generateSnapshot() {
		const snapshot = Array.from(this.values.keys()).map(key => {
			const item = this.values.get(key);
			const res = {
				key,
				value: item.value,
				labels: item.labels,
				timestamp: item.timestamp
			};

			if (item.rate) res.rate = item.rate.rate;

			return res;
		});

		return snapshot;
	}
Generate a snapshot.

@returns {Array<Object>}
@memberof GaugeMetric