chrome/browser/history/in_memory_url_index.cc

// Copyright (c) 2011 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/history/in_memory_url_index.h"

#include <algorithm>
#include <functional>
#include <iterator>
#include <limits>
#include <numeric>

#include "base/file_util.h"
#include "base/i18n/break_iterator.h"
#include "base/i18n/case_conversion.h"
#include "base/metrics/histogram.h"
#include "base/string_util.h"
#include "base/threading/thread_restrictions.h"
#include "base/time.h"
#include "base/utf_string_conversions.h"
#include "chrome/browser/autocomplete/autocomplete.h"
#include "chrome/browser/autocomplete/history_provider_util.h"
#include "chrome/browser/history/url_database.h"
#include "chrome/browser/profiles/profile.h"
#include "chrome/common/url_constants.h"
#include "googleurl/src/url_parse.h"
#include "googleurl/src/url_util.h"
#include "net/base/escape.h"
#include "net/base/net_util.h"
#include "third_party/protobuf/src/google/protobuf/repeated_field.h"
#include "ui/base/l10n/l10n_util.h"

using google::protobuf::RepeatedField;
using google::protobuf::RepeatedPtrField;
using in_memory_url_index::InMemoryURLIndexCacheItem;

namespace history {

typedef imui::InMemoryURLIndexCacheItem_WordListItem WordListItem;
typedef imui::InMemoryURLIndexCacheItem_WordMapItem_WordMapEntry WordMapEntry;
typedef imui::InMemoryURLIndexCacheItem_WordMapItem WordMapItem;
typedef imui::InMemoryURLIndexCacheItem_CharWordMapItem CharWordMapItem;
typedef imui::InMemoryURLIndexCacheItem_CharWordMapItem_CharWordMapEntry
    CharWordMapEntry;
typedef imui::InMemoryURLIndexCacheItem_WordIDHistoryMapItem
    WordIDHistoryMapItem;
typedef imui::
    InMemoryURLIndexCacheItem_WordIDHistoryMapItem_WordIDHistoryMapEntry
    WordIDHistoryMapEntry;
typedef imui::InMemoryURLIndexCacheItem_HistoryInfoMapItem HistoryInfoMapItem;
typedef imui::InMemoryURLIndexCacheItem_HistoryInfoMapItem_HistoryInfoMapEntry
    HistoryInfoMapEntry;

const size_t InMemoryURLIndex::kNoCachedResultForTerm = -1;

// Score ranges used to get a 'base' score for each of the scoring factors
// (such as recency of last visit, times visited, times the URL was typed,
// and the quality of the string match). There is a matching value range for
// each of these scores for each factor.
const int kScoreRank[] = { 1425, 1200, 900, 400 };

ScoredHistoryMatch::ScoredHistoryMatch()
    : raw_score(0),
      can_inline(false) {}

ScoredHistoryMatch::ScoredHistoryMatch(const URLRow& url_info)
    : HistoryMatch(url_info, 0, false, false),
      raw_score(0),
      can_inline(false) {}

ScoredHistoryMatch::~ScoredHistoryMatch() {}

// Comparison function for sorting ScoredMatches by their scores.
bool ScoredHistoryMatch::MatchScoreGreater(const ScoredHistoryMatch& m1,
                                           const ScoredHistoryMatch& m2) {
  return m1.raw_score >= m2.raw_score;
}

InMemoryURLIndex::SearchTermCacheItem::SearchTermCacheItem(
    const WordIDSet& word_id_set,
    const HistoryIDSet& history_id_set)
    : word_id_set_(word_id_set),
      history_id_set_(history_id_set),
      used_(true) {}

InMemoryURLIndex::SearchTermCacheItem::SearchTermCacheItem()
    : used_(true) {}

InMemoryURLIndex::SearchTermCacheItem::~SearchTermCacheItem() {}

// Comparison function for sorting TermMatches by their offsets.
bool MatchOffsetLess(const TermMatch& m1, const TermMatch& m2) {
  return m1.offset < m2.offset;
}

// Comparison function for sorting search terms by descending length.
bool LengthGreater(const string16& string_a, const string16& string_b) {
  return string_a.length() > string_b.length();
}

// std::accumulate helper function to add up TermMatches' lengths.
int AccumulateMatchLength(int total, const TermMatch& match) {
  return total + match.length;
}

// Converts a raw value for some particular scoring factor into a score
// component for that factor.  The conversion function is piecewise linear, with
// input values provided in |value_ranks| and resulting output scores from
// |kScoreRank| (mathematically, f(value_rank[i]) = kScoreRank[i]).  A score
// cannot be higher than kScoreRank[0], and drops directly to 0 if lower than
// kScoreRank[3].
//
// For example, take |value| == 70 and |value_ranks| == { 100, 50, 30, 10 }.
// Because 70 falls between ranks 0 (100) and 1 (50), the score is given by the
// linear function:
//   score = m * value + b, where
//   m = (kScoreRank[0] - kScoreRank[1]) / (value_ranks[0] - value_ranks[1])
//   b = value_ranks[1]
// Any value higher than 100 would be scored as if it were 100, and any value
// lower than 10 scored 0.
int ScoreForValue(int value, const int* value_ranks) {
  int i = 0;
  int rank_count = arraysize(kScoreRank);
  while ((i < rank_count) && ((value_ranks[0] < value_ranks[1]) ?
         (value > value_ranks[i]) : (value < value_ranks[i])))
    ++i;
  if (i >= rank_count)
    return 0;
  int score = kScoreRank[i];
  if (i > 0) {
    score += (value - value_ranks[i]) *
        (kScoreRank[i - 1] - kScoreRank[i]) /
        (value_ranks[i - 1] - value_ranks[i]);
  }
  return score;
}

InMemoryURLIndex::InMemoryURLIndex(const FilePath& history_dir)
    : history_dir_(history_dir),
      history_item_count_(0) {
  InMemoryURLIndex::InitializeSchemeWhitelist(&scheme_whitelist_);
}

