src/bin/config_parser/src/privacy/error_calculator.go

// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package privacy

import (
	"config"
	"fmt"
	"math"
)

type ErrorCalculator struct {
	ParamsCalc PrivacyEncodingParamsCalculator
}

// Public factory method for creating an ErrorCalculator given a
// PrivacyEncodingParamsCalculator.
func NewErrorCalculator(paramsCalc PrivacyEncodingParamsCalculator) *ErrorCalculator {
	return &ErrorCalculator{paramsCalc}
}

// Public factory method for creating an ErrorCalculator given the file path
// of the PrivacyEncodingParams.
func NewErrorCalculatorFromPrivacyParams(privacyParamsPath string) (*ErrorCalculator, error) {
	paramsCalculator, err := NewPrivacyEncodingParamsCalculator(privacyParamsPath)
	if err != nil {
		return nil, err
	}
	errorCalculator := NewErrorCalculator(*paramsCalculator)
	if err != nil {
		return nil, err
	}
	return errorCalculator, nil
}

// Given a |metric|, |report|, and |params|, estimates the report row error.
//
// Row error is temporarily -1 unless |epsilon| is 0 due to deprecated Rappor
// encoding scheme.
//
// TODO(b/278932979): update this comment once error calculation is implemented for
// Poisson encoding scheme.
func (e *ErrorCalculator) Estimate(metric *config.MetricDefinition, report *config.ReportDefinition, epsilon float64, population uint64, minDenominatorEstimate uint64) (estimate float64, err error) {
	if epsilon == 0 {
		return 0, nil
	}

	var errorEstimate float64
	switch report.GetReportType() {
	case config.ReportDefinition_UNIQUE_DEVICE_HISTOGRAMS:
		fallthrough
	case config.ReportDefinition_UNIQUE_DEVICE_COUNTS:
		fallthrough
	case config.ReportDefinition_HOURLY_VALUE_HISTOGRAMS:
		fallthrough
	case config.ReportDefinition_FLEETWIDE_OCCURRENCE_COUNTS:
		fallthrough
	case config.ReportDefinition_FLEETWIDE_HISTOGRAMS:
		fallthrough
	case config.ReportDefinition_UNIQUE_DEVICE_NUMERIC_STATS:
		fallthrough
	case config.ReportDefinition_HOURLY_VALUE_NUMERIC_STATS:
		fallthrough
	case config.ReportDefinition_FLEETWIDE_MEANS:
		fallthrough
	default:
		reportType := config.ReportDefinition_ReportType_name[int32(report.GetReportType())]
		return -1, fmt.Errorf("error estimation is not supported for reports of type %s", reportType)
	}

	if math.IsNaN(errorEstimate) || math.IsInf(errorEstimate, 0) {
		return errorEstimate, fmt.Errorf("error estimation failed to return valid result due to an invalid or missing field")
	}
	return errorEstimate, nil
}

func meanReportConfigurationError(report *config.ReportDefinition, minDenominatorEstimate uint64) error {
	if minDenominatorEstimate == 0 {
		return fmt.Errorf("user estimate for lower bound on unnoised denominator required for %s", report.GetReportType())
	}
	if report.MaxValue == 0 && report.MinValue == 0 {
		return fmt.Errorf("MinValue and MaxValue required to estimate error for %s", report.GetReportType())
	}
	return nil
}