// Copyright (c) 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 "components/omnibox/browser/history_url_provider.h"

#include <algorithm>
#include <memory>
#include <utility>

#include "base/bind.h"
#include "base/command_line.h"
#include "base/feature_list.h"
#include "base/location.h"
#include "base/metrics/histogram_macros.h"
#include "base/single_thread_task_runner.h"
#include "base/strings/string_util.h"
#include "base/strings/utf_string_conversions.h"
#include "base/threading/sequenced_task_runner_handle.h"
#include "base/time/time.h"
#include "base/trace_event/memory_usage_estimator.h"
#include "base/trace_event/trace_event.h"
#include "components/bookmarks/browser/bookmark_utils.h"
#include "components/history/core/browser/history_backend.h"
#include "components/history/core/browser/history_database.h"
#include "components/history/core/browser/history_service.h"
#include "components/history/core/browser/history_types.h"
#include "components/omnibox/browser/autocomplete_match.h"
#include "components/omnibox/browser/autocomplete_match_classification.h"
#include "components/omnibox/browser/autocomplete_provider.h"
#include "components/omnibox/browser/autocomplete_provider_listener.h"
#include "components/omnibox/browser/autocomplete_result.h"
#include "components/omnibox/browser/history_provider.h"
#include "components/omnibox/browser/in_memory_url_index_types.h"
#include "components/omnibox/browser/omnibox_field_trial.h"
#include "components/omnibox/browser/url_index_private_data.h"
#include "components/omnibox/browser/url_prefix.h"
#include "components/omnibox/common/omnibox_features.h"
#include "components/prefs/pref_service.h"
#include "components/search_engines/omnibox_focus_type.h"
#include "components/search_engines/search_terms_data.h"
#include "components/search_engines/template_url_service.h"
#include "components/url_formatter/url_fixer.h"
#include "components/url_formatter/url_formatter.h"
#include "net/base/registry_controlled_domains/registry_controlled_domain.h"
#include "third_party/metrics_proto/omnibox_input_type.pb.h"
#include "url/gurl.h"
#include "url/third_party/mozilla/url_parse.h"
#include "url/url_util.h"

namespace {

// Acts like the > operator for URLInfo classes.
bool CompareHistoryMatch(const history::HistoryMatch& a,
                         const history::HistoryMatch& b) {
  // A URL that has been typed at all is better than one that has never been
  // typed.  (Note "!"s on each side)
  if (!a.url_info.typed_count() != !b.url_info.typed_count())
    return a.url_info.typed_count() > b.url_info.typed_count();

  // Innermost matches (matches after any scheme or "www.") are better than
  // non-innermost matches.
  if (a.innermost_match != b.innermost_match)
    return a.innermost_match;

  // URLs that have been typed more often are better.
  if (a.url_info.typed_count() != b.url_info.typed_count())
    return a.url_info.typed_count() > b.url_info.typed_count();

  // For URLs that have each been typed once, a host (alone) is better than a
  // page inside.
  if ((a.url_info.typed_count() == 1) && (a.IsHostOnly() != b.IsHostOnly()))
    return a.IsHostOnly();

  // URLs that have been visited more often are better.
  if (a.url_info.visit_count() != b.url_info.visit_count())
    return a.url_info.visit_count() > b.url_info.visit_count();

  // URLs that have been visited more recently are better.
  if (a.url_info.last_visit() != b.url_info.last_visit())
    return a.url_info.last_visit() > b.url_info.last_visit();

  // Use alphabetical order on the url spec as a tie-breaker.
  return a.url_info.url().spec() > b.url_info.url().spec();
}

// Sorts and dedups the given list of matches.
void SortAndDedupMatches(history::HistoryMatches* matches) {
  // Sort by quality, best first.
  std::sort(matches->begin(), matches->end(), &CompareHistoryMatch);

  // Remove duplicate matches (caused by the search string appearing in one of
  // the prefixes as well as after it).  Consider the following scenario:
  //
  // User has visited "http://http.com" once and "http://htaccess.com" twice.
  // User types "http".  The autocomplete search with prefix "http://" returns
  // the first host, while the search with prefix "" returns both hosts.  Now
  // we sort them into rank order:
  //   http://http.com     (innermost_match)
  //   http://htaccess.com (!innermost_match, url_info.visit_count == 2)
  //   http://http.com     (!innermost_match, url_info.visit_count == 1)
  //
  // The above scenario tells us we can't use std::unique(), since our
  // duplicates are not always sequential.  It also tells us we should remove
  // the lower-quality duplicate(s), since otherwise the returned results won't
  // be ordered correctly.  This is easy to do: we just always remove the later
  // element of a duplicate pair.
  // Be careful!  Because the vector contents may change as we remove elements,
  // we use an index instead of an iterator in the outer loop, and don't
  // precalculate the ending position.
  for (size_t i = 0; i < matches->size(); ++i) {
    for (history::HistoryMatches::iterator j(matches->begin() + i + 1);
         j != matches->end(); ) {
      if ((*matches)[i].url_info.url() == j->url_info.url())
        j = matches->erase(j);
      else
        ++j;
    }
  }
}

// Calculates a new relevance score applying half-life time decaying to |count|
// using |time_since_last_visit| and |score_buckets|.  This function will never
// return a score higher than |undecayed_relevance|; in other words, it can only
// demote the old score.
double CalculateRelevanceUsingScoreBuckets(
    const HUPScoringParams::ScoreBuckets& score_buckets,
    const base::TimeDelta& time_since_last_visit,
    int undecayed_relevance,
    int undecayed_count) {
  // Back off if above relevance cap.
  if ((score_buckets.relevance_cap() != -1) &&
      (undecayed_relevance >= score_buckets.relevance_cap()))
    return undecayed_relevance;

  // Time based decay using half-life time.
  double decayed_count = undecayed_count;
  double decay_factor = score_buckets.HalfLifeTimeDecay(time_since_last_visit);
  if (decayed_count > 0)
    decayed_count *= decay_factor;

  const HUPScoringParams::ScoreBuckets::CountMaxRelevance* score_bucket =
      nullptr;
  const double factor = (score_buckets.use_decay_factor() ?
      decay_factor : decayed_count);
  for (size_t i = 0; i < score_buckets.buckets().size(); ++i) {
    score_bucket = &score_buckets.buckets()[i];
    if (factor >= score_bucket->first)
      break;
  }

  return (score_bucket && (undecayed_relevance > score_bucket->second)) ?
      score_bucket->second : undecayed_relevance;
}

// Returns a new relevance score for the given |match| based on the
// |old_relevance| score and |scoring_params|.  The new relevance score is
// guaranteed to be less than or equal to |old_relevance|.  In other words, this
// function can only demote a score, never boost it.  Returns |old_relevance| if
// experimental scoring is disabled.
int CalculateRelevanceScoreUsingScoringParams(
    const history::HistoryMatch& match,
    int old_relevance,
    const HUPScoringParams& scoring_params) {
  const base::TimeDelta time_since_last_visit =
      base::Time::Now() - match.url_info.last_visit();

  int relevance = CalculateRelevanceUsingScoreBuckets(
      scoring_params.typed_count_buckets, time_since_last_visit, old_relevance,
      match.url_info.typed_count());

