BrightspaceUI · AllanKerr · May 19, 2020 · May 11, 2020 · May 11, 2020 · May 12, 2020
diff --git a/README.md b/README.md
@@ -22,6 +22,7 @@ npm install @brightspace-ui/core
   * [Colors](components/colors/): color palette
   * [Dialogs](components/dialog/): generic and confirmation dialogs
   * [Dropdowns](components/dropdown/): dropdown openers and content containers
+  * [Expand Collapse](components/expand-collapse): component to create expandable and collapsible content
   * [Focus Trap](components/focus-trap/): generic container that traps focus
   * [Icons](components/icons/): iconography SVGs and web components
   * [Inputs](components/inputs/): text, search, select, checkbox and radio inputs

diff --git a/components/expand-collapse/README.md b/components/expand-collapse/README.md
@@ -0,0 +1,34 @@
+# Expand Collapse
+
+## Expand Collapse Content
+
+The `d2l-expand-collapse-content` element can be used to used to create expandable and collapsible content. This component only provides the logic to expand and collapse the content; controlling when and how it expands or collapses is the responsibility of the user.
+
+![Expand Collapse Content](./screenshots/expand-collapse-content.gif?raw=true)
+
+```html
+<script type="module">
+  import '@brightspace-ui/core/components/expand-collapse/expand-collapse-content.js';
+</script>
+
+<d2l-expand-collapse-content expanded>
+  <p>My expand collapse content.</p>
+</d2l-expand-collapse-content>
+```
+
+**Properties:**
+
+- `expanded` (Boolean, default: `false`): Specifies the expanded/collapsed state of the content
+
+**Events:**
+
+- `d2l-expand-collapse-content-expand`: dispatched when the content starts to expand. The `detail` contains an `expandComplete` promise that can be waited on to determine when the content has finished expanding.
+- `d2l-expand-collapse-content-collapse`: dispatched when the content starts to collapse. The `detail` contains a `collapseComplete` promise that can be waited on to determine when the content has finished collapsing.
+
+**Accessibility:**
+
+To make your usage of `d2l-expand-collapse-content` accessible, the [`aria-expanded` attribute](https://www.w3.org/TR/wai-aria/#aria-expanded) should be added to the element that controls expanding and collapsing the content with `"true"` or `"false"` to indicate that the content is expanded or collapsed.
+
+## Future Enhancements
+
+Looking for an enhancement not listed here? Create a GitHub issue!
diff --git a/components/expand-collapse/demo/expand-collapse-content.html b/components/expand-collapse/demo/expand-collapse-content.html
@@ -0,0 +1,58 @@
+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+	<meta name="viewport" content="width=device-width, initial-scale=1.0">
+	<meta http-equiv="X-UA-Compatible" content="ie=edge">
+	<meta charset="UTF-8">
+	<link rel="stylesheet" href="../../demo/styles.css" type="text/css">
+	<script src="/node_modules/@webcomponents/webcomponentsjs/webcomponents-loader.js"></script>
+	<script type="module">
+		import '../../button/button.js';
+		import '../../demo/demo-page.js';
+		import '../expand-collapse-content.js';
+	</script>
+</head>
+
+<body unresolved>
+
+	<d2l-demo-page page-title="d2l-expand-collapse-content">
+
+		<h2>Default</h2>
+		<d2l-demo-snippet>
+			<template>
+				<d2l-button primary>Toggle</d2l-button>
+				<d2l-expand-collapse-content>
+					<p>
+					Yar Pirate Ipsum
+					Crow's nest chase guns coxswain belay coffer jib Shiver me timbers tackle piracy Buccaneer. Overhaul topsail Cat o'nine
+					tails lee wherry Sink me smartly ballast Sail ho hardtack. Bowsprit aft quarterdeck killick pirate black jack hands
+					crimp interloper yawl.
