package main

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"net/http"
	"reflect"
	"sync"
	"time"

	messages "git.tornberg.me/go-cart-actor/proto"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"
	"k8s.io/apimachinery/pkg/watch"
)

// ---------------------------------------------------------------------------
// Metrics shared by the cart pool implementation.
// ---------------------------------------------------------------------------

var (
	poolGrains = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_grains_in_pool",
		Help: "The total number of grains in the local pool",
	})
	poolSize = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_pool_size",
		Help: "Configured capacity of the cart pool",
	})
	poolUsage = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_grain_pool_usage",
		Help: "Current utilisation of the cart pool",
	})
	negotiationCount = promauto.NewCounter(prometheus.CounterOpts{
		Name: "cart_remote_negotiation_total",
		Help: "The total number of remote host negotiations",
	})
	connectedRemotes = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_connected_remotes",
		Help: "Number of connected remote hosts",
	})
	cartMutationsTotal = promauto.NewCounter(prometheus.CounterOpts{
		Name: "cart_mutations_total",
		Help: "Total number of cart state mutations applied",
	})
	cartMutationFailuresTotal = promauto.NewCounter(prometheus.CounterOpts{
		Name: "cart_mutation_failures_total",
		Help: "Total number of failed cart state mutations",
	})
	cartMutationLatencySeconds = promauto.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "cart_mutation_latency_seconds",
		Help:    "Latency of cart mutations in seconds",
		Buckets: prometheus.DefBuckets,
	}, []string{"mutation"})
	cartActiveGrains = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_active_grains",
		Help: "Number of active (resident) local grains",
	})
)

// GrainPool is the interface exposed to HTTP handlers and other subsystems.
type GrainPool interface {
	Apply(id CartId, mutation interface{}) (*CartGrain, error)
	Get(id CartId) (*CartGrain, error)
	OwnerHost(id CartId) (Host, bool)
	Hostname() string
	TakeOwnership(id CartId)
	IsHealthy() bool
	Close()
}

// Host abstracts a remote node capable of proxying cart requests.
type Host interface {
	Name() string
	Proxy(id CartId, w http.ResponseWriter, r *http.Request) (bool, error)
}

// Ttl tracks the expiry deadline for an in-memory grain.
type Ttl struct {
	Expires time.Time
	Grain   *CartGrain
}

// CartPool merges the responsibilities that previously belonged to
// GrainLocalPool and SyncedPool. It provides local grain storage together
// with cluster coordination, ownership negotiation and expiry signalling.
type CartPool struct {
	// Local grain state -----------------------------------------------------
	localMu  sync.RWMutex
	grains   map[uint64]*CartGrain
	expiry   []Ttl
	spawn    func(id CartId) (*CartGrain, error)
	ttl      time.Duration
	poolSize int

	// Cluster coordination --------------------------------------------------
	hostname             string
	remoteMu             sync.RWMutex
	remoteOwners         map[CartId]*RemoteHostGRPC
	remoteHosts          map[string]*RemoteHostGRPC
	discardedHostHandler *DiscardedHostHandler

	// House-keeping ---------------------------------------------------------
	purgeTicker *time.Ticker
}

// RemoteHostGRPC mirrors the lightweight controller used for remote node
// interaction.
type RemoteHostGRPC struct {
	Host          string
	HTTPBase      string
	Conn          *grpc.ClientConn
	Transport     *http.Transport
	Client        *http.Client
	ControlClient messages.ControlPlaneClient
	MissedPings   int
}

