// Copyright 2013 The Prometheus Authors
// Copyright 2021 The Pyroscope 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 scrape

import (
	"errors"
	"fmt"
	"hash/fnv"
	"net"
	"net/url"
	"strconv"
	"strings"
	"sync"
	"time"
	"unicode/utf8"

	"github.com/pyroscope-io/pyroscope/pkg/scrape/config"
	"github.com/pyroscope-io/pyroscope/pkg/scrape/discovery/targetgroup"
	"github.com/pyroscope-io/pyroscope/pkg/scrape/labels"
	"github.com/pyroscope-io/pyroscope/pkg/scrape/model"
	"github.com/pyroscope-io/pyroscope/pkg/scrape/relabel"
)

// TargetHealth describes the health state of a target.
type TargetHealth string

// The possible health states of a target based on the last performed scrape.
const (
	HealthUnknown TargetHealth = "unknown"
	HealthGood    TargetHealth = "up"
	HealthBad     TargetHealth = "down"

	spyName = "gospy"
)

// Target refers to a singular HTTP or HTTPS endpoint.
type Target struct {
	// Labels before any processing.
	discoveredLabels labels.Labels
	// Any labels that are added to this target and its metrics.
	labels labels.Labels
	// Additional parameters including profile path, URL params,
	// and sample-type settings.
	config *config.Profile

	mtx                sync.RWMutex
	lastError          error
	lastScrape         time.Time
	lastScrapeDuration time.Duration
	health             TargetHealth
}

// NewTarget creates a reasonably configured target for querying.
func NewTarget(origLabels, discoveredLabels labels.Labels, profile *config.Profile) *Target {
	return &Target{
		labels:           origLabels,
		discoveredLabels: discoveredLabels,
		config:           profile,
		health:           HealthUnknown,
	}
}

func (t *Target) String() string {
	return t.URL().String()
}

// hash returns an identifying hash for the target.
func (t *Target) hash() uint64 {
	h := fnv.New64a()
	_, _ = h.Write([]byte(fmt.Sprintf("%016d", t.labels.Hash())))
	_, _ = h.Write([]byte(t.URL().String()))
	return h.Sum64()
}

// offset returns the time until the next scrape cycle for the target.
func (t *Target) offset(interval time.Duration) time.Duration {
	now := time.Now().UnixNano()

	// Base is a pinned to absolute time, no matter how often offset is called.
	var (
		base   = int64(interval) - now%int64(interval)
		offset = t.hash() % uint64(interval)
		next   = base + int64(offset)
	)

	if next > int64(interval) {
		next -= int64(interval)
	}
	return time.Duration(next)
}

func (t *Target) SpyName() string {
	for _, l := range t.labels {
		if l.Name == model.SpyNameLabel && l.Value != "" {
			return l.Value
		}
	}
	// N.B: There is no need to check discovered labels:
	// in most cases, the label is created at relabeling.
	for _, l := range t.discoveredLabels {
		if l.Name == model.SpyNameLabel && l.Value != "" {
			return l.Value
		}
	}
	return spyName
}

func (t *Target) IsCumulative() bool {
	for _, x := range t.config.SampleTypes {
		if x.Cumulative {
			return true
		}
	}
	return false
}

// Labels returns a copy of the set of all public labels of the target.
func (t *Target) Labels() labels.Labels {
	lset := make(labels.Labels, 0, len(t.labels))
	for _, l := range t.labels {
		if l.Name == model.AppNameLabel || !strings.HasPrefix(l.Name, model.ReservedLabelPrefix) {
			lset = append(lset, l)
		}
	}
	return lset
}

// DiscoveredLabels returns a copy of the target's labels before any processing.
func (t *Target) DiscoveredLabels() labels.Labels {
	t.mtx.Lock()
	defer t.mtx.Unlock()
	lset := make(labels.Labels, len(t.discoveredLabels))
	copy(lset, t.discoveredLabels)
	return lset
}

// SetDiscoveredLabels sets new DiscoveredLabels
func (t *Target) SetDiscoveredLabels(l labels.Labels) {
	t.mtx.Lock()
	defer t.mtx.Unlock()
	t.discoveredLabels = l
}

// URL returns a copy of the target's URL.
func (t *Target) URL() *url.URL {
	u := url.URL{
		Scheme: t.labels.Get(model.SchemeLabel),
		Host:   t.labels.Get(model.AddressLabel),
		Path:   t.config.Path,
	}
	if t.config.Params != nil {
		u.RawQuery = t.config.Params.Encode()
	}
	return &u
}

// LastError returns the error encountered during the last scrape.
func (t *Target) LastError() error {
	t.mtx.RLock()
	defer t.mtx.RUnlock()
	return t.lastError
}

// LastScrape returns the time of the last scrape.
func (t *Target) LastScrape() time.Time {
	t.mtx.RLock()
	defer t.mtx.RUnlock()
	return t.lastScrape
}

