/*
 * decaffeinate suggestions:
 * DS101: Remove unnecessary use of Array.from
 * DS102: Remove unnecessary code created because of implicit returns
 * DS205: Consider reworking code to avoid use of IIFEs
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
 */
const prom = require('prom-client');
const registry = require('prom-client').register;
const metrics = new Map();


const optsKey = function(opts) {
	let keys = Object.keys(opts);
	if (keys.length === 0) { return ''; }

	keys = keys.sort();

	let hash = '';
	for (let key of Array.from(keys)) {
		if (hash.length) { hash += ","; }
		hash += `${key}:${opts[key]}`;
	}

	return hash;
};

const extendOpts = function(opts, labelNames) {
	for (let label of Array.from(labelNames)) {
		if (!opts[label]) { opts[label] = ''; }
	}
	return opts;
};

const optsAsArgs = function(opts, labelNames) {
	const args = [];
	for (let label of Array.from(labelNames)) {
		args.push(opts[label] || '');
	}
	return args;
};


const PromWrapper = {
	ttlInMinutes: 0,
	registry,

	metric(type, name) {
		return metrics.get(name) || new MetricWrapper(type, name);
	},

	collectDefaultMetrics: prom.collectDefaultMetrics
};


class MetricWrapper {
	constructor(type, name) {
		metrics.set(name, this);
		this.name = name;
		this.instances = new Map();
		this.lastAccess = new Date();
		this.metric = (() => { switch (type) {
			case "counter":
				return new prom.Counter({
					name,
					help: name,
					labelNames: ['app','host','status','method', 'path']
				});
			case "summary":
				return new prom.Summary({
					name,
					help: name,
					maxAgeSeconds: 60,
					ageBuckets: 10,
					labelNames: ['app', 'host', 'path', 'status_code', 'method', 'collection', 'query']
				});
			case "gauge":
				return new prom.Gauge({
					name,
					help: name,
					labelNames: ['app','host', 'status']
				});
		} })();
	}

	inc(opts, value) {
		return this._execMethod('inc', opts, value);
	}

	observe(opts, value) {
		return this._execMethod('observe', opts, value);
	}

	set(opts, value) {
		return this._execMethod('set', opts, value);
	}

	sweep() {
		const thresh = new Date(Date.now() - (1000 * 60 * PromWrapper.ttlInMinutes));
		this.instances.forEach((instance, key) => {
			if (thresh > instance.time) {
				if (process.env['DEBUG_METRICS']) {
					console.log("Sweeping stale metric instance", this.name, {opts: instance.opts}, key);
				}
				return this.metric.remove(...Array.from(optsAsArgs(instance.opts, this.metric.labelNames) || []));
			}
		});

		if (thresh > this.lastAccess) {
			if (process.env['DEBUG_METRICS']) {
				console.log("Sweeping stale metric", this.name, thresh, this.lastAccess);
			}
			metrics.delete(this.name);
			return registry.removeSingleMetric(this.name);
		}
	}

	_execMethod(method, opts, value) {
		opts = extendOpts(opts, this.metric.labelNames);
		const key = optsKey(opts);
		if (key !== '') { this.instances.set(key, { time: new Date(), opts }); }
		this.lastAccess = new Date();
		return this.metric[method](opts, value);
	}
}


if (!PromWrapper.sweepRegistered) {
	if (process.env['DEBUG_METRICS']) {
		console.log("Registering sweep method");
	}
	PromWrapper.sweepRegistered = true;
	setInterval(
		function() {
			if (PromWrapper.ttlInMinutes) {
				if (process.env['DEBUG_METRICS']) {
					console.log("Sweeping metrics");
				}
				return metrics.forEach((metric, key) => {
					return metric.sweep();
				});
			}
		},
	60000);
}


module.exports = PromWrapper;