// Copyright 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.

#include "chrome/browser/sync/glue/bookmark_model_associator.h"

#include <stack>

#include "base/bind.h"
#include "base/command_line.h"
#include "base/containers/hash_tables.h"
#include "base/format_macros.h"
#include "base/location.h"
#include "base/macros.h"
#include "base/message_loop/message_loop.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "base/strings/utf_string_conversions.h"
#include "chrome/browser/profiles/profile.h"
#include "chrome/browser/sync/glue/bookmark_change_processor.h"
#include "chrome/browser/undo/bookmark_undo_service.h"
#include "chrome/browser/undo/bookmark_undo_service_factory.h"
#include "chrome/browser/undo/bookmark_undo_utils.h"
#include "components/bookmarks/browser/bookmark_client.h"
#include "components/bookmarks/browser/bookmark_model.h"
#include "content/public/browser/browser_thread.h"
#include "sync/api/sync_error.h"
#include "sync/internal_api/public/delete_journal.h"
#include "sync/internal_api/public/read_node.h"
#include "sync/internal_api/public/read_transaction.h"
#include "sync/internal_api/public/write_node.h"
#include "sync/internal_api/public/write_transaction.h"
#include "sync/internal_api/syncapi_internal.h"
#include "sync/syncable/syncable_write_transaction.h"
#include "sync/util/cryptographer.h"
#include "sync/util/data_type_histogram.h"

using content::BrowserThread;

namespace browser_sync {

// The sync protocol identifies top-level entities by means of well-known tags,
// which should not be confused with titles.  Each tag corresponds to a
// singleton instance of a particular top-level node in a user's share; the
// tags are consistent across users. The tags allow us to locate the specific
// folders whose contents we care about synchronizing, without having to do a
// lookup by name or path.  The tags should not be made user-visible.
// For example, the tag "bookmark_bar" represents the permanent node for
// bookmarks bar in Chrome. The tag "other_bookmarks" represents the permanent
// folder Other Bookmarks in Chrome.
//
// It is the responsibility of something upstream (at time of writing,
// the sync server) to create these tagged nodes when initializing sync
// for the first time for a user.  Thus, once the backend finishes
// initializing, the ProfileSyncService can rely on the presence of tagged
// nodes.
//
// TODO(ncarter): Pull these tags from an external protocol specification
// rather than hardcoding them here.
const char kBookmarkBarTag[] = "bookmark_bar";
const char kMobileBookmarksTag[] = "synced_bookmarks";
const char kOtherBookmarksTag[] = "other_bookmarks";

// Maximum number of bytes to allow in a title (must match sync's internal
// limits; see write_node.cc).
const int kTitleLimitBytes = 255;

// Bookmark comparer for map of bookmark nodes.
class BookmarkComparer {
 public:
  // Compares the two given nodes and returns whether node1 should appear
  // before node2 in strict weak ordering.
  bool operator()(const BookmarkNode* node1,
                  const BookmarkNode* node2) const {
    DCHECK(node1);
    DCHECK(node2);

    // Keep folder nodes before non-folder nodes.
    if (node1->is_folder() != node2->is_folder())
      return node1->is_folder();

    // Truncate bookmark titles in the form sync does internally to avoid
    // mismatches due to sync munging titles.
    std::string title1 = base::UTF16ToUTF8(node1->GetTitle());
    syncer::SyncAPINameToServerName(title1, &title1);
    base::TruncateUTF8ToByteSize(title1, kTitleLimitBytes, &title1);

    std::string title2 = base::UTF16ToUTF8(node2->GetTitle());
    syncer::SyncAPINameToServerName(title2, &title2);
    base::TruncateUTF8ToByteSize(title2, kTitleLimitBytes, &title2);

    int result = title1.compare(title2);
    if (result != 0)
      return result < 0;

    return node1->url() < node2->url();
  }
};

