// Copyright 2013 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package web

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	stdlog "log"
	"math"
	"net"
	"net/http"
	"net/http/pprof"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"regexp"
	"runtime"
	"sort"
	"strings"
	"sync"
	template_text "text/template"
	"time"

	"github.com/alecthomas/units"
	"github.com/go-kit/log"
	"github.com/go-kit/log/level"
	conntrack "github.com/mwitkow/go-conntrack"
	"github.com/opentracing-contrib/go-stdlib/nethttp"
	opentracing "github.com/opentracing/opentracing-go"
	"github.com/pkg/errors"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	io_prometheus_client "github.com/prometheus/client_model/go"
	"github.com/prometheus/common/model"
	"github.com/prometheus/common/route"
	"github.com/prometheus/common/server"
	toolkit_web "github.com/prometheus/exporter-toolkit/web"
	"go.uber.org/atomic"
	"golang.org/x/net/netutil"

	"github.com/prometheus/prometheus/config"
	"github.com/prometheus/prometheus/notifier"
	"github.com/prometheus/prometheus/promql"
	"github.com/prometheus/prometheus/rules"
	"github.com/prometheus/prometheus/scrape"
	"github.com/prometheus/prometheus/storage"
	"github.com/prometheus/prometheus/template"
	"github.com/prometheus/prometheus/tsdb"
	"github.com/prometheus/prometheus/tsdb/index"
	"github.com/prometheus/prometheus/util/httputil"
	api_v1 "github.com/prometheus/prometheus/web/api/v1"
	"github.com/prometheus/prometheus/web/ui"
)

// Paths that are handled by the React / Reach router that should all be served the main React app's index.html.
var reactRouterPaths = []string{
	"/alerts",
	"/config",
	"/flags",
	"/graph",
	"/rules",
	"/service-discovery",
	"/status",
	"/targets",
	"/tsdb-status",
	"/starting",
}

// withStackTrace logs the stack trace in case the request panics. The function
// will re-raise the error which will then be handled by the net/http package.
// It is needed because the go-kit log package doesn't manage properly the
// panics from net/http (see https://github.com/go-kit/kit/issues/233).
func withStackTracer(h http.Handler, l log.Logger) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if err := recover(); err != nil {
				const size = 64 << 10
				buf := make([]byte, size)
				buf = buf[:runtime.Stack(buf, false)]
				level.Error(l).Log("msg", "panic while serving request", "client", r.RemoteAddr, "url", r.URL, "err", err, "stack", buf)
				panic(err)
			}
		}()
		h.ServeHTTP(w, r)
	})
}

type metrics struct {
	requestCounter  *prometheus.CounterVec
	requestDuration *prometheus.HistogramVec
	responseSize    *prometheus.HistogramVec
}

func newMetrics(r prometheus.Registerer) *metrics {
	m := &metrics{
		requestCounter: prometheus.NewCounterVec(
			prometheus.CounterOpts{
				Name: "prometheus_http_requests_total",
				Help: "Counter of HTTP requests.",
			},
			[]string{"handler", "code"},
		),
		requestDuration: prometheus.NewHistogramVec(
			prometheus.HistogramOpts{
				Name:    "prometheus_http_request_duration_seconds",
				Help:    "Histogram of latencies for HTTP requests.",
				Buckets: []float64{.1, .2, .4, 1, 3, 8, 20, 60, 120},
			},
			[]string{"handler"},
		),
		responseSize: prometheus.NewHistogramVec(
			prometheus.HistogramOpts{
				Name:    "prometheus_http_response_size_bytes",
				Help:    "Histogram of response size for HTTP requests.",
				Buckets: prometheus.ExponentialBuckets(100, 10, 8),
			},
			[]string{"handler"},
		),
	}

	if r != nil {
		r.MustRegister(m.requestCounter, m.requestDuration, m.responseSize)
		registerFederationMetrics(r)
	}
	return m
}

func (m *metrics) instrumentHandlerWithPrefix(prefix string) func(handlerName string, handler http.HandlerFunc) http.HandlerFunc {
	return func(handlerName string, handler http.HandlerFunc) http.HandlerFunc {
		return m.instrumentHandler(prefix+handlerName, handler)
	}
}

func (m *metrics) instrumentHandler(handlerName string, handler http.HandlerFunc) http.HandlerFunc {
	return promhttp.InstrumentHandlerCounter(
		m.requestCounter.MustCurryWith(prometheus.Labels{"handler": handlerName}),
		promhttp.InstrumentHandlerDuration(
			m.requestDuration.MustCurryWith(prometheus.Labels{"handler": handlerName}),
			promhttp.InstrumentHandlerResponseSize(
				m.responseSize.MustCurryWith(prometheus.Labels{"handler": handlerName}),
				handler,
			),
		),
	)
}

