// Copyright (c) 2013, Prometheus Team
// All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// A simple example of how to use this instrumentation framework in the context
// of having something that emits values into its collectors.
//
// The emitted values correspond to uniform, normal, and exponential
// distributions.
package main

import (
	"flag"
	"github.com/prometheus/client_golang/prometheus"
	"math/rand"
	"net/http"
	"time"
)

var (
	barDomain = flag.Float64("random.fooDomain", 200, "The domain for the random parameter foo.")
	barMean   = flag.Float64("random.barDomain", 10, "The domain for the random parameter bar.")
	fooDomain = flag.Float64("random.barMean", 100, "The mean for the random parameter bar.")

	// Create a histogram to track fictitious interservice RPC latency for three
	// distinct services.
	rpcLatency = prometheus.NewHistogram(&prometheus.HistogramSpecification{
		// Four distinct histogram buckets for values:
		// - equally-sized,
		// - 0 to 50, 50 to 100, 100 to 150, and 150 to 200.
		Starts: prometheus.EquallySizedBucketsFor(0, 200, 4),
		// Create histogram buckets using an accumulating bucket, a bucket that
		// holds sample values subject to an eviction policy:
		// - 50 elements are allowed per bucket.
		// - Once 50 have been reached, the bucket empties 10 elements, averages the
		//   evicted elements, and re-appends that back to the bucket.
		BucketBuilder: prometheus.AccumulatingBucketBuilder(prometheus.EvictAndReplaceWith(10, prometheus.AverageReducer), 50),
		// The histogram reports percentiles 1, 5, 50, 90, and 99.
		ReportablePercentiles: []float64{0.01, 0.05, 0.5, 0.90, 0.99},
	})

	rpcCalls = prometheus.NewCounter()

	// If for whatever reason you are resistant to the idea of having a static
	// registry for metrics, which is a really bad idea when using Prometheus-
	// enabled library code, you can create your own.
	customRegistry = prometheus.NewRegistry()
)

func main() {
	flag.Parse()

	go func() {
		for {
			rpcLatency.Add(map[string]string{"service": "foo"}, rand.Float64()**fooDomain)
			rpcCalls.Increment(map[string]string{"service": "foo"})

			rpcLatency.Add(map[string]string{"service": "bar"}, (rand.NormFloat64()**barDomain)+*barMean)
			rpcCalls.Increment(map[string]string{"service": "bar"})

			rpcLatency.Add(map[string]string{"service": "zed"}, rand.ExpFloat64())
			rpcCalls.Increment(map[string]string{"service": "zed"})

			time.Sleep(100 * time.Millisecond)
		}
	}()

	http.Handle(prometheus.ExpositionResource, customRegistry.Handler())
	http.ListenAndServe(*listeningAddress, nil)
}

func init() {
	customRegistry.Register("rpc_latency_microseconds", "RPC latency.", prometheus.NilLabels, rpcLatency)
	customRegistry.Register("rpc_calls_total", "RPC calls.", prometheus.NilLabels, rpcCalls)
}

var (
	listeningAddress = flag.String("listeningAddress", ":8080", "The address to listen to requests on.")
)