Separate the NTP app ordering from the app list app ordering

chrome/browser/ui/app_list/app_list_extension_sorting.h

Index: chrome/browser/ui/app_list/app_list_extension_sorting.h
diff --git a/chrome/browser/ui/app_list/app_list_extension_sorting.h b/chrome/browser/ui/app_list/app_list_extension_sorting.h
new file mode 100644
index 0000000000000000000000000000000000000000..55a85b7e0551f7aee870084c56c0fde052b11e01
--- /dev/null
+++ b/chrome/browser/ui/app_list/app_list_extension_sorting.h
@@ -0,0 +1,109 @@
+// Copyright (c) 2013 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_APP_LIST_APP_LIST_EXTENSION_SORTING_H_
+#define CHROME_BROWSER_UI_APP_LIST_APP_LIST_EXTENSION_SORTING_H_
+
+#include <map>
+#include <set>
+#include <string>
+
+#include "chrome/common/extensions/extension.h"
+#include "sync/api/string_ordinal.h"
+
+class ExtensionScopedPrefs;
+class ExtensionServiceInterface;
+class PrefService;
+
+// The order of apps in the app list. This class defines the order by assigning
+// each app a single string ordinal. This class works on an in-memory map of
+// ordinals which it uses to resolve conflicts generated by sync and which it
+// commits to prefs for persistence. The information represented in the in-
+// memory map and prefs should always match once Initialize() is called.
+class AppListExtensionSorting {
+ public:
+  explicit AppListExtensionSorting(
+      ExtensionScopedPrefs* extension_scoped_prefs);
+  ~AppListExtensionSorting();
+  // Set the ExtensionService to syncs order changes.
+  void SetExtensionService(ExtensionServiceInterface* extension_service);
+
+  // Initialize internal data structures that require |extension_ids|. After
+  // this is called, the prefs and our internal data structures should always
+  // reflect the same data.

[koz (OOO until 15th September), 2013/07/08 01:02:24]

Could you elaborate more on what |extension_ids| is supposed to contain? From
the code it seems that it will always include the default apps on CROS, but
never the WebStore and Chrome apps on other platforms. (Is that right?)

[calamity, 2013/07/11 03:31:00]

It has all installed apps but I think component apps are loaded elsewhere.

[koz (OOO until 15th September), 2013/07/12 00:46:29]

I meant to elaborate in the comment :-) The correctness of this code depends on
exactly what |extension_ids| are expected here.

[calamity, 2013/07/15 07:02:32]

Done.

+  void Initialize(const extensions::ExtensionIdList& extension_ids);
+
+  syncer::StringOrdinal GetAppListOrdinalFromPrefs(
+      const std::string& extension_id);
+
+  // Processes extensions sync data by setting the ordinal for the given
+  // |extension_id| as |ordinal|. This can result in ordinal collisions so
+  // FixSyncCollisions() should be called after all extensions are synced.
+  // There should not be an existing ordinal for |extension_id|.
+  void UpdateAppListOrdinalFromSync(const std::string& extension_id,
+                                const syncer::StringOrdinal& ordinal);
+
+  // Resolves any conflicts that might be created as a result result of calls to
+  // SetAppListOrdinalForSync() that results in two extensions having the same
+  // position in the order. After this is called, it is guaranteed that there
+  // will be no collisions.
+  void FixSyncCollisions();
+
+  // Add an extension so that it precedes all other extensions in the order.
+  void InsertAtFront(const std::string& extension_id);
+
+  // Add an extension so that all other extensions precede it in the order.
+  void InsertAtBack(const std::string& extension_id);
+
+  // Updates the moved extension in the order so that it is now located after
+  // the given predecessor and before the successor. Empty strings are used to
+  // indicate no successor or predecessor.
+  void OnExtensionMoved(const std::string& moved_extension_id,
+                        const std::string& predecessor_extension_id,
+                        const std::string& successor_extension_id);
+
+  // Removes an app from the order. Does nothing if |extension_id| is not in
+  // the order.
+  void Erase(const std::string& extension_id);
+
+  // Returns true if |extension1| appears before |extension2| in the order.
+  bool ExtensionPrecedes(const std::string& extension_id1,
+                         const std::string& extension_id2);
+
+  // Returns true if |extension_id| is in the order.
+  bool Contains(const std::string& extension_id);
+
+ private:
+  typedef std::set<std::string> ExtensionIdSet;
+  typedef std::map<syncer::StringOrdinal, ExtensionIdSet,
+      syncer::StringOrdinal::LessThanFn> AppListOrdinalMap;
+
+  // Sets the ordinal for the extension to the ordinal found in prefs. Adds the
+  // extension id to |uninitialized_extensions| if no ordinal is found in the
+  // prefs.
+  void InitializeOrdinalForExtension(
+      const std::string extension_id,
+      std::vector<std::string>& uninitialized_extensions);

[koz (OOO until 15th September), 2013/07/08 01:02:24]

nit: newline after this line

[calamity, 2013/07/11 03:31:00]

Done.

+  // Sets the ordinal for any extension in |uninitialized_extensions| which has
+  // a default order defined.
+  void InitializeWithDefaultOrdinals(
+    const std::vector<std::string>& uninitialized_extensions);
+
+  void SetAppListOrdinal(const std::string& extension_id,
+                         const syncer::StringOrdinal& ordinal);
+  void EraseAppListOrdinal(const std::string& extension_id);
+  void UpdatePrefs(const std::string& extension_id,
+                   const syncer::StringOrdinal& ordinal);
+  void UpdatePrefsAndSync(const std::string& extension_id,
+                   const syncer::StringOrdinal& ordinal);
+
+  extensions::ExtensionIdList default_initialized_extensions_;
+  AppListOrdinalMap app_list_ordinal_map_;
+  ExtensionScopedPrefs* extension_scoped_prefs_;  // Weak, owns this instance.
+  ExtensionServiceInterface* extension_service_;  // Weak.
+
+  DISALLOW_COPY_AND_ASSIGN(AppListExtensionSorting);
+};
+
+#endif  // CHROME_BROWSER_UI_APP_LIST_APP_LIST_EXTENSION_SORTING_H_