// Copyright 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 v1

import (
	"context"
	"crypto/sha1"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"math"
	"math/rand"
	"net"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"slices"
	"sort"
	"strconv"
	"strings"
	"time"

	"github.com/grafana/regexp"
	jsoniter "github.com/json-iterator/go"
	"github.com/munnerz/goautoneg"
	remoteapi "github.com/prometheus/client_golang/exp/api/remote"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/common/model"
	"github.com/prometheus/common/route"
	"google.golang.org/protobuf/encoding/protojson"

	"github.com/prometheus/prometheus/config"
	"github.com/prometheus/prometheus/model/labels"
	"github.com/prometheus/prometheus/model/metadata"
	"github.com/prometheus/prometheus/model/relabel"
	"github.com/prometheus/prometheus/model/timestamp"
	"github.com/prometheus/prometheus/promql"
	"github.com/prometheus/prometheus/promql/parser"
	"github.com/prometheus/prometheus/rules"
	"github.com/prometheus/prometheus/scrape"
	"github.com/prometheus/prometheus/storage"
	"github.com/prometheus/prometheus/storage/remote"
	"github.com/prometheus/prometheus/tsdb"
	"github.com/prometheus/prometheus/tsdb/index"
	"github.com/prometheus/prometheus/util/annotations"
	"github.com/prometheus/prometheus/util/features"
	"github.com/prometheus/prometheus/util/httputil"
	"github.com/prometheus/prometheus/util/notifications"
	"github.com/prometheus/prometheus/util/stats"
)

type status string

const (
	statusSuccess status = "success"
	statusError   status = "error"

	// Non-standard status code (originally introduced by nginx) for the case when a client closes
	// the connection while the server is still processing the request.
	statusClientClosedConnection = 499

	// checkContextEveryNIterations is used in some tight loops to check if the context is done.
	checkContextEveryNIterations = 128
)

type errorNum int

type errorType struct {
	num errorNum
	str string
}

const (
	ErrorNone errorNum = iota
	ErrorTimeout
	ErrorCanceled
	ErrorExec
	ErrorBadData
	ErrorInternal
	ErrorUnavailable
	ErrorNotFound
	ErrorNotAcceptable
)

var (
	errorNone          = errorType{ErrorNone, ""}
	errorTimeout       = errorType{ErrorTimeout, "timeout"}
	errorCanceled      = errorType{ErrorCanceled, "canceled"}
	errorExec          = errorType{ErrorExec, "execution"}
	errorBadData       = errorType{ErrorBadData, "bad_data"}
	errorInternal      = errorType{ErrorInternal, "internal"}
	errorUnavailable   = errorType{ErrorUnavailable, "unavailable"}
	errorNotFound      = errorType{ErrorNotFound, "not_found"}
	errorNotAcceptable = errorType{ErrorNotAcceptable, "not_acceptable"}
)

// OverrideErrorCode can be used to override status code for different error types.
// Return false to fall back to default status code.
type OverrideErrorCode func(errorNum, error) (code int, override bool)

var LocalhostRepresentations = []string{"127.0.0.1", "localhost", "::1"}

type apiError struct {
	typ errorType
	err error
}

func (e *apiError) Error() string {
	return fmt.Sprintf("%s: %s", e.typ.str, e.err)
}

// ScrapePoolsRetriever provide the list of all scrape pools.
type ScrapePoolsRetriever interface {
	ScrapePools() []string
}

// TargetRetriever provides the list of active/dropped targets to scrape or not.
type TargetRetriever interface {
	TargetsActive() map[string][]*scrape.Target
	TargetsDropped() map[string][]*scrape.Target
	TargetsDroppedCounts() map[string]int
	ScrapePoolConfig(string) (*config.ScrapeConfig, error)
}

// AlertmanagerRetriever provides a list of all/dropped AlertManager URLs.
type AlertmanagerRetriever interface {
	Alertmanagers() []*url.URL
	DroppedAlertmanagers() []*url.URL
}

// RulesRetriever provides a list of active rules and alerts.
type RulesRetriever interface {
	RuleGroups() []*rules.Group
	AlertingRules() []*rules.AlertingRule
}

// StatsRenderer converts engine statistics into a format suitable for the API.
type StatsRenderer func(context.Context, *stats.Statistics, string) stats.QueryStats

// DefaultStatsRenderer is the default stats renderer for the API.
func DefaultStatsRenderer(_ context.Context, s *stats.Statistics, param string) stats.QueryStats {
	if param != "" {
		return stats.NewQueryStats(s)
	}
	return nil
}

// PrometheusVersion contains build information about Prometheus.
type PrometheusVersion struct {
	Version   string `json:"version"`
	Revision  string `json:"revision"`
	Branch    string `json:"branch"`
	BuildUser string `json:"buildUser"`
	BuildDate string `json:"buildDate"`
	GoVersion string `json:"goVersion"`
}

// RuntimeInfo contains runtime information about Prometheus.
type RuntimeInfo struct {
	StartTime           time.Time `json:"startTime"`
	CWD                 string    `json:"CWD"`
	Hostname            string    `json:"hostname"`
	ServerTime          time.Time `json:"serverTime"`
	ReloadConfigSuccess bool      `json:"reloadConfigSuccess"`
	LastConfigTime      time.Time `json:"lastConfigTime"`
	CorruptionCount     int64     `json:"corruptionCount"`
	GoroutineCount      int       `json:"goroutineCount"`
	GOMAXPROCS          int       `json:"GOMAXPROCS"`
	GOMEMLIMIT          int64     `json:"GOMEMLIMIT"`
	GOGC                string    `json:"GOGC"`
	GODEBUG             string    `json:"GODEBUG"`
	StorageRetention    string    `json:"storageRetention"`
}

// Response contains a response to a HTTP API request.
type Response struct {
	Status    status   `json:"status"`
	Data      any      `json:"data,omitempty"`
	ErrorType string   `json:"errorType,omitempty"`
	Error     string   `json:"error,omitempty"`
	Warnings  []string `json:"warnings,omitempty"`
	Infos     []string `json:"infos,omitempty"`
}

type apiFuncResult struct {
	data      any
	err       *apiError
	warnings  annotations.Annotations
	finalizer func()
}

type apiFunc func(r *http.Request) apiFuncResult

// TSDBAdminStats defines the tsdb interfaces used by the v1 API for admin operations as well as statistics.
type TSDBAdminStats interface {
	CleanTombstones() error
	Delete(ctx context.Context, mint, maxt int64, ms ...*labels.Matcher) error
	Snapshot(dir string, withHead bool) error
	Stats(statsByLabelName string, limit int) (*tsdb.Stats, error)
	WALReplayStatus() (tsdb.WALReplayStatus, error)
	BlockMetas() ([]tsdb.BlockMeta, error)
}

type QueryOpts interface {
	EnablePerStepStats() bool
	LookbackDelta() time.Duration
}

// API can register a set of endpoints in a router and handle
// them using the provided storage and query engine.
type API struct {
	Queryable         storage.SampleAndChunkQueryable
	QueryEngine       promql.QueryEngine
	ExemplarQueryable storage.ExemplarQueryable

	scrapePoolsRetriever  func(context.Context) ScrapePoolsRetriever
	targetRetriever       func(context.Context) TargetRetriever
	alertmanagerRetriever func(context.Context) AlertmanagerRetriever
	rulesRetriever        func(context.Context) RulesRetriever
	now                   func() time.Time
	config                func() config.Config
	flagsMap              map[string]string
	ready                 func(http.HandlerFunc) http.HandlerFunc
	globalURLOptions      GlobalURLOptions

	db                  TSDBAdminStats
	dbDir               string
	enableAdmin         bool
	logger              *slog.Logger
	CORSOrigin          *regexp.Regexp
	buildInfo           *PrometheusVersion
	runtimeInfo         func() (RuntimeInfo, error)
	gatherer            prometheus.Gatherer
	isAgent             bool
	statsRenderer       StatsRenderer
	notificationsGetter func() []notifications.Notification
	notificationsSub    func() (<-chan notifications.Notification, func(), bool)
	// Allows customizing the default mapping
	overrideErrorCode OverrideErrorCode

	remoteWriteHandler http.Handler
	remoteReadHandler  http.Handler
	otlpWriteHandler   http.Handler

	codecs []Codec

	featureRegistry features.Collector
	openAPIBuilder  *OpenAPIBuilder

	parser parser.Parser
}

// NewAPI returns an initialized API type.
func NewAPI(
	qe promql.QueryEngine,
	q storage.SampleAndChunkQueryable,
	ap storage.Appendable, apV2 storage.AppendableV2,
	eq storage.ExemplarQueryable,
	spsr func(context.Context) ScrapePoolsRetriever,
	tr func(context.Context) TargetRetriever,
	ar func(context.Context) AlertmanagerRetriever,
	configFunc func() config.Config,
	flagsMap map[string]string,
	globalURLOptions GlobalURLOptions,
	readyFunc func(http.HandlerFunc) http.HandlerFunc,
	db TSDBAdminStats,
	dbDir string,
	enableAdmin bool,
	logger *slog.Logger,
	rr func(context.Context) RulesRetriever,
	remoteReadSampleLimit int,
	remoteReadConcurrencyLimit int,
	remoteReadMaxBytesInFrame int,
	isAgent bool,
	corsOrigin *regexp.Regexp,
	runtimeInfo func() (RuntimeInfo, error),
	buildInfo *PrometheusVersion,
	notificationsGetter func() []notifications.Notification,
	notificationsSub func() (<-chan notifications.Notification, func(), bool),
	gatherer prometheus.Gatherer,
	registerer prometheus.Registerer,
	statsRenderer StatsRenderer,
	rwEnabled bool,
	acceptRemoteWriteProtoMsgs remoteapi.MessageTypes,
	otlpEnabled, otlpDeltaToCumulative, otlpNativeDeltaIngestion bool,
	stZeroIngestionEnabled bool,
	lookbackDelta time.Duration,
	enableTypeAndUnitLabels bool,
	appendMetadata bool,
	overrideErrorCode OverrideErrorCode,
	featureRegistry features.Collector,
	openAPIOptions OpenAPIOptions,
	promqlParser parser.Parser,
) *API {
	a := &API{
		QueryEngine:       qe,
		Queryable:         q,
		ExemplarQueryable: eq,