// LastScrapeDuration returns how long the last scrape of the target took.
func (t *Target) LastScrapeDuration() time.Duration {
	t.mtx.RLock()
	defer t.mtx.RUnlock()
	return t.lastScrapeDuration
}

// Health returns the last known health state of the target.
func (t *Target) Health() TargetHealth {
	t.mtx.RLock()
	defer t.mtx.RUnlock()
	return t.health
}

// intervalAndTimeout returns the interval and timeout derived from
// the targets labels.
func (t *Target) intervalAndTimeout(defaultInterval, defaultDuration time.Duration) (time.Duration, time.Duration, error) {
	t.mtx.RLock()
	defer t.mtx.RUnlock()

	intervalLabel := t.labels.Get(model.ScrapeIntervalLabel)
	interval, err := time.ParseDuration(intervalLabel)
	if err != nil {
		return defaultInterval, defaultDuration, fmt.Errorf("parsing interval label %q: %w", intervalLabel, err)
	}
	timeoutLabel := t.labels.Get(model.ScrapeTimeoutLabel)
	timeout, err := time.ParseDuration(timeoutLabel)
	if err != nil {
		return defaultInterval, defaultDuration, fmt.Errorf("parsing timeout label %q: %w", timeoutLabel, err)
	}

	return interval, timeout, nil
}

func (t *Target) deltaDuration() (time.Duration, error) {
	t.mtx.RLock()
	defer t.mtx.RUnlock()
	// TODO(kolesnikovae): Delta duration from/to labels.
	d, ok := t.config.Params["seconds"]
	if !ok || len(d) != 1 {
		return 0, fmt.Errorf("delta duration is not defined")
	}
	seconds, err := strconv.Atoi(d[0])
	if err != nil {
		return 0, fmt.Errorf("invlid delta duration format %q: %w", d[0], err)
	}
	return time.Second * time.Duration(seconds), nil
}

// GetValue gets a label value from the entire label set.
func (t *Target) GetValue(name string) string {
	return t.labels.Get(name)
}

// Targets is a sortable list of targets.
type Targets []*Target

func (ts Targets) Len() int           { return len(ts) }
func (ts Targets) Less(i, j int) bool { return ts[i].URL().String() < ts[j].URL().String() }
func (ts Targets) Swap(i, j int)      { ts[i], ts[j] = ts[j], ts[i] }

// PopulateLabels builds a label set from the given label set and scrape configuration.
// It returns a label set before relabeling was applied as the second return value.
// Returns the original discovered label set found before relabelling was applied if the target is dropped during relabeling.
func PopulateLabels(lset labels.Labels, cfg *config.Config) (res, orig labels.Labels, err error) {
	// Copy labels into the labelset for the target if they are not set already.
	scrapeLabels := []labels.Label{
		{Name: model.JobLabel, Value: cfg.JobName},
		{Name: model.ScrapeIntervalLabel, Value: cfg.ScrapeInterval.String()},
		{Name: model.ScrapeTimeoutLabel, Value: cfg.ScrapeTimeout.String()},
		{Name: model.SchemeLabel, Value: cfg.Scheme},
	}
	lb := labels.NewBuilder(lset)

	for _, l := range scrapeLabels {
		if lv := lset.Get(l.Name); lv == "" {
			lb.Set(l.Name, l.Value)
		}
	}

	preRelabelLabels := lb.Labels()
	lset = relabel.Process(preRelabelLabels, cfg.RelabelConfigs...)

	// Check if the target was dropped.
	if lset == nil {
		return nil, preRelabelLabels, nil
	}
	addr := lset.Get(model.AddressLabel)
	if addr == "" {
		return nil, nil, errors.New("no address")
	}
	if v := lset.Get(model.AppNameLabel); v == "" {
		return nil, nil, errors.New("no app name")
	}

	lb = labels.NewBuilder(lset)
	// addPort checks whether we should add a default port to the address.
	// If the address is not valid, we don't append a port either.
	addPort := func(s string) bool {
		// If we can split, a port exists and we don't have to add one.
		if _, _, err := net.SplitHostPort(s); err == nil {
			return false
		}
		// If adding a port makes it valid, the previous error
		// was not due to an invalid address and we can append a port.
		_, _, err := net.SplitHostPort(s + ":1234")
		return err == nil
	}