// Called only by unit tests.
InMemoryURLIndex::InMemoryURLIndex()
    : history_item_count_(0) {
  InMemoryURLIndex::InitializeSchemeWhitelist(&scheme_whitelist_);
}

InMemoryURLIndex::~InMemoryURLIndex() {}

// static
void InMemoryURLIndex::InitializeSchemeWhitelist(
    std::set<std::string>* whitelist) {
  DCHECK(whitelist);
  whitelist->insert(std::string(chrome::kAboutScheme));
  whitelist->insert(std::string(chrome::kChromeUIScheme));
  whitelist->insert(std::string(chrome::kFileScheme));
  whitelist->insert(std::string(chrome::kFtpScheme));
  whitelist->insert(std::string(chrome::kHttpScheme));
  whitelist->insert(std::string(chrome::kHttpsScheme));
  whitelist->insert(std::string(chrome::kMailToScheme));
}

// Indexing

bool InMemoryURLIndex::Init(history::URLDatabase* history_db,
                            const std::string& languages) {
  // TODO(mrossetti): Register for profile/language change notifications.
  languages_ = languages;
  return ReloadFromHistory(history_db, false);
}

void InMemoryURLIndex::ShutDown() {
  // Write our cache.
  SaveToCacheFile();
}

bool InMemoryURLIndex::IndexRow(const URLRow& row) {
  const GURL& gurl(row.url());

  // Index only URLs with a whitelisted scheme.
  if (!InMemoryURLIndex::URLSchemeIsWhitelisted(gurl))
    return true;

  string16 url(net::FormatUrl(gurl, languages_,
      net::kFormatUrlOmitUsernamePassword,
      UnescapeRule::SPACES | UnescapeRule::URL_SPECIAL_CHARS,
      NULL, NULL, NULL));

  HistoryID history_id = static_cast<HistoryID>(row.id());
  DCHECK_LT(row.id(), std::numeric_limits<HistoryID>::max());

  // Add the row for quick lookup in the history info store.
  URLRow new_row(GURL(url), row.id());
  new_row.set_visit_count(row.visit_count());
  new_row.set_typed_count(row.typed_count());
  new_row.set_last_visit(row.last_visit());
  new_row.set_title(row.title());
  history_info_map_[history_id] = new_row;

  // Split URL into individual, unique words then add in the title words.
  url = base::i18n::ToLower(url);
  String16Set url_words = WordSetFromString16(url);
  String16Set title_words = WordSetFromString16(row.title());
  String16Set words;
  std::set_union(url_words.begin(), url_words.end(),
                 title_words.begin(), title_words.end(),
                 std::insert_iterator<String16Set>(words, words.begin()));
  for (String16Set::iterator word_iter = words.begin();
       word_iter != words.end(); ++word_iter)
    AddWordToIndex(*word_iter, history_id);

  ++history_item_count_;
  return true;
}

bool InMemoryURLIndex::ReloadFromHistory(history::URLDatabase* history_db,
                                         bool clear_cache) {
  ClearPrivateData();

  if (!history_db)
    return false;

  if (clear_cache || !RestoreFromCacheFile()) {
    base::TimeTicks beginning_time = base::TimeTicks::Now();
    // The index has to be built from scratch.
    URLDatabase::URLEnumerator history_enum;
    if (!history_db->InitURLEnumeratorForSignificant(&history_enum))
      return false;
    URLRow row;
    while (history_enum.GetNextURL(&row)) {
      if (!IndexRow(row))
        return false;
    }
    UMA_HISTOGRAM_TIMES("History.InMemoryURLIndexingTime",
                        base::TimeTicks::Now() - beginning_time);
    SaveToCacheFile();
  }
  return true;
}

void InMemoryURLIndex::ClearPrivateData() {
  history_item_count_ = 0;
  word_list_.clear();
  word_map_.clear();
  char_word_map_.clear();
  word_id_history_map_.clear();
  history_info_map_.clear();
  search_term_cache_.clear();
}

bool InMemoryURLIndex::RestoreFromCacheFile() {
  // TODO(mrossetti): Figure out how to determine if the cache is up-to-date.
  // That is: ensure that the database has not been modified since the cache
  // was last saved. DB file modification date is inadequate. There are no
  // SQLite table checksums automatically stored.
  // FIXME(mrossetti): Move File IO to another thread.
  base::ThreadRestrictions::ScopedAllowIO allow_io;
  base::TimeTicks beginning_time = base::TimeTicks::Now();
  FilePath file_path;
  if (!GetCacheFilePath(&file_path) || !file_util::PathExists(file_path))
    return false;
  std::string data;
  if (!file_util::ReadFileToString(file_path, &data)) {
    LOG(WARNING) << "Failed to read InMemoryURLIndex cache from "
                 << file_path.value();
    return false;
  }

  InMemoryURLIndexCacheItem index_cache;
  if (!index_cache.ParseFromArray(data.c_str(), data.size())) {
    LOG(WARNING) << "Failed to parse InMemoryURLIndex cache data read from "
                 << file_path.value();
    return false;
  }

  if (!RestorePrivateData(index_cache)) {
    ClearPrivateData();  // Back to square one -- must build from scratch.
    return false;
  }

  UMA_HISTOGRAM_TIMES("History.InMemoryURLIndexRestoreCacheTime",
                      base::TimeTicks::Now() - beginning_time);
  UMA_HISTOGRAM_COUNTS("History.InMemoryURLHistoryItems", history_item_count_);
  UMA_HISTOGRAM_COUNTS("History.InMemoryURLCacheSize", data.size());
  UMA_HISTOGRAM_COUNTS_10000("History.InMemoryURLWords", word_map_.size());
  UMA_HISTOGRAM_COUNTS_10000("History.InMemoryURLChars", char_word_map_.size());
  return true;
}

bool InMemoryURLIndex::SaveToCacheFile() {
  // TODO(mrossetti): Move File IO to another thread.
  base::ThreadRestrictions::ScopedAllowIO allow_io;
  base::TimeTicks beginning_time = base::TimeTicks::Now();
  InMemoryURLIndexCacheItem index_cache;
  SavePrivateData(&index_cache);
  std::string data;
  if (!index_cache.SerializeToString(&data)) {
    LOG(WARNING) << "Failed to serialize the InMemoryURLIndex cache.";
    return false;
  }

