// 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"
	"strconv"
	"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
	IsAgent                    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.IsAgent,
		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
		}
		defer func() { _ = f.Close() }()
		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))
		replacedIdx = bytes.ReplaceAll(replacedIdx, []byte("PROMETHEUS_AGENT_MODE_PLACEHOLDER"), []byte(strconv.FormatBool(h.options.IsAgent)))
		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,
		nil,
	)
	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,
		nil,
	)
	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)))
		}
	}
}