		scrapePoolsRetriever:  spsr,
		targetRetriever:       tr,
		alertmanagerRetriever: ar,

		now:                 time.Now,
		config:              configFunc,
		flagsMap:            flagsMap,
		ready:               readyFunc,
		globalURLOptions:    globalURLOptions,
		db:                  db,
		dbDir:               dbDir,
		enableAdmin:         enableAdmin,
		rulesRetriever:      rr,
		logger:              logger,
		CORSOrigin:          corsOrigin,
		runtimeInfo:         runtimeInfo,
		buildInfo:           buildInfo,
		gatherer:            gatherer,
		isAgent:             isAgent,
		statsRenderer:       DefaultStatsRenderer,
		notificationsGetter: notificationsGetter,
		notificationsSub:    notificationsSub,
		overrideErrorCode:   overrideErrorCode,
		featureRegistry:     featureRegistry,
		openAPIBuilder:      NewOpenAPIBuilder(openAPIOptions, logger),
		parser:              promqlParser,

		remoteReadHandler: remote.NewReadHandler(logger, registerer, q, configFunc, remoteReadSampleLimit, remoteReadConcurrencyLimit, remoteReadMaxBytesInFrame),
	}

	if a.parser == nil {
		a.parser = parser.NewParser(parser.Options{})
	}

	a.InstallCodec(JSONCodec{})

	if statsRenderer != nil {
		a.statsRenderer = statsRenderer
	}

	if (ap == nil || apV2 == nil) && (rwEnabled || otlpEnabled) {
		panic("remote write or otlp write enabled, but no appender passed in.")
	}

	if rwEnabled {
		a.remoteWriteHandler = remote.NewWriteHandler(logger, registerer, ap, acceptRemoteWriteProtoMsgs, stZeroIngestionEnabled, enableTypeAndUnitLabels, appendMetadata)
	}
	if otlpEnabled {
		a.otlpWriteHandler = remote.NewOTLPWriteHandler(logger, registerer, apV2, configFunc, remote.OTLPOptions{
			ConvertDelta:            otlpDeltaToCumulative,
			NativeDelta:             otlpNativeDeltaIngestion,
			LookbackDelta:           lookbackDelta,
			EnableTypeAndUnitLabels: enableTypeAndUnitLabels,
		})
	}

	return a
}

// InstallCodec adds codec to this API's available codecs.
// Codecs installed first take precedence over codecs installed later when evaluating wildcards in Accept headers.
// The first installed codec is used as a fallback when the Accept header cannot be satisfied or if there is no Accept header.
func (api *API) InstallCodec(codec Codec) {
	api.codecs = append(api.codecs, codec)
}

// ClearCodecs removes all available codecs from this API, including the default codec installed by NewAPI.
func (api *API) ClearCodecs() {
	api.codecs = nil
}

func setUnavailStatusOnTSDBNotReady(r apiFuncResult) apiFuncResult {
	if r.err != nil && errors.Is(r.err.err, tsdb.ErrNotReady) {
		r.err.typ = errorUnavailable
	}
	return r
}

// Register the API's endpoints in the given router.
func (api *API) Register(r *route.Router) {
	wrap := func(f apiFunc) http.HandlerFunc {
		hf := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			httputil.SetCORS(w, api.CORSOrigin, r)
			result := setUnavailStatusOnTSDBNotReady(f(r))
			if result.finalizer != nil {
				defer result.finalizer()
			}
			if result.err != nil {
				api.respondError(w, result.err, result.data)
				return
			}

			if result.data != nil {
				api.respond(w, r, result.data, result.warnings, r.FormValue("query"))
				return
			}
			w.WriteHeader(http.StatusNoContent)
		})
		return api.ready(httputil.CompressionHandler{
			Handler: api.openAPIBuilder.WrapHandler(hf),
		}.ServeHTTP)
	}

	wrapAgent := func(f apiFunc) http.HandlerFunc {
		return wrap(func(r *http.Request) apiFuncResult {
			if api.isAgent {
				return apiFuncResult{nil, &apiError{errorExec, errors.New("unavailable with Prometheus Agent")}, nil, nil}
			}
			return f(r)
		})
	}

	r.Options("/*path", wrap(api.options))

	r.Get("/query", wrapAgent(api.query))
	r.Post("/query", wrapAgent(api.query))
	r.Get("/query_range", wrapAgent(api.queryRange))
	r.Post("/query_range", wrapAgent(api.queryRange))
	r.Get("/query_exemplars", wrapAgent(api.queryExemplars))
	r.Post("/query_exemplars", wrapAgent(api.queryExemplars))

	r.Get("/format_query", wrapAgent(api.formatQuery))
	r.Post("/format_query", wrapAgent(api.formatQuery))

	r.Get("/parse_query", wrapAgent(api.parseQuery))
	r.Post("/parse_query", wrapAgent(api.parseQuery))

	r.Get("/labels", wrapAgent(api.labelNames))
	r.Post("/labels", wrapAgent(api.labelNames))
	r.Get("/label/:name/values", wrapAgent(api.labelValues))

	r.Get("/series", wrapAgent(api.series))
	r.Post("/series", wrapAgent(api.series))

	r.Get("/scrape_pools", wrap(api.scrapePools))
	r.Get("/targets", wrap(api.targets))
	r.Get("/targets/metadata", wrap(api.targetMetadata))
	r.Get("/targets/relabel_steps", wrap(api.targetRelabelSteps))
	r.Get("/alertmanagers", wrapAgent(api.alertmanagers))

	r.Get("/metadata", wrap(api.metricMetadata))

	r.Get("/status/config", wrap(api.serveConfig))
	r.Get("/status/runtimeinfo", wrap(api.serveRuntimeInfo))
	r.Get("/status/buildinfo", wrap(api.serveBuildInfo))
	r.Get("/status/flags", wrap(api.serveFlags))
	r.Get("/status/tsdb", wrapAgent(api.serveTSDBStatus))
	r.Get("/status/tsdb/blocks", wrapAgent(api.serveTSDBBlocks))
	r.Get("/status/self_metrics", wrap(api.selfMetrics))
	r.Get("/features", wrap(api.features))
	r.Get("/status/walreplay", api.serveWALReplayStatus)
	r.Get("/notifications", api.notifications)
	r.Get("/notifications/live", api.notificationsSSE)
	r.Post("/read", api.ready(api.remoteRead))
	r.Post("/write", api.ready(api.remoteWrite))
	r.Post("/otlp/v1/metrics", api.ready(api.otlpWrite))

	r.Get("/alerts", wrapAgent(api.alerts))
	r.Get("/rules", wrapAgent(api.rules))

	// Admin APIs
	r.Post("/admin/tsdb/delete_series", wrapAgent(api.deleteSeries))
	r.Post("/admin/tsdb/clean_tombstones", wrapAgent(api.cleanTombstones))
	r.Post("/admin/tsdb/snapshot", wrapAgent(api.snapshot))

	r.Put("/admin/tsdb/delete_series", wrapAgent(api.deleteSeries))
	r.Put("/admin/tsdb/clean_tombstones", wrapAgent(api.cleanTombstones))
	r.Put("/admin/tsdb/snapshot", wrapAgent(api.snapshot))

	// OpenAPI endpoint.
	r.Get("/openapi.yaml", api.ready(api.openAPIBuilder.ServeOpenAPI))
}

type QueryData struct {
	ResultType parser.ValueType `json:"resultType"`
	Result     parser.Value     `json:"result"`
	Stats      stats.QueryStats `json:"stats,omitempty"`
}

func invalidParamError(err error, parameter string) apiFuncResult {
	return apiFuncResult{nil, &apiError{
		errorBadData, fmt.Errorf("invalid parameter %q: %w", parameter, err),
	}, nil, nil}
}

func (*API) options(*http.Request) apiFuncResult {
	return apiFuncResult{nil, nil, nil, nil}
}

func (api *API) query(r *http.Request) (result apiFuncResult) {
	limit, err := parseLimitParam(r.FormValue("limit"))
	if err != nil {
		return invalidParamError(err, "limit")
	}
	ts, err := parseTimeParam(r, "time", api.now())
	if err != nil {
		return invalidParamError(err, "time")
	}
	ctx := r.Context()
	if to := r.FormValue("timeout"); to != "" {
		var cancel context.CancelFunc
		timeout, err := parseDuration(to)
		if err != nil {
			return invalidParamError(err, "timeout")
		}

		ctx, cancel = context.WithDeadline(ctx, api.now().Add(timeout))
		defer cancel()
	}

	opts, err := extractQueryOpts(r)
	if err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
	}
	qry, err := api.QueryEngine.NewInstantQuery(ctx, api.Queryable, opts, r.FormValue("query"), ts)
	if err != nil {
		return invalidParamError(err, "query")
	}