// Provides the following abstraction: given a parent bookmark node, find best
// matching child node for many sync nodes.
class BookmarkNodeFinder {
 public:
  // Creates an instance with the given parent bookmark node.
  explicit BookmarkNodeFinder(const BookmarkNode* parent_node);

  // Finds the bookmark node that matches the given url, title and folder
  // attribute. Returns the matching node if one exists; NULL otherwise. If a
  // matching node is found, it's removed for further matches.
  const BookmarkNode* FindBookmarkNode(const GURL& url,
                                       const std::string& title,
                                       bool is_folder);

 private:
  typedef std::multiset<const BookmarkNode*, BookmarkComparer> BookmarkNodesSet;

  const BookmarkNode* parent_node_;
  BookmarkNodesSet child_nodes_;

  DISALLOW_COPY_AND_ASSIGN(BookmarkNodeFinder);
};

class ScopedAssociationUpdater {
 public:
  explicit ScopedAssociationUpdater(BookmarkModel* model) {
    model_ = model;
    model->BeginExtensiveChanges();
  }

  ~ScopedAssociationUpdater() {
    model_->EndExtensiveChanges();
  }

 private:
  BookmarkModel* model_;

  DISALLOW_COPY_AND_ASSIGN(ScopedAssociationUpdater);
};

BookmarkNodeFinder::BookmarkNodeFinder(const BookmarkNode* parent_node)
    : parent_node_(parent_node) {
  for (int i = 0; i < parent_node_->child_count(); ++i) {
    child_nodes_.insert(parent_node_->GetChild(i));
  }
}

const BookmarkNode* BookmarkNodeFinder::FindBookmarkNode(
    const GURL& url, const std::string& title, bool is_folder) {
  // Create a bookmark node from the given bookmark attributes.
  BookmarkNode temp_node(url);
  temp_node.SetTitle(base::UTF8ToUTF16(title));
  if (is_folder)
    temp_node.set_type(BookmarkNode::FOLDER);
  else
    temp_node.set_type(BookmarkNode::URL);

  const BookmarkNode* result = NULL;
  BookmarkNodesSet::iterator iter = child_nodes_.find(&temp_node);
  if (iter != child_nodes_.end()) {
    result = *iter;
    // Remove the matched node so we don't match with it again.
    child_nodes_.erase(iter);
  }

  return result;
}

// Helper class to build an index of bookmark nodes by their IDs.
class BookmarkNodeIdIndex {
 public:
  BookmarkNodeIdIndex() { }
  ~BookmarkNodeIdIndex() { }

  // Adds the given bookmark node and all its descendants to the ID index.
  // Does nothing if node is NULL.
  void AddAll(const BookmarkNode* node);

  // Finds the bookmark node with the given ID.
  // Returns NULL if none exists with the given id.
  const BookmarkNode* Find(int64 id) const;

  // Returns the count of nodes in the index.
  size_t count() const { return node_index_.size(); }

 private:
  typedef base::hash_map<int64, const BookmarkNode*> BookmarkIdMap;
  // Map that holds nodes indexed by their ids.
  BookmarkIdMap node_index_;

  DISALLOW_COPY_AND_ASSIGN(BookmarkNodeIdIndex);
};

void BookmarkNodeIdIndex::AddAll(const BookmarkNode* node) {
  if (!node)
    return;

  node_index_[node->id()] = node;

  if (!node->is_folder())
    return;

  for (int i = 0; i < node->child_count(); ++i)
    AddAll(node->GetChild(i));
}

const BookmarkNode* BookmarkNodeIdIndex::Find(int64 id) const {
  BookmarkIdMap::const_iterator iter = node_index_.find(id);
  return iter == node_index_.end() ? NULL : iter->second;
}

