@metrics/client/lib/summary.js

A streaming metric producer. Allows producing counters, gauges, histograms and summaries in a way that is independent of your metrics system.

"use strict";

const assert = require("assert");
const { EventEmitter } = require("events");
const timeSpan = require("time-span");
const Metric = require("@metrics/metric");

const Summary = class Summary extends EventEmitter {
	constructor(options) {
		super();

		assert(typeof options === "object", `argument 'options' must be provided`);

		// TODO: validate optional quantiles option

		Object.defineProperty(this, "options", {
			value: {
				labels: {},
				...options,
			},
		});
	}

	observe(value, options = {}) {
		assert(typeof value === "number", `argument 'value' to method .observe() must be of type 'number'`);

		const labelsObject = {
			...(this.options.labels || {}),
			...(options.labels || {}),
		};

		const labels = Object.keys(labelsObject).map((label) => ({
			name: label,
			value: labelsObject[label],
		}));

		const metric = {
			name: this.options.name,
			description: this.options.description,
			type: 7,
			value,
			labels,
		};

		if (this.options.quantiles) {
			metric.meta = {
				quantiles: this.options.quantiles,
			};
		}

		this.emit("metric", new Metric(metric));
	}

	timer(options = {}) {
		const end = timeSpan();
		return (opts = {}) => {
			const labels = {
				...(options.labels || {}),
				...(opts.labels || {}),
			};
			this.observe(end.seconds(), { labels });
		};
	}
};

module.exports = Summary;