  // Additional demotion (on top of typed_count demotion) of URLs that were
  // never typed.
  if (match.url_info.typed_count() == 0) {
    relevance = CalculateRelevanceUsingScoreBuckets(
        scoring_params.visited_count_buckets, time_since_last_visit, relevance,
        match.url_info.visit_count());
  }

  DCHECK_LE(relevance, old_relevance);
  return relevance;
}

// Extracts typed_count, visit_count, and last_visited time from the URLRow and
// puts them in the additional info field of the |match| for display in
// about:omnibox.
void RecordAdditionalInfoFromUrlRow(const history::URLRow& info,
                                    AutocompleteMatch* match) {
  match->RecordAdditionalInfo("typed count", info.typed_count());
  match->RecordAdditionalInfo("visit count", info.visit_count());
  match->RecordAdditionalInfo("last visit", info.last_visit());
}

// If |create_if_necessary| is true, ensures that |matches| contains an entry
// for |info|, creating a new such entry if necessary (using |match_template|
// to get all the other match data).
//
// If |promote| is true, this also ensures the entry is the first element in
// |matches|, moving or adding it to the front as appropriate.  When |promote|
// is false, existing matches are left in place, and newly added matches are
// placed at the back.
//
// It's OK to call this function with both |create_if_necessary| and |promote|
// false, in which case we'll do nothing.
//
// Returns whether the match exists regardless if it was promoted/created.
bool CreateOrPromoteMatch(const history::URLRow& info,
                          const history::HistoryMatch& match_template,
                          history::HistoryMatches* matches,
                          bool create_if_necessary,
                          bool promote) {
  // |matches| may already have an entry for this.
  for (history::HistoryMatches::iterator i(matches->begin());
       i != matches->end(); ++i) {
    if (i->url_info.url() == info.url()) {
      // Rotate it to the front if the caller wishes.
      if (promote)
        std::rotate(matches->begin(), i, i + 1);
      return true;
    }
  }

  if (!create_if_necessary)
    return false;

  // No entry, so create one using |match_template| as a basis.
  history::HistoryMatch match = match_template;
  match.url_info = info;
  if (promote)
    matches->push_front(match);
  else
    matches->push_back(match);

  return true;
}

// Returns whether |match| is suitable for inline autocompletion.
bool CanPromoteMatchForInlineAutocomplete(const history::HistoryMatch& match) {
  // We can promote this match if it's been typed at least n times, where n == 1
  // for "simple" (host-only) URLs and n == 2 for others.  We set a higher bar
  // for these long URLs because it's less likely that users will want to visit
  // them again.  Even though we don't increment the typed_count for pasted-in
  // URLs, if the user manually edits the URL or types some long thing in by
  // hand, we wouldn't want to immediately start autocompleting it.
  return match.url_info.typed_count() &&
      ((match.url_info.typed_count() > 1) || match.IsHostOnly());
}

// Given the user's |input| and a |match| created from it, reduce the match's
// URL to just a host.  If this host still matches the user input, return it.
// Returns the empty string on failure.
GURL ConvertToHostOnly(const history::HistoryMatch& match,
                       const base::string16& input) {
  // See if we should try to do host-only suggestions for this URL. Nonstandard
  // schemes means there's no authority section, so suggesting the host name
  // is useless. File URLs are standard, but host suggestion is not useful for
  // them either.
  const GURL& url = match.url_info.url();
  if (!url.is_valid() || !url.IsStandard() || url.SchemeIsFile())
    return GURL();

  // Transform to a host-only match.  Bail if the host no longer matches the
  // user input (e.g. because the user typed more than just a host).
  GURL host = url.GetWithEmptyPath();
  if ((host.spec().length() < (match.input_location + input.length())))
    return GURL();  // User typing is longer than this host suggestion.

  const base::string16 spec = base::UTF8ToUTF16(host.spec());
  if (spec.compare(match.input_location, input.length(), input))
    return GURL();  // User typing is no longer a prefix.

  return host;
}

}  // namespace

// -----------------------------------------------------------------
// SearchTermsDataSnapshot

// Implementation of SearchTermsData that takes a snapshot of another
// SearchTermsData by copying all the responses to the different getters into
// member strings, then returning those strings when its own getters are called.
// This will typically be constructed on the UI thread from
// UIThreadSearchTermsData but is subsequently safe to use on any thread.
class SearchTermsDataSnapshot : public SearchTermsData {
 public:
  explicit SearchTermsDataSnapshot(const SearchTermsData* search_terms_data);
  ~SearchTermsDataSnapshot() override;
  SearchTermsDataSnapshot(const SearchTermsDataSnapshot&) = delete;
  SearchTermsDataSnapshot& operator=(const SearchTermsDataSnapshot&) = delete;

  std::string GoogleBaseURLValue() const override;
  std::string GetApplicationLocale() const override;
  base::string16 GetRlzParameterValue(bool from_app_list) const override;
  std::string GetSearchClient() const override;
  std::string GoogleImageSearchSource() const override;

  // Estimates dynamic memory usage.
  // See base/trace_event/memory_usage_estimator.h for more info.
  size_t EstimateMemoryUsage() const override;

 private:
  std::string google_base_url_value_;
  std::string application_locale_;
  base::string16 rlz_parameter_value_;
  std::string search_client_;
  std::string google_image_search_source_;
};

SearchTermsDataSnapshot::SearchTermsDataSnapshot(
    const SearchTermsData* search_terms_data) {
  if (search_terms_data) {
    google_base_url_value_ = search_terms_data->GoogleBaseURLValue();
    application_locale_ = search_terms_data->GetApplicationLocale();
    rlz_parameter_value_ = search_terms_data->GetRlzParameterValue(false);
    search_client_ = search_terms_data->GetSearchClient();
    google_image_search_source_ = search_terms_data->GoogleImageSearchSource();
  }
}

SearchTermsDataSnapshot::~SearchTermsDataSnapshot() {
}

std::string SearchTermsDataSnapshot::GoogleBaseURLValue() const {
  return google_base_url_value_;
}

std::string SearchTermsDataSnapshot::GetApplicationLocale() const {
  return application_locale_;
}

base::string16 SearchTermsDataSnapshot::GetRlzParameterValue(
    bool from_app_list) const {
  return rlz_parameter_value_;
}

std::string SearchTermsDataSnapshot::GetSearchClient() const {
  return search_client_;
}

std::string SearchTermsDataSnapshot::GoogleImageSearchSource() const {
  return google_image_search_source_;
}

size_t SearchTermsDataSnapshot::EstimateMemoryUsage() const {
  size_t res = 0;

  res += base::trace_event::EstimateMemoryUsage(google_base_url_value_);
  res += base::trace_event::EstimateMemoryUsage(application_locale_);
  res += base::trace_event::EstimateMemoryUsage(rlz_parameter_value_);
  res += base::trace_event::EstimateMemoryUsage(search_client_);
  res += base::trace_event::EstimateMemoryUsage(google_image_search_source_);

  return res;
}

// -----------------------------------------------------------------
// HistoryURLProvider

