♻️ Refactor Google Pay preview button

Mainly, separate the preview code into three main parts:
- Configuration
- Button
- ButtonManager

Remove dependency from DOM structure

modules/ppcp-googlepay/resources/js/boot-admin.js

@@ -1,7 +1,327 @@
 import {loadCustomScript} from "@paypal/paypal-js";
 import GooglepayButton from "./GooglepayButton";
+import merge from "deepmerge";
 import widgetBuilder from "../../../ppcp-button/resources/js/modules/Renderer/WidgetBuilder";
 
+/**
+ * Button manager instance; we usually only need a single instance of this object.
+ *
+ * @see buttonManager()
+ */
+let managerInstance = null;
+
+/**
+ * Default attributes for new buttons.
+ */
+const defaultAttributes = {
+    button: {
+        style: {
+            type: 'pay',
+            color: 'black',
+            language: 'en'
+        }
+    }
+};
+
+/**
+ * Accessor that creates and returns a single PreviewButtonManager instance.
+ */
+const buttonManager = () => {
+    if (!managerInstance) {
+        managerInstance = new PreviewButtonManager({
+            // Internal, for logging.
+            name: 'GooglePay',
+            // WooCommerce configuration object.
+            buttonConfig: window.wc_ppcp_googlepay_admin,
+            // Internal widgetBuilder instance.
+            widgetBuilder,
+            // Default button styles.
+            defaultAttributes,
+            // Returns an async function that fetches the button configuration.
+            cbFetchConfig: () => widgetBuilder?.paypal?.Googlepay()?.config,
+            // Returns the CSS selector to render the given button.
+            cbInitButton: (button) => {
+                button.selector = `${button.wrapper}GooglePay`
+                button.customClasses = 'ppcp-button-googlepay'
+            }
+        });
+    }
+
+    return managerInstance;
+}
+
+
+// ----------------------------------------------------------------------------
+
+
+/**
+ * Returns a new object which contains a copy of all public properties of the
+ * input object.
+ */
+const cloneObject = obj => JSON.parse(JSON.stringify(obj));
+
+/**
+ * Convenience function to attach an event handler to the document node.
+ * The callback handler will not receive the first argument (event), as this
+ * argument is not used by our module.
+ */
+const onDocumentEvent = (name, handler) => jQuery(document).on(name, (ev, ...args) => handler(...args));
+
+
+// ----------------------------------------------------------------------------
+
+
+/**
+ * A single GooglePay preview button instance.
+ */
+class PreviewButton {
+    constructor({wrapperSelector, configResponse, defaultAttributes, cbInitButton}) {
+        // Do not clone this object. It's generated by an API and might contain methods.
+        this.configResponse = configResponse;
+
+        this.defaultAttributes = cloneObject(defaultAttributes);
+        this.buttonConfig = {};
+        this.ppcpConfig = {};
+
+        this.wrapper = wrapperSelector;
+        this.selector = wrapperSelector + 'Button';
+        this.customClasses = '';
+
+        cbInitButton(this);
+
+        this.domWrapper = jQuery(this.selector);
+        this.payButton = null;
+    }
+
+    createNewWrapper() {
+        const previewId = this.selector.replace('#', '')
+        const previewClass = `ppcp-button-apm ${this.customClasses}`;
+
+        return jQuery(`<div id="${previewId}" class="${previewClass}">`)
+    }
+
+    config(buttonConfig, ppcpConfig) {
+        if (ppcpConfig) {
+            this.ppcpConfig = cloneObject(ppcpConfig);
+        }
+
+        if (buttonConfig) {
+            this.buttonConfig = merge(this.defaultAttributes, buttonConfig)
+            this.buttonConfig.button.wrapper = this.selector
+        }
+
+        return this;
+    }
+
+    render() {
+        this.remove();
+
+        const newDomWrapper = this.createNewWrapper();
+
+        if (this.domWrapper?.length) {
+            this.domWrapper.replaceWith(newDomWrapper);
+        } else {
+            jQuery(this.ppcpConfig.button.wrapper).after(newDomWrapper);
+        }
+        this.domWrapper = newDomWrapper;
+
+        this.payButton = new GooglepayButton(
+            'preview',
+            null,
+            this.buttonConfig,
+            this.ppcpConfig,
+        );
+
+        this.payButton.init(this.configResponse);
+        return this;
+    }
+
+    remove() {
+        // The payButton has no remove/cleanup function.
+        this.payButton = null;
+
+        if (this.domWrapper) {
+            this.domWrapper.remove();
+            this.domWrapper = null;
+        }
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+/**
+ * Manages all GooglePay preview buttons on this page.
+ */
+class PreviewButtonManager {
+    constructor({
+        name,
+        buttonConfig,
+        widgetBuilder,
+        defaultAttributes,
+        cbFetchConfig,
+        cbInitButton
+    }) {
+        this.name = name;
+        this.buttonConfig = buttonConfig;
+        this.widgetBuilder = widgetBuilder;
+        this.defaultAttributes = defaultAttributes;
+        this.cbInitButton = cbInitButton;
+        this.cbFetchConfig = cbFetchConfig;