	// From now on, we must only return with a finalizer in the result (to
	// be called by the caller) or call qry.Close ourselves (which is
	// required in the case of a panic).
	defer func() {
		if result.finalizer == nil {
			qry.Close()
		}
	}()

	ctx = httputil.ContextFromRequest(ctx, r)

	res := qry.Exec(ctx)
	if res.Err != nil {
		return apiFuncResult{nil, returnAPIError(res.Err), res.Warnings, qry.Close}
	}

	warnings := res.Warnings
	if limit > 0 {
		var isTruncated bool

		res, isTruncated = truncateResults(res, limit)
		if isTruncated {
			warnings = warnings.Add(errors.New("results truncated due to limit"))
		}
	}
	// Optional stats field in response if parameter "stats" is not empty.
	sr := api.statsRenderer
	if sr == nil {
		sr = DefaultStatsRenderer
	}
	qs := sr(ctx, qry.Stats(), r.FormValue("stats"))

	return apiFuncResult{&QueryData{
		ResultType: res.Value.Type(),
		Result:     res.Value,
		Stats:      qs,
	}, nil, warnings, qry.Close}
}

func (api *API) formatQuery(r *http.Request) (result apiFuncResult) {
	expr, err := api.parser.ParseExpr(r.FormValue("query"))
	if err != nil {
		return invalidParamError(err, "query")
	}

	return apiFuncResult{expr.Pretty(0), nil, nil, nil}
}

func (api *API) parseQuery(r *http.Request) apiFuncResult {
	expr, err := api.parser.ParseExpr(r.FormValue("query"))
	if err != nil {
		return invalidParamError(err, "query")
	}

	return apiFuncResult{data: translateAST(expr), err: nil, warnings: nil, finalizer: nil}
}

func extractQueryOpts(r *http.Request) (promql.QueryOpts, error) {
	var duration time.Duration

	if strDuration := r.FormValue("lookback_delta"); strDuration != "" {
		parsedDuration, err := parseDuration(strDuration)
		if err != nil {
			return nil, fmt.Errorf("error parsing lookback delta duration: %w", err)
		}
		duration = parsedDuration
	}

	return promql.NewPrometheusQueryOpts(r.FormValue("stats") == "all", duration), nil
}

func (api *API) queryRange(r *http.Request) (result apiFuncResult) {
	limit, err := parseLimitParam(r.FormValue("limit"))
	if err != nil {
		return invalidParamError(err, "limit")
	}
	start, err := parseTime(r.FormValue("start"))
	if err != nil {
		return invalidParamError(err, "start")
	}
	end, err := parseTime(r.FormValue("end"))
	if err != nil {
		return invalidParamError(err, "end")
	}
	if end.Before(start) {
		return invalidParamError(errors.New("end timestamp must not be before start time"), "end")
	}

	step, err := parseDuration(r.FormValue("step"))
	if err != nil {
		return invalidParamError(err, "step")
	}

	if step <= 0 {
		return invalidParamError(errors.New("zero or negative query resolution step widths are not accepted. Try a positive integer"), "step")
	}

	// For safety, limit the number of returned points per timeseries.
	// This is sufficient for 60s resolution for a week or 1h resolution for a year.
	if end.Sub(start)/step > 11000 {
		err := errors.New("exceeded maximum resolution of 11,000 points per timeseries. Try decreasing the query resolution (?step=XX)")
		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
	}

	ctx := r.Context()
	if to := r.FormValue("timeout"); to != "" {
		var cancel context.CancelFunc
		timeout, err := parseDuration(to)
		if err != nil {
			return invalidParamError(err, "timeout")
		}

		ctx, cancel = context.WithTimeout(ctx, timeout)
		defer cancel()
	}

	opts, err := extractQueryOpts(r)
	if err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
	}
	qry, err := api.QueryEngine.NewRangeQuery(ctx, api.Queryable, opts, r.FormValue("query"), start, end, step)
	if err != nil {
		return invalidParamError(err, "query")
	}
	// From now on, we must only return with a finalizer in the result (to
	// be called by the caller) or call qry.Close ourselves (which is
	// required in the case of a panic).
	defer func() {
		if result.finalizer == nil {
			qry.Close()
		}
	}()

	ctx = httputil.ContextFromRequest(ctx, r)

	res := qry.Exec(ctx)
	if res.Err != nil {
		return apiFuncResult{nil, returnAPIError(res.Err), res.Warnings, qry.Close}
	}

	warnings := res.Warnings
	if limit > 0 {
		var isTruncated bool

		res, isTruncated = truncateResults(res, limit)
		if isTruncated {
			warnings = warnings.Add(errors.New("results truncated due to limit"))
		}
	}

	// Optional stats field in response if parameter "stats" is not empty.
	sr := api.statsRenderer
	if sr == nil {
		sr = DefaultStatsRenderer
	}
	qs := sr(ctx, qry.Stats(), r.FormValue("stats"))

	return apiFuncResult{&QueryData{
		ResultType: res.Value.Type(),
		Result:     res.Value,
		Stats:      qs,
	}, nil, warnings, qry.Close}
}

func (api *API) queryExemplars(r *http.Request) apiFuncResult {
	start, err := parseTimeParam(r, "start", MinTime)
	if err != nil {
		return invalidParamError(err, "start")
	}
	end, err := parseTimeParam(r, "end", MaxTime)
	if err != nil {
		return invalidParamError(err, "end")
	}
	if end.Before(start) {
		err := errors.New("end timestamp must not be before start timestamp")
		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
	}

	expr, err := api.parser.ParseExpr(r.FormValue("query"))
	if err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
	}

	selectors := parser.ExtractSelectors(expr)
	if len(selectors) < 1 {
		return apiFuncResult{nil, nil, nil, nil}
	}

	ctx := r.Context()
	eq, err := api.ExemplarQueryable.ExemplarQuerier(ctx)
	if err != nil {
		return apiFuncResult{nil, returnAPIError(err), nil, nil}
	}

	res, err := eq.Select(timestamp.FromTime(start), timestamp.FromTime(end), selectors...)
	if err != nil {
		return apiFuncResult{nil, returnAPIError(err), nil, nil}
	}

	return apiFuncResult{res, nil, nil, nil}
}

func returnAPIError(err error) *apiError {
	if err == nil {
		return nil
	}

	var eqc promql.ErrQueryCanceled
	var eqt promql.ErrQueryTimeout
	var es promql.ErrStorage
	switch {
	case errors.As(err, &eqc):
		return &apiError{errorCanceled, err}
	case errors.As(err, &eqt):
		return &apiError{errorTimeout, err}
	case errors.As(err, &es):
		return &apiError{errorInternal, err}
	}

	if errors.Is(err, context.Canceled) {
		return &apiError{errorCanceled, err}
	}

	return &apiError{errorExec, err}
}

func (api *API) labelNames(r *http.Request) apiFuncResult {
	limit, err := parseLimitParam(r.FormValue("limit"))
	if err != nil {
		return invalidParamError(err, "limit")
	}

	start, err := parseTimeParam(r, "start", MinTime)
	if err != nil {
		return invalidParamError(err, "start")
	}
	end, err := parseTimeParam(r, "end", MaxTime)
	if err != nil {
		return invalidParamError(err, "end")
	}

	matcherSets, err := api.parseMatchersParam(r.Form["match[]"])
	if err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
	}

	hints := &storage.LabelHints{
		Limit: toHintLimit(limit),
	}

	q, err := api.Queryable.Querier(timestamp.FromTime(start), timestamp.FromTime(end))
	if err != nil {
		return apiFuncResult{nil, returnAPIError(err), nil, nil}
	}
	defer q.Close()

	var (
		names    []string
		warnings annotations.Annotations
	)
	if len(matcherSets) > 1 {
		labelNamesSet := make(map[string]struct{})

		for _, matchers := range matcherSets {
			vals, callWarnings, err := q.LabelNames(r.Context(), hints, matchers...)
			if err != nil {
				return apiFuncResult{nil, returnAPIError(err), warnings, nil}
			}

			warnings.Merge(callWarnings)
			for _, val := range vals {
				labelNamesSet[val] = struct{}{}
			}
		}

		// Convert the map to an array.
		names = make([]string, 0, len(labelNamesSet))
		for key := range labelNamesSet {
			names = append(names, key)
		}
		slices.Sort(names)
	} else {
		var matchers []*labels.Matcher
		if len(matcherSets) == 1 {
			matchers = matcherSets[0]
		}
		names, warnings, err = q.LabelNames(r.Context(), hints, matchers...)
		if err != nil {
			return apiFuncResult{nil, &apiError{errorExec, err}, warnings, nil}
		}
	}

	if names == nil {
		names = []string{}
	}

	if limit > 0 && len(names) > limit {
		names = names[:limit]
		warnings = warnings.Add(errors.New("results truncated due to limit"))
	}
	return apiFuncResult{names, nil, warnings, nil}
}

func (api *API) labelValues(r *http.Request) (result apiFuncResult) {
	ctx := r.Context()
	name := route.Param(ctx, "name")

	if strings.HasPrefix(name, "U__") {
		name = model.UnescapeName(name, model.ValueEncodingEscaping)
	}

	if !model.UTF8Validation.IsValidLabelName(name) {
		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("invalid label name: %q", name)}, nil, nil}
	}

	limit, err := parseLimitParam(r.FormValue("limit"))
	if err != nil {
		return invalidParamError(err, "limit")
	}

	start, err := parseTimeParam(r, "start", MinTime)
	if err != nil {
		return invalidParamError(err, "start")
	}
	end, err := parseTimeParam(r, "end", MaxTime)
	if err != nil {
		return invalidParamError(err, "end")
	}

	matcherSets, err := api.parseMatchersParam(r.Form["match[]"])
	if err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
	}

	hints := &storage.LabelHints{
		Limit: toHintLimit(limit),
	}

	q, err := api.Queryable.Querier(timestamp.FromTime(start), timestamp.FromTime(end))
	if err != nil {
		return apiFuncResult{nil, &apiError{errorExec, err}, nil, nil}
	}
	// From now on, we must only return with a finalizer in the result (to
	// be called by the caller) or call q.Close ourselves (which is required
	// in the case of a panic).
	defer func() {
		if result.finalizer == nil {
			q.Close()
		}
	}()
	closer := func() {
		q.Close()
	}