// These ugly magic numbers will go away once we switch all scoring
// behavior (including URL-what-you-typed) to HistoryQuick provider.
const int HistoryURLProvider::kScoreForBestInlineableResult = 1413;
const int HistoryURLProvider::kScoreForUnvisitedIntranetResult = 1403;
const int HistoryURLProvider::kScoreForWhatYouTypedResult = 1203;
const int HistoryURLProvider::kBaseScoreForNonInlineableResult = 900;

// VisitClassifier is used to classify the type of visit to a particular url.
class HistoryURLProvider::VisitClassifier {
 public:
  enum Type {
    INVALID,             // Navigations to the URL are not allowed.
    UNVISITED_INTRANET,  // A navigable URL for which we have no visit data but
                         // which is known to refer to a visited intranet host.
    VISITED,             // The site has been previously visited.
  };

  VisitClassifier(HistoryURLProvider* provider,
                  const AutocompleteInput& input,
                  history::URLDatabase* db);

  VisitClassifier(const VisitClassifier&) = delete;
  VisitClassifier& operator=(const VisitClassifier&) = delete;

  // Returns the type of visit for the specified input.
  Type type() const { return type_; }

  // Returns the URLRow for the visit.
  // If the type of the visit is UNVISITED_INTRANET, the return value of this
  // function does not have any visit data; only the URL field is set.
  const history::URLRow& url_row() const { return url_row_; }

 private:
  HistoryURLProvider* provider_;
  history::URLDatabase* db_;
  Type type_;
  history::URLRow url_row_;
};

HistoryURLProvider::VisitClassifier::VisitClassifier(
    HistoryURLProvider* provider,
    const AutocompleteInput& input,
    history::URLDatabase* db)
    : provider_(provider),
      db_(db),
      type_(INVALID) {
  // Detect email addresses.  These cases will look like "http://user@site/",
  // and because the history backend strips auth creds, we'll get a bogus exact
  // match below if the user has visited "site".
  if ((input.type() == metrics::OmniboxInputType::UNKNOWN) &&
      input.parts().username.is_nonempty() &&
      !input.parts().password.is_nonempty() &&
      !input.parts().path.is_nonempty())
    return;

  // If the input can be canonicalized to a valid URL, look up all
  // prefix+input combinations in the URL database to determine if the input
  // corresponds to any visited URL.
  if (!input.canonicalized_url().is_valid())
    return;

  // Iterate over all prefixes in ascending number of components (i.e. from the
  // empty prefix to those that have most components).
  const std::string& desired_tld = input.desired_tld();
  const URLPrefixes& url_prefixes = URLPrefix::GetURLPrefixes();
  for (auto prefix_it = url_prefixes.rbegin(); prefix_it != url_prefixes.rend();
       ++prefix_it) {
    const GURL url_with_prefix = url_formatter::FixupURL(
        base::UTF16ToUTF8(prefix_it->prefix + input.text()), desired_tld);
    if (url_with_prefix.is_valid() &&
        db_->GetRowForURL(url_with_prefix, &url_row_) && !url_row_.hidden()) {
      type_ = VISITED;
      return;
    }
  }

  // If the input does not correspond to a visited URL, we check if the
  // canonical URL has an intranet hostname that the user visited (albeit with a
  // different port and/or path) before. If this is true, |url_row_| will be
  // mostly empty: the URL field will be set to an unvisited URL with the same
  // scheme and host as some visited URL in the db.
  const GURL as_known_intranet_url = provider_->AsKnownIntranetURL(db_, input);
  if (as_known_intranet_url.is_valid()) {
    url_row_ = history::URLRow(as_known_intranet_url);
    type_ = UNVISITED_INTRANET;
  }
}

HistoryURLProviderParams::HistoryURLProviderParams(
    const AutocompleteInput& input,
    const AutocompleteInput& input_before_fixup,
    bool trim_http,
    const AutocompleteMatch& what_you_typed_match,
    const TemplateURL* default_search_provider,
    const SearchTermsData* search_terms_data)
    : origin_task_runner(base::SequencedTaskRunnerHandle::Get()),
      input(input),
      input_before_fixup(input_before_fixup),
      trim_http(trim_http),
      what_you_typed_match(what_you_typed_match),
      failed(false),
      exact_suggestion_is_in_history(false),
      promote_type(NEITHER),
      default_search_provider(
          default_search_provider
              ? new TemplateURL(default_search_provider->data())
              : nullptr),
      search_terms_data(new SearchTermsDataSnapshot(search_terms_data)) {}

HistoryURLProviderParams::~HistoryURLProviderParams() {
}

size_t HistoryURLProviderParams::EstimateMemoryUsage() const {
  size_t res = 0;

  res += base::trace_event::EstimateMemoryUsage(input);
  res += base::trace_event::EstimateMemoryUsage(what_you_typed_match);
  res += base::trace_event::EstimateMemoryUsage(matches);
  res += base::trace_event::EstimateMemoryUsage(default_search_provider);
  res += base::trace_event::EstimateMemoryUsage(search_terms_data);

  return res;
}

HistoryURLProvider::HistoryURLProvider(AutocompleteProviderClient* client,
                                       AutocompleteProviderListener* listener)
    : HistoryProvider(AutocompleteProvider::TYPE_HISTORY_URL, client),
      listener_(listener),
      params_(nullptr),
      search_url_database_(OmniboxFieldTrial::HUPSearchDatabase()) {
  // Initialize the default HUP scoring params.
  OmniboxFieldTrial::GetDefaultHUPScoringParams(&scoring_params_);
  // Initialize HUP scoring params based on the current experiment.
  OmniboxFieldTrial::GetExperimentalHUPScoringParams(&scoring_params_);
}

void HistoryURLProvider::Start(const AutocompleteInput& input,
                               bool minimal_changes) {
  TRACE_EVENT0("omnibox", "HistoryURLProvider::Start");
  // NOTE: We could try hard to do less work in the |minimal_changes| case
  // here; some clever caching would let us reuse the raw matches from the
  // history DB without re-querying.  However, we'd still have to go back to
  // the history thread to mark these up properly, and if pass 2 is currently
  // running, we'd need to wait for it to return to the main thread before
  // doing this (we can't just write new data for it to read due to thread
  // safety issues).  At that point it's just as fast, and easier, to simply
  // re-run the query from scratch and ignore |minimal_changes|.

