getFilename(metric, item) {
		const metricName = this.formatMetricName(metric.name);
		if (this.opts.filenameFormatter)
			return this.opts.filenameFormatter.call(this, metricName, metric, item);

		switch (this.opts.mode) {
			case MODE_METRIC: {
				return path.join(this.folder, `${metricName}.csv`);
			}
			case MODE_LABEL: {
				const labelStr = this.labelsToStr(item.labels);
				return path.join(
					this.folder,
					metricName,
					`${metricName}${labelStr ? "--" + labelStr : ""}.csv`
				);
			}
		}
	}
Get filename for metric
@param {*} metric
@param {*} item