	var (
		vals     []string
		warnings annotations.Annotations
	)
	if len(matcherSets) > 1 {
		var callWarnings annotations.Annotations
		labelValuesSet := make(map[string]struct{})
		for _, matchers := range matcherSets {
			vals, callWarnings, err = q.LabelValues(ctx, name, hints, matchers...)
			if err != nil {
				return apiFuncResult{nil, &apiError{errorExec, err}, warnings, closer}
			}
			warnings.Merge(callWarnings)
			for _, val := range vals {
				labelValuesSet[val] = struct{}{}
			}
		}

		vals = make([]string, 0, len(labelValuesSet))
		for val := range labelValuesSet {
			vals = append(vals, val)
		}
	} else {
		var matchers []*labels.Matcher
		if len(matcherSets) == 1 {
			matchers = matcherSets[0]
		}
		vals, warnings, err = q.LabelValues(ctx, name, hints, matchers...)
		if err != nil {
			return apiFuncResult{nil, &apiError{errorExec, err}, warnings, closer}
		}

		if vals == nil {
			vals = []string{}
		}
	}

	slices.Sort(vals)

	if limit > 0 && len(vals) > limit {
		vals = vals[:limit]
		warnings = warnings.Add(errors.New("results truncated due to limit"))
	}

	return apiFuncResult{vals, nil, warnings, closer}
}

var (
	// MinTime is the default timestamp used for the start of optional time ranges.
	// Exposed to let downstream projects reference it.
	//
	// Historical note: This should just be time.Unix(math.MinInt64/1000, 0).UTC(),
	// but it was set to a higher value in the past due to a misunderstanding.
	// The value is still low enough for practical purposes, so we don't want
	// to change it now, avoiding confusion for importers of this variable.
	MinTime = time.Unix(math.MinInt64/1000+62135596801, 0).UTC()

	// MaxTime is the default timestamp used for the end of optional time ranges.
	// Exposed to let downstream projects to reference it.
	//
	// Historical note: This should just be time.Unix(math.MaxInt64/1000, 0).UTC(),
	// but it was set to a lower value in the past due to a misunderstanding.
	// The value is still high enough for practical purposes, so we don't want
	// to change it now, avoiding confusion for importers of this variable.
	MaxTime = time.Unix(math.MaxInt64/1000-62135596801, 999999999).UTC()

	minTimeFormatted = MinTime.Format(time.RFC3339Nano)
	maxTimeFormatted = MaxTime.Format(time.RFC3339Nano)
)

func (api *API) series(r *http.Request) (result apiFuncResult) {
	ctx := r.Context()

	if err := r.ParseForm(); err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("error parsing form values: %w", err)}, nil, nil}
	}
	if len(r.Form["match[]"]) == 0 {
		return apiFuncResult{nil, &apiError{errorBadData, errors.New("no match[] parameter provided")}, nil, nil}
	}

	limit, err := parseLimitParam(r.FormValue("limit"))
	if err != nil {
		return invalidParamError(err, "limit")
	}

	start, err := parseTimeParam(r, "start", MinTime)
	if err != nil {
		return invalidParamError(err, "start")
	}
	end, err := parseTimeParam(r, "end", MaxTime)
	if err != nil {
		return invalidParamError(err, "end")
	}

	matcherSets, err := api.parseMatchersParam(r.Form["match[]"])
	if err != nil {
		return invalidParamError(err, "match[]")
	}

	q, err := api.Queryable.Querier(timestamp.FromTime(start), timestamp.FromTime(end))
	if err != nil {
		return apiFuncResult{nil, returnAPIError(err), nil, nil}
	}
	// From now on, we must only return with a finalizer in the result (to
	// be called by the caller) or call q.Close ourselves (which is required
	// in the case of a panic).
	defer func() {
		if result.finalizer == nil {
			q.Close()
		}
	}()
	closer := func() {
		q.Close()
	}

	hints := &storage.SelectHints{
		Start: timestamp.FromTime(start),
		End:   timestamp.FromTime(end),
		Func:  "series", // There is no series function, this token is used for lookups that don't need samples.
		Limit: toHintLimit(limit),
	}
	var set storage.SeriesSet

	if len(matcherSets) > 1 {
		var sets []storage.SeriesSet
		for _, mset := range matcherSets {
			// We need to sort this select results to merge (deduplicate) the series sets later.
			s := q.Select(ctx, true, hints, mset...)
			sets = append(sets, s)
		}
		set = storage.NewMergeSeriesSet(sets, 0, storage.ChainedSeriesMerge)
	} else {
		// At this point at least one match exists.
		set = q.Select(ctx, false, hints, matcherSets[0]...)
	}

	metrics := []labels.Labels{}

	warnings := set.Warnings()

	i := 1
	for set.Next() {
		if i%checkContextEveryNIterations == 0 {
			if err := ctx.Err(); err != nil {
				return apiFuncResult{nil, returnAPIError(err), warnings, closer}
			}
		}
		i++

		metrics = append(metrics, set.At().Labels())

		if limit > 0 && len(metrics) > limit {
			metrics = metrics[:limit]
			warnings.Add(errors.New("results truncated due to limit"))
			return apiFuncResult{metrics, nil, warnings, closer}
		}
	}
	if set.Err() != nil {
		return apiFuncResult{nil, returnAPIError(set.Err()), warnings, closer}
	}

	return apiFuncResult{metrics, nil, warnings, closer}
}

// Target has the information for one target.
type Target struct {
	// Labels before any processing.
	DiscoveredLabels labels.Labels `json:"discoveredLabels"`
	// Any labels that are added to this target and its metrics.
	Labels labels.Labels `json:"labels"`

	ScrapePool string `json:"scrapePool"`
	ScrapeURL  string `json:"scrapeUrl"`
	GlobalURL  string `json:"globalUrl"`

	LastError          string              `json:"lastError"`
	LastScrape         time.Time           `json:"lastScrape"`
	LastScrapeDuration float64             `json:"lastScrapeDuration"`
	Health             scrape.TargetHealth `json:"health"`

	ScrapeInterval string `json:"scrapeInterval"`
	ScrapeTimeout  string `json:"scrapeTimeout"`
}

type ScrapePoolsDiscovery struct {
	ScrapePools []string `json:"scrapePools"`
}

// DroppedTarget has the information for one target that was dropped during relabelling.
type DroppedTarget struct {
	// Labels before any processing.
	DiscoveredLabels labels.Labels `json:"discoveredLabels"`
	ScrapePool       string        `json:"scrapePool"`
}

// TargetDiscovery has all the active targets.
type TargetDiscovery struct {
	ActiveTargets       []*Target        `json:"activeTargets"`
	DroppedTargets      []*DroppedTarget `json:"droppedTargets"`
	DroppedTargetCounts map[string]int   `json:"droppedTargetCounts"`
}

// GlobalURLOptions contains fields used for deriving the global URL for local targets.
type GlobalURLOptions struct {
	ListenAddress string
	Host          string
	Scheme        string
}

// sanitizeSplitHostPort acts like net.SplitHostPort.
// Additionally, if there is no port in the host passed as input, we return the
// original host, making sure that IPv6 addresses are not surrounded by square
// brackets.
func sanitizeSplitHostPort(input string) (string, string, error) {
	host, port, err := net.SplitHostPort(input)
	if err != nil && strings.HasSuffix(err.Error(), "missing port in address") {
		var errWithPort error
		host, _, errWithPort = net.SplitHostPort(input + ":80")
		if errWithPort == nil {
			err = nil
		}
	}
	return host, port, err
}

func getGlobalURL(u *url.URL, opts GlobalURLOptions) (*url.URL, error) {
	host, port, err := sanitizeSplitHostPort(u.Host)
	if err != nil {
		return u, err
	}

	for _, lhr := range LocalhostRepresentations {
		if host == lhr {
			_, ownPort, err := net.SplitHostPort(opts.ListenAddress)
			if err != nil {
				return u, err
			}

			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.Scheme
				u.Host = opts.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 := sanitizeSplitHostPort(opts.Host)
				if err != nil {
					return u, err
				}
				u.Host = host
				if port != "" {
					u.Host = net.JoinHostPort(u.Host, port)
				}
			}
			break
		}
	}

	return u, nil
}

func (api *API) scrapePools(r *http.Request) apiFuncResult {
	names := api.scrapePoolsRetriever(r.Context()).ScrapePools()
	sort.Strings(names)
	res := &ScrapePoolsDiscovery{ScrapePools: names}
	return apiFuncResult{data: res, err: nil, warnings: nil, finalizer: nil}
}

func (api *API) targets(r *http.Request) apiFuncResult {
	getSortedPools := func(targets map[string][]*scrape.Target) ([]string, int) {
		var n int
		pools := make([]string, 0, len(targets))
		for p, t := range targets {
			pools = append(pools, p)
			n += len(t)
		}
		slices.Sort(pools)
		return pools, n
	}

	scrapePool := r.URL.Query().Get("scrapePool")
	state := strings.ToLower(r.URL.Query().Get("state"))
	showActive := state == "" || state == "any" || state == "active"
	showDropped := state == "" || state == "any" || state == "dropped"
	res := &TargetDiscovery{}
	builder := labels.NewBuilder(labels.EmptyLabels())

	if showActive {
		targetsActive := api.targetRetriever(r.Context()).TargetsActive()
		activePools, numTargets := getSortedPools(targetsActive)
		res.ActiveTargets = make([]*Target, 0, numTargets)

		for _, pool := range activePools {
			if scrapePool != "" && pool != scrapePool {
				continue
			}
			for _, target := range targetsActive[pool] {
				lastErrStr := ""
				lastErr := target.LastError()
				if lastErr != nil {
					lastErrStr = lastErr.Error()
				}

