package prometheus_client

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"regexp"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/internal"
	"github.com/influxdata/telegraf/plugins/outputs"
	"github.com/prometheus/client_golang/prometheus"
)

var invalidNameCharRE = regexp.MustCompile(`[^a-zA-Z0-9_]`)

// SampleID uniquely identifies a Sample
type SampleID string

// Sample represents the current value of a series.
type Sample struct {
	// Labels are the Prometheus labels.
	Labels map[string]string
	// Value is the value in the Prometheus output.
	Value float64
	// Expiration is the deadline that this Sample is valid until.
	Expiration time.Time
}

// MetricFamily contains the data required to build valid prometheus Metrics.
type MetricFamily struct {
	// Samples are the Sample belonging to this MetricFamily.
	Samples map[SampleID]*Sample
	// Type of the Value.
	ValueType prometheus.ValueType
	// LabelSet is the label counts for all Samples.
	LabelSet map[string]int
}

type PrometheusClient struct {
	Listen             string
	ExpirationInterval internal.Duration `toml:"expiration_interval"`

	server *http.Server

	sync.Mutex
	// fam is the non-expired MetricFamily by Prometheus metric name.
	fam map[string]*MetricFamily
	// now returns the current time.
	now func() time.Time
}

var sampleConfig = `
  ## Address to listen on
  # listen = ":9273"

  ## Interval to expire metrics and not deliver to prometheus, 0 == no expiration
  # expiration_interval = "60s"
`

func (p *PrometheusClient) Start() error {
	prometheus.Register(p)

	if p.Listen == "" {
		p.Listen = "localhost:9273"
	}

	mux := http.NewServeMux()
	mux.Handle("/metrics", prometheus.Handler())

	p.server = &http.Server{
		Addr:    p.Listen,
		Handler: mux,
	}

	go func() {
		if err := p.server.ListenAndServe(); err != nil {
			if err != http.ErrServerClosed {
				log.Printf("E! Error creating prometheus metric endpoint, err: %s\n",
					err.Error())
			}
		}
	}()
	return nil
}

func (p *PrometheusClient) Stop() {
	// plugin gets cleaned up in Close() already.
}

func (p *PrometheusClient) Connect() error {
	// This service output does not need to make any further connections
	return nil
}

func (p *PrometheusClient) Close() error {
	ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
	defer cancel()
	err := p.server.Shutdown(ctx)
	prometheus.Unregister(p)
	return err
}

func (p *PrometheusClient) SampleConfig() string {
	return sampleConfig
}

func (p *PrometheusClient) Description() string {
	return "Configuration for the Prometheus client to spawn"
}

// Implements prometheus.Collector
func (p *PrometheusClient) Describe(ch chan<- *prometheus.Desc) {
	prometheus.NewGauge(prometheus.GaugeOpts{Name: "Dummy", Help: "Dummy"}).Describe(ch)
}

// Expire removes Samples that have expired.
func (p *PrometheusClient) Expire() {
	now := p.now()
	for name, family := range p.fam {
		for key, sample := range family.Samples {
			if p.ExpirationInterval.Duration != 0 && now.After(sample.Expiration) {
				for k, _ := range sample.Labels {
					family.LabelSet[k]--
				}
				delete(family.Samples, key)

				if len(family.Samples) == 0 {
					delete(p.fam, name)
				}
			}
		}
	}
}

// Collect implements prometheus.Collector
func (p *PrometheusClient) Collect(ch chan<- prometheus.Metric) {
	p.Lock()
	defer p.Unlock()

	p.Expire()

	for name, family := range p.fam {
		// Get list of all labels on MetricFamily
		var labelNames []string
		for k, v := range family.LabelSet {
			if v > 0 {
				labelNames = append(labelNames, k)
			}
		}
		desc := prometheus.NewDesc(name, "Telegraf collected metric", labelNames, nil)

		for _, sample := range family.Samples {
			// Get labels for this sample; unset labels will be set to the
			// empty string
			var labels []string
			for _, label := range labelNames {
				v := sample.Labels[label]
				labels = append(labels, v)
			}

			metric, err := prometheus.NewConstMetric(desc, family.ValueType, sample.Value, labels...)
			if err != nil {
				log.Printf("E! Error creating prometheus metric, "+
					"key: %s, labels: %v,\nerr: %s\n",
					name, labels, err.Error())
			}

			ch <- metric
		}
	}
}

func sanitize(value string) string {
	return invalidNameCharRE.ReplaceAllString(value, "_")
}

func valueType(tt telegraf.ValueType) prometheus.ValueType {
	switch tt {
	case telegraf.Counter:
		return prometheus.CounterValue
	case telegraf.Gauge:
		return prometheus.GaugeValue
	default:
		return prometheus.UntypedValue
	}
}

// CreateSampleID creates a SampleID based on the tags of a telegraf.Metric.
func CreateSampleID(tags map[string]string) SampleID {
	pairs := make([]string, 0, len(tags))
	for k, v := range tags {
		pairs = append(pairs, fmt.Sprintf("%s=%s", k, v))
	}
	sort.Strings(pairs)
	return SampleID(strings.Join(pairs, ","))
}

func (p *PrometheusClient) Write(metrics []telegraf.Metric) error {
	p.Lock()
	defer p.Unlock()

	now := p.now()

	for _, point := range metrics {
		tags := point.Tags()
		vt := valueType(point.Type())
		sampleID := CreateSampleID(tags)

		labels := make(map[string]string)
		for k, v := range tags {
			labels[sanitize(k)] = v
		}

		for fn, fv := range point.Fields() {
			// Ignore string and bool fields.
			var value float64
			switch fv := fv.(type) {
			case int64:
				value = float64(fv)
			case float64:
				value = fv
			default:
				continue
			}

			sample := &Sample{
				Labels:     labels,
				Value:      value,
				Expiration: now.Add(p.ExpirationInterval.Duration),
			}

			// Special handling of value field; supports passthrough from
			// the prometheus input.
			var mname string
			if fn == "value" {
				mname = sanitize(point.Name())
			} else {
				mname = sanitize(fmt.Sprintf("%s_%s", point.Name(), fn))
			}

			var fam *MetricFamily
			var ok bool
			if fam, ok = p.fam[mname]; !ok {
				fam = &MetricFamily{
					Samples:   make(map[SampleID]*Sample),
					ValueType: vt,
					LabelSet:  make(map[string]int),
				}
				p.fam[mname] = fam
			} else {
				if fam.ValueType != vt {
					// Don't return an error since this would be a permanent error
					log.Printf("Mixed ValueType for measurement %q; dropping point", point.Name())
					break
				}
			}

			for k, _ := range sample.Labels {
				fam.LabelSet[k]++
			}

			fam.Samples[sampleID] = sample
		}
	}
	return nil
}

func init() {
	outputs.Add("prometheus_client", func() telegraf.Output {
		return &PrometheusClient{
			ExpirationInterval: internal.Duration{Duration: time.Second * 60},
			fam:                make(map[string]*MetricFamily),
			now:                time.Now,
		}
	})
}