  // TODO(mrossetti): Write the cache to a file then swap it for the old cache,
  // if any, and delete the old cache.
  FilePath file_path;
  if (!GetCacheFilePath(&file_path))
    return false;

  int size = data.size();
  if (file_util::WriteFile(file_path, data.c_str(), size) != size) {
    LOG(WARNING) << "Failed to write " << file_path.value();
    return false;
  }
  UMA_HISTOGRAM_TIMES("History.InMemoryURLIndexSaveCacheTime",
                      base::TimeTicks::Now() - beginning_time);
  return true;
}

void InMemoryURLIndex::UpdateURL(URLID row_id, const URLRow& row) {
  // The row may or may not already be in our index. If it is not already
  // indexed and it qualifies then it gets indexed. If it is already
  // indexed and still qualifies then it gets updated, otherwise it
  // is deleted from the index.
  HistoryInfoMap::iterator row_pos = history_info_map_.find(row_id);
  if (row_pos == history_info_map_.end()) {
    // This new row should be indexed if it qualifies.
    if (RowQualifiesAsSignificant(row, base::Time()))
      IndexRow(row);
  } else if (RowQualifiesAsSignificant(row, base::Time())) {
    // This indexed row still qualifies and will be re-indexed.
    // The url won't have changed but the title, visit count, etc.
    // might have changed.
    URLRow& old_row = row_pos->second;
    old_row.set_visit_count(row.visit_count());
    old_row.set_typed_count(row.typed_count());
    old_row.set_last_visit(row.last_visit());
    // TODO(mrossetti): When we start indexing the title the next line
    // will need attention.
    old_row.set_title(row.title());
  } else {
    // This indexed row no longer qualifies and will be de-indexed.
    history_info_map_.erase(row_id);
  }
  // This invalidates the cache.
  search_term_cache_.clear();
  // TODO(mrossetti): Record this transaction in the cache.
}

void InMemoryURLIndex::DeleteURL(URLID row_id) {
  // Note that this does not remove any reference to this row from the
  // word_id_history_map_. That map will continue to contain (and return)
  // hits against this row until that map is rebuilt, but since the
  // history_info_map_ no longer references the row no erroneous results
  // will propagate to the user.
  history_info_map_.erase(row_id);
  // This invalidates the word cache.
  search_term_cache_.clear();
  // TODO(mrossetti): Record this transaction in the cache.
}

// Searching

ScoredHistoryMatches InMemoryURLIndex::HistoryItemsForTerms(
    const String16Vector& terms) {
  ScoredHistoryMatches scored_items;
  if (!terms.empty()) {
    // Reset used_ flags for search_term_cache_. We use a basic mark-and-sweep
    // approach.
    ResetSearchTermCache();

    // Lowercase the terms.
    // TODO(mrossetti): Another opportunity for a transform algorithm.
    String16Vector lower_terms;
    for (String16Vector::const_iterator term_iter = terms.begin();
         term_iter != terms.end(); ++term_iter)
      lower_terms.push_back(base::i18n::ToLower(*term_iter));

    string16 all_terms(JoinString(lower_terms, ' '));
    HistoryIDSet history_id_set = HistoryIDSetFromWords(all_terms);

    // Don't perform any scoring (and don't return any matches) if the
    // candidate pool is large. (See comments in header.)
    const size_t kItemsToScoreLimit = 500;
    if (history_id_set.size() <= kItemsToScoreLimit) {
      // Pass over all of the candidates filtering out any without a proper
      // substring match, inserting those which pass in order by score.
      scored_items = std::for_each(history_id_set.begin(), history_id_set.end(),
          AddHistoryMatch(*this, lower_terms)).ScoredMatches();

      // Select and sort only the top kMaxMatches results.
      if (scored_items.size() > AutocompleteProvider::kMaxMatches) {
        std::partial_sort(scored_items.begin(),
                          scored_items.begin() +
                              AutocompleteProvider::kMaxMatches,
                          scored_items.end(),
                          ScoredHistoryMatch::MatchScoreGreater);
          scored_items.resize(AutocompleteProvider::kMaxMatches);
      } else {
        std::sort(scored_items.begin(), scored_items.end(),
                  ScoredHistoryMatch::MatchScoreGreater);
      }
    }
  }

  // Remove any stale SearchTermCacheItems.
  for (SearchTermCacheMap::iterator cache_iter = search_term_cache_.begin();
       cache_iter != search_term_cache_.end(); ) {
    if (!cache_iter->second.used_)
      search_term_cache_.erase(cache_iter++);
    else
      ++cache_iter;
  }

  return scored_items;
}

void InMemoryURLIndex::ResetSearchTermCache() {
  for (SearchTermCacheMap::iterator iter = search_term_cache_.begin();
       iter != search_term_cache_.end(); ++iter)
    iter->second.used_ = false;
}

InMemoryURLIndex::HistoryIDSet InMemoryURLIndex::HistoryIDSetFromWords(
    const string16& uni_string) {
  // Break the terms down into individual terms (words), get the candidate
  // set for each term, and intersect each to get a final candidate list.
  // Note that a single 'term' from the user's perspective might be
  // a string like "http://www.somewebsite.com" which, from our perspective,
  // is four words: 'http', 'www', 'somewebsite', and 'com'.
  HistoryIDSet history_id_set;
  String16Vector terms = WordVectorFromString16(uni_string, true);
  // Sort the terms into the longest first as such are likely to narrow down
  // the results quicker. Also, single character terms are the most expensive
  // to process so save them for last.
  std::sort(terms.begin(), terms.end(), LengthGreater);
  for (String16Vector::iterator iter = terms.begin(); iter != terms.end();
       ++iter) {
    string16 uni_word = *iter;
    HistoryIDSet term_history_set = HistoryIDsForTerm(uni_word);
    if (term_history_set.empty()) {
      history_id_set.clear();
      break;
    }
    if (iter == terms.begin()) {
      history_id_set.swap(term_history_set);
    } else {
      HistoryIDSet new_history_id_set;
      std::set_intersection(history_id_set.begin(), history_id_set.end(),
                            term_history_set.begin(), term_history_set.end(),
                            std::inserter(new_history_id_set,
                                          new_history_id_set.begin()));
      history_id_set.swap(new_history_id_set);
    }
  }
  return history_id_set;
}

