props.collapseLhs || this.state.collapseLhs || false}
                             disabled={this.props.leftDisabled}
                         />
+                        <ResizeHandle/>
                         <main className='mx_MatrixChat_middlePanel'>
                             { page_element }
                         </main>
+                        <ResizeHandle reverse={true}/>
                         { right_panel }
                     </div>
                 </DragDropContext>

src/components/structures/TopLeftMenu.js

@@ -17,7 +17,6 @@ limitations under the License.
 import React from 'react';
 import PropTypes from 'prop-types';
 import sdk from '../../index';
-import dis from '../../dispatcher';
 
 class TopLeftMenu extends React.Component {
 
@@ -30,7 +29,7 @@ class TopLeftMenu extends React.Component {
     render() {
         const BaseAvatar = sdk.getComponent('avatars.BaseAvatar');
         const avatarHeight = 28;
-        const name = "My stuff"
+        const name = "My stuff";
 
         return (
             <div className="mx_TopLeftMenu">
@@ -43,7 +42,7 @@ class TopLeftMenu extends React.Component {
                 <div className="mx_TopLeftMenu_name">
                     { name }
                 </div>
-                <img className="mx_TopLeftMenu_chevron" src="img/topleft-chevron.svg" width="11" height="6"/>
+                <img className="mx_TopLeftMenu_chevron" src="img/topleft-chevron.svg" width="11" height="6" />
             </div>
         );
     }

src/components/views/elements/ResizeHandle.js

@@ -0,0 +1,26 @@
+
+import React from 'react'; // eslint-disable-line no-unused-vars
+import PropTypes from 'prop-types';
+
+//see src/resizer for the actual resizing code, this is just the DOM for the resize handle
+const ResizeHandle = (props) => {
+    const classNames = ['mx_ResizeHandle'];
+    if (props.vertical) {
+        classNames.push('mx_ResizeHandle_vertical');
+    } else {
+        classNames.push('mx_ResizeHandle_horizontal');
+    }
+    if (props.reverse) {
+        classNames.push('mx_ResizeHandle_reverse');
+    }
+    return (
+        <div className={classNames.join(' ')} />
+    );
+};
+
+ResizeHandle.propTypes = {
+    vertical: PropTypes.bool,
+    reverse: PropTypes.bool,
+};
+
+export default ResizeHandle;

src/components/views/rooms/RoomTile.js

@@ -337,10 +337,8 @@ module.exports = React.createClass({
                     { dmIndicator }
                 </div>
             </div>
-            <div className="mx_RoomTile_nameContainer">
+            { label }
-                { label }
+            { badge }
-                { badge }
-            </div>
             { /* { incomingCallBox } */ }
             { tooltip }
         </AccessibleButton>;

src/resizer/distributors.js

@@ -0,0 +1,128 @@
+/*
+Copyright 2018 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+distributors translate a moving cursor into
+CSS/DOM changes by calling the sizer
+
+they have one method, `resize` that receives
+the offset from the container edge of where
+the mouse cursor is.
+*/
+class FixedDistributor {
+    constructor(sizer, item, config) {
+        this.sizer = sizer;
+        this.item = item;
+        this.beforeOffset = sizer.getItemOffset(this.item);
+        this.onResized = config.onResized;
+    }
+
+    resize(offset) {
+        const itemSize = offset - this.beforeOffset;
+        this.sizer.setItemSize(this.item, itemSize);
+        if (this.onResized) {
+            this.onResized(itemSize, this.item);
+        }
+        return itemSize;
+    }
+
+    sizeFromOffset(offset) {
+        return offset - this.beforeOffset;
+    }
+}
+
+
+class CollapseDistributor extends FixedDistributor {
+    constructor(sizer, item, config) {
+        super(sizer, item, config);
+        this.toggleSize = config && config.toggleSize;
+        this.onCollapsed = config && config.onCollapsed;
+        this.isCollapsed = false;
+    }
+
+    resize(offset) {
+        const newSize = this.sizeFromOffset(offset);
+        const isCollapsedSize = newSize < this.toggleSize;
+        if (isCollapsedSize && !this.isCollapsed) {
+            this.isCollapsed = true;
+            if (this.onCollapsed) {
+                this.onCollapsed(true, this.item);
+            }
+        } else if (!isCollapsedSize && this.isCollapsed) {
+            if (this.onCollapsed) {
+                this.onCollapsed(false, this.item);
+            }
+            this.isCollapsed = false;
+        }
+        if (!isCollapsedSize) {
+            super.resize(offset);
+        }
+    }
+}
+
+class PercentageDistributor {
+
+    constructor(sizer, item, _config, items, container) {
+        this.container = container;
+        this.totalSize = sizer.getTotalSize();
+        this.sizer = sizer;
+
+        const itemIndex = items.indexOf(item);
+        this.beforeItems = items.slice(0, itemIndex);
+        this.afterItems = items.slice(itemIndex);
+        const percentages = PercentageDistributor._getPercentages(sizer, items);
+        this.beforePercentages = percentages.slice(0, itemIndex);
+        this.afterPercentages = percentages.slice(itemIndex);
+    }
+
+    resize(offset) {
+        const percent = offset / this.totalSize;
+        const beforeSum =
+            this.beforePercentages.reduce((total, p) => total + p, 0);
+        const beforePercentages =
+            this.beforePercentages.map(p => (p / beforeSum) * percent);
+        const afterSum =
+            this.afterPercentages.reduce((total, p) => total + p, 0);
+        const afterPercentages =
+            this.afterPercentages.map(p => (p / afterSum) * (1 - percent));
+
+        this.beforeItems.forEach((item, index) => {
+            this.sizer.setItemPercentage(item, beforePercentages[index]);
+        });
+        this.afterItems.forEach((item, index) => {
+            this.sizer.setItemPercentage(item, afterPercentages[index]);
+        });
+    }
+
+    static _getPercentages(sizer, items) {
+        const percentages = items.map(i => sizer.getItemPercentage(i));
+        const setPercentages = percentages.filter(p => p !== null);
+        const unsetCount = percentages.length - setPercentages.length;
+        const setTotal = setPercentages.reduce((total, p) => total + p, 0);
+        const implicitPercentage = (1 - setTotal) / unsetCount;
+        return percentages.map(p => p === null ? implicitPercentage : p);
+    }
+
+    static setPercentage(el, percent) {
+        el.style.flexGrow = Math.round(percent * 1000);
+    }
+}
+
+module.exports = {
+    FixedDistributor,
+    CollapseDistributor,
+    PercentageDistributor,
+};

