const prometheus = require('prom-client');

const requestStats = require('request-stats');

// No need to namespace these metric names.

// Prometheus adds a job label automatically, so clashes aren't a problem.

const metric = {

HTTPRequestsTotal: 'http_requests_total',

HTTPResponsesTotal: 'http_responses_total',

HTTPInboundBytes: 'http_request_inbound_bytes_total',

HTTPOutboundBytes: 'http_request_outbound_bytes_total',

HTTPDurationSeconds: 'http_request_duration_seconds',

};

const requestCounter = new prometheus.Counter({

name: metric.HTTPRequestsTotal,

help: 'The number of HTTP requests received.',

labelNames: ['method'],

});

const inboundByteCounter = new prometheus.Counter({

name: metric.HTTPInboundBytes,

help: 'The number of bytes received from the client.',

labelNames: ['method'],

});

const outboundByteCounter = new prometheus.Counter({

name: metric.HTTPOutboundBytes,

help: 'The number of bytes sent back to the client.',

labelNames: ['method'],

});

const responseTimeHistogram = new prometheus.Histogram({

name: metric.HTTPDurationSeconds,

help: 'The total time from a request received to response sent.',

labelNames: ['method'],

});

const responseCounter = new prometheus.Counter({

name: metric.HTTPResponsesTotal,

help: 'The number of HTTP responses the app is serving',

labelNames: ['method', 'status'],

});

function monitorRoutes(app) {

app.use('*', (req, res, next) => {

requestCounter.labels(req.method).inc();

next();

});

}

function monitorServer(server, stats) {

// Allow stats to be passed for easier testing

stats = stats || requestStats(server);

// Ensure that metrics that look for 500 status codes return an initial count

// of 0. Without setting this explicitly when the server is started,

// 'undefined' is returned instead, causing the Grafana chart to display

// 'No data' instead of a series of 0 values.

responseCounter.labels('GET', '500').inc(0);

stats.on('complete', ({ req, res, time: ms }) => {

inboundByteCounter.labels(req.method).inc(req.bytes);

outboundByteCounter.labels(req.method).inc(res.bytes);

responseTimeHistogram.labels(req.method).observe(ms / 1000);

responseCounter.labels(req.method, res.status).inc();

});

}

const monitor = {

routes: monitorRoutes,

server: monitorServer,

};

module.exports = {

metric,

monitor,

};