+					</p>
+					<ul>
+						<li>Coffee</li>
+						<li>Tea</li>
+						<li>Milk</li>
+					</ul>
+					<p>
+					Me trysail gangplank Plate Fleet Sink me hang the jib lanyard parrel square-rigged stern. Gangplank chandler brigantine
+					spyglass scurvy rope's end plunder lugger topmast trysail. Admiral of the Black cackle fruit hearties maroon bounty
+					Blimey yo-ho-ho sutler pillage boom.
+					</p>
+				</d2l-expand-collapse-content>
+				<script type="module">
+					const button = document.querySelector('d2l-button');
+					button.addEventListener('click', () => {
+						const section = document.querySelector('d2l-expand-collapse-content');
+						section.expanded = !section.expanded;
+						button.setAttribute('aria-expanded', section.expanded ? 'true' : 'false');
+					});
+				</script>
+			</template>
+		</d2l-demo-snippet>
+
+	</d2l-demo-page>
+
+</body>
+
+</html>
diff --git a/components/expand-collapse/expand-collapse-content.js b/components/expand-collapse/expand-collapse-content.js
@@ -0,0 +1,151 @@
+import { css, html, LitElement } from 'lit-element/lit-element.js';
+import { styleMap } from 'lit-html/directives/style-map.js';
+
+const reduceMotion = matchMedia('(prefers-reduced-motion: reduce)').matches;
+
+const states = {
+	PRECOLLAPSING: 'precollapsing', // setting up the styles so the collapse transition will run
+	COLLAPSING: 'collapsing', // in the process of collapsing
+	COLLAPSED: 'collapsed', // fully collapsed
+	PREEXPANDING: 'preexpanding', // setting up the styles so the expand transition will run
+	EXPANDING: 'expanding', // in the process of expanding
+	EXPANDED: 'expanded', // fully expanded
+};
+
+class ExpandCollapseContent extends LitElement {
+
+	static get properties() {
+		return {
+			expanded: { type: Boolean, reflect: true },
+			_height: { type: String },
+			_state: { type: String }
+		};
+	}
+
+	static get styles() {
+		return css`
+			:host {
+				display: block;
+			}
+
+			:host([hidden]) {
+				display: none;
+			}
+
+			.d2l-expand-collapse-content-container {
+				display: none;
+				overflow: hidden;
+				transition: height 400ms cubic-bezier(0, 0.7, 0.5, 1);
+			}
+
+			.d2l-expand-collapse-content-container:not([data-state="collapsed"]) {
+				display: block;
+			}
+
+			.d2l-expand-collapse-content-container[data-state="expanded"] {
+				overflow: visible;
+			}
+
+			/* prevent margin colapse on slotted children */
+			.d2l-expand-collapse-content-inner:before,
+			.d2l-expand-collapse-content-inner:after {
+				content: ' ';
+				display: table;
+			}
+
+			@media (prefers-reduced-motion: reduce) {
+				.d2l-expand-collapse-content-container {
+					transition: none;
+				}
+			}
+		`;
+	}
+
+	constructor() {
+		super();
+		this.expanded = false;
+		this._height = '0';
+		this._isFirstUpdate = true;
+		this._state = states.COLLAPSED;
+	}
+
+	updated(changedProperties) {
+		super.updated(changedProperties);
+		if (changedProperties.has('expanded')) {
+			this._expandedChanged(this.expanded, this._isFirstUpdate);
+			this._isFirstUpdate = false;
+		}
+	}
+
+	render() {
+		const styles = { height: this._height };
+		return html`
+			<div class="d2l-expand-collapse-content-container" data-state="${this._state}" @transitionend=${this._onTransitionEnd} style=${styleMap(styles)}>
+				<div class="d2l-expand-collapse-content-inner">
+					<slot></slot>
+				</div>
+			</div>
+		`;
+	}
+
+	async _expandedChanged(val, firstUpdate) {
+		const eventPromise = new Promise(resolve => this._eventPromiseResolve = resolve);
+		if (val) {
+			if (!firstUpdate) {