InMemoryURLIndex::HistoryIDSet InMemoryURLIndex::HistoryIDsForTerm(
    const string16& term) {
  if (term.empty())
    return HistoryIDSet();

  // TODO(mrossetti): Consider optimizing for very common terms such as
  // 'http[s]', 'www', 'com', etc. Or collect the top 100 more frequently
  // occuring words in the user's searches.

  size_t term_length = term.length();
  InMemoryURLIndex::WordIDSet word_id_set;
  if (term_length > 1) {
    // See if this term or a prefix thereof is present in the cache.
    SearchTermCacheMap::iterator best_prefix(search_term_cache_.end());
    for (SearchTermCacheMap::iterator cache_iter = search_term_cache_.begin();
         cache_iter != search_term_cache_.end(); ++cache_iter) {
      if (StartsWith(term, cache_iter->first, false) &&
          (best_prefix == search_term_cache_.end() ||
           cache_iter->first.length() > best_prefix->first.length()))
        best_prefix = cache_iter;
    }

    // If a prefix was found then determine the leftover characters to be used
    // for further refining the results from that prefix.
    Char16Set prefix_chars;
    string16 leftovers(term);
    if (best_prefix != search_term_cache_.end()) {
      // If the prefix is an exact match for the term then grab the cached
      // results and we're done.
      size_t prefix_length = best_prefix->first.length();
      if (prefix_length == term_length) {
        best_prefix->second.used_ = true;
        return best_prefix->second.history_id_set_;
      }

      // Otherwise we have a handy starting point.
      // If there are no history results for this prefix then we can bail early
      // as there will be no history results for the full term.
      if (best_prefix->second.history_id_set_.empty()) {
        search_term_cache_[term] = SearchTermCacheItem();
        return HistoryIDSet();
      }
      word_id_set = best_prefix->second.word_id_set_;
      prefix_chars = Char16SetFromString16(best_prefix->first);
      leftovers = term.substr(prefix_length);
    }

    // Filter for each remaining, unique character in the term.
    Char16Set leftover_chars = Char16SetFromString16(leftovers);
    Char16Set unique_chars;
    std::set_difference(leftover_chars.begin(), leftover_chars.end(),
                        prefix_chars.begin(), prefix_chars.end(),
                        std::inserter(unique_chars, unique_chars.begin()));

    // Reduce the word set with any leftover, unprocessed characters.
    if (!unique_chars.empty()) {
      WordIDSet leftover_set(WordIDSetForTermChars(unique_chars));
      // We might come up empty on the leftovers.
      if (leftover_set.empty()) {
        search_term_cache_[term] = SearchTermCacheItem();
        return HistoryIDSet();
      }
      // Or there may not have been a prefix from which to start.
      if (prefix_chars.empty()) {
        word_id_set.swap(leftover_set);
      } else {
        WordIDSet new_word_id_set;
        std::set_intersection(word_id_set.begin(), word_id_set.end(),
                              leftover_set.begin(), leftover_set.end(),
                              std::inserter(new_word_id_set,
                                            new_word_id_set.begin()));
        word_id_set.swap(new_word_id_set);
      }
    }

    // We must filter the word list because the resulting word set surely
    // contains words which do not have the search term as a proper subset.
    for (WordIDSet::iterator word_set_iter = word_id_set.begin();
         word_set_iter != word_id_set.end(); ) {
      if (word_list_[*word_set_iter].find(term) == string16::npos)
        word_id_set.erase(word_set_iter++);
      else
        ++word_set_iter;
    }
  } else {
    word_id_set = WordIDSetForTermChars(Char16SetFromString16(term));
  }

  // If any words resulted then we can compose a set of history IDs by unioning
  // the sets from each word.
  HistoryIDSet history_id_set;
  if (!word_id_set.empty()) {
    for (WordIDSet::iterator word_id_iter = word_id_set.begin();
         word_id_iter != word_id_set.end(); ++word_id_iter) {
      WordID word_id = *word_id_iter;
      WordIDHistoryMap::iterator word_iter = word_id_history_map_.find(word_id);
      if (word_iter != word_id_history_map_.end()) {
        HistoryIDSet& word_history_id_set(word_iter->second);
        history_id_set.insert(word_history_id_set.begin(),
                              word_history_id_set.end());
      }
    }
  }

  // Record a new cache entry for this word if the term is longer than
  // a single character.
  if (term_length > 1)
    search_term_cache_[term] = SearchTermCacheItem(word_id_set, history_id_set);

  return history_id_set;
}

// Utility Functions

// static
InMemoryURLIndex::String16Set InMemoryURLIndex::WordSetFromString16(
    const string16& uni_string) {
  const size_t kMaxWordLength = 64;
  String16Vector words = WordVectorFromString16(uni_string, false);
  String16Set word_set;
  for (String16Vector::const_iterator iter = words.begin(); iter != words.end();
       ++iter)
    word_set.insert(base::i18n::ToLower(*iter).substr(0, kMaxWordLength));
  return word_set;
}