				globalURL, err := getGlobalURL(target.URL(), api.globalURLOptions)

				res.ActiveTargets = append(res.ActiveTargets, &Target{
					DiscoveredLabels: target.DiscoveredLabels(builder),
					Labels:           target.Labels(builder),
					ScrapePool:       pool,
					ScrapeURL:        target.URL().String(),
					GlobalURL:        globalURL.String(),
					LastError: func() string {
						switch {
						case err == nil && lastErrStr == "":
							return ""
						case err != nil:
							return fmt.Errorf("%s: %w", lastErrStr, err).Error()
						default:
							return lastErrStr
						}
					}(),
					LastScrape:         target.LastScrape(),
					LastScrapeDuration: target.LastScrapeDuration().Seconds(),
					Health:             target.Health(),
					ScrapeInterval:     target.GetValue(model.ScrapeIntervalLabel),
					ScrapeTimeout:      target.GetValue(model.ScrapeTimeoutLabel),
				})
			}
		}
	} else {
		res.ActiveTargets = []*Target{}
	}
	if showDropped {
		res.DroppedTargetCounts = api.targetRetriever(r.Context()).TargetsDroppedCounts()

		targetsDropped := api.targetRetriever(r.Context()).TargetsDropped()
		droppedPools, numTargets := getSortedPools(targetsDropped)
		res.DroppedTargets = make([]*DroppedTarget, 0, numTargets)
		for _, pool := range droppedPools {
			if scrapePool != "" && pool != scrapePool {
				continue
			}
			for _, target := range targetsDropped[pool] {
				res.DroppedTargets = append(res.DroppedTargets, &DroppedTarget{
					DiscoveredLabels: target.DiscoveredLabels(builder),
					ScrapePool:       pool,
				})
			}
		}
	} else {
		res.DroppedTargets = []*DroppedTarget{}
	}
	return apiFuncResult{res, nil, nil, nil}
}

func matchLabels(lset labels.Labels, matchers []*labels.Matcher) bool {
	for _, m := range matchers {
		if !m.Matches(lset.Get(m.Name)) {
			return false
		}
	}
	return true
}

func (api *API) targetMetadata(r *http.Request) apiFuncResult {
	limit := -1
	if s := r.FormValue("limit"); s != "" {
		var err error
		if limit, err = strconv.Atoi(s); err != nil {
			return apiFuncResult{nil, &apiError{errorBadData, errors.New("limit must be a number")}, nil, nil}
		}
	}

	matchTarget := r.FormValue("match_target")
	var matchers []*labels.Matcher
	var err error
	if matchTarget != "" {
		matchers, err = api.parser.ParseMetricSelector(matchTarget)
		if err != nil {
			return invalidParamError(err, "match_target")
		}
	}

	builder := labels.NewBuilder(labels.EmptyLabels())
	metric := r.FormValue("metric")
	res := []metricMetadata{}
	for _, tt := range api.targetRetriever(r.Context()).TargetsActive() {
		for _, t := range tt {
			if limit >= 0 && len(res) >= limit {
				break
			}
			targetLabels := t.Labels(builder)
			// Filter targets that don't satisfy the label matchers.
			if matchTarget != "" && !matchLabels(targetLabels, matchers) {
				continue
			}
			// If no metric is specified, get the full list for the target.
			if metric == "" {
				for _, md := range t.ListMetadata() {
					res = append(res, metricMetadata{
						Target:       targetLabels,
						MetricFamily: md.MetricFamily,
						Type:         md.Type,
						Help:         md.Help,
						Unit:         md.Unit,
					})
				}
				continue
			}
			// Get metadata for the specified metric.
			if md, ok := t.GetMetadata(metric); ok {
				res = append(res, metricMetadata{
					Target: targetLabels,
					Type:   md.Type,
					Help:   md.Help,
					Unit:   md.Unit,
				})
			}
		}
	}

	return apiFuncResult{res, nil, nil, nil}
}

type metricMetadata struct {
	Target       labels.Labels    `json:"target"`
	MetricFamily string           `json:"metric,omitempty"`
	Type         model.MetricType `json:"type"`
	Help         string           `json:"help"`
	Unit         string           `json:"unit"`
}

type RelabelStep struct {
	Rule   *relabel.Config `json:"rule"`
	Output labels.Labels   `json:"output"`
	Keep   bool            `json:"keep"`
}

type RelabelStepsResponse struct {
	Steps []RelabelStep `json:"steps"`
}

func (api *API) targetRelabelSteps(r *http.Request) apiFuncResult {
	scrapePool := r.FormValue("scrapePool")
	if scrapePool == "" {
		return apiFuncResult{nil, &apiError{errorBadData, errors.New("no scrapePool parameter provided")}, nil, nil}
	}
	labelsJSON := r.FormValue("labels")
	if labelsJSON == "" {
		return apiFuncResult{nil, &apiError{errorBadData, errors.New("no labels parameter provided")}, nil, nil}
	}
	var lbls labels.Labels
	if err := json.Unmarshal([]byte(labelsJSON), &lbls); err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("error parsing labels: %w", err)}, nil, nil}
	}

	scrapeConfig, err := api.targetRetriever(r.Context()).ScrapePoolConfig(scrapePool)
	if err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("error retrieving scrape config: %w", err)}, nil, nil}
	}

	rules := scrapeConfig.RelabelConfigs
	steps := make([]RelabelStep, len(rules))
	lb := labels.NewBuilder(lbls)
	keep := true
	for i, rule := range rules {
		if keep {
			keep = relabel.ProcessBuilder(lb, rule)
		}

		outLabels := labels.EmptyLabels()
		if keep {
			outLabels = lb.Labels()
		}

		steps[i] = RelabelStep{Rule: rule, Output: outLabels, Keep: keep}
	}

	return apiFuncResult{&RelabelStepsResponse{Steps: steps}, nil, nil, nil}
}

// AlertmanagerDiscovery has all the active Alertmanagers.
type AlertmanagerDiscovery struct {
	ActiveAlertmanagers  []*AlertmanagerTarget `json:"activeAlertmanagers"`
	DroppedAlertmanagers []*AlertmanagerTarget `json:"droppedAlertmanagers"`
}

// AlertmanagerTarget has info on one AM.
type AlertmanagerTarget struct {
	URL string `json:"url"`
}

func (api *API) alertmanagers(r *http.Request) apiFuncResult {
	urls := api.alertmanagerRetriever(r.Context()).Alertmanagers()
	droppedURLS := api.alertmanagerRetriever(r.Context()).DroppedAlertmanagers()
	ams := &AlertmanagerDiscovery{ActiveAlertmanagers: make([]*AlertmanagerTarget, len(urls)), DroppedAlertmanagers: make([]*AlertmanagerTarget, len(droppedURLS))}
	for i, url := range urls {
		ams.ActiveAlertmanagers[i] = &AlertmanagerTarget{URL: url.String()}
	}
	for i, url := range droppedURLS {
		ams.DroppedAlertmanagers[i] = &AlertmanagerTarget{URL: url.String()}
	}
	return apiFuncResult{ams, nil, nil, nil}
}

// AlertDiscovery has info for all active alerts.
type AlertDiscovery struct {
	Alerts []*Alert `json:"alerts"`
}

// Alert has info for an alert.
type Alert struct {
	Labels          labels.Labels `json:"labels"`
	Annotations     labels.Labels `json:"annotations"`
	State           string        `json:"state"`
	ActiveAt        *time.Time    `json:"activeAt,omitempty"`
	KeepFiringSince *time.Time    `json:"keepFiringSince,omitempty"`
	Value           string        `json:"value"`
}

func (api *API) alerts(r *http.Request) apiFuncResult {
	alertingRules := api.rulesRetriever(r.Context()).AlertingRules()
	alerts := []*Alert{}

	for _, alertingRule := range alertingRules {
		alerts = append(
			alerts,
			rulesAlertsToAPIAlerts(alertingRule.ActiveAlerts())...,
		)
	}

	res := &AlertDiscovery{Alerts: alerts}

	return apiFuncResult{res, nil, nil, nil}
}

func rulesAlertsToAPIAlerts(rulesAlerts []*rules.Alert) []*Alert {
	apiAlerts := make([]*Alert, len(rulesAlerts))
	for i, ruleAlert := range rulesAlerts {
		apiAlerts[i] = &Alert{
			Labels:      ruleAlert.Labels,
			Annotations: ruleAlert.Annotations,
			State:       ruleAlert.State.String(),
			ActiveAt:    &ruleAlert.ActiveAt,
			Value:       strconv.FormatFloat(ruleAlert.Value, 'e', -1, 64),
		}
		if !ruleAlert.KeepFiringSince.IsZero() {
			apiAlerts[i].KeepFiringSince = &ruleAlert.KeepFiringSince
		}
	}

	return apiAlerts
}

func (api *API) metricMetadata(r *http.Request) apiFuncResult {
	metrics := map[string]map[metadata.Metadata]struct{}{}

	limit := -1
	if s := r.FormValue("limit"); s != "" {
		var err error
		if limit, err = strconv.Atoi(s); err != nil {
			return apiFuncResult{nil, &apiError{errorBadData, errors.New("limit must be a number")}, nil, nil}
		}
	}
	limitPerMetric := -1
	if s := r.FormValue("limit_per_metric"); s != "" {
		var err error
		if limitPerMetric, err = strconv.Atoi(s); err != nil {
			return apiFuncResult{nil, &apiError{errorBadData, errors.New("limit_per_metric must be a number")}, nil, nil}
		}
	}

	metric := r.FormValue("metric")
	for _, tt := range api.targetRetriever(r.Context()).TargetsActive() {
		for _, t := range tt {
			if metric == "" {
				for _, mm := range t.ListMetadata() {
					m := metadata.Metadata{Type: mm.Type, Help: mm.Help, Unit: mm.Unit}
					ms, ok := metrics[mm.MetricFamily]

					if limitPerMetric > 0 && len(ms) >= limitPerMetric {
						continue
					}

					if !ok {
						ms = map[metadata.Metadata]struct{}{}
						metrics[mm.MetricFamily] = ms
					}
					ms[m] = struct{}{}
				}
				continue
			}

			if md, ok := t.GetMetadata(metric); ok {
				m := metadata.Metadata{Type: md.Type, Help: md.Help, Unit: md.Unit}
				ms, ok := metrics[md.MetricFamily]

				if limitPerMetric > 0 && len(ms) >= limitPerMetric {
					continue
				}

				if !ok {
					ms = map[metadata.Metadata]struct{}{}
					metrics[md.MetricFamily] = ms
				}
				ms[m] = struct{}{}
			}
		}
	}

