[MD Extensions] Add support for URL navigation

chrome/browser/resources/md_extensions/page_state.js

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * The different pages that can be shown at a time.
+ * Note: This must remain in sync with the order in manager.html!
+ * @enum {string}
+ */
+var Page = {
+  LIST: '0',

[michaelpg, 2017/04/14 20:23:53]

could these values be IDs? neon-animated-pages should be able to key off those,
and then you wouldn't have to worry about order (which should be irrelevant),
and you could assert that each ID exists in the DOM to self-enforce this.

[Devlin, 2017/04/17 23:29:24]

Using ids doesn't seem to work...  I thought neon-animated-pages.selected always
used index?

[michaelpg, 2017/04/18 22:03:11]

it's using iron-selector, which has the "attrForSelected" property:

    <neon-animated-pages attr-for-selected="id"> <foo id="..."> ...

I *assume* "id" would work there.
https://github.com/PolymerElements/iron-selector/blob/master/iron-selectable....

+  DETAILS: '1',
+  SHORTCUTS: '2',
+  ERRORS: '3',
+};
+
+/** @enum {string} */
+var Subpage = {
+  OPTIONS: 'options',
+};
+
+/** @typedef {{page: Page,
+               id: (string|undefined),
+               subpage: (!Subpage|undefined)}} */
+var PageEntry;
+
+cr.define('extensions', function() {
+  'use strict';
+
+  /** @constructor */

[michaelpg, 2017/04/14 20:23:53]

document what PageState is for.
also type and document the changePage param.

[Devlin, 2017/04/17 23:29:24]

Done.

+  function PageState(changePage) {

[michaelpg, 2017/04/14 20:23:53]

should this be a singleton, since it manipulates history? Or is it intended as
an auxiliary helper class that basically notifies its owner of a page change?

[Devlin, 2017/04/17 23:29:24]

Conceptually, it should be a singleton (just as manager should be), but it
seemed unnecessary to strictly enforce that.

[michaelpg, 2017/04/18 22:03:11]

Sure. The new naming makes it clearer, too.

+    this.changePage_ = changePage;
+    window.addEventListener('popstate', this.onPopState_.bind(this));
+  }
+
+  PageState.prototype = {
+    /** @private */
+    onPopState_: function() {
+      var state = this.getCurrentPage();

[michaelpg, 2017/04/14 20:23:53]

nit: skip variable declaration

[Devlin, 2017/04/17 23:29:24]

Done.

+      this.changePage_(state, false);
+    },
+
+    /**
+     * Returns the page that should be displayed for the current URL.
+     * @return {!PageEntry}
+     */
+    getCurrentPage: function() {
+      if (location.search == '' && location.pathname == '/')
+        return {page: Page.LIST};
+
+      var search = new URLSearchParams(location.search);
+      var id = search.get('id');
+      if (id)
+        return {page: Page.DETAILS, id: id};
+      id = search.get('options');
+      if (id)
+        return {page: Page.DETAILS, id: id, subpage: Subpage.OPTIONS};
+      var id = search.get('errors');

[michaelpg, 2017/04/14 20:23:53]

remove "var"

[Devlin, 2017/04/17 23:29:24]

Done.

+      if (id)
+        return {page: Page.ERRORS, id: id};
+
+      if (location.pathname == '/shortcuts')
+        return {page: Page.SHORTCUTS};
+
+      return {page: Page.LIST};
+    },
+
+    /**
+     * Called when a page changes, and pushes state to history to reflect it.
+     * @param {!PageEntry} entry
+     */
+    onPageChange: function(entry) {
+      var relative;
+      switch (entry.page) {
+        case Page.LIST:
+          relative = '/';
+          break;
+        case Page.DETAILS:
+          if (entry.subpage) {
+            assert(entry.subpage == Subpage.OPTIONS);
+            relative = '/?options=' + entry.id;
+          } else {
+            relative = '/?id=' + entry.id;
+          }
+          break;
+        case Page.SHORTCUTS:
+          relative = '/shortcuts';
+          break;
+        case Page.ERRORS:
+          relative = '/?errors=' + entry.id;
+      }
+      if (relative) {
+        var state = {url: relative};
+        var currentPage = this.getCurrentPage();
+        var isSubpageNavigation =
+            currentPage.page == entry.page &&
+            currentPage.id == entry.id;
+        // Navigating to a subpage doesn't visually change pages; it just opens
+        // a dialog. As such, we replace state rather than pushing a new state
+        // on the stack so that hitting the back button doesn't just toggle the
+        // dialog.
+        if (isSubpageNavigation)
+          history.replaceState(state, '', relative);
+        else
+          history.pushState(state, '', relative);
+
+      }
+    },
+  };
+
+  return {PageState: PageState};
+});