Initial commit of sync engine code to browser/sync....

chrome/browser/sync/engine/change_reorder_buffer.h

+// Copyright (c) 2006-2009 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.
+//
+// Defines ChangeReorderBuffer, which can be used to sort a list of item
+// actions to achieve the ordering constraint required by the SyncObserver
+// interface of the SyncAPI.
+
+#ifndef CHROME_BROWSER_SYNC_ENGINE_CHANGE_REORDER_BUFFER_H_
+#define CHROME_BROWSER_SYNC_ENGINE_CHANGE_REORDER_BUFFER_H_
+
+#include <map>
+#include <vector>
+
+#include "chrome/browser/sync/engine/syncapi.h"
+
+namespace sync_api {
+
+// ChangeReorderBuffer is a utility type which accepts an unordered set
+// of changes (via its Push methods), and yields a vector of ChangeRecords
+// (via the GetAllChangesInTreeOrder method) that are in the order that
+// the SyncObserver expects them to be. A buffer is initially empty.
+//
+// The ordering produced by ChangeReorderBuffer is as follows:
+//  (a) All Deleted items appear first.
+//  (b) For Updated and/or Added items, parents appear before their children.
+//  (c) When there are changes to the sibling order (this means Added items,
+//      or Updated items with the |position_changed| parameter set to true),
+//      all siblings under a parent will appear in the output, even if they
+//      are not explicitly pushed.  The sibling order will be preserved in
+//      the output list -- items will appear before their sibling-order
+//      successors.
+//  (d) When there are no changes to the sibling order under a parent node,
+//      the sibling order is not necessarily preserved in the output for
+//      its children.
+class ChangeReorderBuffer {
+ public:
+  typedef SyncManager::ChangeRecord ChangeRecord;
+  ChangeReorderBuffer() { }
+
+  // Insert an item, identified by the metahandle |id|, into the reorder
+  // buffer. This item will appear in the output list as an ACTION_ADD
+  // ChangeRecord.
+  void PushAddedItem(int64 id) {
+    operations_[id] = OP_ADD;
+  }
+
+  // Insert an item, identified by the metahandle |id|, into the reorder
+  // buffer. This item will appear in the output list as an ACTION_DELETE
+  // ChangeRecord.
+  void PushDeletedItem(int64 id) {
+    operations_[id] = OP_DELETE;
+  }
+
+  // Insert an item, identified by the metahandle |id|, into the reorder
+  // buffer. This item will appear in the output list as an ACTION_UPDATE
+  // ChangeRecord. Also, if |position_changed| is true, all siblings of this
+  // item will appear in the output list as well; if it wasn't explicitly
+  // pushed, the siblings will have an ACTION_UPDATE ChangeRecord.
+  void PushUpdatedItem(int64 id, bool position_changed) {
+    operations_[id] = position_changed ? OP_UPDATE_POSITION_AND_PROPERTIES :
+                                         OP_UPDATE_PROPERTIES_ONLY;
+  }
+
+  // Reset the buffer, forgetting any pushed items, so that it can be used
+  // again to reorder a new set of changes.
+  void Clear() {
+    operations_.clear();
+  }
+
+  bool IsEmpty() const {
+    return operations_.empty();
+  }
+
+  // Output a reordered list of changes to |changelist| using the items
+  // that were pushed into the reorder buffer. |sync_trans| is used
+  // to determine the ordering.
+  void GetAllChangesInTreeOrder(const BaseTransaction* sync_trans,
+                                std::vector<ChangeRecord>* changelist);
+
+ private:
+  class Traversal;
+  enum Operation {
+    OP_ADD,                             // AddedItem.
+    OP_DELETE,                          // DeletedItem.
+    OP_UPDATE_PROPERTIES_ONLY,          // UpdatedItem with position_changed=0.
+    OP_UPDATE_POSITION_AND_PROPERTIES,  // UpdatedItem with position_changed=1.
+  };
+  typedef std::map<int64, Operation> OperationMap;
+
+  // Stores the items that have been pushed into the buffer, and the
+  // type of operation that was associated with them.
+  OperationMap operations_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChangeReorderBuffer);
+};
+
+}  // namespace sync_api
+
+#endif  // CHROME_BROWSER_SYNC_ENGINE_CHANGE_REORDER_BUFFER_H_