// PrometheusVersion contains build information about Prometheus.
type PrometheusVersion = api_v1.PrometheusVersion

type LocalStorage interface {
	storage.Storage
	api_v1.TSDBAdminStats
}

// Handler serves various HTTP endpoints of the Prometheus server
type Handler struct {
	logger log.Logger

	gatherer prometheus.Gatherer
	metrics  *metrics

	scrapeManager   *scrape.Manager
	ruleManager     *rules.Manager
	queryEngine     *promql.Engine
	lookbackDelta   time.Duration
	context         context.Context
	storage         storage.Storage
	localStorage    LocalStorage
	exemplarStorage storage.ExemplarQueryable
	notifier        *notifier.Manager

	apiV1 *api_v1.API

	router      *route.Router
	quitCh      chan struct{}
	quitOnce    sync.Once
	reloadCh    chan chan error
	options     *Options
	config      *config.Config
	versionInfo *PrometheusVersion
	birth       time.Time
	cwd         string
	flagsMap    map[string]string

	mtx sync.RWMutex
	now func() model.Time

	ready atomic.Uint32 // ready is uint32 rather than boolean to be able to use atomic functions.
}

// ApplyConfig updates the config field of the Handler struct
func (h *Handler) ApplyConfig(conf *config.Config) error {
	h.mtx.Lock()
	defer h.mtx.Unlock()

	h.config = conf

	return nil
}

// Options for the web Handler.
type Options struct {
	Context               context.Context
	TSDBRetentionDuration model.Duration
	TSDBDir               string
	TSDBMaxBytes          units.Base2Bytes
	LocalStorage          LocalStorage
	Storage               storage.Storage
	ExemplarStorage       storage.ExemplarQueryable
	QueryEngine           *promql.Engine
	LookbackDelta         time.Duration
	ScrapeManager         *scrape.Manager
	RuleManager           *rules.Manager
	Notifier              *notifier.Manager
	Version               *PrometheusVersion
	Flags                 map[string]string

	ListenAddress              string
	CORSOrigin                 *regexp.Regexp
	ReadTimeout                time.Duration
	MaxConnections             int
	ExternalURL                *url.URL
	RoutePrefix                string
	UseLocalAssets             bool
	UserAssetsPath             string
	ConsoleTemplatesPath       string
	ConsoleLibrariesPath       string
	EnableLifecycle            bool
	EnableAdminAPI             bool
	PageTitle                  string
	RemoteReadSampleLimit      int
	RemoteReadConcurrencyLimit int
	RemoteReadBytesInFrame     int
	RemoteWriteReceiver        bool

	Gatherer   prometheus.Gatherer
	Registerer prometheus.Registerer
}

// New initializes a new web Handler.
func New(logger log.Logger, o *Options) *Handler {
	if logger == nil {
		logger = log.NewNopLogger()
	}

	m := newMetrics(o.Registerer)
	router := route.New().
		WithInstrumentation(m.instrumentHandler).
		WithInstrumentation(setPathWithPrefix(""))

	cwd, err := os.Getwd()
	if err != nil {
		cwd = "<error retrieving current working directory>"
	}

	h := &Handler{
		logger: logger,

		gatherer: o.Gatherer,
		metrics:  m,

		router:      router,
		quitCh:      make(chan struct{}),
		reloadCh:    make(chan chan error),
		options:     o,
		versionInfo: o.Version,
		birth:       time.Now().UTC(),
		cwd:         cwd,
		flagsMap:    o.Flags,

		context:         o.Context,
		scrapeManager:   o.ScrapeManager,
		ruleManager:     o.RuleManager,
		queryEngine:     o.QueryEngine,
		lookbackDelta:   o.LookbackDelta,
		storage:         o.Storage,
		localStorage:    o.LocalStorage,
		exemplarStorage: o.ExemplarStorage,
		notifier:        o.Notifier,

		now: model.Now,
	}
	h.ready.Store(0)

	factoryTr := func(_ context.Context) api_v1.TargetRetriever { return h.scrapeManager }
	factoryAr := func(_ context.Context) api_v1.AlertmanagerRetriever { return h.notifier }
	FactoryRr := func(_ context.Context) api_v1.RulesRetriever { return h.ruleManager }