+				this.dispatchEvent(new CustomEvent(
+					'd2l-expand-collapse-content-expand',
+					{ bubbles: true, detail: { expandComplete: eventPromise } }
+				));
+			}
+			if (reduceMotion || firstUpdate) {
+				this._state = states.EXPANDED;
+				this._height = 'auto';
+				this._eventPromiseResolve();
+			} else {
+				this._state = states.PREEXPANDING;
+				await this.updateComplete;
+				await new Promise((r) => requestAnimationFrame(() => requestAnimationFrame(r)));
+				if (this._state === states.PREEXPANDING) {
+					this._state = states.EXPANDING;
+					const content = this.shadowRoot.querySelector('.d2l-expand-collapse-content-inner');
+					this._height = `${content.scrollHeight}px`;
+				}
+			}
+		} else {
+			if (!firstUpdate) {
+				this.dispatchEvent(new CustomEvent(
+					'd2l-expand-collapse-content-collapse',
+					{ bubbles: true, detail: { collapseComplete: eventPromise } }
+				));
+			}
+			if (reduceMotion || firstUpdate) {
+				this._state = states.COLLAPSED;
+				this._height = '0';
+				this._eventPromiseResolve();
+			} else {
+				this._state = states.PRECOLLAPSING;
+				const content = this.shadowRoot.querySelector('.d2l-expand-collapse-content-inner');
+				this._height = `${content.scrollHeight}px`;
+				await this.updateComplete;
+				await new Promise((r) => requestAnimationFrame(() => requestAnimationFrame(r)));
+				if (this._state === states.PRECOLLAPSING) {
+					this._state = states.COLLAPSING;
+					this._height = '0';
+				}
+			}
+		}
+	}
+
+	_onTransitionEnd() {
+		if (this._state === states.EXPANDING) {
+			this._state = states.EXPANDED;
+			this._height = 'auto';
+			this._eventPromiseResolve();
+		} else if (this._state === states.COLLAPSING) {
+			this._state = states.COLLAPSED;
+			this._eventPromiseResolve();
+		}
+	}
+
+}
+customElements.define('d2l-expand-collapse-content', ExpandCollapseContent);
diff --git a/components/expand-collapse/screenshots/expand-collapse-content.gif b/components/expand-collapse/screenshots/expand-collapse-content.gif
diff --git a/components/expand-collapse/test/.eslintrc.json b/components/expand-collapse/test/.eslintrc.json
@@ -0,0 +1,3 @@
+{
+	"extends": "brightspace/open-wc-testing-config"
+}
diff --git a/components/expand-collapse/test/expand-collapse-content.test.js b/components/expand-collapse/test/expand-collapse-content.test.js
@@ -0,0 +1,40 @@
+import '../expand-collapse-content.js';
+import { fixture, html } from '@open-wc/testing';
+import { runConstructor } from '../../../tools/constructor-test-helper.js';
+
+const collapsedContentFixture = html`<d2l-expand-collapse-content>A message.</d2l-expand-collapse-content>`;
+const expandedContentFixture = html`<d2l-expand-collapse-content expanded>A message.</d2l-expand-collapse-content>`;
+
+describe('d2l-expand-collapse-content', () => {
+
+	describe('constructor', () => {
+
+		it('should construct', () => {
+			runConstructor('d2l-expand-collapse-content');
+		});
+
+	});
+
+	describe('events', () => {
+
+		it('should fire d2l-expand-collapse-content-expand event with complete promise', async() => {
+			const content = await fixture(collapsedContentFixture);
+			setTimeout(() => content.expanded = true);
+			const e = await new Promise(resolve => {
+				content.addEventListener('d2l-expand-collapse-content-expand', (e) => resolve(e), { once: true });
+			});
+			await e.detail.expandComplete;
+		});
+
+		it('should fire d2l-expand-collapse-content-collapse event with complete promise', async() => {
+			const content = await fixture(expandedContentFixture);
+			setTimeout(() => content.expanded = false);