BookmarkModelAssociator::BookmarkModelAssociator(
    BookmarkModel* bookmark_model,
    Profile* profile,
    syncer::UserShare* user_share,
    DataTypeErrorHandler* unrecoverable_error_handler,
    bool expect_mobile_bookmarks_folder)
    : bookmark_model_(bookmark_model),
      profile_(profile),
      user_share_(user_share),
      unrecoverable_error_handler_(unrecoverable_error_handler),
      expect_mobile_bookmarks_folder_(expect_mobile_bookmarks_folder),
      weak_factory_(this) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  DCHECK(bookmark_model_);
  DCHECK(user_share_);
  DCHECK(unrecoverable_error_handler_);
}

BookmarkModelAssociator::~BookmarkModelAssociator() {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
}

void BookmarkModelAssociator::UpdatePermanentNodeVisibility() {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  DCHECK(bookmark_model_->loaded());

  BookmarkNode::Type bookmark_node_types[] = {
    BookmarkNode::BOOKMARK_BAR,
    BookmarkNode::OTHER_NODE,
    BookmarkNode::MOBILE,
  };
  for (size_t i = 0; i < arraysize(bookmark_node_types); ++i) {
    int64 id = bookmark_model_->PermanentNode(bookmark_node_types[i])->id();
    bookmark_model_->SetPermanentNodeVisible(
      bookmark_node_types[i],
      id_map_.find(id) != id_map_.end());
  }

  // Note: the root node may have additional extra nodes. Currently their
  // visibility is not affected by sync.
}

syncer::SyncError BookmarkModelAssociator::DisassociateModels() {
  id_map_.clear();
  id_map_inverse_.clear();
  dirty_associations_sync_ids_.clear();
  return syncer::SyncError();
}

int64 BookmarkModelAssociator::GetSyncIdFromChromeId(const int64& node_id) {
  BookmarkIdToSyncIdMap::const_iterator iter = id_map_.find(node_id);
  return iter == id_map_.end() ? syncer::kInvalidId : iter->second;
}

const BookmarkNode* BookmarkModelAssociator::GetChromeNodeFromSyncId(
    int64 sync_id) {
  SyncIdToBookmarkNodeMap::const_iterator iter = id_map_inverse_.find(sync_id);
  return iter == id_map_inverse_.end() ? NULL : iter->second;
}

bool BookmarkModelAssociator::InitSyncNodeFromChromeId(
    const int64& node_id,
    syncer::BaseNode* sync_node) {
  DCHECK(sync_node);
  int64 sync_id = GetSyncIdFromChromeId(node_id);
  if (sync_id == syncer::kInvalidId)
    return false;
  if (sync_node->InitByIdLookup(sync_id) != syncer::BaseNode::INIT_OK)
    return false;
  DCHECK(sync_node->GetId() == sync_id);
  return true;
}

void BookmarkModelAssociator::Associate(const BookmarkNode* node,
                                        int64 sync_id) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  int64 node_id = node->id();
  DCHECK_NE(sync_id, syncer::kInvalidId);
  DCHECK(id_map_.find(node_id) == id_map_.end());
  DCHECK(id_map_inverse_.find(sync_id) == id_map_inverse_.end());
  id_map_[node_id] = sync_id;
  id_map_inverse_[sync_id] = node;
  dirty_associations_sync_ids_.insert(sync_id);
  PostPersistAssociationsTask();
  UpdatePermanentNodeVisibility();
}

void BookmarkModelAssociator::Disassociate(int64 sync_id) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  SyncIdToBookmarkNodeMap::iterator iter = id_map_inverse_.find(sync_id);
  if (iter == id_map_inverse_.end())
    return;
  id_map_.erase(iter->second->id());
  id_map_inverse_.erase(iter);
  dirty_associations_sync_ids_.erase(sync_id);
}