	var app storage.Appendable
	if o.RemoteWriteReceiver {
		app = h.storage
	}

	h.apiV1 = api_v1.NewAPI(h.queryEngine, h.storage, app, h.exemplarStorage, factoryTr, factoryAr,
		func() config.Config {
			h.mtx.RLock()
			defer h.mtx.RUnlock()
			return *h.config
		},
		o.Flags,
		api_v1.GlobalURLOptions{
			ListenAddress: o.ListenAddress,
			Host:          o.ExternalURL.Host,
			Scheme:        o.ExternalURL.Scheme,
		},
		h.testReady,
		h.options.LocalStorage,
		h.options.TSDBDir,
		h.options.EnableAdminAPI,
		logger,
		FactoryRr,
		h.options.RemoteReadSampleLimit,
		h.options.RemoteReadConcurrencyLimit,
		h.options.RemoteReadBytesInFrame,
		h.options.CORSOrigin,
		h.runtimeInfo,
		h.versionInfo,
		o.Gatherer,
		o.Registerer,
	)

	if o.RoutePrefix != "/" {
		// If the prefix is missing for the root path, prepend it.
		router.Get("/", func(w http.ResponseWriter, r *http.Request) {
			http.Redirect(w, r, o.RoutePrefix, http.StatusFound)
		})
		router = router.WithPrefix(o.RoutePrefix)
	}

	readyf := h.testReady

	router.Get("/", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, path.Join(o.ExternalURL.Path, "/graph"), http.StatusFound)
	})
	router.Get("/classic/", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, path.Join(o.ExternalURL.Path, "/classic/graph"), http.StatusFound)
	})

	// Redirect the original React UI's path (under "/new") to its new path at the root.
	router.Get("/new/*path", func(w http.ResponseWriter, r *http.Request) {
		p := route.Param(r.Context(), "path")
		http.Redirect(w, r, path.Join(o.ExternalURL.Path, p)+"?"+r.URL.RawQuery, http.StatusFound)
	})

	router.Get("/classic/alerts", readyf(h.alerts))
	router.Get("/classic/graph", readyf(h.graph))
	router.Get("/classic/status", readyf(h.status))
	router.Get("/classic/flags", readyf(h.flags))
	router.Get("/classic/config", readyf(h.serveConfig))
	router.Get("/classic/rules", readyf(h.rules))
	router.Get("/classic/targets", readyf(h.targets))
	router.Get("/classic/service-discovery", readyf(h.serviceDiscovery))
	router.Get("/classic/static/*filepath", func(w http.ResponseWriter, r *http.Request) {
		r.URL.Path = path.Join("/static", route.Param(r.Context(), "filepath"))
		fs := server.StaticFileServer(ui.Assets)
		fs.ServeHTTP(w, r)
	})
	// Make sure that "<path-prefix>/classic" is redirected to "<path-prefix>/classic/" and
	// not just the naked "/classic/", which would be the default behavior of the router
	// with the "RedirectTrailingSlash" option (https://pkg.go.dev/github.com/julienschmidt/httprouter#Router.RedirectTrailingSlash),
	// and which breaks users with a --web.route-prefix that deviates from the path derived
	// from the external URL.
	// See https://github.com/prometheus/prometheus/issues/6163#issuecomment-553855129.
	router.Get("/classic", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, path.Join(o.ExternalURL.Path, "classic")+"/", http.StatusFound)
	})

	router.Get("/version", h.version)
	router.Get("/metrics", promhttp.Handler().ServeHTTP)

	router.Get("/federate", readyf(httputil.CompressionHandler{
		Handler: http.HandlerFunc(h.federation),
	}.ServeHTTP))

	router.Get("/consoles/*filepath", readyf(h.consoles))

	serveReactApp := func(w http.ResponseWriter, r *http.Request) {
		f, err := ui.Assets.Open("/static/react/index.html")
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			fmt.Fprintf(w, "Error opening React index.html: %v", err)
			return
		}
		idx, err := ioutil.ReadAll(f)
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			fmt.Fprintf(w, "Error reading React index.html: %v", err)
			return
		}
		replacedIdx := bytes.ReplaceAll(idx, []byte("CONSOLES_LINK_PLACEHOLDER"), []byte(h.consolesPath()))
		replacedIdx = bytes.ReplaceAll(replacedIdx, []byte("TITLE_PLACEHOLDER"), []byte(h.options.PageTitle))
		w.Write(replacedIdx)
	}

	// Serve the React app.
	for _, p := range reactRouterPaths {
		router.Get(p, serveReactApp)
	}

	// The favicon and manifest are bundled as part of the React app, but we want to serve
	// them on the root.
	for _, p := range []string{"/favicon.ico", "/manifest.json"} {
		assetPath := "/static/react" + p
		router.Get(p, func(w http.ResponseWriter, r *http.Request) {
			r.URL.Path = assetPath
			fs := server.StaticFileServer(ui.Assets)
			fs.ServeHTTP(w, r)
		})
	}

