wp-admin-pwa.php

admin-pwa.php

<?php
/**
 * Plugin Name: Admin PWA
 */

namespace Preseto\Admin_PWA;

const ACTION_QUERY_VAR = 'admin-pwa';

function manifest_url() {
	return admin_url( '/wp-admin.manifest' );
}

function service_worker_url() {
	return admin_url( '/wp-admin.service-worker', __FILE__ );
}

add_action(
	'admin_head',
	function () {
		printf(
			'<link rel="manifest" href="%s" />',
			esc_attr( manifest_url() )
		);
		printf(
			'<script>if ( "serviceWorker" in navigator ) { navigator.serviceWorker.register( "%s" ); }</script>',
			service_worker_url()
		);
	}
);

// Remember to flush the rewrite rules by visiting the permalinks settings page.
add_action(
	'init',
	function () {
		add_rewrite_rule(
			sprintf( '^%s$', preg_quote( ltrim( wp_parse_url( manifest_url(), PHP_URL_PATH ), '/' ), '/' ) ),
			sprintf( 'index.php?%s=manifest', ACTION_QUERY_VAR )
		);
		add_rewrite_rule(
			sprintf( '^%s$', preg_quote( ltrim( wp_parse_url( service_worker_url(), PHP_URL_PATH ), '/' ), '/' ) ),
			sprintf( 'index.php?%s=service-worker', ACTION_QUERY_VAR )
		);
	}
);

add_filter(
	'query_vars',
	function ( $query_vars ) {
		$query_vars[] = ACTION_QUERY_VAR;

		return $query_vars;
	}
);

add_action(
	'template_redirect',
	function () {
		$action = get_query_var( ACTION_QUERY_VAR );

		if ( 'manifest' === $action ) {
			wp_send_json(
				[
					'display' => 'standalone',
					'theme_color' => '#363b3f', // Match the admin bar background.
					'background_color' => '#f1f1f1', // Match the admin body background.
					'name' => html_entity_decode( get_bloginfo( 'name' ) ),
					'short_name' => html_entity_decode( get_bloginfo( 'name' ) ),
					'description' => html_entity_decode( get_bloginfo( 'description' ) ),
					'start_url' => admin_url( 'index.php' ),
					'icons' => [
						[
							'src' => admin_url( '/images/wordpress-logo-white.svg' ),
							'sizes' => 'any',
							'type' => 'image/svg+xml',
							'purpose' => 'any'
						],
					],
				]
			);
		} elseif ( 'service-worker' === $action ) {
			header( 'Content-Type: text/javascript' );
			echo file_get_contents( __DIR__ . '/service-worker.js' );
			exit;
		}
	}
);

service-worker.js

const CACHE_NAME = "wp-admin-v1";

const ASSETS_TO_CACHE = [
	'/wp-admin/',
	'/wp-admin/index.php',
];

self.addEventListener(
	'install',
	( event ) => {
		event.waitUntil(
			caches.open( CACHE_NAME )
				.then( ( cache ) => cache.addAll( ASSETS_TO_CACHE ) )
				.catch( console.warn )
		);
	}
);

self.addEventListener(
	'activate',
	( event ) => {
		// TODO: Delete entries with keys different from the current revision.
	}
);

self.addEventListener(
	'fetch', 
	( event ) => {
		// TODO: Respond with cached entries if offline.  
	}
);