  // Cancel any in-progress query.
  Stop(false, false);

  matches_.clear();

  if (input.focus_type() != OmniboxFocusType::DEFAULT ||
      (input.type() == metrics::OmniboxInputType::EMPTY))
    return;

  // Do some fixup on the user input before matching against it, so we provide
  // good results for local file paths, input with spaces, etc.
  const FixupReturn fixup_return(FixupUserInput(input));
  if (!fixup_return.first)
    return;
  url::Parsed parts;
  url_formatter::SegmentURL(fixup_return.second, &parts);
  AutocompleteInput fixed_up_input(input);
  fixed_up_input.UpdateText(fixup_return.second, base::string16::npos, parts);

  // Create a match for what the user typed.
  const bool trim_http = !AutocompleteInput::HasHTTPScheme(input.text());
  AutocompleteMatch what_you_typed_match(SuggestExactInput(
      fixed_up_input, fixed_up_input.canonicalized_url(), trim_http));

  // If the input fix-up above added characters, show them as an
  // autocompletion, unless directed not to.
  if (!input.prevent_inline_autocomplete() &&
      fixed_up_input.text().size() > input.text().size() &&
      base::StartsWith(fixed_up_input.text(), input.text(),
                       base::CompareCase::SENSITIVE)) {
    what_you_typed_match.fill_into_edit = fixed_up_input.text();
    what_you_typed_match.inline_autocompletion =
        fixed_up_input.text().substr(input.text().size());
    what_you_typed_match.contents_class.push_back(
        {input.text().length(), ACMatchClassification::URL});
  }

  what_you_typed_match.relevance = CalculateRelevance(WHAT_YOU_TYPED, 0);

  // Add the what-you-typed match as a fallback in case we can't get the history
  // service or URL DB; otherwise, we'll replace this match lower down.  Don't
  // do this for queries, though -- while we can sometimes mark up a match for
  // them, it's not what the user wants, and just adds noise.
  if (fixed_up_input.type() != metrics::OmniboxInputType::QUERY)
    matches_.push_back(what_you_typed_match);

  // We'll need the history service to run both passes, so try to obtain it.
  history::HistoryService* const history_service =
      client()->GetHistoryService();
  if (!history_service)
    return;

  // Get the default search provider and search terms data now since we have to
  // retrieve these on the UI thread, and the second pass runs on the history
  // thread. |template_url_service| can be null when testing.
  TemplateURLService* template_url_service = client()->GetTemplateURLService();
  const TemplateURL* default_search_provider = template_url_service ?
      template_url_service->GetDefaultSearchProvider() : nullptr;
  const SearchTermsData* search_terms_data =
      template_url_service ? &template_url_service->search_terms_data()
                           : nullptr;

  // Create the data structure for the autocomplete passes.  We'll save this off
  // onto the |params_| member for later deletion below if we need to run pass
  // 2.
  std::unique_ptr<HistoryURLProviderParams> params(new HistoryURLProviderParams(
      fixed_up_input, input, trim_http, what_you_typed_match,
      default_search_provider, search_terms_data));

  // Pass 1: Get the in-memory URL database, and use it to find and promote
  // the inline autocomplete match, if any.
  history::URLDatabase* url_db = history_service->InMemoryDatabase();
  // url_db can be null if it hasn't finished initializing (or failed to
  // initialize).  In this case all we can do is fall back on the second pass.
  //
  // TODO(pkasting): We should just block here until this loads.  Any time
  // someone unloads the history backend, we'll get inconsistent inline
  // autocomplete behavior here.
  if (url_db) {
    DoAutocomplete(nullptr, url_db, params.get());
    matches_.clear();
    PromoteMatchesIfNecessary(*params);
    // NOTE: We don't reset |params| here since at least the |promote_type|
    // field on it will be read by the second pass -- see comments in
    // DoAutocomplete().
  }

  // Pass 2: Ask the history service to call us back on the history thread,
  // where we can read the full on-disk DB.
  if (search_url_database_ && input.want_asynchronous_matches()) {
    done_ = false;
    params_ = params.release();  // This object will be destroyed in
                                 // QueryComplete() once we're done with it.
    history_service->ScheduleAutocomplete(
        base::BindOnce(&HistoryURLProvider::ExecuteWithDB, this, params_));
  }
}

void HistoryURLProvider::Stop(bool clear_cached_results,
                              bool due_to_user_inactivity) {
  done_ = true;

  if (params_)
    params_->cancel_flag.Set();
}

size_t HistoryURLProvider::EstimateMemoryUsage() const {
  size_t res = HistoryProvider::EstimateMemoryUsage();

  if (params_)
    res += base::trace_event::EstimateMemoryUsage(*params_);
  res += base::trace_event::EstimateMemoryUsage(scoring_params_);

  return res;
}

AutocompleteMatch HistoryURLProvider::SuggestExactInput(
    const AutocompleteInput& input,
    const GURL& destination_url,
    bool trim_http) {
  // The FormattedStringWithEquivalentMeaning() call below requires callers to
  // be on the main thread.
  DCHECK(thread_checker_.CalledOnValidThread());

  AutocompleteMatch match(this, 0, false,
                          AutocompleteMatchType::URL_WHAT_YOU_TYPED);

  if (destination_url.is_valid()) {
    match.destination_url = destination_url;

    // If the input explicitly contains "http://", callers must set |trim_http|
    // to false. Otherwise, |trim_http| may be either true or false.
    DCHECK(!(trim_http && AutocompleteInput::HasHTTPScheme(input.text())));
    base::string16 display_string(url_formatter::FormatUrl(
        destination_url,
        url_formatter::kFormatUrlOmitDefaults &
            ~url_formatter::kFormatUrlOmitHTTP,
        net::UnescapeRule::SPACES, nullptr, nullptr, nullptr));
    if (trim_http)
      TrimHttpPrefix(&display_string);
    match.fill_into_edit =
        AutocompleteInput::FormattedStringWithEquivalentMeaning(
            destination_url, display_string, client()->GetSchemeClassifier(),
            nullptr);
    // The what-you-typed match is generally only allowed to be default for
    // URL inputs or when there is no default search provider.  (It's also
    // allowed to be default for UNKNOWN inputs where the destination is a known
    // intranet site.  In this case, |allowed_to_be_default_match| is revised in
    // FixupExactSuggestion().)
    const bool has_default_search_provider =
       client()->GetTemplateURLService() &&
       client()->GetTemplateURLService()->GetDefaultSearchProvider();
    match.allowed_to_be_default_match =
        (input.type() == metrics::OmniboxInputType::URL) ||
        !has_default_search_provider;
    // NOTE: Don't set match.inline_autocompletion to something non-empty here;
    // it's surprising and annoying.