	// Static files required by the React app.
	router.Get("/static/*filepath", func(w http.ResponseWriter, r *http.Request) {
		r.URL.Path = path.Join("/static/react/static", route.Param(r.Context(), "filepath"))
		fs := server.StaticFileServer(ui.Assets)
		fs.ServeHTTP(w, r)
	})

	if o.UserAssetsPath != "" {
		router.Get("/user/*filepath", route.FileServe(o.UserAssetsPath))
	}

	if o.EnableLifecycle {
		router.Post("/-/quit", h.quit)
		router.Put("/-/quit", h.quit)
		router.Post("/-/reload", h.reload)
		router.Put("/-/reload", h.reload)
	} else {
		forbiddenAPINotEnabled := func(w http.ResponseWriter, _ *http.Request) {
			w.WriteHeader(http.StatusForbidden)
			w.Write([]byte("Lifecycle API is not enabled."))
		}
		router.Post("/-/quit", forbiddenAPINotEnabled)
		router.Put("/-/quit", forbiddenAPINotEnabled)
		router.Post("/-/reload", forbiddenAPINotEnabled)
		router.Put("/-/reload", forbiddenAPINotEnabled)
	}
	router.Get("/-/quit", func(w http.ResponseWriter, _ *http.Request) {
		w.WriteHeader(http.StatusMethodNotAllowed)
		w.Write([]byte("Only POST or PUT requests allowed"))
	})
	router.Get("/-/reload", func(w http.ResponseWriter, _ *http.Request) {
		w.WriteHeader(http.StatusMethodNotAllowed)
		w.Write([]byte("Only POST or PUT requests allowed"))
	})

	router.Get("/debug/*subpath", serveDebug)
	router.Post("/debug/*subpath", serveDebug)

	router.Get("/-/healthy", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
		fmt.Fprintf(w, "Prometheus is Healthy.\n")
	})
	router.Get("/-/ready", readyf(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
		fmt.Fprintf(w, "Prometheus is Ready.\n")
	}))

	return h
}

func serveDebug(w http.ResponseWriter, req *http.Request) {
	ctx := req.Context()
	subpath := route.Param(ctx, "subpath")

	if subpath == "/pprof" {
		http.Redirect(w, req, req.URL.Path+"/", http.StatusMovedPermanently)
		return
	}

	if !strings.HasPrefix(subpath, "/pprof/") {
		http.NotFound(w, req)
		return
	}
	subpath = strings.TrimPrefix(subpath, "/pprof/")

	switch subpath {
	case "cmdline":
		pprof.Cmdline(w, req)
	case "profile":
		pprof.Profile(w, req)
	case "symbol":
		pprof.Symbol(w, req)
	case "trace":
		pprof.Trace(w, req)
	default:
		req.URL.Path = "/debug/pprof/" + subpath
		pprof.Index(w, req)
	}
}

// Ready sets Handler to be ready.
func (h *Handler) Ready() {
	h.ready.Store(1)
}

// Verifies whether the server is ready or not.
func (h *Handler) isReady() bool {
	return h.ready.Load() > 0
}

// Checks if server is ready, calls f if it is, returns 503 if it is not.
func (h *Handler) testReady(f http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if h.isReady() {
			f(w, r)
		} else {
			w.WriteHeader(http.StatusServiceUnavailable)
			fmt.Fprintf(w, "Service Unavailable")
		}
	}
}

// Quit returns the receive-only quit channel.
func (h *Handler) Quit() <-chan struct{} {
	return h.quitCh
}

// Reload returns the receive-only channel that signals configuration reload requests.
func (h *Handler) Reload() <-chan chan error {
	return h.reloadCh
}

// Listener creates the TCP listener for web requests.
func (h *Handler) Listener() (net.Listener, error) {
	level.Info(h.logger).Log("msg", "Start listening for connections", "address", h.options.ListenAddress)

	listener, err := net.Listen("tcp", h.options.ListenAddress)
	if err != nil {
		return listener, err
	}
	listener = netutil.LimitListener(listener, h.options.MaxConnections)

