Add handler support for settings fields

Add settings SubElementsHandler

modules/ppcp-wc-gateway/resources/js/SettingsHandler/SubElementsHandler.js

@@ -0,0 +1,51 @@
+
+class SubElementsHandler {
+    constructor(element, options) {
+        const fieldSelector = 'input, select, textarea';
+
+        this.element = element;
+        this.values = options.values;
+        this.elements = options.elements;
+
+        this.elementsSelector = this.elements.join(',');
+
+        this.input = jQuery(this.element).is(fieldSelector)
+            ? this.element
+            : jQuery(this.element).find(fieldSelector).get(0);
+
+        this.updateElementsVisibility();
+
+        jQuery(this.input).change(() => {
+            this.updateElementsVisibility();
+        });
+    }
+
+    updateElementsVisibility() {
+        const $elements = jQuery(this.elementsSelector);
+
+        let value = this.getValue(this.input);
+        value = (value !== null ? value.toString() : value);
+
+        if (this.values.indexOf(value) !== -1) {
+            $elements.show();
+        } else {
+            $elements.hide();
+        }
+    }
+
+    getValue(element) {
+        const $el = jQuery(element);
+
+        if ($el.is(':checkbox') || $el.is(':radio')) {
+            if ($el.is(':checked')) {
+                return $el.val();
+            } else {
+                return null;
+            }
+        } else {
+            return $el.val();
+        }
+    }
+}
+
+export default SubElementsHandler;