src/resizer/index.js

@@ -0,0 +1,27 @@
+/*
+Copyright 2018 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {Sizer} from "./sizer";
+import {FixedDistributor, CollapseDistributor, PercentageDistributor} from "./distributors";
+import {Resizer} from "./resizer";
+
+module.exports = {
+    Resizer,
+    Sizer,
+    FixedDistributor,
+    CollapseDistributor,
+    PercentageDistributor,
+};

src/resizer/resizer.js

@@ -0,0 +1,138 @@
+/*
+Copyright 2018 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {Sizer} from "./sizer";
+
+/*
+classNames:
+    // class on resize-handle
+    handle: string
+    // class on resize-handle
+    reverse: string
+    // class on resize-handle
+    vertical: string
+    // class on container
+    resizing: string
+*/
+
+export class Resizer {
+    constructor(container, distributorCtor, distributorCfg, sizerCtor = Sizer) {
+        this.container = container;
+        this.distributorCtor = distributorCtor;
+        this.distributorCfg = distributorCfg;
+        this.sizerCtor = sizerCtor;
+        this.classNames = {
+            handle: "resizer-handle",
+            reverse: "resizer-reverse",
+            vertical: "resizer-vertical",
+            resizing: "resizer-resizing",
+        };
+        this._onMouseDown = this._onMouseDown.bind(this);
+    }
+
+    setClassNames(classNames) {
+        this.classNames = classNames;
+    }
+
+    attach() {
+        this.container.addEventListener("mousedown", this._onMouseDown, false);
+    }
+
+    detach() {
+        this.container.removeEventListener("mousedown", this._onMouseDown, false);
+    }
+
+    /**
+    Gives the distributor for a specific resize handle, as if you would have started
+    to drag that handle. Can be used to manipulate the size of an item programmatically.
+    @param {number} handleIndex the index of the resize handle in the container
+    @return {Distributor} a new distributor for the given handle
+    */
+    forHandleAt(handleIndex) {
+        const handles = this._getResizeHandles();
+        const handle = handles[handleIndex];
+        const {distributor} = this._createSizerAndDistributor(handle);
+        return distributor;
+    }
+
+    _isResizeHandle(el) {
+        return el && el.classList.contains(this.classNames.handle);
+    }
+
+    _onMouseDown(event) {
+        const target = event.target;
+        if (!this._isResizeHandle(target) || target.parentElement !== this.container) {
+            return;
+        }
+        // prevent starting a drag operation
+        event.preventDefault();
+        // mark as currently resizing
+        if (this.classNames.resizing) {
+            this.container.classList.add(this.classNames.resizing);
+        }
+
+        const {sizer, distributor} = this._createSizerAndDistributor(target);
+
+        const onMouseMove = (event) => {
+            const offset = sizer.offsetFromEvent(event);
+            distributor.resize(offset);
+        };
+
+        const body = document.body;
+        const onMouseUp = (event) => {
+            if (this.classNames.resizing) {
+                this.container.classList.remove(this.classNames.resizing);
+            }
+            body.removeEventListener("mouseup", onMouseUp, false);
+            body.removeEventListener("mousemove", onMouseMove, false);
+        };
+        body.addEventListener("mouseup", onMouseUp, false);
+        body.addEventListener("mousemove", onMouseMove, false);
+    }
+
+    _createSizerAndDistributor(resizeHandle) {
+        const vertical = resizeHandle.classList.contains(this.classNames.vertical);
+        const reverse = resizeHandle.classList.contains(this.classNames.reverse);
+
+        // eslint-disable-next-line new-cap
+        const sizer = new this.sizerCtor(this.container, vertical, reverse);
+
+        const items = this._getResizableItems();
+        const prevItem = resizeHandle.previousElementSibling;
+        // if reverse, resize the item after the handle instead of before, so + 1
+        const itemIndex = items.indexOf(prevItem) + (reverse ? 1 : 0);
+        const item = items[itemIndex];
+        // eslint-disable-next-line new-cap
+        const distributor = new this.distributorCtor(
+            sizer, item, this.distributorCfg,
+            items, this.container);
+        return {sizer, distributor};
+    }
+
+    _getResizableItems() {
+        return Array.from(this.container.children).filter(el => {
+            return !this._isResizeHandle(el) && (
+                this._isResizeHandle(el.previousElementSibling) ||
+                this._isResizeHandle(el.nextElementSibling));
+        });
+    }
+
+    _getResizeHandles() {
+        return Array.from(this.container.children).filter(el => {
+            return this._isResizeHandle(el);
+        });
+    }
+}