	// Monitor incoming connections with conntrack.
	listener = conntrack.NewListener(listener,
		conntrack.TrackWithName("http"),
		conntrack.TrackWithTracing())

	return listener, nil
}

// Run serves the HTTP endpoints.
func (h *Handler) Run(ctx context.Context, listener net.Listener, webConfig string) error {
	if listener == nil {
		var err error
		listener, err = h.Listener()
		if err != nil {
			return err
		}
	}
	operationName := nethttp.OperationNameFunc(func(r *http.Request) string {
		return fmt.Sprintf("%s %s", r.Method, r.URL.Path)
	})
	mux := http.NewServeMux()
	mux.Handle("/", h.router)

	apiPath := "/api"
	if h.options.RoutePrefix != "/" {
		apiPath = h.options.RoutePrefix + apiPath
		level.Info(h.logger).Log("msg", "Router prefix", "prefix", h.options.RoutePrefix)
	}
	av1 := route.New().
		WithInstrumentation(h.metrics.instrumentHandlerWithPrefix("/api/v1")).
		WithInstrumentation(setPathWithPrefix(apiPath + "/v1"))
	h.apiV1.Register(av1)

	mux.Handle(apiPath+"/v1/", http.StripPrefix(apiPath+"/v1", av1))

	errlog := stdlog.New(log.NewStdlibAdapter(level.Error(h.logger)), "", 0)

	httpSrv := &http.Server{
		Handler:     withStackTracer(nethttp.Middleware(opentracing.GlobalTracer(), mux, operationName), h.logger),
		ErrorLog:    errlog,
		ReadTimeout: h.options.ReadTimeout,
	}

	errCh := make(chan error)
	go func() {
		errCh <- toolkit_web.Serve(listener, httpSrv, webConfig, h.logger)
	}()

	select {
	case e := <-errCh:
		return e
	case <-ctx.Done():
		httpSrv.Shutdown(ctx)
		return nil
	}
}

func (h *Handler) alerts(w http.ResponseWriter, r *http.Request) {

	var groups []*rules.Group
	for _, group := range h.ruleManager.RuleGroups() {
		if group.HasAlertingRules() {
			groups = append(groups, group)
		}
	}

	alertStatus := AlertStatus{
		Groups: groups,
		AlertStateToRowClass: map[rules.AlertState]string{
			rules.StateInactive: "success",
			rules.StatePending:  "warning",
			rules.StateFiring:   "danger",
		},
		Counts: alertCounts(groups),
	}
	h.executeTemplate(w, "alerts.html", alertStatus)
}

func alertCounts(groups []*rules.Group) AlertByStateCount {
	result := AlertByStateCount{}

	for _, group := range groups {
		for _, alert := range group.AlertingRules() {
			switch alert.State() {
			case rules.StateInactive:
				result.Inactive++
			case rules.StatePending:
				result.Pending++
			case rules.StateFiring:
				result.Firing++
			}
		}
	}
	return result
}

func (h *Handler) consoles(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	name := route.Param(ctx, "filepath")

	file, err := http.Dir(h.options.ConsoleTemplatesPath).Open(name)
	if err != nil {
		http.Error(w, err.Error(), http.StatusNotFound)
		return
	}
	defer file.Close()
	text, err := ioutil.ReadAll(file)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	ctx = httputil.ContextFromRequest(ctx, r)

	// Provide URL parameters as a map for easy use. Advanced users may have need for
	// parameters beyond the first, so provide RawParams.
	rawParams, err := url.ParseQuery(r.URL.RawQuery)
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	params := map[string]string{}
	for k, v := range rawParams {
		params[k] = v[0]
	}

	externalLabels := map[string]string{}
	h.mtx.RLock()
	els := h.config.GlobalConfig.ExternalLabels
	h.mtx.RUnlock()
	for _, el := range els {
		externalLabels[el.Name] = el.Value
	}

	// Inject some convenience variables that are easier to remember for users
	// who are not used to Go's templating system.
	defs := []string{
		"{{$rawParams := .RawParams }}",
		"{{$params := .Params}}",
		"{{$path := .Path}}",
		"{{$externalLabels := .ExternalLabels}}",
	}

	data := struct {
		RawParams      url.Values
		Params         map[string]string
		Path           string
		ExternalLabels map[string]string
	}{
		RawParams:      rawParams,
		Params:         params,
		Path:           strings.TrimLeft(name, "/"),
		ExternalLabels: externalLabels,
	}

	tmpl := template.NewTemplateExpander(
		ctx,
		strings.Join(append(defs, string(text)), ""),
		"__console_"+name,
		data,
		h.now(),
		template.QueryFunc(rules.EngineQueryFunc(h.queryEngine, h.storage)),
		h.options.ExternalURL,
	)
	filenames, err := filepath.Glob(h.options.ConsoleLibrariesPath + "/*.lib")
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	result, err := tmpl.ExpandHTML(filenames)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	io.WriteString(w, result)
}

func (h *Handler) graph(w http.ResponseWriter, r *http.Request) {
	h.executeTemplate(w, "graph.html", nil)
}