// static
InMemoryURLIndex::String16Vector InMemoryURLIndex::WordVectorFromString16(
    const string16& uni_string,
    bool break_on_space) {
  base::i18n::BreakIterator iter(
      uni_string,
      break_on_space ? base::i18n::BreakIterator::BREAK_SPACE
                     : base::i18n::BreakIterator::BREAK_WORD);
  String16Vector words;
  if (!iter.Init())
    return words;
  while (iter.Advance()) {
    if (break_on_space || iter.IsWord()) {
      string16 word = iter.GetString();
      if (break_on_space)
        TrimWhitespace(word, TRIM_ALL, &word);
      if (!word.empty())
        words.push_back(word);
    }
  }
  return words;
}

// static
InMemoryURLIndex::Char16Set InMemoryURLIndex::Char16SetFromString16(
    const string16& term) {
  Char16Set characters;
  for (string16::const_iterator iter = term.begin(); iter != term.end();
       ++iter)
    characters.insert(*iter);
  return characters;
}

void InMemoryURLIndex::AddWordToIndex(const string16& term,
                                      HistoryID history_id) {
  WordMap::iterator word_pos = word_map_.find(term);
  if (word_pos != word_map_.end())
    UpdateWordHistory(word_pos->second, history_id);
  else
    AddWordHistory(term, history_id);
}

void InMemoryURLIndex::UpdateWordHistory(WordID word_id, HistoryID history_id) {
    WordIDHistoryMap::iterator history_pos = word_id_history_map_.find(word_id);
    DCHECK(history_pos != word_id_history_map_.end());
    HistoryIDSet& history_id_set(history_pos->second);
    history_id_set.insert(history_id);
}

// Add a new word to the word list and the word map, and then create a
// new entry in the word/history map.
void InMemoryURLIndex::AddWordHistory(const string16& term,
                                      HistoryID history_id) {
  word_list_.push_back(term);
  WordID word_id = word_list_.size() - 1;
  word_map_[term] = word_id;
  HistoryIDSet history_id_set;
  history_id_set.insert(history_id);
  word_id_history_map_[word_id] = history_id_set;
  // For each character in the newly added word (i.e. a word that is not
  // already in the word index), add the word to the character index.
  Char16Set characters = Char16SetFromString16(term);
  for (Char16Set::iterator uni_char_iter = characters.begin();
       uni_char_iter != characters.end(); ++uni_char_iter) {
    char16 uni_char = *uni_char_iter;
    CharWordIDMap::iterator char_iter = char_word_map_.find(uni_char);
    if (char_iter != char_word_map_.end()) {
      // Update existing entry in the char/word index.
      WordIDSet& word_id_set(char_iter->second);
      word_id_set.insert(word_id);
    } else {
      // Create a new entry in the char/word index.
      WordIDSet word_id_set;
      word_id_set.insert(word_id);
      char_word_map_[uni_char] = word_id_set;
    }
  }
}

InMemoryURLIndex::WordIDSet InMemoryURLIndex::WordIDSetForTermChars(
    const Char16Set& term_chars) {
  WordIDSet word_id_set;
  for (Char16Set::const_iterator c_iter = term_chars.begin();
       c_iter != term_chars.end(); ++c_iter) {
    CharWordIDMap::iterator char_iter = char_word_map_.find(*c_iter);
    if (char_iter == char_word_map_.end()) {
      // A character was not found so there are no matching results: bail.
      word_id_set.clear();
      break;
    }
    WordIDSet& char_word_id_set(char_iter->second);
    // It is possible for there to no longer be any words associated with
    // a particular character. Give up in that case.
    if (char_word_id_set.empty()) {
      word_id_set.clear();
      break;
    }

    if (c_iter == term_chars.begin()) {
      // First character results becomes base set of results.
      word_id_set = char_word_id_set;
    } else {
      // Subsequent character results get intersected in.
      WordIDSet new_word_id_set;
      std::set_intersection(word_id_set.begin(), word_id_set.end(),
                            char_word_id_set.begin(), char_word_id_set.end(),
                            std::inserter(new_word_id_set,
                                          new_word_id_set.begin()));
      word_id_set.swap(new_word_id_set);
    }
  }
  return word_id_set;
}

// static
TermMatches InMemoryURLIndex::MatchTermInString(const string16& term,
                                                const string16& string,
                                                int term_num) {
  const size_t kMaxCompareLength = 2048;
  const string16& short_string = (string.length() > kMaxCompareLength) ?
      string.substr(0, kMaxCompareLength) : string;
  TermMatches matches;
  for (size_t location = short_string.find(term); location != string16::npos;
       location = short_string.find(term, location + 1)) {
    matches.push_back(TermMatch(term_num, location, term.length()));
  }
  return matches;
}

// static
TermMatches InMemoryURLIndex::SortAndDeoverlap(const TermMatches& matches) {
  if (matches.empty())
    return matches;
  TermMatches sorted_matches = matches;
  std::sort(sorted_matches.begin(), sorted_matches.end(), MatchOffsetLess);
  TermMatches clean_matches;
  TermMatch last_match = sorted_matches[0];
  clean_matches.push_back(last_match);
  for (TermMatches::const_iterator iter = sorted_matches.begin() + 1;
       iter != sorted_matches.end(); ++iter) {
    if (iter->offset >= last_match.offset + last_match.length) {
      last_match = *iter;
      clean_matches.push_back(last_match);
    }
  }
  return clean_matches;
}

// static
std::vector<size_t> InMemoryURLIndex::OffsetsFromTermMatches(
    const TermMatches& matches) {
  std::vector<size_t> offsets;
  for (TermMatches::const_iterator i = matches.begin(); i != matches.end(); ++i)
    offsets.push_back(i->offset);
  return offsets;
}

// static
TermMatches InMemoryURLIndex::ReplaceOffsetsInTermMatches(
    const TermMatches& matches,
    const std::vector<size_t>& offsets) {
  DCHECK_EQ(matches.size(), offsets.size());
  TermMatches new_matches;
  std::vector<size_t>::const_iterator offset_iter = offsets.begin();
  for (TermMatches::const_iterator term_iter = matches.begin();
       term_iter != matches.end(); ++term_iter, ++offset_iter) {
    if (*offset_iter != string16::npos) {
      TermMatch new_match(*term_iter);
      new_match.offset = *offset_iter;
      new_matches.push_back(new_match);
    }
  }
  return new_matches;
}