bool BookmarkModelAssociator::SyncModelHasUserCreatedNodes(bool* has_nodes) {
  DCHECK(has_nodes);
  *has_nodes = false;
  bool has_mobile_folder = true;
  int64 bookmark_bar_sync_id;
  if (!GetSyncIdForTaggedNode(kBookmarkBarTag, &bookmark_bar_sync_id)) {
    return false;
  }
  int64 other_bookmarks_sync_id;
  if (!GetSyncIdForTaggedNode(kOtherBookmarksTag, &other_bookmarks_sync_id)) {
    return false;
  }
  int64 mobile_bookmarks_sync_id;
  if (!GetSyncIdForTaggedNode(kMobileBookmarksTag, &mobile_bookmarks_sync_id)) {
    has_mobile_folder = false;
  }

  syncer::ReadTransaction trans(FROM_HERE, user_share_);

  syncer::ReadNode bookmark_bar_node(&trans);
  if (bookmark_bar_node.InitByIdLookup(bookmark_bar_sync_id) !=
          syncer::BaseNode::INIT_OK) {
    return false;
  }

  syncer::ReadNode other_bookmarks_node(&trans);
  if (other_bookmarks_node.InitByIdLookup(other_bookmarks_sync_id) !=
          syncer::BaseNode::INIT_OK) {
    return false;
  }

  syncer::ReadNode mobile_bookmarks_node(&trans);
  if (has_mobile_folder &&
      mobile_bookmarks_node.InitByIdLookup(mobile_bookmarks_sync_id) !=
          syncer::BaseNode::INIT_OK) {
    return false;
  }

  // Sync model has user created nodes if any of the permanent nodes has
  // children.
  *has_nodes = bookmark_bar_node.HasChildren() ||
      other_bookmarks_node.HasChildren() ||
      (has_mobile_folder && mobile_bookmarks_node.HasChildren());
  return true;
}

bool BookmarkModelAssociator::NodesMatch(
    const BookmarkNode* bookmark,
    const syncer::BaseNode* sync_node) const {
  std::string truncated_title = base::UTF16ToUTF8(bookmark->GetTitle());
  base::TruncateUTF8ToByteSize(truncated_title,
                               kTitleLimitBytes,
                               &truncated_title);
  if (truncated_title != sync_node->GetTitle())
    return false;
  if (bookmark->is_folder() != sync_node->GetIsFolder())
    return false;
  if (bookmark->is_url()) {
    if (bookmark->url() != GURL(sync_node->GetBookmarkSpecifics().url()))
      return false;
  }
  // Don't compare favicons here, because they are not really
  // user-updated and we don't have versioning information -- a site changing
  // its favicon shouldn't result in a bookmark mismatch.
  return true;
}

bool BookmarkModelAssociator::AssociateTaggedPermanentNode(
    const BookmarkNode* permanent_node, const std::string&tag) {
  // Do nothing if |permanent_node| is already initialized and associated.
  int64 sync_id = GetSyncIdFromChromeId(permanent_node->id());
  if (sync_id != syncer::kInvalidId)
    return true;
  if (!GetSyncIdForTaggedNode(tag, &sync_id))
    return false;

  Associate(permanent_node, sync_id);
  return true;
}

bool BookmarkModelAssociator::GetSyncIdForTaggedNode(const std::string& tag,
                                                     int64* sync_id) {
  syncer::ReadTransaction trans(FROM_HERE, user_share_);
  syncer::ReadNode sync_node(&trans);
  if (sync_node.InitByTagLookupForBookmarks(
      tag.c_str()) != syncer::BaseNode::INIT_OK)
    return false;
  *sync_id = sync_node.GetId();
  return true;
}

syncer::SyncError BookmarkModelAssociator::AssociateModels(
    syncer::SyncMergeResult* local_merge_result,
    syncer::SyncMergeResult* syncer_merge_result) {
  // Since any changes to the bookmark model made here are not user initiated,
  // these change should not be undoable and so suspend the undo tracking.
#if !defined(OS_ANDROID)
  ScopedSuspendBookmarkUndo suspend_undo(profile_);
#endif
  syncer::SyncError error = CheckModelSyncState(local_merge_result,
                                                syncer_merge_result);
  if (error.IsSet())
    return error;

