feat(router): implement a function create router state out of a candidate

modules/@angular/router/src/create_router_state.ts

@@ -0,0 +1,42 @@
+import { RouterStateCandidate, ActivatedRouteCandidate, RouterState, ActivatedRoute } from './router_state';
+import { TreeNode } from './utils/tree';
+import { BehaviorSubject } from 'rxjs/BehaviorSubject';
+
+export function createRouterState(curr: RouterStateCandidate, prev: RouterStateCandidate, prevState: RouterState): RouterState {
+  const root = createNode(curr._root, prev ? prev._root : null, prevState ? prevState._root : null);
+  const queryParams = prevState ? prevState.queryParams : new BehaviorSubject(curr.queryParams);
+  const fragment = prevState ? prevState.fragment : new BehaviorSubject(curr.fragment);
+  return new RouterState(root, queryParams, fragment);
+}
+
+function createNode(curr:TreeNode<ActivatedRouteCandidate>, prev?:TreeNode<ActivatedRouteCandidate>, prevState?:TreeNode<ActivatedRoute>):TreeNode<ActivatedRoute> {
+  if (prev && equalRouteCandidates(prev.value, curr.value)) {
+    const value = prevState.value;
+    const children = createOrReuseChildren(curr, prev, prevState);
+    return new TreeNode<ActivatedRoute>(value, children);
+
+  } else {
+    const value = createActivatedRoute(curr.value);
+    const children = curr.children.map(c => createNode(c));
+    return new TreeNode<ActivatedRoute>(value, children);
+  }
+}
+
+function createOrReuseChildren(curr:TreeNode<ActivatedRouteCandidate>, prev:TreeNode<ActivatedRouteCandidate>, prevState:TreeNode<ActivatedRoute>) {
+  return curr.children.map(child => {
+    const index = prev.children.findIndex(p => equalRouteCandidates(p.value, child.value));
+    if (index >= 0) {
+      return createNode(child, prev.children[index], prevState.children[index]);
+    } else {
+      return createNode(child);
+    }
+  });
+}
+
+function createActivatedRoute(c:ActivatedRouteCandidate) {
+  return new ActivatedRoute(new BehaviorSubject(c.urlSegments), new BehaviorSubject(c.params), c.outlet, c.component);
+}
+
+function equalRouteCandidates(a: ActivatedRouteCandidate, b: ActivatedRouteCandidate): boolean {
+  return a._routeConfig === b._routeConfig;
+}