    // Try to highlight "innermost" match location.  If we fix up "w" into
    // "www.w.com", we want to highlight the fifth character, not the first.
    // This relies on match.destination_url being the non-prefix-trimmed version
    // of match.contents.
    match.contents = display_string;

    TermMatches termMatches = {{0, 0, input.text().length()}};
    match.contents_class = ClassifyTermMatches(
        termMatches, match.contents.size(),
        ACMatchClassification::MATCH | ACMatchClassification::URL,
        ACMatchClassification::URL);
  }

  return match;
}

void HistoryURLProvider::ExecuteWithDB(HistoryURLProviderParams* params,
                                       history::HistoryBackend* backend,
                                       history::URLDatabase* db) {
  // We may get called with a null database if it couldn't be properly
  // initialized.
  if (!db) {
    params->failed = true;
  } else if (!params->cancel_flag.IsSet()) {
    base::TimeTicks beginning_time = base::TimeTicks::Now();

    DoAutocomplete(backend, db, params);

    UMA_HISTOGRAM_TIMES("Autocomplete.HistoryAsyncQueryTime",
                        base::TimeTicks::Now() - beginning_time);
  }

  // Return the results (if any) to the originating sequence.
  params->origin_task_runner->PostTask(
      FROM_HERE,
      base::BindOnce(&HistoryURLProvider::QueryComplete, this, params));
}

HistoryURLProvider::~HistoryURLProvider() {
  // Note: This object can get leaked on shutdown if there are pending
  // requests on the database (which hold a reference to us). Normally, these
  // messages get flushed for each thread. We do a round trip from main, to
  // history, back to main while holding a reference. If the main thread
  // completes before the history thread, the message to delegate back to the
  // main thread will not run and the reference will leak. Therefore, don't do
  // anything on destruction.
}

// static
int HistoryURLProvider::CalculateRelevance(MatchType match_type,
                                           int match_number) {
  switch (match_type) {
    case INLINE_AUTOCOMPLETE:
      return kScoreForBestInlineableResult;

    case UNVISITED_INTRANET:
      return kScoreForUnvisitedIntranetResult;

    case WHAT_YOU_TYPED:
      return kScoreForWhatYouTypedResult;

    default:  // NORMAL
      return kBaseScoreForNonInlineableResult + match_number;
  }
}

// static
ACMatchClassifications HistoryURLProvider::ClassifyDescription(
    const base::string16& input_text,
    const base::string16& description) {
  TermMatches term_matches = FindTermMatches(input_text, description);
  return ClassifyTermMatches(term_matches, description.size(),
                             ACMatchClassification::MATCH,
                             ACMatchClassification::NONE);
}

void HistoryURLProvider::DoAutocomplete(history::HistoryBackend* backend,
                                        history::URLDatabase* db,
                                        HistoryURLProviderParams* params) {
  // Get the matching URLs from the DB.
  params->matches.clear();
  history::URLRows url_matches;

  if (search_url_database_) {
    const URLPrefixes& prefixes = URLPrefix::GetURLPrefixes();
    const bool hide_visits_from_cct =
        base::FeatureList::IsEnabled(omnibox::kHideVisitsFromCct);
    for (auto i(prefixes.begin()); i != prefixes.end(); ++i) {
      if (params->cancel_flag.IsSet())
        return;  // Canceled in the middle of a query, give up.

      // We only need provider_max_matches_ results in the end, but before we
      // get there we need to promote lower-quality matches that are prefixes of
      // higher- quality matches, and remove lower-quality redirects.  So we ask
      // for more results than we need, of every prefix type, in hopes this will
      // give us far more than enough to work with.  CullRedirects() will then
      // reduce the list to the best provider_max_matches_ results.
      std::string prefixed_input =
          base::UTF16ToUTF8(i->prefix + params->input.text());
      db->AutocompleteForPrefix(prefixed_input, provider_max_matches_ * 2,
                                !backend, &url_matches);
      for (history::URLRows::const_iterator j(url_matches.begin());
           j != url_matches.end(); ++j) {
        if (hide_visits_from_cct && backend) {
          history::VisitVector visits;
          if (db->GetVisitsForUrl2(j->id(), &visits) &&
              URLIndexPrivateData::ShouldExcludeBecauseOfCctVisits(visits))
            continue;
        }
        const GURL& row_url = j->url();
        const URLPrefix* best_prefix = URLPrefix::BestURLPrefix(
            base::UTF8ToUTF16(row_url.spec()), base::string16());
        DCHECK(best_prefix);
        history::HistoryMatch match;
        match.url_info = *j;
        match.input_location = i->prefix.length();
        match.innermost_match =
            i->num_components >= best_prefix->num_components;

        AutocompleteMatch::GetMatchComponents(
            row_url, {{match.input_location, prefixed_input.length()}},
            &match.match_in_scheme, &match.match_in_subdomain);

        params->matches.push_back(std::move(match));
      }
    }

    // Create sorted list of suggestions.
    CullPoorMatches(params);
    SortAndDedupMatches(&params->matches);
  }

  // Try to create a shorter suggestion from the best match.
  // We consider the what you typed match eligible for display when it's
  // navigable and there's a reasonable chance the user intended to do
  // something other than search.  We use a variety of heuristics to determine
  // this, e.g. whether the user explicitly typed a scheme, or if omnibox
  // searching has been disabled by policy. In the cases where we've parsed as
  // UNKNOWN, we'll still show an accidental search infobar if need be.
  VisitClassifier classifier(this, params->input, db);
  params->have_what_you_typed_match =
      (params->input.type() != metrics::OmniboxInputType::QUERY) &&
      ((params->input.type() != metrics::OmniboxInputType::UNKNOWN) ||
       (classifier.type() == VisitClassifier::UNVISITED_INTRANET) ||
       !params->trim_http ||
       (AutocompleteInput::NumNonHostComponents(params->input.parts()) > 0) ||
       !params->default_search_provider);
  const bool have_shorter_suggestion_suitable_for_inline_autocomplete =
      PromoteOrCreateShorterSuggestion(db, params);

  // Check whether what the user typed appears in history.
  const bool can_check_history_for_exact_match =
      // Checking what_you_typed_match.destination_url.is_valid() tells us
      // whether SuggestExactInput() succeeded in constructing a valid match.
      params->what_you_typed_match.destination_url.is_valid() &&
      // Additionally, in the case where the user has typed "foo.com" and
      // visited (but not typed) "foo/", and the input is "foo", the first pass
      // will fall into the FRONT_HISTORY_MATCH case for "foo.com" but the
      // second pass can suggest the exact input as a better URL.  Since we need
      // both passes to agree, and since during the first pass there's no way to
      // know about "foo/", ensure that if the promote type was set to
      // FRONT_HISTORY_MATCH during the first pass, the second pass will not
      // consider the exact suggestion to be in history and therefore will not
      // suggest the exact input as a better match.  (Note that during the first
      // pass, this conditional will always succeed since |promote_type| is
      // initialized to NEITHER.)
      (params->promote_type != HistoryURLProviderParams::FRONT_HISTORY_MATCH);
  params->exact_suggestion_is_in_history = can_check_history_for_exact_match &&
      FixupExactSuggestion(db, classifier, params);

