Experiment: Admin PWA

.github/CODEOWNERS

@@ -127,6 +127,11 @@
 /lib/class-wp-theme-json-resolver-gutenberg.php @timothybjabocs @spacedmonkey @nosolosw
 /phpunit/class-wp-theme-json-test.php           @nosolosw
 
+# Web App
+/packages/admin-manifest                        @ellatrix
+/lib/pwa.php                                    @ellatrix
+/lib/service-worker.js                          @ellatrix
+
 # Native (Unowned)
 *.native.js                                     @ghost
 *.android.js                                    @ghost

docs/manifest.json

@@ -1301,6 +1301,12 @@
 		"markdown_source": "../packages/a11y/README.md",
 		"parent": "packages"
 	},
+	{
+		"title": "@wordpress/admin-manifest",
+		"slug": "packages-admin-manifest",
+		"markdown_source": "../packages/admin-manifest/README.md",
+		"parent": "packages"
+	},
 	{
 		"title": "@wordpress/annotations",
 		"slug": "packages-annotations",

lib/load.php

@@ -118,6 +118,7 @@ function gutenberg_is_experiment_enabled( $name ) {
 require __DIR__ . '/navigation-page.php';
 require __DIR__ . '/experiments-page.php';
 require __DIR__ . '/global-styles.php';
+require __DIR__ . '/pwa.php';
 
 require __DIR__ . '/block-supports/generated-classname.php';
 require __DIR__ . '/block-supports/elements.php';

lib/pwa.php

@@ -0,0 +1,34 @@
+<?php
+/**
+ * Progressive Web App
+ *
+ * @package gutenberg
+ */
+
+add_filter(
+	'admin_head',
+	function() {
+		$l10n = array(
+			'logo'      => file_get_contents( ABSPATH . 'wp-admin/images/wordpress-logo-white.svg' ),
+			'siteTitle' => get_bloginfo( 'name' ),
+			'adminUrl'  => admin_url(),
+		);
+		wp_enqueue_script( 'wp-admin-manifest' );
+		wp_localize_script( 'wp-admin-manifest', 'wpAdminManifestL10n', $l10n );
+	}
+);
+
+add_filter(
+	'load-index.php',
+	function() {
+		if ( ! isset( $_GET['service-worker'] ) ) {
+			return;
+		}
+
+		header( 'Content-Type: text/javascript' );
+		// Must be at the admin root so the scope is correct. Move to the
+		// wp-admin folder when merging with core.
+		echo file_get_contents( __DIR__ . '/service-worker.js' );
+		exit;
+	}
+);

lib/service-worker.js

@@ -0,0 +1,14 @@
+/* global self */
+
+// https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerGlobalScope/skipWaiting
+self.addEventListener( 'install', function ( event ) {
+	event.waitUntil( self.skipWaiting() );
+} );
+
+// https://developer.mozilla.org/en-US/docs/Web/API/Clients/claim
+self.addEventListener( 'activate', function ( event ) {
+	event.waitUntil( self.clients.claim() );
+} );
+
+// Necessary for Chrome to show the install button.
+self.addEventListener( 'fetch', function () {} );

package.json

@@ -23,6 +23,7 @@
 	},
 	"dependencies": {
 		"@wordpress/a11y": "file:packages/a11y",
+		"@wordpress/admin-manifest": "file:packages/admin-manifest",
 		"@wordpress/annotations": "file:packages/annotations",
 		"@wordpress/api-fetch": "file:packages/api-fetch",
 		"@wordpress/autop": "file:packages/autop",

packages/admin-manifest/.npmrc

@@ -0,0 +1 @@
+package-lock=false

packages/admin-manifest/README.md

@@ -0,0 +1,3 @@
+# Admin Manifest
+
+Dynamically creates a Web App [manifest](https://w3c.github.io/manifest/) and registers the service worker for the admin.

packages/admin-manifest/package.json

@@ -0,0 +1,33 @@
+{
+	"name": "@wordpress/admin-manifest",
+	"version": "1.0.0",
+	"description": "Dynamically creates a Web App manifest and registers the service worker for the admin.",
+	"author": "The WordPress Contributors",
+	"license": "GPL-2.0-or-later",
+	"keywords": [
+		"wordpress",
+		"gutenberg",
+		"manifest"
+	],
+	"homepage": "https://github.com/WordPress/gutenberg/tree/HEAD/packages/admin-manifest/README.md",
+	"repository": {
+		"type": "git",
+		"url": "https://github.com/WordPress/gutenberg.git",
+		"directory": "packages/admin-manifest"
+	},
+	"bugs": {
+		"url": "https://github.com/WordPress/gutenberg/issues"
+	},
+	"engines": {
+		"node": ">=12"
+	},
+	"main": "build/index.js",
+	"module": "build-module/index.js",
+	"react-native": "src/index",
+	"dependencies": {
+		"@babel/runtime": "^7.13.10"
+	},
+	"publishConfig": {
+		"access": "public"
+	}
+}