  scoped_ptr<ScopedAssociationUpdater> association_updater(
      new ScopedAssociationUpdater(bookmark_model_));
  DisassociateModels();

  return BuildAssociations(local_merge_result, syncer_merge_result);
}

syncer::SyncError BookmarkModelAssociator::BuildAssociations(
    syncer::SyncMergeResult* local_merge_result,
    syncer::SyncMergeResult* syncer_merge_result) {
  // Algorithm description:
  // Match up the roots and recursively do the following:
  // * For each sync node for the current sync parent node, find the best
  //   matching bookmark node under the corresponding bookmark parent node.
  //   If no matching node is found, create a new bookmark node in the same
  //   position as the corresponding sync node.
  //   If a matching node is found, update the properties of it from the
  //   corresponding sync node.
  // * When all children sync nodes are done, add the extra children bookmark
  //   nodes to the sync parent node.
  //
  // This algorithm will do a good job of merging when folder names are a good
  // indicator of the two folders being the same. It will handle reordering and
  // new node addition very well (without creating duplicates).
  // This algorithm will not do well if the folder name has changes but the
  // children under them are all the same.

  DCHECK(bookmark_model_->loaded());

  // To prime our association, we associate the top-level nodes, Bookmark Bar
  // and Other Bookmarks.
  if (!AssociateTaggedPermanentNode(bookmark_model_->bookmark_bar_node(),
                                    kBookmarkBarTag)) {
    return unrecoverable_error_handler_->CreateAndUploadError(
        FROM_HERE,
        "Bookmark bar node not found",
        model_type());
  }

  if (!AssociateTaggedPermanentNode(bookmark_model_->other_node(),
                                    kOtherBookmarksTag)) {
    return unrecoverable_error_handler_->CreateAndUploadError(
        FROM_HERE,
        "Other bookmarks node not found",
        model_type());
  }

  if (!AssociateTaggedPermanentNode(bookmark_model_->mobile_node(),
                                    kMobileBookmarksTag) &&
      expect_mobile_bookmarks_folder_) {
    return unrecoverable_error_handler_->CreateAndUploadError(
        FROM_HERE,
        "Mobile bookmarks node not found",
        model_type());
  }

  // Note: the root node may have additional extra nodes. Currently none of
  // them are meant to sync.

  int64 bookmark_bar_sync_id = GetSyncIdFromChromeId(
      bookmark_model_->bookmark_bar_node()->id());
  DCHECK_NE(bookmark_bar_sync_id, syncer::kInvalidId);
  int64 other_bookmarks_sync_id = GetSyncIdFromChromeId(
      bookmark_model_->other_node()->id());
  DCHECK_NE(other_bookmarks_sync_id, syncer::kInvalidId);
  int64 mobile_bookmarks_sync_id = GetSyncIdFromChromeId(
       bookmark_model_->mobile_node()->id());
  if (expect_mobile_bookmarks_folder_) {
    DCHECK_NE(syncer::kInvalidId, mobile_bookmarks_sync_id);
  }

  // WARNING: The order in which we push these should match their order in the
  // bookmark model (see BookmarkModel::DoneLoading(..)).
  std::stack<int64> dfs_stack;
  dfs_stack.push(bookmark_bar_sync_id);
  dfs_stack.push(other_bookmarks_sync_id);
  if (mobile_bookmarks_sync_id != syncer::kInvalidId)
    dfs_stack.push(mobile_bookmarks_sync_id);

  syncer::WriteTransaction trans(FROM_HERE, user_share_);
  syncer::ReadNode bm_root(&trans);
  if (bm_root.InitTypeRoot(syncer::BOOKMARKS) == syncer::BaseNode::INIT_OK) {
    syncer_merge_result->set_num_items_before_association(
        bm_root.GetTotalNodeCount());
  }
  local_merge_result->set_num_items_before_association(
      bookmark_model_->root_node()->GetTotalNodeCount());