  // If we succeeded in fixing up the exact match based on the user's history,
  // we should treat it as the best match regardless of input type.  If not,
  // then we check whether there's an inline autocompletion we can create from
  // this input, so we can promote that as the best match.
  if (params->exact_suggestion_is_in_history) {
    params->promote_type = HistoryURLProviderParams::WHAT_YOU_TYPED_MATCH;
  } else if (!params->matches.empty() &&
             (have_shorter_suggestion_suitable_for_inline_autocomplete ||
              CanPromoteMatchForInlineAutocomplete(params->matches[0]))) {
    // Note that we promote this inline-autocompleted match even when
    // params->prevent_inline_autocomplete is true.  This is safe because in
    // this case the match will be marked as "not allowed to be default", and
    // a non-inlined match that is "allowed to be default" will be reordered
    // above it by the controller/AutocompleteResult.  We ensure there is such
    // a match in two ways:
    //   * If params->have_what_you_typed_match is true, we force the
    //     what-you-typed match to be added in this case.  See comments in
    //     PromoteMatchesIfNecessary().
    //   * Otherwise, we should have some sort of QUERY or UNKNOWN input that
    //     the SearchProvider will provide a defaultable what-you-typed match
    //     for.
    params->promote_type = HistoryURLProviderParams::FRONT_HISTORY_MATCH;
  } else {
    // Failed to promote any URLs.  Use the What You Typed match, if we have it.
    params->promote_type = params->have_what_you_typed_match ?
        HistoryURLProviderParams::WHAT_YOU_TYPED_MATCH :
        HistoryURLProviderParams::NEITHER;
  }

  const size_t max_results =
      provider_max_matches_ + (params->exact_suggestion_is_in_history ? 1 : 0);
  if (backend) {
    // Remove redirects and trim list to size.  We want to provide up to
    // provider_max_matches_ results plus the What You Typed result, if it was
    // added to params->matches above.
    CullRedirects(backend, &params->matches, max_results);
  } else if (params->matches.size() > max_results) {
    // Simply trim the list to size.
    params->matches.resize(max_results);
  }
}

void HistoryURLProvider::PromoteMatchesIfNecessary(
    const HistoryURLProviderParams& params) {
  if (params.promote_type == HistoryURLProviderParams::NEITHER)
    return;
  if (params.promote_type == HistoryURLProviderParams::FRONT_HISTORY_MATCH) {
    matches_.push_back(
        HistoryMatchToACMatch(params, 0,
                              CalculateRelevance(INLINE_AUTOCOMPLETE, 0)));
  }
  // There are two cases where we need to add the what-you-typed-match:
  //   * If params.promote_type is WHAT_YOU_TYPED_MATCH, we're being explicitly
  //     directed to.
  //   * If params.have_what_you_typed_match is true, then params.promote_type
  //     can't be NEITHER (see code near the end of DoAutocomplete()), so if
  //     it's not WHAT_YOU_TYPED_MATCH, it must be FRONT_HISTORY_MATCH, and
  //     we'll have promoted the history match above.  If
  //     params.prevent_inline_autocomplete is also true, then this match
  //     will be marked "not allowed to be default", and we need to add the
  //     what-you-typed match to ensure there's a legal default match for the
  //     controller/AutocompleteResult to promote.  (If
  //     params.have_what_you_typed_match is false, the SearchProvider should
  //     take care of adding this defaultable match.)
  if ((params.promote_type == HistoryURLProviderParams::WHAT_YOU_TYPED_MATCH) ||
      (!matches_.back().allowed_to_be_default_match &&
       params.have_what_you_typed_match)) {
    matches_.push_back(params.what_you_typed_match);
  }
}

void HistoryURLProvider::QueryComplete(
    HistoryURLProviderParams* params_gets_deleted) {
  TRACE_EVENT0("omnibox", "HistoryURLProvider::QueryComplete");
  // Ensure |params_gets_deleted| gets deleted on exit.
  std::unique_ptr<HistoryURLProviderParams> params(params_gets_deleted);

  // If the user hasn't already started another query, clear our member pointer
  // so we can't write into deleted memory.
  if (params_ == params_gets_deleted)
    params_ = nullptr;

  // Don't send responses for queries that have been canceled.
  if (params->cancel_flag.IsSet())
    return;  // Already set done_ when we canceled, no need to set it again.

  // Don't modify |matches_| if the query failed, since it might have a default
  // match in it, whereas |params->matches| will be empty.
  if (!params->failed) {
    matches_.clear();
    PromoteMatchesIfNecessary(*params);

    // Determine relevance of highest scoring match, if any.
    int relevance = matches_.empty() ?
        CalculateRelevance(NORMAL,
                           static_cast<int>(params->matches.size() - 1)) :
        matches_[0].relevance;

    // Convert the history matches to autocomplete matches.  If we promoted the
    // first match, skip over it.
    const size_t first_match =
        (params->exact_suggestion_is_in_history ||
         (params->promote_type ==
             HistoryURLProviderParams::FRONT_HISTORY_MATCH)) ? 1 : 0;
    for (size_t i = first_match; i < params->matches.size(); ++i) {
      // All matches score one less than the previous match.
      --relevance;
      // The experimental scoring must not change the top result's score.
      if (!matches_.empty()) {
        relevance = CalculateRelevanceScoreUsingScoringParams(
            params->matches[i], relevance, scoring_params_);
      }
      matches_.push_back(HistoryMatchToACMatch(*params, i, relevance));
    }
  }

  done_ = true;
  listener_->OnProviderUpdate(true);
}

bool HistoryURLProvider::FixupExactSuggestion(
    history::URLDatabase* db,
    const VisitClassifier& classifier,
    HistoryURLProviderParams* params) const {
  MatchType type = INLINE_AUTOCOMPLETE;

  switch (classifier.type()) {
    case VisitClassifier::INVALID:
      return false;
    case VisitClassifier::UNVISITED_INTRANET:
      params->what_you_typed_match.destination_url = classifier.url_row().url();
      type = UNVISITED_INTRANET;
      break;
    default:
      DCHECK_EQ(VisitClassifier::VISITED, classifier.type());
      // We have data for this match, use it.
      params->what_you_typed_match.deletable = true;
      auto title = classifier.url_row().title();
      if (OmniboxFieldTrial::RichAutocompletionShowTitles())
        params->what_you_typed_match.fill_into_edit_additional_text = title;
      params->what_you_typed_match.description = title;
      params->what_you_typed_match.destination_url = classifier.url_row().url();
      RecordAdditionalInfoFromUrlRow(classifier.url_row(),
                                     &params->what_you_typed_match);
      params->what_you_typed_match.description_class = ClassifyDescription(
          params->input.text(), params->what_you_typed_match.description);
      if (!classifier.url_row().typed_count()) {
        // If we reach here, we must be in the second pass, and we must not have
        // this row's data available during the first pass.  That means we
        // either scored it as WHAT_YOU_TYPED or UNVISITED_INTRANET, and to
        // maintain the ordering between passes consistent, we need to score it
        // the same way here.
        const GURL as_known_intranet_url =
            AsKnownIntranetURL(db, params->input);
        type = as_known_intranet_url.is_valid() ? UNVISITED_INTRANET
                                                : WHAT_YOU_TYPED;
      }
      break;
  }