	// If it's an address with no trailing port, infer it based on the used scheme.
	if addPort(addr) {
		// Addresses reaching this point are already wrapped in [] if necessary.
		switch lset.Get(model.SchemeLabel) {
		case "http", "":
			addr = addr + ":80"
		case "https":
			addr = addr + ":443"
		default:
			return nil, nil, fmt.Errorf("invalid scheme: %q", cfg.Scheme)
		}
		lb.Set(model.AddressLabel, addr)
	}

	if err = config.CheckTargetAddress(addr); err != nil {
		return nil, nil, err
	}

	var interval string
	var intervalDuration time.Duration
	if interval = lset.Get(model.ScrapeIntervalLabel); interval != cfg.ScrapeInterval.String() {
		intervalDuration, err = time.ParseDuration(interval)
		if err != nil {
			return nil, nil, fmt.Errorf("error parsing scrape interval: %w", err)
		}
		if intervalDuration == 0 {
			return nil, nil, errors.New("scrape interval cannot be 0")
		}
	}

	var timeout string
	var timeoutDuration time.Duration
	if timeout = lset.Get(model.ScrapeTimeoutLabel); timeout != cfg.ScrapeTimeout.String() {
		timeoutDuration, err = time.ParseDuration(timeout)
		if err != nil {
			return nil, nil, fmt.Errorf("error parsing scrape timeout: %w", err)
		}
		if timeoutDuration == 0 {
			return nil, nil, errors.New("scrape timeout cannot be 0")
		}
	}

	if timeoutDuration > intervalDuration {
		return nil, nil, fmt.Errorf("scrape timeout cannot be greater than scrape interval (%q > %q)", timeout, interval)
	}

	// Meta labels are deleted after relabelling. Other internal labels propagate to
	// the target which decides whether they will be part of their label set.
	for _, l := range lset {
		if strings.HasPrefix(l.Name, model.MetaLabelPrefix) {
			lb.Del(l.Name)
		}
	}

	// Default the instance label to the target address.
	if v := lset.Get(model.InstanceLabel); v == "" {
		lb.Set(model.InstanceLabel, addr)
	}

	res = lb.Labels()
	for _, l := range res {
		// Check label values are valid, drop the target if not.
		if !isValidLabelValue(l.Value) {
			return nil, nil, fmt.Errorf("invalid label value for %q: %q", l.Name, l.Value)
		}
	}

	return res, preRelabelLabels, nil
}

func isValidLabelValue(v string) bool { return utf8.ValidString(v) }

// TargetsFromGroup builds targets based on the given TargetGroup and config.
func TargetsFromGroup(tg *targetgroup.Group, cfg *config.Config) ([]*Target, []error) {
	targets := make([]*Target, 0, len(tg.Targets))
	failures := []error{}

	for i, tlset := range tg.Targets {
		lbls := make([]labels.Label, 0, len(tlset)+len(tg.Labels))
		for ln, lv := range tlset {
			lbls = append(lbls, labels.Label{Name: string(ln), Value: string(lv)})
		}
		for ln, lv := range tg.Labels {
			if _, ok := tlset[ln]; !ok {
				lbls = append(lbls, labels.Label{Name: string(ln), Value: string(lv)})
			}
		}

		lset := labels.New(lbls...)
		lbls, origLabels, err := PopulateLabels(lset, cfg)
		if err != nil {
			failures = append(failures, fmt.Errorf("instance %d in group %s: %w", i, tg.Source, err))
		}
		if lbls == nil || origLabels == nil {
			continue
		}

		// TODO(kolesnikovae):
		//  Should we allow overrides for sample types, limits, etc?
		//  Add all the configuration prams (e.g. URL params) to labels?
		m := labels.Labels(lbls).Map()
		for profileName := range cfg.Profiles {
			if c, ok := buildConfig(cfg, profileName, m); ok {
				// Targets should not have identical labels.
				// origLabels is immutable.
				labelsCopy := make([]labels.Label, len(lbls), len(lbls)+2)
				copy(labelsCopy, lbls)
				labelsCopy = append(labelsCopy,
					labels.Label{Name: model.ProfilePathLabel, Value: c.Path},
					labels.Label{Name: model.ProfileNameLabel, Value: profileName})
				targets = append(targets, NewTarget(labelsCopy, origLabels, c))
			}
		}
	}

	return targets, failures
}

func buildConfig(cfg *config.Config, profileName string, lbls map[string]string) (*config.Profile, bool) {
	prefix := model.ProfileLabelPrefix + profileName + "_"
	// Note that input profile labels don't have '__' suffix.
	switch lbls[prefix+"enabled"] {
	case "true":
	case "false":
		return nil, false
	default:
		if !cfg.IsProfileEnabled(profileName) {
			return nil, false
		}
	}
	defaultConfig, ok := cfg.Profiles[profileName]
	if !ok {
		return nil, false
	}
	// It is assumed SampleTypes is immutable,
	// therefore we can copy Profile value safely.
	var c config.Profile
	c = *defaultConfig
	if path, ok := lbls[prefix+"path"]; ok {
		c.Path = path
	}
	params := make(url.Values, len(c.Params))
	for k, v := range c.Params {
		params[k] = v
	}
	for k, v := range lbls {
		pp := prefix + "param"
		if !strings.HasPrefix(k, pp) {
			continue
		}
		ks := k[len(pp):]
		if len(params[k]) > 0 {
			params[ks][0] = v
		} else {
			params[ks] = []string{v}
		}
	}
	c.Params = params
	return &c, true
}