change_reorder_buffer.h

// Copyright (c) 2012 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 SYNC_INTERNAL_API_CHANGE_REORDER_BUFFER_H_
#define SYNC_INTERNAL_API_CHANGE_REORDER_BUFFER_H_

#include <map>
#include <vector>

#include "base/compiler_specific.h"
#include "base/memory/linked_ptr.h"
#include "sync/internal_api/public/change_record.h"
#include "sync/protocol/sync.pb.h"

namespace syncer {

class BaseTransaction;

// ChangeReorderBuffer is a utility type which accepts an unordered set
// of changes (via its Push methods), and yields an ImmutableChangeRecordList
// (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.
//
// The sibling order is not necessarily preserved.
class ChangeReorderBuffer {
 public:
  ChangeReorderBuffer();
  ~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);

  // 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);

  // 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.
  void PushUpdatedItem(int64 id);

  void SetExtraDataForId(int64 id, ExtraPasswordChangeRecordData* extra);

  void SetSpecificsForId(int64 id, const sync_pb::EntitySpecifics& specifics);

  // Reset the buffer, forgetting any pushed items, so that it can be used again
  // to reorder a new set of changes.
  void Clear();

  bool IsEmpty() const;

  // Output a reordered list of changes to |changes| using the items
  // that were pushed into the reorder buffer. |sync_trans| is used to
  // determine the ordering.  Returns true if successful, or false if
  // an error was encountered.
  bool GetAllChangesInTreeOrder(
      const BaseTransaction* sync_trans,
      ImmutableChangeRecordList* changes) WARN_UNUSED_RESULT;

 private:
  class Traversal;
  typedef std::map<int64, ChangeRecord::Action> OperationMap;
  typedef std::map<int64, sync_pb::EntitySpecifics> SpecificsMap;
  typedef std::map<int64, linked_ptr<ExtraPasswordChangeRecordData> >
      ExtraDataMap;

  // Stores the items that have been pushed into the buffer, and the type of
  // operation that was associated with them.
  OperationMap operations_;

  // Stores entity-specific ChangeRecord data per-ID.
  SpecificsMap specifics_;

  // Stores type-specific extra data per-ID.
  ExtraDataMap extra_data_;

  DISALLOW_COPY_AND_ASSIGN(ChangeReorderBuffer);
};

}  // namespace syncer

#endif  // SYNC_INTERNAL_API_CHANGE_REORDER_BUFFER_H_