+			const e = await new Promise(resolve => {
+				content.addEventListener('d2l-expand-collapse-content-collapse', (e) => resolve(e), { once: true });
+			});
+			await e.detail.collapseComplete;
+		});
+
+	});
+
+});
diff --git a/components/expand-collapse/test/expand-collapse-content.visual-diff.html b/components/expand-collapse/test/expand-collapse-content.visual-diff.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+	<link rel="stylesheet" href="../../../test/styles.css" type="text/css">
+	<script src="/node_modules/@webcomponents/webcomponentsjs/webcomponents-loader.js"></script>
+	<script type="module">
+		import '../../typography/typography.js';
+		import '../expand-collapse-content.js';
+	</script>
+	<title>d2l-expand-collapse-content</title>
+	<meta name="viewport" content="width=device-width, initial-scale=1.0">
+	<meta http-equiv="X-UA-Compatible" content="ie=edge">
+	<meta charset="UTF-8">
+	<style>
+		ul {
+			border: 4px solid green;
+		}
+		d2l-expand-collapse-content {
+			border: 4px solid blue;
+		}
+	</style>
+</head>
+
+<body class="d2l-typography">
+	<div class="visual-diff">
+		<d2l-expand-collapse-content id="collapsed">
+			<ul>
+				<li>Coffee</li>
+				<li>Tea</li>
+				<li>Milk</li>
+			</ul>
+		</d2l-expand-collapse-content>
+	</div>
+	<div class="visual-diff">
+		<d2l-expand-collapse-content id="expanded" expanded>
+			<ul>
+				<li>Coffee</li>
+				<li>Tea</li>
+				<li>Milk</li>
+			</ul>
+		</d2l-expand-collapse-content>
+	</div>
+</body>
+
+</html>
diff --git a/components/expand-collapse/test/expand-collapse-content.visual-diff.js b/components/expand-collapse/test/expand-collapse-content.visual-diff.js
@@ -0,0 +1,30 @@
+const puppeteer = require('puppeteer');
+const VisualDiff = require('@brightspace-ui/visual-diff');
+
+describe('d2l-expand-collapse-content', () => {
+
+	const visualDiff = new VisualDiff('expand-collapse-content', __dirname);
+
+	let browser, page;
+
+	before(async() => {
+		browser = await puppeteer.launch();
+		page = await visualDiff.createPage(browser, { viewport: { width: 400, height: 400 } });
+		await page.goto(`${visualDiff.getBaseUrl()}/components/expand-collapse/test/expand-collapse-content.visual-diff.html`, { waitUntil: ['networkidle0', 'load'] });
+		await page.bringToFront();
+	});
+
+	after(async() => await browser.close());
+
+	[
+		'collapsed',
+		'expanded'
+	].forEach((testName) => {
+		it(testName, async function() {
+			const selector = `#${testName}`;
+			const rect = await visualDiff.getRect(page, selector);
+			await visualDiff.screenshotAndCompare(page, this.test.fullTitle(), { clip: rect });
+		});
+	});
+
+});
diff --git a/...ots/ci/golden/expand-collapse-content/d2l-expand-collapse-content-collapsed.png b/...ots/ci/golden/expand-collapse-content/d2l-expand-collapse-content-collapsed.png
diff --git a/...hots/ci/golden/expand-collapse-content/d2l-expand-collapse-content-expanded.png b/...hots/ci/golden/expand-collapse-content/d2l-expand-collapse-content-expanded.png
diff --git a/index.html b/index.html
@@ -57,6 +57,7 @@ <h2 class="d2l-heading-3">Components</h2>
 				<li><a href="components/dropdown/demo/dropdown-tabs.html">d2l-dropdown-tabs</a></li>
 			</ul>
 		</li>
+		<li><a href="components/expand-collapse/demo/expand-collapse-content.html">d2l-expand-collapse-content</a></li>
 		<li><a href="components/focus-trap/demo/focus-trap.html">d2l-focus-trap</a></li>
 		<li><a href="components/hierarchical-view/demo/hierarchical-view.html">d2l-hierarchical-view</a></li>
 		<li><a href="components/icons/demo/icon.html">d2l-icon</a></li>