  // Remove obsolete bookmarks according to sync delete journal.
  local_merge_result->set_num_items_deleted(
      ApplyDeletesFromSyncJournal(&trans));

  while (!dfs_stack.empty()) {
    int64 sync_parent_id = dfs_stack.top();
    dfs_stack.pop();

    syncer::ReadNode sync_parent(&trans);
    if (sync_parent.InitByIdLookup(sync_parent_id) !=
            syncer::BaseNode::INIT_OK) {
      return unrecoverable_error_handler_->CreateAndUploadError(
          FROM_HERE,
          "Failed to lookup node.",
          model_type());
    }
    // Only folder nodes are pushed on to the stack.
    DCHECK(sync_parent.GetIsFolder());

    const BookmarkNode* parent_node = GetChromeNodeFromSyncId(sync_parent_id);
    DCHECK(parent_node->is_folder());

    BookmarkNodeFinder node_finder(parent_node);

    std::vector<int64> children;
    sync_parent.GetChildIds(&children);
    int index = 0;
    for (std::vector<int64>::const_iterator it = children.begin();
         it != children.end(); ++it) {
      int64 sync_child_id = *it;
      syncer::ReadNode sync_child_node(&trans);
      if (sync_child_node.InitByIdLookup(sync_child_id) !=
              syncer::BaseNode::INIT_OK) {
        return unrecoverable_error_handler_->CreateAndUploadError(
            FROM_HERE,
            "Failed to lookup node.",
            model_type());
      }

      const BookmarkNode* child_node = NULL;
      child_node = node_finder.FindBookmarkNode(
          GURL(sync_child_node.GetBookmarkSpecifics().url()),
          sync_child_node.GetTitle(),
          sync_child_node.GetIsFolder());
      if (child_node) {
        Associate(child_node, sync_child_id);

        // All bookmarks are currently modified at association time, even if
        // nothing has changed.
        // TODO(sync): Only modify the bookmark model if necessary.
        BookmarkChangeProcessor::UpdateBookmarkWithSyncData(
            sync_child_node, bookmark_model_, child_node, profile_);
        bookmark_model_->Move(child_node, parent_node, index);
        local_merge_result->set_num_items_modified(
            local_merge_result->num_items_modified() + 1);
      } else {
        child_node = BookmarkChangeProcessor::CreateBookmarkNode(
            &sync_child_node, parent_node, bookmark_model_, profile_, index);
        if (child_node)
          Associate(child_node, sync_child_id);
        local_merge_result->set_num_items_added(
            local_merge_result->num_items_added() + 1);
      }
      if (sync_child_node.GetIsFolder())
        dfs_stack.push(sync_child_id);
      ++index;
    }

    // At this point all the children nodes of the parent sync node have
    // corresponding children in the parent bookmark node and they are all in
    // the right positions: from 0 to index - 1.
    // So the children starting from index in the parent bookmark node are the
    // ones that are not present in the parent sync node. So create them.
    for (int i = index; i < parent_node->child_count(); ++i) {
      int64 sync_child_id = BookmarkChangeProcessor::CreateSyncNode(
          parent_node, bookmark_model_, i, &trans, this,
          unrecoverable_error_handler_);
      if (syncer::kInvalidId == sync_child_id) {
        return unrecoverable_error_handler_->CreateAndUploadError(
            FROM_HERE,
            "Failed to create sync node.",
            model_type());
      }
      syncer_merge_result->set_num_items_added(
          syncer_merge_result->num_items_added() + 1);
      if (parent_node->GetChild(i)->is_folder())
        dfs_stack.push(sync_child_id);
    }
  }

  local_merge_result->set_num_items_after_association(
      bookmark_model_->root_node()->GetTotalNodeCount());
  syncer_merge_result->set_num_items_after_association(
      bm_root.GetTotalNodeCount());

