// 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"
	stdlog "log"
	"math"
	"net"
	"net/http"
	"net/http/pprof"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"runtime"
	"runtime/debug"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/alecthomas/units"
	"github.com/go-kit/log"
	"github.com/go-kit/log/level"
	"github.com/grafana/regexp"
	"github.com/mwitkow/go-conntrack"
	"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.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
	"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/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{
	"/config",
	"/flags",
	"/service-discovery",
	"/status",
	"/targets",
	"/starting",
}

// Paths that are handled by the React router when the Agent mode is set.
var reactRouterAgentPaths = []string{
	"/agent",
}

// Paths that are handled by the React router when the Agent mode is not set.
var reactRouterServerPaths = []string{
	"/alerts",
	"/graph",
	"/rules",
	"/tsdb-status",
}

// 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
	readyStatus     prometheus.Gauge
}

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},
				NativeHistogramBucketFactor:     1.1,
				NativeHistogramMaxBucketNumber:  100,
				NativeHistogramMinResetDuration: 1 * time.Hour,
			},
			[]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"},
		),
		readyStatus: prometheus.NewGauge(prometheus.GaugeOpts{
			Name: "prometheus_ready",
			Help: "Whether Prometheus startup was fully completed and the server is ready for normal operation.",
		}),
	}

	if r != nil {
		r.MustRegister(m.requestCounter, m.requestDuration, m.responseSize, m.readyStatus)
		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 {
	m.requestCounter.WithLabelValues(handlerName, "200")
	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
	EnableRemoteWriteReceiver       bool
	RemoteWriteReceiverProtoTypes   []config.RemoteWriteProtoType
	RemoteWriteReceiverCompressions []config.RemoteWriteCompression
	EnableOTLPWriteReceiver         bool
	IsAgent                         bool
	AppName                         string

	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.SetReady(false)

	factorySPr := func(_ context.Context) api_v1.ScrapePoolsRetriever { return h.scrapeManager }
	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.EnableRemoteWriteReceiver || o.EnableOTLPWriteReceiver {
		app = h.storage
	}

	h.apiV1 = api_v1.NewAPI(h.queryEngine, h.storage, app, h.exemplarStorage, factorySPr, 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,
		nil,
		o.EnableRemoteWriteReceiver,
		o.RemoteWriteReceiverProtoTypes,
		o.RemoteWriteReceiverCompressions,
		o.EnableOTLPWriteReceiver,
	)

	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)
	}

	homePage := "/graph"
	if o.IsAgent {
		homePage = "/agent"
	}

	readyf := h.testReady

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

	// The console library examples at 'console_libraries/prom.lib' still depend on old asset files being served under `classic`.
	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)
	})

	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 := io.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("AGENT_MODE_PLACEHOLDER"), []byte(strconv.FormatBool(h.options.IsAgent)))
		replacedIdx = bytes.ReplaceAll(replacedIdx, []byte("READY_PLACEHOLDER"), []byte(strconv.FormatBool(h.isReady())))
		w.Write(replacedIdx)
	}

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

	if h.options.IsAgent {
		for _, p := range reactRouterAgentPaths {
			router.Get(p, serveReactApp)
		}
	} else {
		for _, p := range reactRouterServerPaths {
			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, o.AppName+" is Healthy.\n")
	})
	router.Head("/-/healthy", func(w http.ResponseWriter, _ *http.Request) {
		w.WriteHeader(http.StatusOK)
	})
	router.Get("/-/ready", readyf(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
		fmt.Fprintf(w, o.AppName+" is Ready.\n")
	}))
	router.Head("/-/ready", readyf(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
	}))

	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)
	}
}

// SetReady sets the ready status of our web Handler.
func (h *Handler) SetReady(v bool) {
	if v {
		h.ready.Store(1)
		h.metrics.readyStatus.Set(1)
		return
	}

	h.ready.Store(0)
	h.metrics.readyStatus.Set(0)
}

// 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
		}
	}

	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)

	spanNameFormatter := otelhttp.WithSpanNameFormatter(func(_ string, r *http.Request) string {
		return fmt.Sprintf("%s %s", r.Method, r.URL.Path)
	})

	httpSrv := &http.Server{
		Handler:     withStackTracer(otelhttp.NewHandler(mux, "", spanNameFormatter), h.logger),
		ErrorLog:    errlog,
		ReadTimeout: h.options.ReadTimeout,
	}

	errCh := make(chan error, 1)
	go func() {
		errCh <- toolkit_web.Serve(listener, httpSrv, &toolkit_web.FlagConfig{WebConfigFile: &webConfig}, h.logger)
	}()

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

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 := io.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]
	}

	h.mtx.RLock()
	els := h.config.GlobalConfig.ExternalLabels
	h.mtx.RUnlock()
	externalLabels := els.Map()

	// 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) runtimeInfo() (api_v1.RuntimeInfo, error) {
	status := api_v1.RuntimeInfo{
		StartTime:      h.birth,
		CWD:            h.cwd,
		GoroutineCount: runtime.NumGoroutine(),
		GOMAXPROCS:     runtime.GOMAXPROCS(0),
		GOMEMLIMIT:     debug.SetMemoryLimit(-1),
		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 += " or "
		}
		status.StorageRetention += h.options.TSDBMaxBytes.String()
	}

	metrics, err := h.gatherer.Gather()
	if err != nil {
		return status, fmt.Errorf("error gathering runtime status: %w", 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) version(w http.ResponseWriter, _ *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, _ *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, _ *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 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)))
		}
	}
}