Add plugin: h5p-postmessage.

This is needed to allow H5P to send postMessage events to the parent
frame, allowing "completion" events in openlab-modules.

See #3364.

wp-content/plugins/h5p-postmessage/.eslintrc

@@ -0,0 +1,6 @@
+{
+  "extends": [ "plugin:@wordpress/eslint-plugin/recommended" ],
+  "rules": {
+    "prettier/prettier": "off"
+  }
+}

wp-content/plugins/h5p-postmessage/assets/src/frontend.js

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+/* global H5P */
+(() => {
+	if ( 'undefined' === typeof H5P ) {
+		return;
+	}
+
+	const getPostMessageData = ( event ) => {
+		const { data } = event;
+
+		if ( ! data ) {
+			return null;
+		}
+
+		const { statement } = data;
+
+		if ( ! statement ) {
+			return null;
+		}
+
+		const { object } = statement;
+
+		if ( ! object ) {
+			return null;
+		}
+
+		const objectId = object.id;
+
+		const verb = event.getVerb();
+
+		const baseData = {
+			objectId,
+			source: 'h5p-postmessage',
+			verb
+		}
+
+		switch ( verb ) {
+			case 'attempted' :
+				return baseData;
+
+			case 'answered' :
+				const isComplete = event.getScore() === event.getMaxScore() && event.getMaxScore() > 0
+
+				if ( ! isComplete ) {
+					return null;
+				}
+
+				return {
+					...baseData,
+					verb: 'completed'
+				};
+		}
+	}
+
+	H5P.externalDispatcher.on('xAPI', function (event) {
+		const postMessageData = getPostMessageData( event );
+
+		if ( ! postMessageData ) {
+			return;
+		}
+
+		window.parent.postMessage( postMessageData, '*' );
+	});
+})();

wp-content/plugins/h5p-postmessage/build/frontend.asset.php

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+<?php return array('dependencies' => array(), 'version' => '43f963599a1854222e61');

wp-content/plugins/h5p-postmessage/h5p-postmessage.php

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+<?php
+
+/**
+ * Plugin Name: H5P PostMessage
+ * Description: Adds postMessage support to H5P.
+ * Version: 1.0
+ * Author: City Tech OpenLab
+ * Author URI: https://openlab.citytech.cuny.edu
+ */
+
+// Exit if accessed directly
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+add_action(
+	'wp_enqueue_scripts',
+	function() {
+	}
+);
+
+add_action(
+	'h5p_additional_embed_head_tags',
+	function( &$tags ) {
+		$blocks_dir        = __DIR__ . '/build/';
+		$blocks_asset_file = include $blocks_dir . 'frontend.asset.php';
+
+		// Add the script to the tags.
+		$tags[] = sprintf(
+			'<script src="%s"></script>',
+			plugin_dir_url( __FILE__ ) . 'build/frontend.js'
+		);
+
+		return $tags;
+	}
+);