func generateStatFor()

in core/flow/rule_manager.go [404:466]
55 lines of code
12 McCabe index (conditional complexity)

func generateStatFor(rule *Rule) (*standaloneStatistic, error) {
	if !rule.needStatistic() {
		return nopStat, nil
	}

	intervalInMs := rule.StatIntervalInMs

	var retStat standaloneStatistic

	var resNode *stat.ResourceNode
	if rule.RelationStrategy == AssociatedResource {
		// use associated statistic
		resNode = stat.GetOrCreateResourceNode(rule.RefResource, base.ResTypeCommon)
	} else {
		resNode = stat.GetOrCreateResourceNode(rule.Resource, base.ResTypeCommon)
	}
	if intervalInMs == 0 || intervalInMs == config.MetricStatisticIntervalMs() {
		// default case, use the resource's default statistic
		readStat := resNode.DefaultMetric()
		retStat.reuseResourceStat = true
		retStat.readOnlyMetric = readStat
		retStat.writeOnlyMetric = nil
		return &retStat, nil
	}

	sampleCount := uint32(0)
	//calculate the sample count
	if intervalInMs > config.GlobalStatisticIntervalMsTotal() {
		sampleCount = 1
	} else if intervalInMs < config.GlobalStatisticBucketLengthInMs() {
		sampleCount = 1
	} else {
		if intervalInMs%config.GlobalStatisticBucketLengthInMs() == 0 {
			sampleCount = intervalInMs / config.GlobalStatisticBucketLengthInMs()
		} else {
			sampleCount = 1
		}
	}
	err := base.CheckValidityForReuseStatistic(sampleCount, intervalInMs, config.GlobalStatisticSampleCountTotal(), config.GlobalStatisticIntervalMsTotal())
	if err == nil {
		// global statistic reusable
		readStat, e := resNode.GenerateReadStat(sampleCount, intervalInMs)
		if e != nil {
			return nil, e
		}
		retStat.reuseResourceStat = true
		retStat.readOnlyMetric = readStat
		retStat.writeOnlyMetric = nil
		return &retStat, nil
	} else if err == base.GlobalStatisticNonReusableError {
		logging.Info("[FlowRuleManager] Flow rule couldn't reuse global statistic and will generate independent statistic", "rule", rule)
		retStat.reuseResourceStat = false
		realLeapArray := sbase.NewBucketLeapArray(sampleCount, intervalInMs)
		metricStat, e := sbase.NewSlidingWindowMetric(sampleCount, intervalInMs, realLeapArray)
		if e != nil {
			return nil, errors.Errorf("fail to generate statistic for warm up rule: %+v, err: %+v", rule, e)
		}
		retStat.readOnlyMetric = metricStat
		retStat.writeOnlyMetric = realLeapArray
		return &retStat, nil
	}
	return nil, errors.Wrapf(err, "fail to new standalone statistic because of invalid StatIntervalInMs in flow.Rule, StatIntervalInMs: %d", intervalInMs)
}