feat(elements): implement extractProjectableNodes()

packages/elements/src/extract-projectable-nodes.ts

@@ -0,0 +1,54 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+// NOTE: This is a (slightly improved) version of what is used in ngUpgrade's
+//       `DowngradeComponentAdapter`.
+// TODO(gkalpak): Investigate if it makes sense to share the code.
+
+import {isElement, matchesSelector} from './utils';
+
+export function extractProjectableNodes(host: HTMLElement, ngContentSelectors: string[]): Node[][] {
+  const nodes = host.childNodes;
+  const projectableNodes: Node[][] = ngContentSelectors.map(() => []);
+  let wildcardIndex = -1;
+
+  ngContentSelectors.some((selector, i) => {
+    if (selector === '*') {
+      wildcardIndex = i;
+      return true;
+    }
+    return false;
+  });
+
+  for (let i = 0, ii = nodes.length; i < ii; ++i) {
+    const node = nodes[i];
+    const ngContentIndex = findMatchingIndex(node, ngContentSelectors, wildcardIndex);
+
+    if (ngContentIndex !== -1) {
+      projectableNodes[ngContentIndex].push(node);
+    }
+  }
+
+  return projectableNodes;
+}
+
+function findMatchingIndex(node: Node, selectors: string[], defaultIndex: number): number {
+  let matchingIndex = defaultIndex;
+
+  if (isElement(node)) {
+    selectors.some((selector, i) => {
+      if ((selector !== '*') && matchesSelector(node, selector)) {
+        matchingIndex = i;
+        return true;
+      }
+      return false;
+    });
+  }
+
+  return matchingIndex;
+}