MD Downloads: track downloads in C++, dispatch discrete JS updates

chrome/browser/ui/webui/md_downloads/downloads_list_tracker.h

+// Copyright 2015 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.
+
+#ifndef CHROME_BROWSER_UI_WEBUI_MD_DOWNLOADS_DOWNLOADS_LIST_TRACKER_H_
+#define CHROME_BROWSER_UI_WEBUI_MD_DOWNLOADS_DOWNLOADS_LIST_TRACKER_H_
+
+#include <set>
+
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/time/time.h"
+#include "base/values.h"
+#include "chrome/browser/download/all_download_item_notifier.h"
+#include "content/public/browser/download_item.h"
+
+namespace content {
+class DownloadManager;
+class WebUI;
+}
+
+// A class that tracks all downloads activity and keeps a sorted representation
+// of the downloads as chrome://downloads wants to display them.
+class DownloadsListTracker : public AllDownloadItemNotifier::Observer {
+ public:
+  DownloadsListTracker(content::DownloadManager* download_manager,
+                       content::WebUI* web_ui);
+  ~DownloadsListTracker() override;
+
+  // Clears all downloads on the page (if it's ready).
+  void CallClearAll();
+
+  // Shows only downloads that match |search_terms|. nullptr or an empty list
+  // shows all downloads. Returns whether this class' search terms changed.
+  bool SetSearchTerms(const base::ListValue& search_terms);
+
+  // Sends a chunk of downloads and enables updates.
+  void Start();
+
+  // Stops sending updates to the page.
+  void Stop();
+
+  content::DownloadManager* GetMainNotifierManager() const;
+  content::DownloadManager* GetOriginalNotifierManager() const;
+
+  // AllDownloadItemNotifier::Observer:
+  void OnDownloadCreated(content::DownloadManager* manager,
+                         content::DownloadItem* download_item) override;
+  void OnDownloadUpdated(content::DownloadManager* manager,
+                         content::DownloadItem* download_item) override;
+  void OnDownloadRemoved(content::DownloadManager* manager,
+                         content::DownloadItem* download_item) override;
+
+ protected:
+  // Testing constructor.
+  DownloadsListTracker(content::DownloadManager* download_manager,
+                       content::WebUI* web_ui,
+                       base::Callback<bool(const content::DownloadItem&)>);
+
+  // Creates a dictionary value that's sent to the page as JSON.
+  virtual scoped_ptr<base::DictionaryValue> CreateDownloadItemValue(
+      content::DownloadItem* item) const;
+
+  content::DownloadItem* GetItemForTesting(size_t index);
+
+ private:
+  struct StartTimeComparator {
+    bool operator() (const content::DownloadItem* a,
+                     const content::DownloadItem* b) const;
+  };
+  using SortedSet = std::set<content::DownloadItem*, StartTimeComparator>;
+
+  // Called by both constructors to initialize common state.
+  void Init();
+
+  // Clears and re-inserts all visible items in a sorted order into
+  // |sorted_visible_items_|.
+  void RebuildSortedSet();
+
+  // Whether |item| should show on the current page.
+  bool ShouldShow(const content::DownloadItem& item) const;
+
+  // Gets a page index for |position| from |sorted_visible_items_|.
+  int GetIndex(const SortedSet::iterator& position) const;
+
+  // Inserts an item into |sorted_visible_items_| and calls "insertItems" if
+  // |sending_updates_|.
+  void InsertItem(const SortedSet::iterator& insert);
+
+  // Inserts from |start| to |end| into |sorted_visible_items_| and notifies the
+  // page if |sending_updates_|.
+  void InsertItems(const SortedSet::iterator& start,
+                   const SortedSet::iterator& end);
+
+  // Calls "updateItem" if |sending_updates_|.
+  void CallUpdateItem(const SortedSet::iterator& update);
+
+  // Removes the item that corresponds to |remove| and sends a "removeItems"
+  // message to the page if |sending_updates_|. May modify |current_offset_|.
+  void RemoveItem(const SortedSet::iterator& remove);
+
+  AllDownloadItemNotifier main_notifier_;
+  scoped_ptr<AllDownloadItemNotifier> original_notifier_;
+
+  // The WebUI object corresponding to the page we care about.
+  content::WebUI* const web_ui_;
+
+  // Callback used to determine if an item should show on the page. Set to
+  // |ShouldShow()| in default constructor, passed in while testing.
+  base::Callback<bool(const content::DownloadItem&)> should_show_;
+
+  // When this is true, all changes to downloads that affect the page are send
+  // via JavaScript.
+  bool sending_updates_ = false;
+
+  SortedSet sorted_visible_items_;
+
+  // Current search terms.
+  base::ListValue search_terms_;
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadsListTracker);
+};
+
+#endif  // CHROME_BROWSER_UI_WEBUI_MD_DOWNLOADS_DOWNLOADS_LIST_TRACKER_H_