func (h *RemoteHostGRPC) Name() string {
	return h.Host
}

func (h *RemoteHostGRPC) Proxy(id CartId, w http.ResponseWriter, r *http.Request) (bool, error) {
	target := fmt.Sprintf("%s%s", h.HTTPBase, r.URL.RequestURI())
	var bodyCopy []byte
	if r.Body != nil && r.Body != http.NoBody {
		var err error
		bodyCopy, err = io.ReadAll(r.Body)
		if err != nil {
			http.Error(w, "proxy read error", http.StatusBadGateway)
			return false, err
		}
	}
	if r.Body != nil {
		r.Body.Close()
	}
	var reqBody io.Reader
	if len(bodyCopy) > 0 {
		reqBody = bytes.NewReader(bodyCopy)
	}
	req, err := http.NewRequestWithContext(r.Context(), r.Method, target, reqBody)
	if err != nil {
		http.Error(w, "proxy build error", http.StatusBadGateway)
		return false, err
	}
	r.Body = io.NopCloser(bytes.NewReader(bodyCopy))
	req.Header.Set("X-Forwarded-Host", r.Host)
	if idStr := id.String(); idStr != "" {
		req.Header.Set("X-Cart-Id", idStr)
	}
	for k, v := range r.Header {
		for _, vv := range v {
			req.Header.Add(k, vv)
		}
	}
	res, err := h.Client.Do(req)
	if err != nil {
		http.Error(w, "proxy request error", http.StatusBadGateway)
		return false, err
	}
	defer res.Body.Close()
	for k, v := range res.Header {
		for _, vv := range v {
			w.Header().Add(k, vv)
		}
	}
	w.Header().Set("X-Cart-Owner-Routed", "true")
	if res.StatusCode >= 200 && res.StatusCode <= 299 {
		w.WriteHeader(res.StatusCode)
		_, copyErr := io.Copy(w, res.Body)
		if copyErr != nil {
			return true, copyErr
		}
		return true, nil
	}
	return false, fmt.Errorf("proxy response status %d", res.StatusCode)
}

func (r *RemoteHostGRPC) IsHealthy() bool {
	return r.MissedPings < 3
}

// NewCartPool constructs a unified pool. Discovery may be nil for standalone
// deployments.
func NewCartPool(size int, ttl time.Duration, hostname string, spawn func(id CartId) (*CartGrain, error), discovery Discovery) (*CartPool, error) {
	p := &CartPool{
		grains:       make(map[uint64]*CartGrain),
		expiry:       make([]Ttl, 0),
		spawn:        spawn,
		ttl:          ttl,
		poolSize:     size,
		hostname:     hostname,
		remoteOwners: make(map[CartId]*RemoteHostGRPC),
		remoteHosts:  make(map[string]*RemoteHostGRPC),
	}

	p.discardedHostHandler = NewDiscardedHostHandler(1338)
	p.discardedHostHandler.SetReconnectHandler(p.AddRemote)

	p.purgeTicker = time.NewTicker(time.Minute)
	go func() {
		for range p.purgeTicker.C {
			p.Purge()
		}
	}()

	if discovery != nil {
		go p.startDiscovery(discovery)
	} else {
		log.Printf("No discovery configured; expecting manual AddRemote or static host injection")
	}

	return p, nil
}

// startDiscovery subscribes to cluster events and adds/removes hosts.
func (p *CartPool) startDiscovery(discovery Discovery) {
	time.Sleep(3 * time.Second) // allow gRPC server startup
	log.Printf("Starting discovery watcher")
	ch, err := discovery.Watch()
	if err != nil {
		log.Printf("Discovery error: %v", err)
		return
	}
	for evt := range ch {
		if evt.Host == "" {
			continue
		}
		switch evt.Type {
		case watch.Deleted:
			if p.IsKnown(evt.Host) {
				p.RemoveHost(evt.Host)
			}
		default:
			if !p.IsKnown(evt.Host) {
				log.Printf("Discovered host %s", evt.Host)
				p.AddRemote(evt.Host)
			}
		}
	}
}

// ---------------------------------------------------------------------------
// Local grain management
// ---------------------------------------------------------------------------

func (p *CartPool) statsUpdate() {
	p.localMu.RLock()
	size := len(p.grains)
	cap := p.poolSize
	p.localMu.RUnlock()
	poolGrains.Set(float64(size))
	poolSize.Set(float64(cap))
	if cap > 0 {
		poolUsage.Set(float64(size) / float64(cap))
	}
}

