// +build windows

package main

import (
	"fmt"
	"net/http"
	_ "net/http/pprof"
	"os"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"golang.org/x/sys/windows/svc"

	"github.com/StackExchange/wmi"
	"github.com/martinlindhe/wmi_exporter/collector"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/prometheus/common/log"
	"github.com/prometheus/common/version"
	"gopkg.in/alecthomas/kingpin.v2"
)

// WmiCollector implements the prometheus.Collector interface.
type WmiCollector struct {
	maxScrapeDuration time.Duration
	collectors        map[string]collector.Collector
}

const (
	defaultCollectors            = "cpu,cs,logical_disk,net,os,service,system,textfile"
	defaultCollectorsPlaceholder = "[defaults]"
	serviceName                  = "wmi_exporter"
)

var (
	scrapeDurationDesc = prometheus.NewDesc(
		prometheus.BuildFQName(collector.Namespace, "exporter", "collector_duration_seconds"),
		"wmi_exporter: Duration of a collection.",
		[]string{"collector"},
		nil,
	)
	scrapeSuccessDesc = prometheus.NewDesc(
		prometheus.BuildFQName(collector.Namespace, "exporter", "collector_success"),
		"wmi_exporter: Whether the collector was successful.",
		[]string{"collector"},
		nil,
	)
	scrapeTimeoutDesc = prometheus.NewDesc(
		prometheus.BuildFQName(collector.Namespace, "exporter", "collector_timeout"),
		"wmi_exporter: Whether the collector timed out.",
		[]string{"collector"},
		nil,
	)
	snapshotDuration = prometheus.NewDesc(
		prometheus.BuildFQName(collector.Namespace, "exporter", "perflib_snapshot_duration_seconds"),
		"Duration of perflib snapshot capture",
		nil,
		nil,
	)

	// This can be removed when client_golang exposes this on Windows
	// (See https://github.com/prometheus/client_golang/issues/376)
	startTime     = float64(time.Now().Unix())
	startTimeDesc = prometheus.NewDesc(
		"process_start_time_seconds",
		"Start time of the process since unix epoch in seconds.",
		nil,
		nil,
	)
)

// Describe sends all the descriptors of the collectors included to
// the provided channel.
func (coll WmiCollector) Describe(ch chan<- *prometheus.Desc) {
	ch <- scrapeDurationDesc
	ch <- scrapeSuccessDesc
}

type collectorOutcome int

const (
	pending collectorOutcome = iota
	success
	failed
)

// Collect sends the collected metrics from each of the collectors to
// prometheus.
func (coll WmiCollector) Collect(ch chan<- prometheus.Metric) {
	ch <- prometheus.MustNewConstMetric(
		startTimeDesc,
		prometheus.CounterValue,
		startTime,
	)

	t := time.Now()
	scrapeContext, err := collector.PrepareScrapeContext()
	ch <- prometheus.MustNewConstMetric(
		snapshotDuration,
		prometheus.GaugeValue,
		time.Since(t).Seconds(),
	)
	if err != nil {
		ch <- prometheus.NewInvalidMetric(scrapeSuccessDesc, fmt.Errorf("failed to prepare scrape: %v", err))
		return
	}

	wg := sync.WaitGroup{}
	wg.Add(len(coll.collectors))
	collectorOutcomes := make(map[string]collectorOutcome)
	for name := range coll.collectors {
		collectorOutcomes[name] = pending
	}

	metricsBuffer := make(chan prometheus.Metric)
	l := sync.Mutex{}
	finished := false
	go func() {
		for m := range metricsBuffer {
			l.Lock()
			if !finished {
				ch <- m
			}
			l.Unlock()
		}
	}()

	for name, c := range coll.collectors {
		go func(name string, c collector.Collector) {
			defer wg.Done()
			outcome := execute(name, c, scrapeContext, metricsBuffer)
			l.Lock()
			if !finished {
				collectorOutcomes[name] = outcome
			}
			l.Unlock()
		}(name, c)
	}

	allDone := make(chan struct{})
	go func() {
		wg.Wait()
		close(allDone)
		close(metricsBuffer)
	}()