func (h *Handler) status(w http.ResponseWriter, r *http.Request) {
	status := struct {
		Birth               time.Time
		CWD                 string
		Version             *PrometheusVersion
		Alertmanagers       []*url.URL
		GoroutineCount      int
		GOMAXPROCS          int
		GOGC                string
		GODEBUG             string
		CorruptionCount     int64
		ChunkCount          int64
		TimeSeriesCount     int64
		LastConfigTime      time.Time
		ReloadConfigSuccess bool
		StorageRetention    string
		NumSeries           uint64
		MaxTime             int64
		MinTime             int64
		Stats               *index.PostingsStats
		Duration            string
	}{
		Birth:          h.birth,
		CWD:            h.cwd,
		Version:        h.versionInfo,
		Alertmanagers:  h.notifier.Alertmanagers(),
		GoroutineCount: runtime.NumGoroutine(),
		GOMAXPROCS:     runtime.GOMAXPROCS(0),
		GOGC:           os.Getenv("GOGC"),
		GODEBUG:        os.Getenv("GODEBUG"),
	}

	if h.options.TSDBRetentionDuration != 0 {
		status.StorageRetention = h.options.TSDBRetentionDuration.String()
	}
	if h.options.TSDBMaxBytes != 0 {
		if status.StorageRetention != "" {
			status.StorageRetention = status.StorageRetention + " or "
		}
		status.StorageRetention = status.StorageRetention + h.options.TSDBMaxBytes.String()
	}

	metrics, err := h.gatherer.Gather()
	if err != nil {
		http.Error(w, fmt.Sprintf("error gathering runtime status: %s", err), http.StatusInternalServerError)
		return
	}
	for _, mF := range metrics {
		switch *mF.Name {
		case "prometheus_tsdb_head_chunks":
			status.ChunkCount = int64(toFloat64(mF))
		case "prometheus_tsdb_head_series":
			status.TimeSeriesCount = int64(toFloat64(mF))
		case "prometheus_tsdb_wal_corruptions_total":
			status.CorruptionCount = int64(toFloat64(mF))
		case "prometheus_config_last_reload_successful":
			status.ReloadConfigSuccess = toFloat64(mF) != 0
		case "prometheus_config_last_reload_success_timestamp_seconds":
			status.LastConfigTime = time.Unix(int64(toFloat64(mF)), 0).UTC()
		}
	}

	startTime := time.Now().UnixNano()
	s, err := h.localStorage.Stats("__name__")
	if err != nil {
		if errors.Cause(err) == tsdb.ErrNotReady {
			http.Error(w, tsdb.ErrNotReady.Error(), http.StatusServiceUnavailable)
			return
		}
		http.Error(w, fmt.Sprintf("error gathering local storage statistics: %s", err), http.StatusInternalServerError)
		return
	}
	status.Duration = fmt.Sprintf("%.3f", float64(time.Now().UnixNano()-startTime)/float64(1e9))
	status.Stats = s.IndexPostingStats
	status.NumSeries = s.NumSeries
	status.MaxTime = s.MaxTime
	status.MinTime = s.MinTime

	h.executeTemplate(w, "status.html", status)
}

func (h *Handler) runtimeInfo() (api_v1.RuntimeInfo, error) {
	status := api_v1.RuntimeInfo{
		StartTime:      h.birth,
		CWD:            h.cwd,
		GoroutineCount: runtime.NumGoroutine(),
		GOMAXPROCS:     runtime.GOMAXPROCS(0),
		GOGC:           os.Getenv("GOGC"),
		GODEBUG:        os.Getenv("GODEBUG"),
	}

	if h.options.TSDBRetentionDuration != 0 {
		status.StorageRetention = h.options.TSDBRetentionDuration.String()
	}
	if h.options.TSDBMaxBytes != 0 {
		if status.StorageRetention != "" {
			status.StorageRetention = status.StorageRetention + " or "
		}
		status.StorageRetention = status.StorageRetention + h.options.TSDBMaxBytes.String()
	}

	metrics, err := h.gatherer.Gather()
	if err != nil {
		return status, errors.Errorf("error gathering runtime status: %s", err)
	}
	for _, mF := range metrics {
		switch *mF.Name {
		case "prometheus_tsdb_wal_corruptions_total":
			status.CorruptionCount = int64(toFloat64(mF))
		case "prometheus_config_last_reload_successful":
			status.ReloadConfigSuccess = toFloat64(mF) != 0
		case "prometheus_config_last_reload_success_timestamp_seconds":
			status.LastConfigTime = time.Unix(int64(toFloat64(mF)), 0).UTC()
		}
	}
	return status, nil
}