packages/admin-manifest/src/index.js

@@ -0,0 +1,157 @@
+function addManifest( manifest ) {
+	const link = document.createElement( 'link' );
+	link.rel = 'manifest';
+	link.href = 'data:application/manifest+json,' + JSON.stringify( manifest );
+	document.head.appendChild( link );
+}
+
+function addAppleTouchIcon( size, base64data ) {
+	const iconLink = document.createElement( 'link' );
+	iconLink.rel = 'apple-touch-icon';
+	iconLink.href = base64data;
+	iconLink.sizes = '180x180';
+	document.head.insertBefore( iconLink, document.head.firstElementChild );
+}
+
+function createSvgElement( html ) {
+	const doc = document.implementation.createHTMLDocument( '' );
+	doc.body.innerHTML = html;
+	const { firstElementChild: svgElement } = doc.body;
+	svgElement.setAttribute( 'viewBox', '0 0 80 80' );
+	return svgElement;
+}
+
+function createIcon( { svgElement, size, color, backgroundColor, circle } ) {
+	return new Promise( ( resolve ) => {
+		const canvas = document.createElement( 'canvas' );
+		const context = canvas.getContext( '2d' );
+
+		// Leave 1/8th padding around the logo.
+		const padding = size / 8;
+		// Which leaves 3/4ths of space for the icon.
+		const logoSize = padding * 6;
+
+		// Resize the SVG logo.
+		svgElement.setAttribute( 'width', logoSize );
+		svgElement.setAttribute( 'height', logoSize );
+
+		// Color in the background.
+		svgElement.querySelectorAll( 'path' ).forEach( ( path ) => {
+			path.setAttribute( 'fill', backgroundColor );
+		} );
+
+		// Resize the canvas.
+		canvas.width = size;
+		canvas.height = size;
+
+		// If we're not drawing a circle, set the background color.
+		if ( ! circle ) {
+			context.fillStyle = backgroundColor;
+			context.fillRect( 0, 0, canvas.width, canvas.height );
+		}
+
+		// Fill in the letter (W) and circle around it.
+		context.fillStyle = color;
+		context.beginPath();
+		context.arc( size / 2, size / 2, logoSize / 2 - 1, 0, 2 * Math.PI );
+		context.closePath();
+		context.fill();
+
+		// Create a URL for the SVG to load in an image element.
+		const svgBlob = new window.Blob( [ svgElement.outerHTML ], {
+			type: 'image/svg+xml',
+		} );
+		const url = URL.createObjectURL( svgBlob );
+		const image = document.createElement( 'img' );
+
+		image.src = url;
+		image.width = logoSize;
+		image.height = logoSize;
+		image.onload = () => {
+			// Once the image is loaded, draw it onto the canvas.
+			context.drawImage( image, padding, padding );
+			// Export it to a blob.
+			canvas.toBlob( ( imageBlob ) => {
+				// We no longer need the SVG blob url.
+				URL.revokeObjectURL( url );
+				// Unfortunately blob URLs don't seem to work, so we have to use
+				// base64 encoded data URLs.
+				const reader = new window.FileReader();
+				reader.readAsDataURL( imageBlob );
+				reader.onloadend = () => {
+					resolve( reader.result );
+				};
+			} );
+		};
+	} );
+}
+
+// eslint-disable-next-line @wordpress/no-global-event-listener
+window.addEventListener( 'load', () => {
+	if ( ! ( 'serviceWorker' in window.navigator ) ) {
+		return;
+	}
+
+	const { logo, siteTitle, adminUrl } = window.wpAdminManifestL10n;
+	const manifest = {
+		// Replace spaces with non breaking spaces. Chrome collapses them.
+		name: siteTitle.replace( / /g, ' ' ),
+		display: 'standalone',
+		orientation: 'portrait',
+		start_url: adminUrl,
+		// Open front-end, login page, and any external URLs in a browser
+		// modal.
+		scope: adminUrl,
+		icons: [],
+	};
+
+	const adminBar = document.getElementById( 'wpadminbar' );
+	const { color, backgroundColor } = window.getComputedStyle( adminBar );
+	const svgElement = createSvgElement( logo );
+
+	Promise.all( [
+		// The maskable icon should have its background filled. This is used
+		// for iOS. To do: check which sizes are really needed.
+		...[ 180, 192, 512 ].map( ( size ) =>
+			createIcon( {
+				svgElement,
+				size,
+				color,
+				backgroundColor,
+			} ).then( ( base64data ) => {
+				manifest.icons.push( {
+					src: base64data,
+					sizes: size + 'x' + size,
+					type: 'image/png',
+					purpose: 'maskable',
+				} );
+
+				// iOS doesn't seem to look at the manifest.
+				if ( size === 180 ) {
+					addAppleTouchIcon( size, base64data );
+				}
+			} )
+		),
+		// The "normal" icon should be round. This is used for Chrome
+		// Desktop PWAs. To do: check which sizes are really needed.
+		...[ 180, 192, 512 ].map( ( size ) =>
+			createIcon( {
+				svgElement,
+				size,
+				color,
+				backgroundColor,
+				circle: true,
+			} ).then( ( base64data ) => {
+				manifest.icons.push( {
+					src: base64data,
+					sizes: size + 'x' + size,
+					type: 'image/png',
+					purpose: 'any',
+				} );
+			} )
+		),
+	] ).then( () => {
+		addManifest( manifest );
+		window.navigator.serviceWorker.register( adminUrl + '?service-worker' );
+	} );
+} );