	// Put the elements from the pseudo-set into a slice for marshaling.
	res := map[string][]metadata.Metadata{}
	for name, set := range metrics {
		if limit >= 0 && len(res) >= limit {
			break
		}

		s := []metadata.Metadata{}
		for metadata := range set {
			s = append(s, metadata)
		}
		res[name] = s
	}

	return apiFuncResult{res, nil, nil, nil}
}

// RuleDiscovery has info for all rules.
type RuleDiscovery struct {
	RuleGroups     []*RuleGroup `json:"groups"`
	GroupNextToken string       `json:"groupNextToken,omitempty"`
}

// RuleGroup has info for rules which are part of a group.
type RuleGroup struct {
	Name string `json:"name"`
	File string `json:"file"`
	// In order to preserve rule ordering, while exposing type (alerting or recording)
	// specific properties, both alerting and recording rules are exposed in the
	// same array.
	Rules          []Rule    `json:"rules"`
	Interval       float64   `json:"interval"`
	Limit          int       `json:"limit"`
	EvaluationTime float64   `json:"evaluationTime"`
	LastEvaluation time.Time `json:"lastEvaluation"`
}

type Rule any

type AlertingRule struct {
	// State can be "pending", "firing", "inactive".
	State          string           `json:"state"`
	Name           string           `json:"name"`
	Query          string           `json:"query"`
	Duration       float64          `json:"duration"`
	KeepFiringFor  float64          `json:"keepFiringFor"`
	Labels         labels.Labels    `json:"labels"`
	Annotations    labels.Labels    `json:"annotations"`
	Alerts         []*Alert         `json:"alerts"`
	Health         rules.RuleHealth `json:"health"`
	LastError      string           `json:"lastError,omitempty"`
	EvaluationTime float64          `json:"evaluationTime"`
	LastEvaluation time.Time        `json:"lastEvaluation"`
	// Type of an alertingRule is always "alerting".
	Type string `json:"type"`
}

type RecordingRule struct {
	Name           string           `json:"name"`
	Query          string           `json:"query"`
	Labels         labels.Labels    `json:"labels"`
	Health         rules.RuleHealth `json:"health"`
	LastError      string           `json:"lastError,omitempty"`
	EvaluationTime float64          `json:"evaluationTime"`
	LastEvaluation time.Time        `json:"lastEvaluation"`
	// Type of a recordingRule is always "recording".
	Type string `json:"type"`
}

func (api *API) rules(r *http.Request) apiFuncResult {
	if err := r.ParseForm(); err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("error parsing form values: %w", err)}, nil, nil}
	}

	queryFormToSet := func(values []string) map[string]struct{} {
		set := make(map[string]struct{}, len(values))
		for _, v := range values {
			set[v] = struct{}{}
		}
		return set
	}

	rnSet := queryFormToSet(r.Form["rule_name[]"])
	rgSet := queryFormToSet(r.Form["rule_group[]"])
	fSet := queryFormToSet(r.Form["file[]"])

	matcherSets, err := api.parseMatchersParam(r.Form["match[]"])
	if err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
	}

	ruleGroups := api.rulesRetriever(r.Context()).RuleGroups()
	res := &RuleDiscovery{RuleGroups: make([]*RuleGroup, 0, len(ruleGroups))}
	typ := strings.ToLower(r.URL.Query().Get("type"))

	if typ != "" && typ != "alert" && typ != "record" {
		return invalidParamError(fmt.Errorf("not supported value %q", typ), "type")
	}

	returnAlerts := typ == "" || typ == "alert"
	returnRecording := typ == "" || typ == "record"

	excludeAlerts, err := parseExcludeAlerts(r)
	if err != nil {
		return invalidParamError(err, "exclude_alerts")
	}

	maxGroups, nextToken, parseErr := parseListRulesPaginationRequest(r)
	if parseErr != nil {
		return *parseErr
	}

	rgs := make([]*RuleGroup, 0, len(ruleGroups))

	foundToken := false

	for _, grp := range ruleGroups {
		if maxGroups > 0 && nextToken != "" && !foundToken {
			if nextToken != getRuleGroupNextToken(grp.File(), grp.Name()) {
				continue
			}
			foundToken = true
		}

		if len(rgSet) > 0 {
			if _, ok := rgSet[grp.Name()]; !ok {
				continue
			}
		}

		if len(fSet) > 0 {
			if _, ok := fSet[grp.File()]; !ok {
				continue
			}
		}

		apiRuleGroup := &RuleGroup{
			Name:           grp.Name(),
			File:           grp.File(),
			Interval:       grp.Interval().Seconds(),
			Limit:          grp.Limit(),
			Rules:          []Rule{},
			EvaluationTime: grp.GetEvaluationTime().Seconds(),
			LastEvaluation: grp.GetLastEvaluation(),
		}

		for _, rr := range grp.Rules(matcherSets...) {
			var enrichedRule Rule

			if len(rnSet) > 0 {
				if _, ok := rnSet[rr.Name()]; !ok {
					continue
				}
			}

			lastError := ""
			if rr.LastError() != nil {
				lastError = rr.LastError().Error()
			}
			switch rule := rr.(type) {
			case *rules.AlertingRule:
				if !returnAlerts {
					break
				}
				var activeAlerts []*Alert
				if !excludeAlerts {
					activeAlerts = rulesAlertsToAPIAlerts(rule.ActiveAlerts())
				}

				enrichedRule = AlertingRule{
					State:          rule.State().String(),
					Name:           rule.Name(),
					Query:          rule.Query().String(),
					Duration:       rule.HoldDuration().Seconds(),
					KeepFiringFor:  rule.KeepFiringFor().Seconds(),
					Labels:         rule.Labels(),
					Annotations:    rule.Annotations(),
					Alerts:         activeAlerts,
					Health:         rule.Health(),
					LastError:      lastError,
					EvaluationTime: rule.GetEvaluationDuration().Seconds(),
					LastEvaluation: rule.GetEvaluationTimestamp(),
					Type:           "alerting",
				}

			case *rules.RecordingRule:
				if !returnRecording {
					break
				}
				enrichedRule = RecordingRule{
					Name:           rule.Name(),
					Query:          rule.Query().String(),
					Labels:         rule.Labels(),
					Health:         rule.Health(),
					LastError:      lastError,
					EvaluationTime: rule.GetEvaluationDuration().Seconds(),
					LastEvaluation: rule.GetEvaluationTimestamp(),
					Type:           "recording",
				}
			default:
				err := fmt.Errorf("failed to assert type of rule '%v'", rule.Name())
				return apiFuncResult{nil, &apiError{errorInternal, err}, nil, nil}
			}

			if enrichedRule != nil {
				apiRuleGroup.Rules = append(apiRuleGroup.Rules, enrichedRule)
			}
		}

		// If the rule group response has no rules, skip it - this means we filtered all the rules of this group.
		if len(apiRuleGroup.Rules) > 0 {
			if maxGroups > 0 && len(rgs) == int(maxGroups) {
				// We've reached the capacity of our page plus one. That means that for sure there will be at least one
				// rule group in a subsequent request. Therefore a next token is required.
				res.GroupNextToken = getRuleGroupNextToken(grp.File(), grp.Name())
				break
			}
			rgs = append(rgs, apiRuleGroup)
		}
	}

	if maxGroups > 0 && nextToken != "" && !foundToken {
		return invalidParamError(fmt.Errorf("invalid group_next_token '%v'. were rule groups changed?", nextToken), "group_next_token")
	}

	res.RuleGroups = rgs
	return apiFuncResult{res, nil, nil, nil}
}

func parseExcludeAlerts(r *http.Request) (bool, error) {
	excludeAlertsParam := strings.ToLower(r.URL.Query().Get("exclude_alerts"))

	if excludeAlertsParam == "" {
		return false, nil
	}

	excludeAlerts, err := strconv.ParseBool(excludeAlertsParam)
	if err != nil {
		return false, fmt.Errorf("error converting exclude_alerts: %w", err)
	}
	return excludeAlerts, nil
}

func parseListRulesPaginationRequest(r *http.Request) (int64, string, *apiFuncResult) {
	var (
		parsedMaxGroups int64 = -1
		err             error
	)
	maxGroups := r.URL.Query().Get("group_limit")
	nextToken := r.URL.Query().Get("group_next_token")

	if nextToken != "" && maxGroups == "" {
		errResult := invalidParamError(errors.New("group_limit needs to be present in order to paginate over the groups"), "group_next_token")
		return -1, "", &errResult
	}

	if maxGroups != "" {
		parsedMaxGroups, err = strconv.ParseInt(maxGroups, 10, 32)
		if err != nil {
			errResult := invalidParamError(fmt.Errorf("group_limit needs to be a valid number: %w", err), "group_limit")
			return -1, "", &errResult
		}
		if parsedMaxGroups <= 0 {
			errResult := invalidParamError(errors.New("group_limit needs to be greater than 0"), "group_limit")
			return -1, "", &errResult
		}
	}

	if parsedMaxGroups > 0 {
		return parsedMaxGroups, nextToken, nil
	}

	return -1, "", nil
}

func getRuleGroupNextToken(file, group string) string {
	h := sha1.New()
	h.Write([]byte(file + ";" + group))
	return hex.EncodeToString(h.Sum(nil))
}

type prometheusConfig struct {
	YAML string `json:"yaml"`
}

func (api *API) serveRuntimeInfo(*http.Request) apiFuncResult {
	status, err := api.runtimeInfo()
	if err != nil {
		return apiFuncResult{status, &apiError{errorInternal, err}, nil, nil}
	}
	return apiFuncResult{status, nil, nil, nil}
}

func (api *API) serveBuildInfo(*http.Request) apiFuncResult {
	return apiFuncResult{api.buildInfo, nil, nil, nil}
}

func (api *API) serveConfig(*http.Request) apiFuncResult {
	cfg := &prometheusConfig{
		YAML: api.config().String(),
	}
	return apiFuncResult{cfg, nil, nil, nil}
}

func (api *API) serveFlags(*http.Request) apiFuncResult {
	return apiFuncResult{api.flagsMap, nil, nil, nil}
}

