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      1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 //
      5 // Defines ChangeReorderBuffer, which can be used to sort a list of item
      6 // actions to achieve the ordering constraint required by the SyncObserver
      7 // interface of the SyncAPI.
      8 
      9 #ifndef CHROME_BROWSER_SYNC_ENGINE_CHANGE_REORDER_BUFFER_H_
     10 #define CHROME_BROWSER_SYNC_ENGINE_CHANGE_REORDER_BUFFER_H_
     11 #pragma once
     12 
     13 #include <map>
     14 #include <vector>
     15 
     16 #include "base/memory/linked_ptr.h"
     17 #include "chrome/browser/sync/engine/syncapi.h"
     18 #include "chrome/browser/sync/protocol/sync.pb.h"
     19 
     20 namespace sync_api {
     21 
     22 // ChangeReorderBuffer is a utility type which accepts an unordered set
     23 // of changes (via its Push methods), and yields a vector of ChangeRecords
     24 // (via the GetAllChangesInTreeOrder method) that are in the order that
     25 // the SyncObserver expects them to be. A buffer is initially empty.
     26 //
     27 // The ordering produced by ChangeReorderBuffer is as follows:
     28 //  (a) All Deleted items appear first.
     29 //  (b) For Updated and/or Added items, parents appear before their children.
     30 //  (c) When there are changes to the sibling order (this means Added items,
     31 //      or Updated items with the |position_changed| parameter set to true),
     32 //      all siblings under a parent will appear in the output, even if they
     33 //      are not explicitly pushed.  The sibling order will be preserved in
     34 //      the output list -- items will appear before their sibling-order
     35 //      successors.
     36 //  (d) When there are no changes to the sibling order under a parent node,
     37 //      the sibling order is not necessarily preserved in the output for
     38 //      its children.
     39 class ChangeReorderBuffer {
     40  public:
     41   typedef SyncManager::ChangeRecord ChangeRecord;
     42   typedef SyncManager::ExtraPasswordChangeRecordData ExtraChangeRecordData;
     43 
     44   ChangeReorderBuffer();
     45   ~ChangeReorderBuffer();
     46 
     47   // Insert an item, identified by the metahandle |id|, into the reorder
     48   // buffer. This item will appear in the output list as an ACTION_ADD
     49   // ChangeRecord.
     50   void PushAddedItem(int64 id) {
     51     operations_[id] = OP_ADD;
     52   }
     53 
     54   // Insert an item, identified by the metahandle |id|, into the reorder
     55   // buffer. This item will appear in the output list as an ACTION_DELETE
     56   // ChangeRecord.
     57   void PushDeletedItem(int64 id) {
     58     operations_[id] = OP_DELETE;
     59   }
     60 
     61   // Insert an item, identified by the metahandle |id|, into the reorder
     62   // buffer. This item will appear in the output list as an ACTION_UPDATE
     63   // ChangeRecord. Also, if |position_changed| is true, all siblings of this
     64   // item will appear in the output list as well; if it wasn't explicitly
     65   // pushed, the siblings will have an ACTION_UPDATE ChangeRecord.
     66   void PushUpdatedItem(int64 id, bool position_changed) {
     67     operations_[id] = position_changed ? OP_UPDATE_POSITION_AND_PROPERTIES :
     68                                          OP_UPDATE_PROPERTIES_ONLY;
     69   }
     70 
     71   void SetExtraDataForId(int64 id, ExtraChangeRecordData* extra) {
     72     extra_data_[id] = make_linked_ptr<ExtraChangeRecordData>(extra);
     73   }
     74 
     75   void SetSpecificsForId(int64 id, const sync_pb::EntitySpecifics& specifics) {
     76     specifics_[id] = specifics;
     77   }
     78 
     79   // Reset the buffer, forgetting any pushed items, so that it can be used
     80   // again to reorder a new set of changes.
     81   void Clear() {
     82     operations_.clear();
     83   }
     84 
     85   bool IsEmpty() const {
     86     return operations_.empty();
     87   }
     88 
     89   // Output a reordered list of changes to |changelist| using the items that
     90   // were pushed into the reorder buffer. |sync_trans| is used to determine the
     91   // ordering.
     92   void GetAllChangesInTreeOrder(const BaseTransaction* sync_trans,
     93                                 std::vector<ChangeRecord>* changelist);
     94 
     95  private:
     96   class Traversal;
     97   enum Operation {
     98     OP_ADD,                             // AddedItem.
     99     OP_DELETE,                          // DeletedItem.
    100     OP_UPDATE_PROPERTIES_ONLY,          // UpdatedItem with position_changed=0.
    101     OP_UPDATE_POSITION_AND_PROPERTIES,  // UpdatedItem with position_changed=1.
    102   };
    103   typedef std::map<int64, Operation> OperationMap;
    104   typedef std::map<int64, sync_pb::EntitySpecifics> SpecificsMap;
    105   typedef std::map<int64, linked_ptr<ExtraChangeRecordData> > ExtraDataMap;
    106 
    107   // Stores the items that have been pushed into the buffer, and the type of
    108   // operation that was associated with them.
    109   OperationMap operations_;
    110 
    111   // Stores entity-specific ChangeRecord data per-ID.
    112   SpecificsMap specifics_;
    113 
    114   // Stores type-specific extra data per-ID.
    115   ExtraDataMap extra_data_;
    116 
    117   DISALLOW_COPY_AND_ASSIGN(ChangeReorderBuffer);
    118 };
    119 
    120 }  // namespace sync_api
    121 
    122 #endif  // CHROME_BROWSER_SYNC_ENGINE_CHANGE_REORDER_BUFFER_H_
    123