// static
ScoredHistoryMatch InMemoryURLIndex::ScoredMatchForURL(
    const URLRow& row,
    const String16Vector& terms) {
  ScoredHistoryMatch match(row);
  GURL gurl = row.url();
  if (!gurl.is_valid())
    return match;

  // Figure out where each search term appears in the URL and/or page title
  // so that we can score as well as provide autocomplete highlighting.
  string16 url = base::i18n::ToLower(UTF8ToUTF16(gurl.spec()));
  string16 title = base::i18n::ToLower(row.title());
  int term_num = 0;
  for (String16Vector::const_iterator iter = terms.begin(); iter != terms.end();
       ++iter, ++term_num) {
    string16 term = *iter;
    TermMatches url_term_matches = MatchTermInString(term, url, term_num);
    TermMatches title_term_matches = MatchTermInString(term, title, term_num);
    if (url_term_matches.empty() && title_term_matches.empty())
      return match;  // A term was not found in either URL or title - reject.
    match.url_matches.insert(match.url_matches.end(), url_term_matches.begin(),
                             url_term_matches.end());
    match.title_matches.insert(match.title_matches.end(),
                               title_term_matches.begin(),
                               title_term_matches.end());
  }

  // Sort matches by offset and eliminate any which overlap.
  match.url_matches = SortAndDeoverlap(match.url_matches);
  match.title_matches = SortAndDeoverlap(match.title_matches);

  // We should not (currently) inline autocomplete a result unless both of the
  // following are true:
  //   * There is exactly one substring matches in the URL, and
  //   * The one URL match starts at the beginning of the URL.
  match.can_inline =
      match.url_matches.size() == 1 && match.url_matches[0].offset == 0;

  // Get partial scores based on term matching. Note that the score for
  // each of the URL and title are adjusted by the fraction of the
  // terms appearing in each.
  int url_score = ScoreComponentForMatches(match.url_matches, url.length()) *
      match.url_matches.size() / terms.size();
  int title_score =
      ScoreComponentForMatches(match.title_matches, title.length()) *
      match.title_matches.size() / terms.size();
  // Arbitrarily pick the best.
  // TODO(mrossetti): It might make sense that a term which appears in both the
  // URL and the Title should boost the score a bit.
  int term_score = std::max(url_score, title_score);
  if (term_score == 0)
    return match;

  // Determine scoring factors for the recency of visit, visit count and typed
  // count attributes of the URLRow.
  const int kDaysAgoLevel[] = { 0, 10, 20, 30 };
  int days_ago_value = ScoreForValue((base::Time::Now() -
      row.last_visit()).InDays(), kDaysAgoLevel);
  const int kVisitCountLevel[] = { 30, 10, 5, 3 };
  int visit_count_value = ScoreForValue(row.visit_count(), kVisitCountLevel);
  const int kTypedCountLevel[] = { 10, 5, 3, 1 };
  int typed_count_value = ScoreForValue(row.typed_count(), kTypedCountLevel);

  // The final raw score is calculated by:
  //   - accumulating each contributing factor, some of which are added more
  //     than once giving them more 'influence' on the final score (currently,
  //     visit_count_value is added twice and typed_count_value three times)
  //   - dropping the lowest scores (|kInsignificantFactors|)
  //   - dividing by the remaining significant factors
  // This approach allows emphasis on more relevant factors while reducing the
  // inordinate impact of low scoring factors.
  int factor[] = {term_score, days_ago_value, visit_count_value,
      visit_count_value, typed_count_value, typed_count_value,
      typed_count_value};
  const int kInsignificantFactors = 2;
  const int kSignificantFactors = arraysize(factor) - kInsignificantFactors;
  std::partial_sort(factor, factor + kSignificantFactors,
                    factor + arraysize(factor), std::greater<int>());
  for (int i = 0; i < kSignificantFactors; ++i)
    match.raw_score += factor[i];
  match.raw_score /= kSignificantFactors;

  return match;
}

int InMemoryURLIndex::ScoreComponentForMatches(const TermMatches& matches,
                                               size_t max_length) {
  // TODO(mrossetti): This is good enough for now but must be fine-tuned.
  if (matches.empty())
    return 0;

  // Score component for whether the input terms (if more than one) were found
  // in the same order in the match.  Start with kOrderMaxValue points divided
  // equally among (number of terms - 1); then discount each of those terms that
  // is out-of-order in the match.
  const int kOrderMaxValue = 250;
  int order_value = kOrderMaxValue;
  if (matches.size() > 1) {
    int max_possible_out_of_order = matches.size() - 1;
    int out_of_order = 0;
    for (size_t i = 1; i < matches.size(); ++i) {
      if (matches[i - 1].term_num > matches[i].term_num)
        ++out_of_order;
    }
    order_value = (max_possible_out_of_order - out_of_order) * kOrderMaxValue /
        max_possible_out_of_order;
  }

  // Score component for how early in the match string the first search term
  // appears.  Start with kStartMaxValue points and discount by
  // 1/kMaxSignificantStart points for each character later than the first at
  // which the term begins. No points are earned if the start of the match
  // occurs at or after kMaxSignificantStart.
  const size_t kMaxSignificantStart = 20;
  const int kStartMaxValue = 250;
  int start_value = (kMaxSignificantStart -
      std::min(kMaxSignificantStart, matches[0].offset)) * kStartMaxValue /
      kMaxSignificantStart;

  // Score component for how much of the matched string the input terms cover.
  // kCompleteMaxValue points times the fraction of the URL/page title string
  // that was matched.
  size_t term_length_total = std::accumulate(matches.begin(), matches.end(),
                                             0, AccumulateMatchLength);
  const size_t kMaxSignificantLength = 50;
  size_t max_significant_length =
      std::min(max_length, std::max(term_length_total, kMaxSignificantLength));
  const int kCompleteMaxValue = 500;
  int complete_value =
      term_length_total * kCompleteMaxValue / max_significant_length;

  int raw_score = order_value + start_value + complete_value;
  const int kTermScoreLevel[] = { 1000, 650, 500, 200 };