src/resizer/room.js

@@ -0,0 +1,55 @@
+/*
+Copyright 2018 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {Sizer} from "./sizer";
+import {FixedDistributor} from "./distributors";
+
+class RoomSizer extends Sizer {
+    setItemSize(item, size) {
+        const isString = typeof size === "string";
+        const cl = item.classList;
+        if (isString) {
+            item.style.flex = null;
+            if (size === "show-content") {
+                cl.add("show-content");
+                cl.remove("show-available");
+                item.style.maxHeight = null;
+            }
+        } else {
+            cl.add("show-available");
+            //item.style.flex = `0 1 ${Math.round(size)}px`;
+            item.style.maxHeight = `${Math.round(size)}px`;
+        }
+    }
+
+}
+
+class RoomDistributor extends FixedDistributor {
+    resize(offset) {
+        const itemSize = offset - this.sizer.getItemOffset(this.item);
+
+        if (itemSize > this.item.scrollHeight) {
+            this.sizer.setItemSize(this.item, "show-content");
+        } else {
+            this.sizer.setItemSize(this.item, itemSize);
+        }
+    }
+}
+
+module.exports = {
+    RoomSizer,
+    RoomDistributor,
+};

src/resizer/sizer.js

@@ -0,0 +1,100 @@
+/*
+Copyright 2018 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+implements DOM/CSS operations for resizing.
+The sizer determines what CSS mechanism is used for sizing items, like flexbox, ...
+*/
+class Sizer {
+    constructor(container, vertical, reverse) {
+        this.container = container;
+        this.reverse = reverse;
+        this.vertical = vertical;
+    }
+
+    getItemPercentage(item) {
+        /*
+        const flexGrow = window.getComputedStyle(item).flexGrow;
+        if (flexGrow === "") {
+            return null;
+        }
+        return parseInt(flexGrow) / 1000;
+        */
+        const style = window.getComputedStyle(item);
+        const sizeStr = this.vertical ? style.height : style.width;
+        const size = parseInt(sizeStr, 10);
+        return size / this.getTotalSize();
+    }
+
+    setItemPercentage(item, percent) {
+        item.style.flexGrow = Math.round(percent * 1000);
+    }
+
+    /**
+        @param {Element} item the dom element being resized
+        @return {number} how far the edge of the item is from the edge of the container
+    */
+    getItemOffset(item) {
+        const offset = (this.vertical ? item.offsetTop : item.offsetLeft) - this._getOffset();
+        if (this.reverse) {
+            return this.getTotalSize() - (offset + this.getItemSize(item));
+        } else {
+            return offset;
+        }
+    }
+
+    /**
+        @param {Element} item the dom element being resized
+        @return {number} the width/height of an item in the container
+    */
+    getItemSize(item) {
+        return this.vertical ? item.offsetHeight : item.offsetWidth;
+    }
+
+    /** @return {number} the width/height of the container */
+    getTotalSize() {
+        return this.vertical ? this.container.offsetHeight : this.container.offsetWidth;
+    }
+
+    /** @return {number} container offset to offsetParent */
+    _getOffset() {
+        return this.vertical ? this.container.offsetTop : this.container.offsetLeft;
+    }
+
+    setItemSize(item, size) {
+        if (this.vertical) {
+            item.style.height = `${Math.round(size)}px`;
+        } else {
+            item.style.width = `${Math.round(size)}px`;
+        }
+    }
+
+    /**
+        @param {MouseEvent} event the mouse event
+        @return {number} the distance between the cursor and the edge of the container,
+            along the applicable axis (vertical or horizontal)
+    */
+    offsetFromEvent(event) {
+        const pos = this.vertical ? event.pageY : event.pageX;
+        if (this.reverse) {
+            return (this._getOffset() + this.getTotalSize()) - pos;
+        } else {
+            return pos - this._getOffset();
+        }
+    }
+}
+
+module.exports = {Sizer};