func toFloat64(f *io_prometheus_client.MetricFamily) float64 {
	m := *f.Metric[0]
	if m.Gauge != nil {
		return m.Gauge.GetValue()
	}
	if m.Counter != nil {
		return m.Counter.GetValue()
	}
	if m.Untyped != nil {
		return m.Untyped.GetValue()
	}
	return math.NaN()
}

func (h *Handler) flags(w http.ResponseWriter, r *http.Request) {
	h.executeTemplate(w, "flags.html", h.flagsMap)
}

func (h *Handler) serveConfig(w http.ResponseWriter, r *http.Request) {
	h.mtx.RLock()
	defer h.mtx.RUnlock()

	h.executeTemplate(w, "config.html", h.config.String())
}

func (h *Handler) rules(w http.ResponseWriter, r *http.Request) {
	h.executeTemplate(w, "rules.html", h.ruleManager)
}

func (h *Handler) serviceDiscovery(w http.ResponseWriter, r *http.Request) {
	var index []string
	targets := h.scrapeManager.TargetsAll()
	for job := range targets {
		index = append(index, job)
	}
	sort.Strings(index)
	scrapeConfigData := struct {
		Index   []string
		Targets map[string][]*scrape.Target
		Active  []int
		Dropped []int
		Total   []int
	}{
		Index:   index,
		Targets: make(map[string][]*scrape.Target),
		Active:  make([]int, len(index)),
		Dropped: make([]int, len(index)),
		Total:   make([]int, len(index)),
	}
	for i, job := range scrapeConfigData.Index {
		scrapeConfigData.Targets[job] = make([]*scrape.Target, 0, len(targets[job]))
		scrapeConfigData.Total[i] = len(targets[job])
		for _, target := range targets[job] {
			// Do not display more than 100 dropped targets per job to avoid
			// returning too much data to the clients.
			if target.Labels().Len() == 0 {
				scrapeConfigData.Dropped[i]++
				if scrapeConfigData.Dropped[i] > 100 {
					continue
				}
			} else {
				scrapeConfigData.Active[i]++
			}
			scrapeConfigData.Targets[job] = append(scrapeConfigData.Targets[job], target)
		}
	}

	h.executeTemplate(w, "service-discovery.html", scrapeConfigData)
}

func (h *Handler) targets(w http.ResponseWriter, r *http.Request) {
	tps := h.scrapeManager.TargetsActive()
	for _, targets := range tps {
		sort.Slice(targets, func(i, j int) bool {
			iJobLabel := targets[i].Labels().Get(model.JobLabel)
			jJobLabel := targets[j].Labels().Get(model.JobLabel)
			if iJobLabel == jJobLabel {
				return targets[i].Labels().Get(model.InstanceLabel) < targets[j].Labels().Get(model.InstanceLabel)
			}
			return iJobLabel < jJobLabel
		})
	}

	h.executeTemplate(w, "targets.html", struct {
		TargetPools map[string][]*scrape.Target
	}{
		TargetPools: tps,
	})
}

func (h *Handler) version(w http.ResponseWriter, r *http.Request) {
	dec := json.NewEncoder(w)
	if err := dec.Encode(h.versionInfo); err != nil {
		http.Error(w, fmt.Sprintf("error encoding JSON: %s", err), http.StatusInternalServerError)
	}
}

func (h *Handler) quit(w http.ResponseWriter, r *http.Request) {
	var closed bool
	h.quitOnce.Do(func() {
		closed = true
		close(h.quitCh)
		fmt.Fprintf(w, "Requesting termination... Goodbye!")
	})
	if !closed {
		fmt.Fprintf(w, "Termination already in progress.")
	}
}

func (h *Handler) reload(w http.ResponseWriter, r *http.Request) {
	rc := make(chan error)
	h.reloadCh <- rc
	if err := <-rc; err != nil {
		http.Error(w, fmt.Sprintf("failed to reload config: %s", err), http.StatusInternalServerError)
	}
}

func (h *Handler) consolesPath() string {
	if _, err := os.Stat(h.options.ConsoleTemplatesPath + "/index.html"); !os.IsNotExist(err) {
		return h.options.ExternalURL.Path + "/consoles/index.html"
	}
	if h.options.UserAssetsPath != "" {
		if _, err := os.Stat(h.options.UserAssetsPath + "/index.html"); !os.IsNotExist(err) {
			return h.options.ExternalURL.Path + "/user/index.html"
		}
	}
	return ""
}