  return syncer::SyncError();
}

struct FolderInfo {
  FolderInfo(const BookmarkNode* f, const BookmarkNode* p, int64 id)
      : folder(f), parent(p), sync_id(id) {}
  const BookmarkNode* folder;
  const BookmarkNode* parent;
  int64 sync_id;
};
typedef std::vector<FolderInfo> FolderInfoList;

int64 BookmarkModelAssociator::ApplyDeletesFromSyncJournal(
    syncer::BaseTransaction* trans) {
  int64 num_bookmark_deleted = 0;

  syncer::BookmarkDeleteJournalList bk_delete_journals;
  syncer::DeleteJournal::GetBookmarkDeleteJournals(trans, &bk_delete_journals);
  if (bk_delete_journals.empty())
    return 0;
  size_t num_journals_unmatched = bk_delete_journals.size();

  // Check bookmark model from top to bottom.
  std::stack<const BookmarkNode*> dfs_stack;
  dfs_stack.push(bookmark_model_->bookmark_bar_node());
  dfs_stack.push(bookmark_model_->other_node());
  if (expect_mobile_bookmarks_folder_)
    dfs_stack.push(bookmark_model_->mobile_node());
  // Note: the root node may have additional extra nodes. Currently none of
  // them are meant to sync.

  // Remember folders that match delete journals in first pass but don't delete
  // them in case there are bookmarks left under them. After non-folder
  // bookmarks are removed in first pass, recheck the folders in reverse order
  // to remove empty ones.
  FolderInfoList folders_matched;
  while (!dfs_stack.empty()) {
    const BookmarkNode* parent = dfs_stack.top();
    dfs_stack.pop();

    BookmarkNodeFinder finder(parent);
    // Iterate through journals from back to front. Remove matched journal by
    // moving an unmatched journal at the tail to its position so that we can
    // read unmatched journals off the head in next loop.
    for (int i = num_journals_unmatched - 1; i >= 0; --i) {
      const BookmarkNode* child = finder.FindBookmarkNode(
          GURL(bk_delete_journals[i].specifics.bookmark().url()),
          bk_delete_journals[i].specifics.bookmark().title(),
          bk_delete_journals[i].is_folder);
      if (child) {
        if (child->is_folder()) {
          // Remember matched folder without removing and delete only empty
          // ones later.
          folders_matched.push_back(FolderInfo(child, parent,
                                               bk_delete_journals[i].id));
        } else {
          bookmark_model_->Remove(parent, parent->GetIndexOf(child));
          ++num_bookmark_deleted;
        }
        // Move unmatched journal here and decrement counter.
        bk_delete_journals[i] = bk_delete_journals[--num_journals_unmatched];
      }
    }
    if (num_journals_unmatched == 0)
      break;

    for (int i = 0; i < parent->child_count(); ++i) {
      if (parent->GetChild(i)->is_folder())
        dfs_stack.push(parent->GetChild(i));
    }
  }

  // Ids of sync nodes not found in bookmark model, meaning the deletions are
  // persisted and correponding delete journals can be dropped.
  std::set<int64> journals_to_purge;

  // Remove empty folders from bottom to top.
  for (FolderInfoList::reverse_iterator it = folders_matched.rbegin();
      it != folders_matched.rend(); ++it) {
    if (it->folder->child_count() == 0) {
      bookmark_model_->Remove(it->parent, it->parent->GetIndexOf(it->folder));
      ++num_bookmark_deleted;
    } else {
      // Keep non-empty folder and remove its journal so that it won't match
      // again in the future.
      journals_to_purge.insert(it->sync_id);
    }
  }