  const GURL& url = params->what_you_typed_match.destination_url;
  const url::Parsed& parsed = url.parsed_for_possibly_invalid_spec();
  // If the what-you-typed result looks like a single word (which can be
  // interpreted as an intranet address) followed by a pound sign ("#"), leave
  // the score for the url-what-you-typed result as is and also don't mark it
  // as allowed to be the default match.  It will likely be outscored by a
  // search query from the SearchProvider or, if not, the search query default
  // match will in any case--which is allowed to be the default match--will be
  // reordered to be first.  This test fixes cases such as "c#" and "c# foo"
  // where the user has visited an intranet site "c".  We want the search-what-
  // you-typed score to beat the URL-what-you-typed score in this case.  Most
  // of the below test tries to make sure that this code does not trigger if
  // the user did anything to indicate the desired match is a URL.  For
  // instance, "c/# foo" will not pass the test because that will be classified
  // as input type URL.  The parsed.CountCharactersBefore() in the test looks
  // for the presence of a reference fragment in the URL by checking whether
  // the position differs included the delimiter (pound sign) versus not
  // including the delimiter.  (One cannot simply check url.ref() because it
  // will not distinguish between the input "c" and the input "c#", both of
  // which will have empty reference fragments.)
  if ((type == UNVISITED_INTRANET) &&
      (params->input.type() != metrics::OmniboxInputType::URL) &&
      url.username().empty() && url.password().empty() && url.port().empty() &&
      (url.path_piece() == "/") && url.query().empty() &&
      (parsed.CountCharactersBefore(url::Parsed::REF, true) !=
       parsed.CountCharactersBefore(url::Parsed::REF, false))) {
    return false;
  }

  params->what_you_typed_match.allowed_to_be_default_match = true;
  params->what_you_typed_match.relevance = CalculateRelevance(type, 0);

  // If there are any other matches, then don't promote this match here, in
  // hopes the caller will be able to inline autocomplete a better suggestion.
  // DoAutocomplete() will fall back on this match if inline autocompletion
  // fails.  This matches how we react to never-visited URL inputs in the non-
  // intranet case.
  if (type == UNVISITED_INTRANET && !params->matches.empty())
    return false;

  // Put it on the front of the HistoryMatches for redirect culling.
  CreateOrPromoteMatch(classifier.url_row(), history::HistoryMatch(),
                       &params->matches, true, true);
  return true;
}

GURL HistoryURLProvider::AsKnownIntranetURL(
    history::URLDatabase* db,
    const AutocompleteInput& input) const {
  // Normally passing the first two conditions below ought to guarantee the
  // third condition, but because FixupUserInput() can run and modify the
  // input's text and parts between Parse() and here, it seems better to be
  // paranoid and check.
  if ((input.type() != metrics::OmniboxInputType::UNKNOWN) ||
      !base::LowerCaseEqualsASCII(input.scheme(), url::kHttpScheme) ||
      !input.parts().host.is_nonempty())
    return GURL();

  const std::string host(base::UTF16ToUTF8(
      input.text().substr(input.parts().host.begin, input.parts().host.len)));

  // Check if the host has registry domain.
  if (net::registry_controlled_domains::HostHasRegistryControlledDomain(
          host, net::registry_controlled_domains::EXCLUDE_UNKNOWN_REGISTRIES,
          net::registry_controlled_domains::EXCLUDE_PRIVATE_REGISTRIES))
    return GURL();

  const GURL& url = input.canonicalized_url();
  // Check if the host of the canonical URL can be found in the database.
  std::string scheme_in_db;
  if (db->IsTypedHost(host, &scheme_in_db)) {
    GURL::Replacements replace_scheme;
    replace_scheme.SetSchemeStr(scheme_in_db);
    return url.ReplaceComponents(replace_scheme);
  }

  // Check if appending "www." to the canonicalized URL generates a URL found in
  // the database.
  const std::string alternative_host = "www." + host;
  if (!base::StartsWith(host, "www.", base::CompareCase::INSENSITIVE_ASCII) &&
      db->IsTypedHost(alternative_host, &scheme_in_db)) {
    GURL::Replacements replace_scheme_and_host;
    replace_scheme_and_host.SetHostStr(alternative_host);
    replace_scheme_and_host.SetSchemeStr(scheme_in_db);
    return url.ReplaceComponents(replace_scheme_and_host);
  }

  return GURL();
}

bool HistoryURLProvider::PromoteOrCreateShorterSuggestion(
    history::URLDatabase* db,
    HistoryURLProviderParams* params) {
  if (params->matches.empty())
    return false;  // No matches, nothing to do.

  // Determine the base URL from which to search, and whether that URL could
  // itself be added as a match.  We can add the base iff it's not "effectively
  // the same" as any "what you typed" match.
  const history::HistoryMatch& match = params->matches[0];
  GURL search_base = ConvertToHostOnly(match, params->input.text());
  bool can_add_search_base_to_matches = !params->have_what_you_typed_match;
  if (search_base.is_empty()) {
    // Search from what the user typed when we couldn't reduce the best match
    // to a host.  Careful: use a substring of |match| here, rather than the
    // first match in |params|, because they might have different prefixes.  If
    // the user typed "google.com", params->what_you_typed_match will hold
    // "http://google.com/", but |match| might begin with
    // "http://www.google.com/".
    // TODO: this should be cleaned up, and is probably incorrect for IDN.
    std::string new_match = match.url_info.url().possibly_invalid_spec().
        substr(0, match.input_location + params->input.text().length());
    search_base = GURL(new_match);
    if (search_base.is_empty())
      return false;  // Can't construct a URL from which to start a search.
  } else if (!can_add_search_base_to_matches) {
    can_add_search_base_to_matches =
        (search_base != params->what_you_typed_match.destination_url);
  }
  if (search_base == match.url_info.url())
    return false;  // Couldn't shorten |match|, so no URLs to search over.

  // Search the DB for short URLs between our base and |match|.
  history::URLRow info(search_base);
  bool promote = true;
  // A short URL is only worth suggesting if it's been visited at least a third
  // as often as the longer URL.
  const int min_visit_count = ((match.url_info.visit_count() - 1) / 3) + 1;
  // For stability between the in-memory and on-disk autocomplete passes, when
  // the long URL has been typed before, only suggest shorter URLs that have
  // also been typed.  Otherwise, the on-disk pass could suggest a shorter URL
  // (which hasn't been typed) that the in-memory pass doesn't know about,
  // thereby making the top match, and thus the behavior of inline
  // autocomplete, unstable.
  const int min_typed_count = match.url_info.typed_count() ? 1 : 0;
  if (!db->FindShortestURLFromBase(search_base.possibly_invalid_spec(),
          match.url_info.url().possibly_invalid_spec(), min_visit_count,
          min_typed_count, can_add_search_base_to_matches, &info)) {
    if (!can_add_search_base_to_matches)
      return false;  // Couldn't find anything and can't add the search base.

