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// Copyright 2025 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_VARIATIONS_STICKY_ACTIVATION_MANAGER_H_
#define COMPONENTS_VARIATIONS_STICKY_ACTIVATION_MANAGER_H_
#include <map>
#include <string>
#include "base/component_export.h"
#include "base/memory/raw_ptr.h"
#include "base/metrics/field_trial.h"
class PrefService;
class PrefRegistrySimple;
namespace variations {
// Manages the set of field trials marked with the activation type
// STICKY_AFTER_QUERY. Responsible for persisting information about activated
// trials to Local State and using that information to determine if a trial
// should be activated on the next startup.
//
// A sticky trial should be activated on startup if it was active in the
// previous session (including from stickiness on startup) and its group
// selection did not change (i.e. due to a change to its config or something
// external like the client's randomization inputs).
class COMPONENT_EXPORT(VARIATIONS) StickyActivationManager
: public base::FieldTrialList::Observer {
public:
// Map from trial name to group name. We use std::map since sorted order is
// useful for deterministic serialization to string.
//
// It's possible that base::flat_map would be a better type here, but this
// does get updated many times and current docs are unclear whether its size
// (O(100) entries) qualifies as small.
using TrialNameToGroupNameMap = std::map<std::string, std::string>;
// `local_state` may be null for tests, in which case no prior stickiness
// information will be loaded and none will be saved.
explicit StickyActivationManager(PrefService* local_state,
bool sticky_activation_enabled = false);
StickyActivationManager(const StickyActivationManager&) = delete;
StickyActivationManager& operator=(const StickyActivationManager&) = delete;
~StickyActivationManager() override;
// Registers the prefs used by this class.
static void RegisterPrefs(PrefRegistrySimple& registry);
// Checks if the specified trial should be activated on startup, based on the
// persisted information for sticky trials. Should only be called prior to
// StartMonitoring() and should only be called on sticky activation trials.
// Internally, this marks the trial as sticky for the purpose of monitoring
// its activation state.
bool ShouldActivate(const std::string& trial_name,
const std::string& group_name);
// Starts monitoring field trial activations. May not be called more than
// once. Note: This is a no-op if `sticky_activation_enabled_` is false.
void StartMonitoring();
private:
// base::FieldTrialList::Observer:
void OnFieldTrialGroupFinalized(const base::FieldTrial& trial,
const std::string& group_name) override;
// Updates the pref based on `active_sticky_trials_`.
void UpdatePref();
raw_ptr<PrefService> local_state_;
// Whether support for STICKY_AFTER_QUERY activation for studies is enabled.
// TODO: crbug.com/435630455 - Fully enable and remove this once ready.
bool sticky_activation_enabled_ = false;
// Whether StartMonitoring() has been called. Note: This just tracks that the
// function was called (to prevent it being called multiple times), but may
// not reflect whether monitoring is actually happening, since the function
// can be no-op if `sticky_activation_enabled_` is false.
bool monitoring_started_ = false;
// The field trials loaded at startup from prefs.
// Note: This is cleared upon calling StartMonitoring(), as it is no longer
// needed after that.
TrialNameToGroupNameMap loaded_sticky_trials_;
// The currently active trials, for persistence to prefs. Updated via calls to
// ShouldActivate() and observer callbacks to OnFieldTrialGroupFinalized().
TrialNameToGroupNameMap active_sticky_trials_;
};
} // namespace variations
#endif // COMPONENTS_VARIATIONS_STICKY_ACTIVATION_MANAGER_H_
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