	// Wait until either all collectors finish, or timeout expires
	select {
	case <-allDone:
	case <-time.After(coll.maxScrapeDuration):
	}

	l.Lock()
	finished = true

	remainingCollectorNames := make([]string, 0)
	for name, outcome := range collectorOutcomes {
		var successValue, timeoutValue float64
		if outcome == pending {
			timeoutValue = 1.0
			remainingCollectorNames = append(remainingCollectorNames, name)
		}
		if outcome == success {
			successValue = 1.0
		}

		ch <- prometheus.MustNewConstMetric(
			scrapeSuccessDesc,
			prometheus.GaugeValue,
			successValue,
			name,
		)
		ch <- prometheus.MustNewConstMetric(
			scrapeTimeoutDesc,
			prometheus.GaugeValue,
			timeoutValue,
			name,
		)
	}

	if len(remainingCollectorNames) > 0 {
		log.Warn("Collection timed out, still waiting for ", remainingCollectorNames)
	}

	l.Unlock()
}

func filterAvailableCollectors(collectors string) string {
	var availableCollectors []string
	for _, c := range strings.Split(collectors, ",") {
		_, ok := collector.Factories[c]
		if ok {
			availableCollectors = append(availableCollectors, c)
		}
	}
	return strings.Join(availableCollectors, ",")
}

func execute(name string, c collector.Collector, ctx *collector.ScrapeContext, ch chan<- prometheus.Metric) collectorOutcome {
	t := time.Now()
	err := c.Collect(ctx, ch)
	duration := time.Since(t).Seconds()
	ch <- prometheus.MustNewConstMetric(
		scrapeDurationDesc,
		prometheus.GaugeValue,
		duration,
		name,
	)

	if err != nil {
		log.Errorf("collector %s failed after %fs: %s", name, duration, err)
		return failed
	}
	log.Debugf("collector %s succeeded after %fs.", name, duration)
	return success
}

func expandEnabledCollectors(enabled string) []string {
	expanded := strings.Replace(enabled, defaultCollectorsPlaceholder, defaultCollectors, -1)
	separated := strings.Split(expanded, ",")
	unique := map[string]bool{}
	for _, s := range separated {
		if s != "" {
			unique[s] = true
		}
	}
	result := make([]string, 0, len(unique))
	for s := range unique {
		result = append(result, s)
	}
	return result
}

func loadCollectors(list string) (map[string]collector.Collector, error) {
	collectors := map[string]collector.Collector{}
	enabled := expandEnabledCollectors(list)

	for _, name := range enabled {
		fn, ok := collector.Factories[name]
		if !ok {
			return nil, fmt.Errorf("collector '%s' not available", name)
		}
		c, err := fn()
		if err != nil {
			return nil, err
		}
		collectors[name] = c
	}
	return collectors, nil
}

func initWbem() {
	// This initialization prevents a memory leak on WMF 5+. See
	// https://github.com/martinlindhe/wmi_exporter/issues/77 and linked issues
	// for details.
	log.Debugf("Initializing SWbemServices")
	s, err := wmi.InitializeSWbemServices(wmi.DefaultClient)
	if err != nil {
		log.Fatal(err)
	}
	wmi.DefaultClient.AllowMissingFields = true
	wmi.DefaultClient.SWbemServicesClient = s
}

func main() {
	var (
		listenAddress = kingpin.Flag(
			"telemetry.addr",
			"host:port for WMI exporter.",
		).Default(":9182").String()
		metricsPath = kingpin.Flag(
			"telemetry.path",
			"URL path for surfacing collected metrics.",
		).Default("/metrics").String()
		enabledCollectors = kingpin.Flag(
			"collectors.enabled",
			"Comma-separated list of collectors to use. Use '[defaults]' as a placeholder for all the collectors enabled by default.").
			Default(filterAvailableCollectors(defaultCollectors)).String()
		printCollectors = kingpin.Flag(
			"collectors.print",
			"If true, print available collectors and exit.",
		).Bool()
		timeoutMargin = kingpin.Flag(
			"scrape.timeout-margin",
			"Seconds to subtract from the timeout allowed by the client. Tune to allow for overhead or high loads.",
		).Default("0.5").Float64()
	)

	log.AddFlags(kingpin.CommandLine)
	kingpin.Version(version.Print("wmi_exporter"))
	kingpin.HelpFlag.Short('h')
	kingpin.Parse()