    // Try to get info on the search base itself.  Promote it to the top if the
    // original best match isn't good enough to autocomplete.
    db->GetRowForURL(search_base, &info);
    promote = match.url_info.typed_count() <= 1;
  }

  // Promote or add the desired URL to the list of matches.
  const bool ensure_can_inline =
      promote && CanPromoteMatchForInlineAutocomplete(match);
  return CreateOrPromoteMatch(info, match, &params->matches, true, promote) &&
         ensure_can_inline;
}

void HistoryURLProvider::CullPoorMatches(
    HistoryURLProviderParams* params) const {
  const base::Time& threshold(history::AutocompleteAgeThreshold());
  for (history::HistoryMatches::iterator i(params->matches.begin());
       i != params->matches.end(); ) {
    if (RowQualifiesAsSignificant(i->url_info, threshold) &&
        (!params->default_search_provider ||
         !params->default_search_provider->IsSearchURL(
             i->url_info.url(), *params->search_terms_data))) {
      ++i;
    } else {
      i = params->matches.erase(i);
    }
  }
}

void HistoryURLProvider::CullRedirects(history::HistoryBackend* backend,
                                       history::HistoryMatches* matches,
                                       size_t max_results) const {
  for (size_t source = 0;
       (source < matches->size()) && (source < max_results); ) {
    const GURL& url = (*matches)[source].url_info.url();
    // TODO(brettw) this should go away when everything uses GURL.
    history::RedirectList redirects = backend->QueryRedirectsFrom(url);
    if (!redirects.empty()) {
      // Remove all but the first occurrence of any of these redirects in the
      // search results. We also must add the URL we queried for, since it may
      // not be the first match and we'd want to remove it.
      //
      // For example, when A redirects to B and our matches are [A, X, B],
      // we'll get B as the redirects from, and we want to remove the second
      // item of that pair, removing B. If A redirects to B and our matches are
      // [B, X, A], we'll want to remove A instead.
      redirects.push_back(url);
      source = RemoveSubsequentMatchesOf(matches, source, redirects);
    } else {
      // Advance to next item.
      source++;
    }
  }

  if (matches->size() > max_results)
    matches->resize(max_results);
}

size_t HistoryURLProvider::RemoveSubsequentMatchesOf(
    history::HistoryMatches* matches,
    size_t source_index,
    const std::vector<GURL>& remove) const {
  size_t next_index = source_index + 1;  // return value = item after source

  // Find the first occurrence of any URL in the redirect chain. We want to
  // keep this one since it is rated the highest.
  history::HistoryMatches::iterator first(std::find_first_of(
      matches->begin(), matches->end(), remove.begin(), remove.end(),
      history::HistoryMatch::EqualsGURL));
  DCHECK(first != matches->end()) << "We should have always found at least the "
      "original URL.";

  // Find any following occurrences of any URL in the redirect chain, these
  // should be deleted.
  for (history::HistoryMatches::iterator next(std::find_first_of(first + 1,
           matches->end(), remove.begin(), remove.end(),
           history::HistoryMatch::EqualsGURL));
       next != matches->end(); next = std::find_first_of(next, matches->end(),
           remove.begin(), remove.end(), history::HistoryMatch::EqualsGURL)) {
    // Remove this item. When we remove an item before the source index, we
    // need to shift it to the right and remember that so we can return it.
    next = matches->erase(next);
    if (static_cast<size_t>(next - matches->begin()) < next_index)
      --next_index;
  }
  return next_index;
}

AutocompleteMatch HistoryURLProvider::HistoryMatchToACMatch(
    const HistoryURLProviderParams& params,
    size_t match_number,
    int relevance) {
  // The FormattedStringWithEquivalentMeaning() call below requires callers to
  // be on the main thread.
  DCHECK(thread_checker_.CalledOnValidThread());

  const history::HistoryMatch& history_match = params.matches[match_number];
  const history::URLRow& info = history_match.url_info;
  AutocompleteMatch match(this, relevance,
      !!info.visit_count(), AutocompleteMatchType::HISTORY_URL);
  match.typed_count = info.typed_count();
  match.destination_url = info.url();
  DCHECK(match.destination_url.is_valid());
  size_t inline_autocomplete_offset =
      history_match.input_location + params.input.text().length();

  auto fill_into_edit_format_types = url_formatter::kFormatUrlOmitDefaults;
  if (!params.trim_http || history_match.match_in_scheme)
    fill_into_edit_format_types &= ~url_formatter::kFormatUrlOmitHTTP;
  match.fill_into_edit =
      AutocompleteInput::FormattedStringWithEquivalentMeaning(
          info.url(),
          url_formatter::FormatUrl(info.url(), fill_into_edit_format_types,
                                   net::UnescapeRule::SPACES, nullptr, nullptr,
                                   &inline_autocomplete_offset),
          client()->GetSchemeClassifier(), &inline_autocomplete_offset);

  const auto format_types = AutocompleteMatch::GetFormatTypes(
      params.input.parts().scheme.len > 0 || !params.trim_http ||
          history_match.match_in_scheme,
      history_match.match_in_subdomain);
  match.contents = url_formatter::FormatUrl(info.url(), format_types,
                                            net::UnescapeRule::SPACES, nullptr,
                                            nullptr, nullptr);
  auto term_matches = FindTermMatches(params.input.text(), match.contents);
  match.contents_class = ClassifyTermMatches(
      term_matches, match.contents.size(),
      ACMatchClassification::URL | ACMatchClassification::MATCH,
      ACMatchClassification::URL);

  match.description = info.title();
  match.description_class =
      ClassifyDescription(params.input.text(), match.description);

  // |inline_autocomplete_offset| was guaranteed not to be npos before the call
  // to FormatUrl().  If it is npos now, that means the represented location no
  // longer exists as such in the formatted string, e.g. if the offset pointed
  // into the middle of a punycode sequence fixed up to Unicode.  In this case,
  // there can be no inline autocompletion, and the match must not be allowed to
  // be default.
  if (match.TryRichAutocompletion(match.contents, match.description,
                                  params.input_before_fixup)) {
    // If rich autocompletion applies, we skip trying the alternatives below.
  } else if (inline_autocomplete_offset != base::string16::npos) {
    DCHECK(inline_autocomplete_offset <= match.fill_into_edit.length());
    match.inline_autocompletion =
        match.fill_into_edit.substr(inline_autocomplete_offset);
    match.SetAllowedToBeDefault(params.input_before_fixup);
  }

  RecordAdditionalInfoFromUrlRow(info, &match);
  return match;
}