  // Purge unmatched journals.
  for (size_t i = 0; i < num_journals_unmatched; ++i)
    journals_to_purge.insert(bk_delete_journals[i].id);
  syncer::DeleteJournal::PurgeDeleteJournals(trans, journals_to_purge);

  return num_bookmark_deleted;
}

void BookmarkModelAssociator::PostPersistAssociationsTask() {
  // No need to post a task if a task is already pending.
  if (weak_factory_.HasWeakPtrs())
    return;
  base::MessageLoop::current()->PostTask(
      FROM_HERE,
      base::Bind(
          &BookmarkModelAssociator::PersistAssociations,
          weak_factory_.GetWeakPtr()));
}

void BookmarkModelAssociator::PersistAssociations() {
  // If there are no dirty associations we have nothing to do. We handle this
  // explicity instead of letting the for loop do it to avoid creating a write
  // transaction in this case.
  if (dirty_associations_sync_ids_.empty()) {
    DCHECK(id_map_.empty());
    DCHECK(id_map_inverse_.empty());
    return;
  }

  int64 new_version = syncer::syncable::kInvalidTransactionVersion;
  std::vector<const BookmarkNode*> bnodes;
  {
    syncer::WriteTransaction trans(FROM_HERE, user_share_, &new_version);
    DirtyAssociationsSyncIds::iterator iter;
    for (iter = dirty_associations_sync_ids_.begin();
         iter != dirty_associations_sync_ids_.end();
         ++iter) {
      int64 sync_id = *iter;
      syncer::WriteNode sync_node(&trans);
      if (sync_node.InitByIdLookup(sync_id) != syncer::BaseNode::INIT_OK) {
        unrecoverable_error_handler_->OnSingleDatatypeUnrecoverableError(
            FROM_HERE,
            "Could not lookup bookmark node for ID persistence.");
        return;
      }
      const BookmarkNode* node = GetChromeNodeFromSyncId(sync_id);
      if (node && sync_node.GetExternalId() != node->id()) {
        sync_node.SetExternalId(node->id());
        bnodes.push_back(node);
      }
    }
    dirty_associations_sync_ids_.clear();
  }

  BookmarkChangeProcessor::UpdateTransactionVersion(new_version,
                                                    bookmark_model_,
                                                    bnodes);
}

bool BookmarkModelAssociator::CryptoReadyIfNecessary() {
  // We only access the cryptographer while holding a transaction.
  syncer::ReadTransaction trans(FROM_HERE, user_share_);
  const syncer::ModelTypeSet encrypted_types = trans.GetEncryptedTypes();
  return !encrypted_types.Has(syncer::BOOKMARKS) ||
      trans.GetCryptographer()->is_ready();
}

syncer::SyncError BookmarkModelAssociator::CheckModelSyncState(
    syncer::SyncMergeResult* local_merge_result,
    syncer::SyncMergeResult* syncer_merge_result) const {
  int64 native_version =
      bookmark_model_->root_node()->sync_transaction_version();
  if (native_version != syncer::syncable::kInvalidTransactionVersion) {
    syncer::ReadTransaction trans(FROM_HERE, user_share_);
    local_merge_result->set_pre_association_version(native_version);

    int64 sync_version = trans.GetModelVersion(syncer::BOOKMARKS);
    syncer_merge_result->set_pre_association_version(sync_version);

    if (native_version != sync_version) {
      UMA_HISTOGRAM_ENUMERATION("Sync.LocalModelOutOfSync",
                                ModelTypeToHistogramInt(syncer::BOOKMARKS),
                                syncer::MODEL_TYPE_COUNT);

      // Clear version on bookmark model so that we only report error once.
      bookmark_model_->SetNodeSyncTransactionVersion(
          bookmark_model_->root_node(),
          syncer::syncable::kInvalidTransactionVersion);

      // If the native version is higher, there was a sync persistence failure,
      // and we need to delay association until after a GetUpdates.
      if (sync_version < native_version) {
        std::string message = base::StringPrintf(
            "Native version (%" PRId64 ") does not match sync version (%"
                PRId64 ")",
            native_version,
            sync_version);
        return syncer::SyncError(FROM_HERE,
                                 syncer::SyncError::PERSISTENCE_ERROR,
                                 message,
                                 syncer::BOOKMARKS);
      }
    }
  }
  return syncer::SyncError();
}

}  // namespace browser_sync