// LocalUsage returns the number of resident grains and configured capacity.
func (p *CartPool) LocalUsage() (int, int) {
	p.localMu.RLock()
	defer p.localMu.RUnlock()
	return len(p.grains), p.poolSize
}

// SetAvailable pre-populates placeholder entries.
func (p *CartPool) SetAvailable(availableWithLastChangeUnix map[CartId]int64) {
	p.localMu.Lock()
	defer p.localMu.Unlock()
	for id := range availableWithLastChangeUnix {
		k := uint64(id)
		if _, ok := p.grains[k]; !ok {
			p.grains[k] = nil
			p.expiry = append(p.expiry, Ttl{Expires: time.Now().Add(p.ttl)})
		}
	}
	p.statsUpdate()
}

// Purge removes expired grains and broadcasts expiry announcements so that
// other hosts drop stale ownership hints.
func (p *CartPool) Purge() {
	now := time.Now()
	keepChanged := now.Add(-p.ttl).Unix()
	var expired []CartId

	p.localMu.Lock()
	for i := 0; i < len(p.expiry); {
		entry := p.expiry[i]
		if entry.Grain == nil {
			i++
			continue
		}
		if entry.Expires.After(now) {
			break
		}
		if entry.Grain.GetLastChange() > keepChanged {
			// Recently mutated: move to back.
			p.expiry = append(p.expiry[:i], p.expiry[i+1:]...)
			p.expiry = append(p.expiry, entry)
			continue
		}
		id := entry.Grain.GetId()
		delete(p.grains, uint64(id))
		expired = append(expired, id)
		if i < len(p.expiry)-1 {
			p.expiry = append(p.expiry[:i], p.expiry[i+1:]...)
		} else {
			p.expiry = p.expiry[:i]
		}
	}
	p.localMu.Unlock()

	if len(expired) > 0 {
		p.statsUpdate()
		go p.broadcastExpiry(expired)
	}
}

// RefreshExpiry updates the TTL entry for a given grain.
func (p *CartPool) RefreshExpiry(id CartId) {
	p.localMu.Lock()
	defer p.localMu.Unlock()
	for i := range p.expiry {
		g := p.expiry[i].Grain
		if g != nil && g.Id == id {
			p.expiry[i].Expires = time.Now().Add(p.ttl)
			return
		}
	}
	// If no entry existed, append one (safeguard for newly spawned grains).
	p.expiry = append(p.expiry, Ttl{Expires: time.Now().Add(p.ttl), Grain: p.grains[uint64(id)]})
}

// DebugGrainCount returns the number of locally resident grains.
func (p *CartPool) DebugGrainCount() int {
	p.localMu.RLock()
	defer p.localMu.RUnlock()
	return len(p.grains)
}

// LocalCartIDs returns the currently owned cart ids (for control-plane RPCs).
func (p *CartPool) LocalCartIDs() []uint64 {
	p.localMu.RLock()
	defer p.localMu.RUnlock()
	ids := make([]uint64, 0, len(p.grains))
	for _, g := range p.grains {
		if g == nil {
			continue
		}
		ids = append(ids, uint64(g.GetId()))
	}
	return ids
}

// SnapshotGrains returns a copy of the currently resident grains keyed by id.
func (p *CartPool) SnapshotGrains() map[CartId]*CartGrain {
	p.localMu.RLock()
	defer p.localMu.RUnlock()
	out := make(map[CartId]*CartGrain, len(p.grains))
	for _, g := range p.grains {
		if g != nil {
			out[g.GetId()] = g
		}
	}
	return out
}

func (p *CartPool) removeLocalGrain(id CartId) {
	p.localMu.Lock()
	delete(p.grains, uint64(id))
	for i := range p.expiry {
		if p.expiry[i].Grain != nil && p.expiry[i].Grain.GetId() == id {
			p.expiry = append(p.expiry[:i], p.expiry[i+1:]...)
			break
		}
	}
	p.localMu.Unlock()
	p.statsUpdate()
}

func (p *CartPool) getLocalGrain(id CartId) (*CartGrain, error) {
	key := uint64(id)
	grainLookups.Inc()

