chromium/components/history/core/browser/sync/visit_id_remapper.h

// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_HISTORY_CORE_BROWSER_SYNC_VISIT_ID_REMAPPER_H_
#define COMPONENTS_HISTORY_CORE_BROWSER_SYNC_VISIT_ID_REMAPPER_H_

#include <map>
#include <string>

#include "base/containers/flat_map.h"
#include "components/history/core/browser/history_types.h"

namespace history {

class HistoryBackendForSync;

// VisitIDs are only unique per-device. Therefore, every visit has two sets of
// IDs: The local ones and the "originator" ones (i.e. the ones assigned on the
// device where the visit originally came from). This means that the incoming
// referring_visit and opener_visit IDs need to be remapped into local IDs so
// that "links" in the visit database work correctly.
// VisitIDRemapper is responsible for this remapping. It collects all visits
// that arrived within one Sync update and populates their referring/opener IDs
// based on the corresponding originator IDs.
// For efficiency, it tries to perform the remapping in-memory first, since most
// commonly the referred-to visits should arrive together. Only if the in-memory
// lookup fails does it query the HistoryBackend.
// Note that originator and local IDs are stored in separate columns in the DB,
// so in case no matching local ID can be found, the corresponding DB column
// will simply remain empty (and might be populated by a later remapping).
class VisitIDRemapper { … };

}  // namespace history

#endif  // COMPONENTS_HISTORY_CORE_BROWSER_SYNC_VISIT_ID_REMAPPER_H_