  // Scale the sum of the three components above into a single score component
  // on the same scale as that used in ScoredMatchForURL().
  return ScoreForValue(raw_score, kTermScoreLevel);
}

InMemoryURLIndex::AddHistoryMatch::AddHistoryMatch(
    const InMemoryURLIndex& index,
    const String16Vector& lower_terms)
  : index_(index),
    lower_terms_(lower_terms) {
}

InMemoryURLIndex::AddHistoryMatch::~AddHistoryMatch() {}

void InMemoryURLIndex::AddHistoryMatch::operator()(
    const InMemoryURLIndex::HistoryID history_id) {
  HistoryInfoMap::const_iterator hist_pos =
      index_.history_info_map_.find(history_id);
  // Note that a history_id may be present in the word_id_history_map_ yet not
  // be found in the history_info_map_. This occurs when an item has been
  // deleted by the user or the item no longer qualifies as a quick result.
  if (hist_pos != index_.history_info_map_.end()) {
    const URLRow& hist_item = hist_pos->second;
    ScoredHistoryMatch match(ScoredMatchForURL(hist_item, lower_terms_));
    if (match.raw_score > 0)
      scored_matches_.push_back(match);
  }
}

bool InMemoryURLIndex::GetCacheFilePath(FilePath* file_path) {
  if (history_dir_.empty())
    return false;
  *file_path = history_dir_.Append(FILE_PATH_LITERAL("History Provider Cache"));
  return true;
}

bool InMemoryURLIndex::URLSchemeIsWhitelisted(const GURL& gurl) const {
  return scheme_whitelist_.find(gurl.scheme()) != scheme_whitelist_.end();
}

void InMemoryURLIndex::SavePrivateData(InMemoryURLIndexCacheItem* cache) const {
  DCHECK(cache);
  cache->set_timestamp(base::Time::Now().ToInternalValue());
  cache->set_history_item_count(history_item_count_);
  SaveWordList(cache);
  SaveWordMap(cache);
  SaveCharWordMap(cache);
  SaveWordIDHistoryMap(cache);
  SaveHistoryInfoMap(cache);
}

bool InMemoryURLIndex::RestorePrivateData(
    const InMemoryURLIndexCacheItem& cache) {
  last_saved_ = base::Time::FromInternalValue(cache.timestamp());
  history_item_count_ = cache.history_item_count();
  return (history_item_count_ == 0) || (RestoreWordList(cache) &&
      RestoreWordMap(cache) && RestoreCharWordMap(cache) &&
      RestoreWordIDHistoryMap(cache) && RestoreHistoryInfoMap(cache));
}


void InMemoryURLIndex::SaveWordList(InMemoryURLIndexCacheItem* cache) const {
  if (word_list_.empty())
    return;
  WordListItem* list_item = cache->mutable_word_list();
  list_item->set_word_count(word_list_.size());
  for (String16Vector::const_iterator iter = word_list_.begin();
       iter != word_list_.end(); ++iter)
    list_item->add_word(UTF16ToUTF8(*iter));
}

bool InMemoryURLIndex::RestoreWordList(const InMemoryURLIndexCacheItem& cache) {
  if (!cache.has_word_list())
    return false;
  const WordListItem& list_item(cache.word_list());
  uint32 expected_item_count = list_item.word_count();
  uint32 actual_item_count = list_item.word_size();
  if (actual_item_count == 0 || actual_item_count != expected_item_count)
    return false;
  const RepeatedPtrField<std::string>& words(list_item.word());
  for (RepeatedPtrField<std::string>::const_iterator iter = words.begin();
       iter != words.end(); ++iter)
    word_list_.push_back(UTF8ToUTF16(*iter));
  return true;
}

void InMemoryURLIndex::SaveWordMap(InMemoryURLIndexCacheItem* cache) const {
  if (word_map_.empty())
    return;
  WordMapItem* map_item = cache->mutable_word_map();
  map_item->set_item_count(word_map_.size());
  for (WordMap::const_iterator iter = word_map_.begin();
       iter != word_map_.end(); ++iter) {
    WordMapEntry* map_entry = map_item->add_word_map_entry();
    map_entry->set_word(UTF16ToUTF8(iter->first));
    map_entry->set_word_id(iter->second);
  }
}

bool InMemoryURLIndex::RestoreWordMap(const InMemoryURLIndexCacheItem& cache) {
  if (!cache.has_word_map())
    return false;
  const WordMapItem& list_item(cache.word_map());
  uint32 expected_item_count = list_item.item_count();
  uint32 actual_item_count = list_item.word_map_entry_size();
  if (actual_item_count == 0 || actual_item_count != expected_item_count)
    return false;
  const RepeatedPtrField<WordMapEntry>& entries(list_item.word_map_entry());
  for (RepeatedPtrField<WordMapEntry>::const_iterator iter = entries.begin();
       iter != entries.end(); ++iter)
    word_map_[UTF8ToUTF16(iter->word())] = iter->word_id();
  return true;
}

void InMemoryURLIndex::SaveCharWordMap(InMemoryURLIndexCacheItem* cache) const {
  if (char_word_map_.empty())
    return;
  CharWordMapItem* map_item = cache->mutable_char_word_map();
  map_item->set_item_count(char_word_map_.size());
  for (CharWordIDMap::const_iterator iter = char_word_map_.begin();
       iter != char_word_map_.end(); ++iter) {
    CharWordMapEntry* map_entry = map_item->add_char_word_map_entry();
    map_entry->set_char_16(iter->first);
    const WordIDSet& word_id_set(iter->second);
    map_entry->set_item_count(word_id_set.size());
    for (WordIDSet::const_iterator set_iter = word_id_set.begin();
         set_iter != word_id_set.end(); ++set_iter)
      map_entry->add_word_id(*set_iter);
  }
}