// featuresData wraps feature flags data to provide custom JSON marshaling without HTML escaping.
// featuresData does not contain user-provided input, and it is more convenient to have unescaped
// representation of PromQL operators like >=.
type featuresData struct {
	data map[string]map[string]bool
}

func (f featuresData) MarshalJSON() ([]byte, error) {
	json := jsoniter.Config{
		EscapeHTML:             false,
		SortMapKeys:            true,
		ValidateJsonRawMessage: true,
	}.Froze()
	return json.Marshal(f.data)
}

func (api *API) features(*http.Request) apiFuncResult {
	if api.featureRegistry == nil {
		return apiFuncResult{nil, &apiError{errorInternal, errors.New("feature registry not configured")}, nil, nil}
	}
	return apiFuncResult{featuresData{data: api.featureRegistry.Get()}, nil, nil, nil}
}

// TSDBStat holds the information about individual cardinality.
type TSDBStat struct {
	Name  string `json:"name"`
	Value uint64 `json:"value"`
}

// HeadStats has information about the TSDB head.
type HeadStats struct {
	NumSeries     uint64 `json:"numSeries"`
	NumLabelPairs int    `json:"numLabelPairs"`
	ChunkCount    int64  `json:"chunkCount"`
	MinTime       int64  `json:"minTime"`
	MaxTime       int64  `json:"maxTime"`
}

// TSDBStatus has information of cardinality statistics from postings.
type TSDBStatus struct {
	HeadStats                   HeadStats  `json:"headStats"`
	SeriesCountByMetricName     []TSDBStat `json:"seriesCountByMetricName"`
	LabelValueCountByLabelName  []TSDBStat `json:"labelValueCountByLabelName"`
	MemoryInBytesByLabelName    []TSDBStat `json:"memoryInBytesByLabelName"`
	SeriesCountByLabelValuePair []TSDBStat `json:"seriesCountByLabelValuePair"`
}

// TSDBStatsFromIndexStats converts a index.Stat slice to a TSDBStat slice.
func TSDBStatsFromIndexStats(stats []index.Stat) []TSDBStat {
	result := make([]TSDBStat, 0, len(stats))
	for _, item := range stats {
		item := TSDBStat{Name: item.Name, Value: item.Count}
		result = append(result, item)
	}
	return result
}

func (api *API) selfMetrics(r *http.Request) apiFuncResult {
	var nameFilter *regexp.Regexp
	if pattern := r.FormValue("metric_name_pattern"); pattern != "" {
		var err error
		nameFilter, err = regexp.Compile("^(?:" + pattern + ")$")
		if err != nil {
			return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("invalid metric_name_pattern: %w", err)}, nil, nil}
		}
	}

	mfs, err := api.gatherer.Gather()
	if err != nil {
		return apiFuncResult{nil, &apiError{errorInternal, fmt.Errorf("error gathering self metrics: %w", err)}, nil, nil}
	}

	marshaler := protojson.MarshalOptions{}
	result := make([]json.RawMessage, 0, len(mfs))
	for _, mf := range mfs {
		if nameFilter != nil && !nameFilter.MatchString(mf.GetName()) {
			continue
		}

		b, err := marshaler.Marshal(mf)
		if err != nil {
			return apiFuncResult{nil, &apiError{errorInternal, fmt.Errorf("error marshaling metric family %q: %w", mf.GetName(), err)}, nil, nil}
		}
		result = append(result, json.RawMessage(b))
	}

	return apiFuncResult{result, nil, nil, nil}
}

func (api *API) serveTSDBBlocks(*http.Request) apiFuncResult {
	blockMetas, err := api.db.BlockMetas()
	if err != nil {
		return apiFuncResult{nil, &apiError{errorInternal, fmt.Errorf("error getting block metadata: %w", err)}, nil, nil}
	}

	return apiFuncResult{
		data: map[string][]tsdb.BlockMeta{
			"blocks": blockMetas,
		},
	}
}

func (api *API) serveTSDBStatus(r *http.Request) apiFuncResult {
	const maxTSDBLimit = 10000
	limit := 10
	if s := r.FormValue("limit"); s != "" {
		var err error
		if limit, err = strconv.Atoi(s); err != nil || limit < 1 {
			return apiFuncResult{nil, &apiError{errorBadData, errors.New("limit must be a positive number")}, nil, nil}
		}
		if limit > maxTSDBLimit {
			return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("limit must not exceed %d", maxTSDBLimit)}, nil, nil}
		}
	}
	s, err := api.db.Stats(labels.MetricName, limit)
	if err != nil {
		return apiFuncResult{nil, &apiError{errorInternal, err}, nil, nil}
	}
	metrics, err := api.gatherer.Gather()
	if err != nil {
		return apiFuncResult{nil, &apiError{errorInternal, fmt.Errorf("error gathering runtime status: %w", err)}, nil, nil}
	}
	chunkCount := int64(math.NaN())
	for _, mF := range metrics {
		if *mF.Name == "prometheus_tsdb_head_chunks" {
			m := mF.Metric[0]
			if m.Gauge != nil {
				chunkCount = int64(m.Gauge.GetValue())
				break
			}
		}
	}
	return apiFuncResult{TSDBStatus{
		HeadStats: HeadStats{
			NumSeries:     s.NumSeries,
			ChunkCount:    chunkCount,
			MinTime:       s.MinTime,
			MaxTime:       s.MaxTime,
			NumLabelPairs: s.IndexPostingStats.NumLabelPairs,
		},
		SeriesCountByMetricName:     TSDBStatsFromIndexStats(s.IndexPostingStats.CardinalityMetricsStats),
		LabelValueCountByLabelName:  TSDBStatsFromIndexStats(s.IndexPostingStats.CardinalityLabelStats),
		MemoryInBytesByLabelName:    TSDBStatsFromIndexStats(s.IndexPostingStats.LabelValueStats),
		SeriesCountByLabelValuePair: TSDBStatsFromIndexStats(s.IndexPostingStats.LabelValuePairsStats),
	}, nil, nil, nil}
}

type walReplayStatus struct {
	Min     int `json:"min"`
	Max     int `json:"max"`
	Current int `json:"current"`
}

func (api *API) serveWALReplayStatus(w http.ResponseWriter, r *http.Request) {
	httputil.SetCORS(w, api.CORSOrigin, r)
	status, err := api.db.WALReplayStatus()
	if err != nil {
		api.respondError(w, &apiError{errorInternal, err}, nil)
		return
	}
	api.respond(w, r, walReplayStatus{
		Min:     status.Min,
		Max:     status.Max,
		Current: status.Current,
	}, nil, "")
}

func (api *API) notifications(w http.ResponseWriter, r *http.Request) {
	httputil.SetCORS(w, api.CORSOrigin, r)
	api.respond(w, r, api.notificationsGetter(), nil, "")
}

func (api *API) notificationsSSE(w http.ResponseWriter, r *http.Request) {
	httputil.SetCORS(w, api.CORSOrigin, r)
	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")

	// Subscribe to notifications.
	notifications, unsubscribe, ok := api.notificationsSub()
	if !ok {
		w.WriteHeader(http.StatusNoContent)
		return
	}
	defer unsubscribe()

	// Set up a flusher to push the response to the client.
	flusher, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "Streaming unsupported", http.StatusInternalServerError)
		return
	}

	// Flush the response to ensure the headers are immediately and eventSource
	// onopen is triggered client-side.
	flusher.Flush()

	for {
		select {
		case notification := <-notifications:
			// Marshal the notification to JSON.
			jsonData, err := json.Marshal(notification)
			if err != nil {
				http.Error(w, err.Error(), http.StatusInternalServerError)
				continue
			}

			// Write the event data in SSE format with JSON content.
			fmt.Fprintf(w, "data: %s\n\n", jsonData)