+
+        this.state = 'enabled'
+        this.buttons = {};
+        this.configResponse = null;
+
+        // Empty promise that resolves instantly when called.
+        this.bootstrapping = Promise.resolve();
+
+        // Add the bootstrap logic to the Promise chain. More `then`s are added by createButton().
+        this.bootstrapping = this.bootstrapping.then(() => this.bootstrap());
+
+        this.registerEventListeners();
+    }
+
+    registerEventListeners() {
+        onDocumentEvent('ppcp_paypal_render_preview', this.createButton.bind(this));
+        onDocumentEvent('DOMContentLoaded', () => this.bootstrapping);
+    }
+
+    /**
+     * Output an error message to the console, with a module-specific prefix.
+     */
+    error(message, ...args) {
+        console.error(`${this.name} ${message}`, ...args)
+    }
+
+    /**
+     * Load dependencies and bootstrap the module.
+     * Returns a Promise that resolves once all dependencies were loaded and the module can be
+     * used without limitation.
+     *
+     * @return {Promise<void>}
+     */
+    async bootstrap() {
+        if (!this.buttonConfig || !this.widgetBuilder) {
+            this.error('Button could not be configured.');
+            return;
+        }
+
+        // Load the custom SDK script.
+        const customScriptPromise = loadCustomScript({url: this.buttonConfig.sdk_url});
+
+        // Wait until PayPal is ready.
+        const paypalPromise = new Promise(resolve => {
+            if (this.widgetBuilder.paypal) {
+                resolve();
+            } else {
+                onDocumentEvent('ppcp-paypal-loaded', resolve);
+            }
+        });
+
+        await Promise.all([customScriptPromise, paypalPromise]);
+
+        const fetchConfig = this.cbFetchConfig()
+        if (!fetchConfig) {
+            this.error('Button could not be initialized');
+            return;
+        }
+
+        this.configResponse = await fetchConfig();
+    }
+
+    /**
+     * Creates a new preview button, that is rendered once the bootstrapping Promise resolves.
+     */
+    createButton(ppcpConfig) {
+        if (!ppcpConfig.button.wrapper) {
+            this.error('Button did not provide a selector', ppcpConfig)
+            return;
+        }
+
+        const wrapper = ppcpConfig.button.wrapper;
+
+        const createButtonInst = () => {
+            if (!this.buttons[wrapper]) {
+                this.buttons[wrapper] = new PreviewButton({
+                    wrapperSelector: wrapper,
+                    configResponse: this.configResponse,
+                    defaultAttributes: this.defaultAttributes,
+                    cbInitButton: this.cbInitButton
+                });
+            }
+
+            this.buttons[wrapper].config(
+                this.buttonConfig,
+                ppcpConfig
+            ).render()
+        }
+
+        if (this.bootstrapping) {
+            this.bootstrapping.then(createButtonInst);
+        } else {
+            createButtonInst();
+        }
+    }
+
+    /**
+     * Changes the button configuration, and re-renders all buttons.
+     */
+    updateConfig(newConfig) {
+        if (!newConfig || 'object' !== typeof newConfig) {
+            return;
+        }
+
+        this.buttonConfig = merge(this.buttonConfig, newConfig)
+
+        Object.values(this.buttons).forEach(button => button.config(this.buttonConfig))
+        this.renderButtons()
+    }
+
+
+    /**
+     * Refreshes all buttons using the latest buttonConfig.
+     */
+    renderButtons() {
+        if ('enabled' === this.state) {
+            Object.values(this.buttons).forEach(button => button.render())
+        } else {
+            Object.values(this.buttons).forEach(button => button.remove())
+        }
+    }
+
+    /**
+     * Enables this payment method, which re-creates or refreshes all buttons.
+     */
+    enable() {
+        if ('enabled' === this.state) {
+            return;
+        }
+        this.state = 'enabled';
+        this.renderButtons()
+    }
+
+    /**
+     * Disables this payment method, effectively removing all preview buttons.
+     */
+    disable() {
+        if ('disabled' === this.state) {
+            return;
+        }
+
+        this.state = 'disabled';
+        this.renderButtons()
+    }
+}
+
+// Initialize the preview button manager.
+buttonManager().enable()
+
+// todo - Expose button manager for testing. Remove this!
+window.gpay = buttonManager()
+
+
+/**
+
 (function ({
    buttonConfig,
    jQuery
@@ -47,11 +367,6 @@ import widgetBuilder from "../../../ppcp-button/resources/js/modules/Renderer/Wi
         }, 100);
     });
 
-    /**
-     * Decides, whether to display the Google Pay preview button.
-     *
-     * @return {boolean}
-     */
     const shouldDisplayPreviewButton = function() {
         // TODO - original condition, which is wrong.
         return jQuery('#ppcp-googlepay_button_enabled').is(':checked');
@@ -154,3 +469,5 @@ import widgetBuilder from "../../../ppcp-button/resources/js/modules/Renderer/Wi
     buttonConfig: window.wc_ppcp_googlepay_admin,
     jQuery: window.jQuery
 });
+
+// */