bool InMemoryURLIndex::RestoreCharWordMap(
    const InMemoryURLIndexCacheItem& cache) {
  if (!cache.has_char_word_map())
    return false;
  const CharWordMapItem& list_item(cache.char_word_map());
  uint32 expected_item_count = list_item.item_count();
  uint32 actual_item_count = list_item.char_word_map_entry_size();
  if (actual_item_count == 0 || actual_item_count != expected_item_count)
    return false;
  const RepeatedPtrField<CharWordMapEntry>&
      entries(list_item.char_word_map_entry());
  for (RepeatedPtrField<CharWordMapEntry>::const_iterator iter =
       entries.begin(); iter != entries.end(); ++iter) {
    expected_item_count = iter->item_count();
    actual_item_count = iter->word_id_size();
    if (actual_item_count == 0 || actual_item_count != expected_item_count)
      return false;
    char16 uni_char = static_cast<char16>(iter->char_16());
    WordIDSet word_id_set;
    const RepeatedField<int32>& word_ids(iter->word_id());
    for (RepeatedField<int32>::const_iterator jiter = word_ids.begin();
         jiter != word_ids.end(); ++jiter)
      word_id_set.insert(*jiter);
    char_word_map_[uni_char] = word_id_set;
  }
  return true;
}

void InMemoryURLIndex::SaveWordIDHistoryMap(InMemoryURLIndexCacheItem* cache)
    const {
  if (word_id_history_map_.empty())
    return;
  WordIDHistoryMapItem* map_item = cache->mutable_word_id_history_map();
  map_item->set_item_count(word_id_history_map_.size());
  for (WordIDHistoryMap::const_iterator iter = word_id_history_map_.begin();
       iter != word_id_history_map_.end(); ++iter) {
    WordIDHistoryMapEntry* map_entry =
        map_item->add_word_id_history_map_entry();
    map_entry->set_word_id(iter->first);
    const HistoryIDSet& history_id_set(iter->second);
    map_entry->set_item_count(history_id_set.size());
    for (HistoryIDSet::const_iterator set_iter = history_id_set.begin();
         set_iter != history_id_set.end(); ++set_iter)
      map_entry->add_history_id(*set_iter);
  }
}

bool InMemoryURLIndex::RestoreWordIDHistoryMap(
    const InMemoryURLIndexCacheItem& cache) {
  if (!cache.has_word_id_history_map())
    return false;
  const WordIDHistoryMapItem& list_item(cache.word_id_history_map());
  uint32 expected_item_count = list_item.item_count();
  uint32 actual_item_count = list_item.word_id_history_map_entry_size();
  if (actual_item_count == 0 || actual_item_count != expected_item_count)
    return false;
  const RepeatedPtrField<WordIDHistoryMapEntry>&
      entries(list_item.word_id_history_map_entry());
  for (RepeatedPtrField<WordIDHistoryMapEntry>::const_iterator iter =
       entries.begin(); iter != entries.end(); ++iter) {
    expected_item_count = iter->item_count();
    actual_item_count = iter->history_id_size();
    if (actual_item_count == 0 || actual_item_count != expected_item_count)
      return false;
    WordID word_id = iter->word_id();
    HistoryIDSet history_id_set;
    const RepeatedField<int64>& history_ids(iter->history_id());
    for (RepeatedField<int64>::const_iterator jiter = history_ids.begin();
         jiter != history_ids.end(); ++jiter)
      history_id_set.insert(*jiter);
    word_id_history_map_[word_id] = history_id_set;
  }
  return true;
}

void InMemoryURLIndex::SaveHistoryInfoMap(
    InMemoryURLIndexCacheItem* cache) const {
  if (history_info_map_.empty())
    return;
  HistoryInfoMapItem* map_item = cache->mutable_history_info_map();
  map_item->set_item_count(history_info_map_.size());
  for (HistoryInfoMap::const_iterator iter = history_info_map_.begin();
       iter != history_info_map_.end(); ++iter) {
    HistoryInfoMapEntry* map_entry = map_item->add_history_info_map_entry();
    map_entry->set_history_id(iter->first);
    const URLRow& url_row(iter->second);
    // Note: We only save information that contributes to the index so there
    // is no need to save search_term_cache_ (not persistent),
    // languages_, etc.
    map_entry->set_visit_count(url_row.visit_count());
    map_entry->set_typed_count(url_row.typed_count());
    map_entry->set_last_visit(url_row.last_visit().ToInternalValue());
    map_entry->set_url(url_row.url().spec());
    map_entry->set_title(UTF16ToUTF8(url_row.title()));
  }
}

bool InMemoryURLIndex::RestoreHistoryInfoMap(
    const InMemoryURLIndexCacheItem& cache) {
  if (!cache.has_history_info_map())
    return false;
  const HistoryInfoMapItem& list_item(cache.history_info_map());
  uint32 expected_item_count = list_item.item_count();
  uint32 actual_item_count = list_item.history_info_map_entry_size();
  if (actual_item_count == 0 || actual_item_count != expected_item_count)
    return false;
  const RepeatedPtrField<HistoryInfoMapEntry>&
      entries(list_item.history_info_map_entry());
  for (RepeatedPtrField<HistoryInfoMapEntry>::const_iterator iter =
       entries.begin(); iter != entries.end(); ++iter) {
    HistoryID history_id = iter->history_id();
    GURL url(iter->url());
    URLRow url_row(url, history_id);
    url_row.set_visit_count(iter->visit_count());
    url_row.set_typed_count(iter->typed_count());
    url_row.set_last_visit(base::Time::FromInternalValue(iter->last_visit()));
    if (iter->has_title()) {
      string16 title(UTF8ToUTF16(iter->title()));
      url_row.set_title(title);
    }
    history_info_map_[history_id] = url_row;
  }
  return true;
}

}  // namespace history