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// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "chrome/browser/privacy_budget/surface_set_valuation.h"
#include <algorithm>
#include <functional>
#include <limits>
#include <tuple>
#include <type_traits>
#include "base/check_op.h"
#include "base/containers/contains.h"
#include "base/numerics/safe_conversions.h"
#include "base/rand_util.h"
#include "base/stl_util.h"
#include "chrome/browser/privacy_budget/representative_surface_set.h"
#include "chrome/browser/privacy_budget/surface_set_equivalence.h"
#include "chrome/common/privacy_budget/field_trial_param_conversions.h"
#include "chrome/common/privacy_budget/privacy_budget_features.h"
#include "chrome/common/privacy_budget/types.h"
#include "third_party/blink/public/common/privacy_budget/identifiable_surface.h"
namespace {
IdentifiableSurfaceCostMap GetPerSurfaceCostsFromFieldTrial() {
return DecodeIdentifiabilityFieldTrialParam<IdentifiableSurfaceCostMap>(
features::kIdentifiabilityStudyPerHashCost.Get());
}
IdentifiableSurfaceTypeCostMap GetPerTypeCostsFromFieldTrial() {
return DecodeIdentifiabilityFieldTrialParam<IdentifiableSurfaceTypeCostMap>(
features::kIdentifiabilityStudyPerTypeCost.Get());
}
} // namespace
SurfaceSetValuation::SurfaceSetValuation(
const SurfaceSetEquivalence& surface_set_equivalence)
: equivalence_sets_(surface_set_equivalence),
per_surface_costs_(GetPerSurfaceCostsFromFieldTrial()),
per_type_costs_(GetPerTypeCostsFromFieldTrial()) {}
SurfaceSetValuation::~SurfaceSetValuation() = default;
// static
const double SurfaceSetValuation::kDefaultCost;
double SurfaceSetValuation::Cost(const IdentifiableSurfaceSet& set) const {
return Cost(equivalence_sets_->GetRepresentatives(set));
}
double SurfaceSetValuation::Cost(const RepresentativeSurfaceSet& set) const {
double cost = 0.0;
// This is a naive calculation that assumes that surfaces within an
// equivalence class is perfectly correlated with each other while surfaces
// that are not in the same class are perfectly independent. In reality
// nothing is quite cut and dry. Until we have a better model we are going to
// use this one.
for (auto surface : set)
cost += Cost(surface);
return cost;
}
double SurfaceSetValuation::Cost(blink::IdentifiableSurface surface) const {
return Cost(equivalence_sets_->GetRepresentative(surface));
}
double SurfaceSetValuation::Cost(RepresentativeSurface surface) const {
auto surface_cost_iter = per_surface_costs_.find(surface.value());
if (surface_cost_iter != per_surface_costs_.end())
return surface_cost_iter->second;
auto type_cost_iter = per_type_costs_.find(surface->GetType());
if (type_cost_iter != per_type_costs_.end())
return type_cost_iter->second;
return kDefaultCost;
}
double SurfaceSetValuation::IncrementalCost(
const RepresentativeSurfaceSet& prior,
RepresentativeSurface new_addition) const {
if (base::Contains(prior, new_addition))
return 0.0;
return Cost(new_addition);
}
size_t SurfaceSetValuation::ExpectedSurfaceCountForCost(double cost) {
// The units are already in expected surface counts.
return base::ClampCeil<size_t>(cost);
}
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