New packages org (#2639)

New packages org

demo-shell/src/app/components/theme-picker/style-manager/style-manager.ts

@@ -0,0 +1,46 @@
+import { Injectable } from '@angular/core';
+
+/**
+ * Class for managing stylesheets. Stylesheets are loaded into named slots so that they can be
+ * removed or changed later.
+ */
+@Injectable()
+export class StyleManager {
+  /**
+   * Set the stylesheet with the specified key.
+   */
+  setStyle(key: string, href: string) {
+    getLinkElementForKey(key).setAttribute('href', href);
+  }
+
+  /**
+   * Remove the stylesheet with the specified key.
+   */
+  removeStyle(key: string) {
+    const existingLinkElement = getExistingLinkElementByKey(key);
+    if (existingLinkElement) {
+      document.head.removeChild(existingLinkElement);
+    }
+  }
+}
+
+function getLinkElementForKey(key: string) {
+  return getExistingLinkElementByKey(key) || createLinkElementWithKey(key);
+}
+
+function getExistingLinkElementByKey(key: string) {
+  return document.head.querySelector(`link[rel="stylesheet"].${getClassNameForKey(key)}`);
+}
+
+function createLinkElementWithKey(key: string) {
+  const linkEl = document.createElement('link');
+  linkEl.setAttribute('rel', 'stylesheet');
+  linkEl.setAttribute('type', 'text/css');
+  linkEl.classList.add(getClassNameForKey(key));
+  document.head.appendChild(linkEl);
+  return linkEl;
+}
+
+function getClassNameForKey(key: string) {
+  return `style-manager-${key}`;
+}