func tmplFuncs(consolesPath string, opts *Options) template_text.FuncMap {
	return template_text.FuncMap{
		"since": func(t time.Time) time.Duration {
			return time.Since(t) / time.Millisecond * time.Millisecond
		},
		"unixToTime": func(i int64) time.Time {
			t := time.Unix(i/int64(time.Microsecond), 0).UTC()
			return t
		},
		"consolesPath": func() string { return consolesPath },
		"pathPrefix":   func() string { return opts.ExternalURL.Path },
		"pageTitle":    func() string { return opts.PageTitle },
		"buildVersion": func() string { return opts.Version.Revision },
		"globalURL": func(u *url.URL) *url.URL {
			host, port, err := net.SplitHostPort(u.Host)
			if err != nil {
				return u
			}
			for _, lhr := range api_v1.LocalhostRepresentations {
				if host == lhr {
					_, ownPort, err := net.SplitHostPort(opts.ListenAddress)
					if err != nil {
						return u
					}

					if port == ownPort {
						// Only in the case where the target is on localhost and its port is
						// the same as the one we're listening on, we know for sure that
						// we're monitoring our own process and that we need to change the
						// scheme, hostname, and port to the externally reachable ones as
						// well. We shouldn't need to touch the path at all, since if a
						// path prefix is defined, the path under which we scrape ourselves
						// should already contain the prefix.
						u.Scheme = opts.ExternalURL.Scheme
						u.Host = opts.ExternalURL.Host
					} else {
						// Otherwise, we only know that localhost is not reachable
						// externally, so we replace only the hostname by the one in the
						// external URL. It could be the wrong hostname for the service on
						// this port, but it's still the best possible guess.
						host, _, err := net.SplitHostPort(opts.ExternalURL.Host)
						if err != nil {
							return u
						}
						u.Host = host + ":" + port
					}
					break
				}
			}
			return u
		},
		"numHealthy": func(pool []*scrape.Target) int {
			alive := len(pool)
			for _, p := range pool {
				if p.Health() != scrape.HealthGood {
					alive--
				}
			}

			return alive
		},
		"targetHealthToClass": func(th scrape.TargetHealth) string {
			switch th {
			case scrape.HealthUnknown:
				return "warning"
			case scrape.HealthGood:
				return "success"
			default:
				return "danger"
			}
		},
		"ruleHealthToClass": func(rh rules.RuleHealth) string {
			switch rh {
			case rules.HealthUnknown:
				return "warning"
			case rules.HealthGood:
				return "success"
			default:
				return "danger"
			}
		},
		"alertStateToClass": func(as rules.AlertState) string {
			switch as {
			case rules.StateInactive:
				return "success"
			case rules.StatePending:
				return "warning"
			case rules.StateFiring:
				return "danger"
			default:
				panic("unknown alert state")
			}
		},
	}
}

func (h *Handler) getTemplate(name string) (string, error) {
	var tmpl string

	appendf := func(name string) error {
		f, err := ui.Assets.Open(path.Join("/templates", name))
		if err != nil {
			return err
		}
		defer f.Close()
		b, err := ioutil.ReadAll(f)
		if err != nil {
			return err
		}
		tmpl += string(b)
		return nil
	}

	err := appendf("_base.html")
	if err != nil {
		return "", errors.Wrap(err, "error reading base template")
	}
	err = appendf(name)
	if err != nil {
		return "", errors.Wrapf(err, "error reading page template %s", name)
	}

	return tmpl, nil
}

func (h *Handler) executeTemplate(w http.ResponseWriter, name string, data interface{}) {
	text, err := h.getTemplate(name)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}

	tmpl := template.NewTemplateExpander(
		h.context,
		text,
		name,
		data,
		h.now(),
		template.QueryFunc(rules.EngineQueryFunc(h.queryEngine, h.storage)),
		h.options.ExternalURL,
	)
	tmpl.Funcs(tmplFuncs(h.consolesPath(), h.options))

	result, err := tmpl.ExpandHTML(nil)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	io.WriteString(w, result)
}

// AlertStatus bundles alerting rules and the mapping of alert states to row classes.
type AlertStatus struct {
	Groups               []*rules.Group
	AlertStateToRowClass map[rules.AlertState]string
	Counts               AlertByStateCount
}

type AlertByStateCount struct {
	Inactive int32
	Pending  int32
	Firing   int32
}

func setPathWithPrefix(prefix string) func(handlerName string, handler http.HandlerFunc) http.HandlerFunc {
	return func(handlerName string, handler http.HandlerFunc) http.HandlerFunc {
		return func(w http.ResponseWriter, r *http.Request) {
			handler(w, r.WithContext(httputil.ContextWithPath(r.Context(), prefix+r.URL.Path)))
		}
	}
}
