Experimental implementation for webapp plugins (#7185)

* Start of experimental implementation for webapp plugins

* Updates to webapp plugin architecture

* Update pluggable test

* Remove debug code

webapp/plugins/index.js

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+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+// EXPERIMENTAL - SUBJECT TO CHANGE
+
+import store from 'stores/redux_store.jsx';
+import {ActionTypes} from 'utils/constants.jsx';
+import {getSiteURL} from 'utils/url.jsx';
+
+window.plugins = {};
+
+export function registerComponents(components) {
+    store.dispatch({
+        type: ActionTypes.RECEIVED_PLUGIN_COMPONENTS,
+        data: components || {}
+    });
+}
+
+export function initializePlugins() {
+    const pluginJson = window.mm_config.Plugins || '[]';
+
+    let pluginManifests;
+    try {
+        pluginManifests = JSON.parse(pluginJson);
+    } catch (error) {
+        console.error('Invalid plugins JSON: ' + error); //eslint-disable-line no-console
+        return;
+    }
+
+    pluginManifests.forEach((m) => {
+        function onLoad() {
+            // Add the plugin's js to the page
+            const script = document.createElement('script');
+            script.type = 'text/javascript';
+            script.text = this.responseText;
+            document.getElementsByTagName('head')[0].appendChild(script);
+
+            // Initialize the plugin
+            console.log('Registering ' + m.id + ' plugin...'); //eslint-disable-line no-console
+            const plugin = window.plugins[m.id];
+            plugin.initialize(registerComponents, store);
+            console.log('...done'); //eslint-disable-line no-console
+        }
+
+        // Fetch the plugin's bundled js
+        const xhrObj = new XMLHttpRequest();
+        xhrObj.open('GET', getSiteURL() + m.bundle_path, true);
+        xhrObj.addEventListener('load', onLoad);
+        xhrObj.send('');
+    });
+}

webapp/plugins/pluggable/index.js

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+// Copyright (c) 2017 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+import {connect} from 'react-redux';
+import {getTheme} from 'mattermost-redux/selectors/entities/preferences';
+
+import Pluggable from './pluggable.jsx';
+
+function mapStateToProps(state, ownProps) {
+    return {
+        ...ownProps,
+        components: state.plugins.components,
+        theme: getTheme(state)
+    };
+}
+
+export default connect(mapStateToProps)(Pluggable);

webapp/plugins/pluggable/pluggable.jsx

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+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+// EXPERIMENTAL - SUBJECT TO CHANGE
+
+import React from 'react';
+import PropTypes from 'prop-types';
+
+export default class Pluggable extends React.PureComponent {
+    static propTypes = {
+
+        /*
+         * Should be a single overridable React component
+         */
+        children: PropTypes.element.isRequired,
+
+        /*
+         * Components for overriding provided by plugins
+         */
+        components: PropTypes.object.isRequired,
+
+        /*
+         * Logged in user's theme
+         */
+        theme: PropTypes.object.isRequired
+    }
+
+    render() {
+        const child = React.Children.only(this.props.children).type;
+        const components = this.props.components;
+
+        if (child == null) {
+            return null;
+        }
+
+        // Include any props passed to this component or to the child component
+        let props = {...this.props};
+        Reflect.deleteProperty(props, 'children');
+        Reflect.deleteProperty(props, 'components');
+        props = {...props, ...this.props.children.props};
+
+        // Override the default component with any registered plugin's component
+        if (components.hasOwnProperty(child.name)) {
+            const PluginComponent = components[child.name];
+            return (
+                <PluginComponent
+                    {...props}
+                    theme={this.props.theme}
+                />
+            );
+        }
+
+        return React.cloneElement(this.props.children, {...props});
+    }
+}