	if *printCollectors {
		collectorNames := make(sort.StringSlice, 0, len(collector.Factories))
		for n := range collector.Factories {
			collectorNames = append(collectorNames, n)
		}
		collectorNames.Sort()
		fmt.Printf("Available collectors:\n")
		for _, n := range collectorNames {
			fmt.Printf(" - %s\n", n)
		}
		return
	}

	initWbem()

	isInteractive, err := svc.IsAnInteractiveSession()
	if err != nil {
		log.Fatal(err)
	}

	stopCh := make(chan bool)
	if !isInteractive {
		go func() {
			err = svc.Run(serviceName, &wmiExporterService{stopCh: stopCh})
			if err != nil {
				log.Errorf("Failed to start service: %v", err)
			}
		}()
	}

	collectors, err := loadCollectors(*enabledCollectors)
	if err != nil {
		log.Fatalf("Couldn't load collectors: %s", err)
	}

	log.Infof("Enabled collectors: %v", strings.Join(keys(collectors), ", "))

	h := &metricsHandler{
		timeoutMargin: *timeoutMargin,
		collectorFactory: func(timeout time.Duration) *WmiCollector {
			return &WmiCollector{
				collectors:        collectors,
				maxScrapeDuration: timeout,
			}
		},
	}

	http.Handle(*metricsPath, h)
	http.HandleFunc("/health", healthCheck)
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, *metricsPath, http.StatusMovedPermanently)
	})

	log.Infoln("Starting WMI exporter", version.Info())
	log.Infoln("Build context", version.BuildContext())

	go func() {
		log.Infoln("Starting server on", *listenAddress)
		log.Fatalf("cannot start WMI exporter: %s", http.ListenAndServe(*listenAddress, nil))
	}()

	for {
		if <-stopCh {
			log.Info("Shutting down WMI exporter")
			break
		}
	}
}

func healthCheck(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	_, err := fmt.Fprintln(w, `{"status":"ok"}`)
	if err != nil {
		log.Debugf("Failed to write to stream: %v", err)
	}
}

func keys(m map[string]collector.Collector) []string {
	ret := make([]string, 0, len(m))
	for key := range m {
		ret = append(ret, key)
	}
	return ret
}

type wmiExporterService struct {
	stopCh chan<- bool
}

func (s *wmiExporterService) Execute(args []string, r <-chan svc.ChangeRequest, changes chan<- svc.Status) (ssec bool, errno uint32) {
	const cmdsAccepted = svc.AcceptStop | svc.AcceptShutdown
	changes <- svc.Status{State: svc.StartPending}
	changes <- svc.Status{State: svc.Running, Accepts: cmdsAccepted}
loop:
	for {
		select {
		case c := <-r:
			switch c.Cmd {
			case svc.Interrogate:
				changes <- c.CurrentStatus
			case svc.Stop, svc.Shutdown:
				s.stopCh <- true
				break loop
			default:
				log.Error(fmt.Sprintf("unexpected control request #%d", c))
			}
		}
	}
	changes <- svc.Status{State: svc.StopPending}
	return
}

type metricsHandler struct {
	timeoutMargin    float64
	collectorFactory func(timeout time.Duration) *WmiCollector
}

func (mh *metricsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	const defaultTimeout = 10.0

	var timeoutSeconds float64
	if v := r.Header.Get("X-Prometheus-Scrape-Timeout-Seconds"); v != "" {
		var err error
		timeoutSeconds, err = strconv.ParseFloat(v, 64)
		if err != nil {
			log.Warnf("Couldn't parse X-Prometheus-Scrape-Timeout-Seconds: %q. Defaulting timeout to %f", v, defaultTimeout)
		}
	}
	if timeoutSeconds == 0 {
		timeoutSeconds = defaultTimeout
	}
	timeoutSeconds = timeoutSeconds - mh.timeoutMargin

	reg := prometheus.NewRegistry()
	reg.MustRegister(mh.collectorFactory(time.Duration(timeoutSeconds * float64(time.Second))))
	reg.MustRegister(
		prometheus.NewProcessCollector(os.Getpid(), ""),
		prometheus.NewGoCollector(),
		version.NewCollector("wmi_exporter"),
	)

	h := promhttp.HandlerFor(reg, promhttp.HandlerOpts{})
	h.ServeHTTP(w, r)
}