			// Flush the response to ensure the data is sent immediately.
			flusher.Flush()
		case <-r.Context().Done():
			return
		}
	}
}

func (api *API) remoteRead(w http.ResponseWriter, r *http.Request) {
	// This is only really for tests - this will never be nil IRL.
	if api.remoteReadHandler != nil {
		api.remoteReadHandler.ServeHTTP(w, r)
	} else {
		http.Error(w, "not found", http.StatusNotFound)
	}
}

func (api *API) remoteWrite(w http.ResponseWriter, r *http.Request) {
	if api.remoteWriteHandler != nil {
		api.remoteWriteHandler.ServeHTTP(w, r)
	} else {
		http.Error(w, "remote write receiver needs to be enabled with --web.enable-remote-write-receiver", http.StatusNotFound)
	}
}

func (api *API) otlpWrite(w http.ResponseWriter, r *http.Request) {
	if api.otlpWriteHandler != nil {
		api.otlpWriteHandler.ServeHTTP(w, r)
	} else {
		http.Error(w, "otlp write receiver needs to be enabled with --web.enable-otlp-receiver", http.StatusNotFound)
	}
}

func (api *API) deleteSeries(r *http.Request) apiFuncResult {
	if !api.enableAdmin {
		return apiFuncResult{nil, &apiError{errorUnavailable, errors.New("admin APIs disabled")}, nil, nil}
	}
	if err := r.ParseForm(); err != nil {
		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("error parsing form values: %w", err)}, nil, nil}
	}
	if len(r.Form["match[]"]) == 0 {
		return apiFuncResult{nil, &apiError{errorBadData, errors.New("no match[] parameter provided")}, nil, nil}
	}

	start, err := parseTimeParam(r, "start", MinTime)
	if err != nil {
		return invalidParamError(err, "start")
	}
	end, err := parseTimeParam(r, "end", MaxTime)
	if err != nil {
		return invalidParamError(err, "end")
	}

	for _, s := range r.Form["match[]"] {
		matchers, err := api.parser.ParseMetricSelector(s)
		if err != nil {
			return invalidParamError(err, "match[]")
		}
		if err := api.db.Delete(r.Context(), timestamp.FromTime(start), timestamp.FromTime(end), matchers...); err != nil {
			return apiFuncResult{nil, &apiError{errorInternal, err}, nil, nil}
		}
	}

	return apiFuncResult{nil, nil, nil, nil}
}

func (api *API) snapshot(r *http.Request) apiFuncResult {
	if !api.enableAdmin {
		return apiFuncResult{nil, &apiError{errorUnavailable, errors.New("admin APIs disabled")}, nil, nil}
	}
	var (
		skipHead bool
		err      error
	)
	if r.FormValue("skip_head") != "" {
		skipHead, err = strconv.ParseBool(r.FormValue("skip_head"))
		if err != nil {
			return invalidParamError(fmt.Errorf("unable to parse boolean: %w", err), "skip_head")
		}
	}

	var (
		snapdir = filepath.Join(api.dbDir, "snapshots")
		name    = fmt.Sprintf("%s-%016x",
			time.Now().UTC().Format("20060102T150405Z0700"),
			rand.Int63())
		dir = filepath.Join(snapdir, name)
	)
	if err := os.MkdirAll(dir, 0o777); err != nil {
		return apiFuncResult{nil, &apiError{errorInternal, fmt.Errorf("create snapshot directory: %w", err)}, nil, nil}
	}
	if err := api.db.Snapshot(dir, !skipHead); err != nil {
		return apiFuncResult{nil, &apiError{errorInternal, fmt.Errorf("create snapshot: %w", err)}, nil, nil}
	}

	return apiFuncResult{struct {
		Name string `json:"name"`
	}{name}, nil, nil, nil}
}

func (api *API) cleanTombstones(*http.Request) apiFuncResult {
	if !api.enableAdmin {
		return apiFuncResult{nil, &apiError{errorUnavailable, errors.New("admin APIs disabled")}, nil, nil}
	}
	if err := api.db.CleanTombstones(); err != nil {
		return apiFuncResult{nil, &apiError{errorInternal, err}, nil, nil}
	}

	return apiFuncResult{nil, nil, nil, nil}
}

// Query string is needed to get the position information for the annotations, and it
// can be empty if the position information isn't needed.
func (api *API) respond(w http.ResponseWriter, req *http.Request, data any, warnings annotations.Annotations, query string) {
	statusMessage := statusSuccess
	warn, info := warnings.AsStrings(query, 10, 10)

	resp := &Response{
		Status:   statusMessage,
		Data:     data,
		Warnings: warn,
		Infos:    info,
	}

	codec, err := api.negotiateCodec(req, resp)
	if err != nil {
		api.respondError(w, &apiError{errorNotAcceptable, err}, nil)
		return
	}

	b, err := codec.Encode(resp)
	if err != nil {
		api.logger.Error("error marshaling response", "url", req.URL, "err", err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", codec.ContentType().String())
	w.WriteHeader(http.StatusOK)
	if n, err := w.Write(b); err != nil {
		api.logger.Error("error writing response", "url", req.URL, "bytesWritten", n, "err", err)
	}
}

func (api *API) negotiateCodec(req *http.Request, resp *Response) (Codec, error) {
	for _, clause := range goautoneg.ParseAccept(req.Header.Get("Accept")) {
		for _, codec := range api.codecs {
			if codec.ContentType().Satisfies(clause) && codec.CanEncode(resp) {
				return codec, nil
			}
		}
	}

	defaultCodec := api.codecs[0]
	if !defaultCodec.CanEncode(resp) {
		return nil, fmt.Errorf("cannot encode response as %s", defaultCodec.ContentType())
	}

	return defaultCodec, nil
}

func (api *API) respondError(w http.ResponseWriter, apiErr *apiError, data any) {
	json := jsoniter.ConfigCompatibleWithStandardLibrary
	b, err := json.Marshal(&Response{
		Status:    statusError,
		ErrorType: apiErr.typ.str,
		Error:     apiErr.err.Error(),
		Data:      data,
	})
	if err != nil {
		api.logger.Error("error marshaling json response", "err", err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	var code int
	if api.overrideErrorCode != nil {
		if newCode, override := api.overrideErrorCode(apiErr.typ.num, apiErr.err); override {
			code = newCode
		} else {
			code = getDefaultErrorCode(apiErr.typ)
		}
	} else {
		code = getDefaultErrorCode(apiErr.typ)
	}

	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(code)
	if n, err := w.Write(b); err != nil {
		api.logger.Error("error writing response", "bytesWritten", n, "err", err)
	}
}

func getDefaultErrorCode(errType errorType) int {
	switch errType {
	case errorBadData:
		return http.StatusBadRequest
	case errorExec:
		return http.StatusUnprocessableEntity
	case errorCanceled:
		return statusClientClosedConnection
	case errorTimeout:
		return http.StatusServiceUnavailable
	case errorInternal:
		return http.StatusInternalServerError
	case errorNotFound:
		return http.StatusNotFound
	case errorNotAcceptable:
		return http.StatusNotAcceptable
	default:
		return http.StatusInternalServerError
	}
}

func parseTimeParam(r *http.Request, paramName string, defaultValue time.Time) (time.Time, error) {
	val := r.FormValue(paramName)
	if val == "" {
		return defaultValue, nil
	}
	result, err := parseTime(val)
	if err != nil {
		return time.Time{}, fmt.Errorf("invalid time value for '%s': %w", paramName, err)
	}
	return result, nil
}

func parseTime(s string) (time.Time, error) {
	if t, err := strconv.ParseFloat(s, 64); err == nil {
		s, ns := math.Modf(t)
		ns = math.Round(ns*1000) / 1000
		return time.Unix(int64(s), int64(ns*float64(time.Second))).UTC(), nil
	}
	if t, err := time.Parse(time.RFC3339Nano, s); err == nil {
		return t, nil
	}

	// Stdlib's time parser can only handle 4 digit years. As a workaround until
	// that is fixed we want to at least support our own boundary times.
	// Context: https://github.com/prometheus/client_golang/issues/614
	// Upstream issue: https://github.com/golang/go/issues/20555
	switch s {
	case minTimeFormatted:
		return MinTime, nil
	case maxTimeFormatted:
		return MaxTime, nil
	}
	return time.Time{}, fmt.Errorf("cannot parse %q to a valid timestamp", s)
}

func parseDuration(s string) (time.Duration, error) {
	if d, err := strconv.ParseFloat(s, 64); err == nil {
		ts := d * float64(time.Second)
		if ts > float64(math.MaxInt64) || ts < float64(math.MinInt64) {
			return 0, fmt.Errorf("cannot parse %q to a valid duration. It overflows int64", s)
		}
		return time.Duration(ts), nil
	}
	if d, err := model.ParseDuration(s); err == nil {
		return time.Duration(d), nil
	}
	return 0, fmt.Errorf("cannot parse %q to a valid duration", s)
}

func (api *API) parseMatchersParam(matchers []string) ([][]*labels.Matcher, error) {
	matcherSets, err := api.parser.ParseMetricSelectors(matchers)
	if err != nil {
		return nil, err
	}

OUTER:
	for _, ms := range matcherSets {
		for _, lm := range ms {
			if lm != nil && !lm.Matches("") {
				continue OUTER
			}
		}
		return nil, errors.New("match[] must contain at least one non-empty matcher")
	}
	return matcherSets, nil
}

// parseLimitParam returning 0 means no limit is to be applied.
func parseLimitParam(limitStr string) (limit int, err error) {
	if limitStr == "" {
		return limit, nil
	}

	limit, err = strconv.Atoi(limitStr)
	if err != nil {
		return limit, err
	}
	if limit < 0 {
		return limit, errors.New("limit must be non-negative")
	}

	return limit, nil
}

// toHintLimit increases the API limit, as returned by parseLimitParam, by 1.
// This allows for emitting warnings when the results are truncated.
func toHintLimit(limit int) int {
	// 0 means no limit and avoid int overflow
	if limit > 0 && limit < math.MaxInt {
		return limit + 1
	}
	return limit
}

// truncateResults truncates result for queryRange() and query().
// No truncation for other types(Scalars or Strings).
func truncateResults(result *promql.Result, limit int) (*promql.Result, bool) {
	isTruncated := false

	switch v := result.Value.(type) {
	case promql.Matrix:
		if len(v) > limit {
			result.Value = v[:limit]
			isTruncated = true
		}
	case promql.Vector:
		if len(v) > limit {
			result.Value = v[:limit]
			isTruncated = true
		}
	}

	// Return the modified result. Unchanged for other types.
	return result, isTruncated
}
