// 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.

#include "components/history/core/browser/sync/visit_id_remapper.h"

#include "components/history/core/browser/sync/history_backend_for_sync.h"
#include "components/sync/protocol/history_specifics.pb.h"

namespace history {

VisitIDRemapper::VisitIDRemapper(HistoryBackendForSync* history_backend)
    : history_backend_(history_backend) {
  DCHECK(history_backend_);
}

VisitIDRemapper::~VisitIDRemapper() = default;

void VisitIDRemapper::RegisterVisit(VisitID local_visit_id,
                                    const std::string& originator_cache_guid,
                                    VisitID originator_visit_id,
                                    VisitID originator_referring_visit_id,
                                    VisitID originator_opener_visit_id) {
  DCHECK_NE(local_visit_id, 0);
  DCHECK(!originator_cache_guid.empty());

  // If this visit came from an old client which didn't populate
  // `originator_visit_id`, then we can't remap. (In this case, the
  // `originator_referring|opener_visit_id`s should anyway be empty too.)
  if (originator_visit_id == 0) {
    return;
  }
  visits_[originator_cache_guid].emplace_back(
      originator_visit_id,
      VisitInfo{local_visit_id, originator_referring_visit_id,
                originator_opener_visit_id});
}

void VisitIDRemapper::RemapIDs() {
  // For each originator:
  for (auto& [originator_cache_guid, originator_visit_ids_and_visits] :
       visits_) {
    // Build a lookup table of this originator's visits, indexed by originator
    // visit ID. (Thankfully, they're already stored in the right format to
    // create a flat_map in-place!)
    base::flat_map<VisitID, VisitInfo> visits_by_originator_id(
        std::move(originator_visit_ids_and_visits));
    // For each visit from this originator:
    for (const auto& [originator_visit_id, visit] : visits_by_originator_id) {
      // Find the local referrer/opener IDs (if any).
      VisitID local_referrer_id =
          FindLocalVisitID(originator_cache_guid, visits_by_originator_id,
                           visit.originator_referring_visit_id);
      VisitID local_opener_id =
          FindLocalVisitID(originator_cache_guid, visits_by_originator_id,
                           visit.originator_opener_visit_id);
      // If either of the local IDs were found, write them to the DB.
      if (local_referrer_id != 0 || local_opener_id != 0) {
        history_backend_->UpdateVisitReferrerOpenerIDs(
            visit.local_visit_id, local_referrer_id, local_opener_id);
      }
      // Note: Theoretically, the remapping might need to be done the other way
      // around too - an existing visit's originator_referring|opener_visit_id
      // might link to the just-added visit. In practice, that should be
      // extremely rare though, so don't bother addressing that case here. (See
      // also History.ForeignVisits* histograms.)
    }
  }
  // Data has been moved out of `visits_`, so clear it just for consistency.
  visits_.clear();
}

VisitID VisitIDRemapper::FindLocalVisitID(
    const std::string& originator_cache_guid,
    const base::flat_map<VisitID, VisitInfo>& visits_by_originator_id,
    VisitID originator_visit_id) {
  if (originator_visit_id == 0) {
    return 0;
  }

  // Try to find the matching visit in the in-memory cache.
  auto it = visits_by_originator_id.find(originator_visit_id);
  if (it != visits_by_originator_id.end()) {
    // Found it!
    const VisitInfo& visit = it->second;
    return visit.local_visit_id;
  }

  // Didn't find it in the cache - try the DB instead.
  VisitRow row;
  if (history_backend_->GetForeignVisit(originator_cache_guid,
                                        originator_visit_id, &row)) {
    return row.visit_id;
  }

  // Didn't find it in the DB either.
  return 0;
}

}  // namespace history