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// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef COMPONENTS_LANGUAGE_CORE_BROWSER_URL_LANGUAGE_HISTOGRAM_H_
#define COMPONENTS_LANGUAGE_CORE_BROWSER_URL_LANGUAGE_HISTOGRAM_H_
#include <string>
#include <vector>
#include "base/memory/raw_ptr.h"
#include "base/time/time.h"
#include "components/keyed_service/core/keyed_service.h"
class PrefRegistrySimple;
class PrefService;
namespace language {
// Collects data about languages in which the user reads the web and provides
// access to current estimated language preferences. The past behaviour is
// discounted so that the histogram reflects changes in browsing habits. This
// histogram does not have to contain all languages that ever appeared in user's
// browsing, languages with insignificant frequency are removed, eventually.
//
// Operates as a "wrapper" around profile preferences: the state of the
// histogram is read from/written to the PrefService in each method call. This
// allows multiple instances of the histogram to be used in a (non-overlapping)
// sequence without any instance-specific state going "out of sync". This
// behaviour is relied on by clients of the histogram.
class UrlLanguageHistogram : public KeyedService {
public:
struct LanguageInfo {
LanguageInfo() = default;
LanguageInfo(const std::string& language_code, float frequency)
: language_code(language_code), frequency(frequency) {}
// The ISO 639 language code.
std::string language_code;
// The current estimated frequency of the language share, a number between 0
// and 1 (can be understood as the probability that the next page the user
// opens is in this language). Frequencies over all LanguageInfos from
// GetTopLanguages() sum to 1 (unless there are no top languages, yet).
float frequency = 0.0f;
};
explicit UrlLanguageHistogram(PrefService* pref_service);
UrlLanguageHistogram(const UrlLanguageHistogram&) = delete;
UrlLanguageHistogram& operator=(const UrlLanguageHistogram&) = delete;
~UrlLanguageHistogram() override;
// Registers profile prefs for the histogram.
static void RegisterProfilePrefs(PrefRegistrySimple* registry);
// Returns a list of the languages currently tracked by the histogram, sorted
// by frequency in decreasing order. The list is empty, if the histogram has
// not enough data points.
std::vector<LanguageInfo> GetTopLanguages() const;
// Returns the estimated frequency for the given language or 0 if the language
// is not among the top languages kept in the histogram.
float GetLanguageFrequency(const std::string& language_code) const;
// Informs the histogram that a page with the given language has been visited.
void OnPageVisited(const std::string& language_code);
// Reflect in the histogram that history from |begin| to |end| gets cleared.
void ClearHistory(base::Time begin, base::Time end);
private:
raw_ptr<PrefService> pref_service_;
};
} // namespace language
#endif // COMPONENTS_LANGUAGE_CORE_BROWSER_URL_LANGUAGE_HISTOGRAM_H_
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