	p.localMu.RLock()
	grain, ok := p.grains[key]
	p.localMu.RUnlock()
	if grain != nil && ok {
		return grain, nil
	}

	p.localMu.Lock()
	defer p.localMu.Unlock()
	grain, ok = p.grains[key]
	if grain == nil || !ok {
		if len(p.grains) >= p.poolSize && len(p.expiry) > 0 {
			if p.expiry[0].Expires.Before(time.Now()) && p.expiry[0].Grain != nil {
				oldID := p.expiry[0].Grain.GetId()
				delete(p.grains, uint64(oldID))
				p.expiry = p.expiry[1:]
				go p.broadcastExpiry([]CartId{oldID})
			} else {
				return nil, fmt.Errorf("pool is full")
			}
		}
		spawned, err := p.spawn(id)
		if err != nil {
			return nil, err
		}
		p.grains[key] = spawned
		p.expiry = append(p.expiry, Ttl{Expires: time.Now().Add(p.ttl), Grain: spawned})
		grain = spawned
	}
	go p.statsUpdate()
	return grain, nil
}

// ---------------------------------------------------------------------------
// Cluster ownership and coordination
// ---------------------------------------------------------------------------

func (p *CartPool) TakeOwnership(id CartId) {
	p.broadcastOwnership([]CartId{id})
}

func (p *CartPool) AddRemote(host string) {
	if host == "" || host == p.hostname {
		return
	}

	p.remoteMu.Lock()
	if _, exists := p.remoteHosts[host]; exists {
		p.remoteMu.Unlock()
		return
	}
	p.remoteMu.Unlock()

	target := fmt.Sprintf("%s:1337", host)
	dialCtx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	conn, err := grpc.DialContext(dialCtx, target, grpc.WithTransportCredentials(insecure.NewCredentials()), grpc.WithBlock())
	cancel()
	if err != nil {
		log.Printf("AddRemote: dial %s failed: %v", target, err)
		return
	}

	controlClient := messages.NewControlPlaneClient(conn)
	for retries := 0; retries < 3; retries++ {
		ctx, pingCancel := context.WithTimeout(context.Background(), time.Second)
		_, pingErr := controlClient.Ping(ctx, &messages.Empty{})
		pingCancel()
		if pingErr == nil {
			break
		}
		if retries == 2 {
			log.Printf("AddRemote: ping %s failed after retries: %v", host, pingErr)
			conn.Close()
			return
		}
		time.Sleep(200 * time.Millisecond)
	}

	transport := &http.Transport{
		MaxIdleConns:        100,
		MaxIdleConnsPerHost: 100,
		IdleConnTimeout:     120 * time.Second,
	}
	client := &http.Client{Transport: transport, Timeout: 10 * time.Second}

	remote := &RemoteHostGRPC{
		Host:          host,
		HTTPBase:      fmt.Sprintf("http://%s:8080/cart", host),
		Conn:          conn,
		Transport:     transport,
		Client:        client,
		ControlClient: controlClient,
	}

	p.remoteMu.Lock()
	p.remoteHosts[host] = remote
	p.remoteMu.Unlock()
	connectedRemotes.Set(float64(p.RemoteCount()))

	log.Printf("Connected to remote host %s", host)

	go p.pingLoop(remote)
	go p.initializeRemote(remote)
	go p.Negotiate()
}

func (p *CartPool) initializeRemote(remote *RemoteHostGRPC) {
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()
	reply, err := remote.ControlClient.GetCartIds(ctx, &messages.Empty{})
	if err != nil {
		log.Printf("Init remote %s: GetCartIds error: %v", remote.Host, err)
		return
	}
	count := 0
	p.remoteMu.Lock()
	for _, cid := range reply.CartIds {
		id := CartId(cid)
		if _, exists := p.remoteOwners[id]; !exists {
			p.remoteOwners[id] = remote
		}
		count++
	}
	p.remoteMu.Unlock()
	log.Printf("Remote %s reported %d remote-owned carts", remote.Host, count)
}

func (p *CartPool) RemoveHost(host string) {
	p.remoteMu.Lock()
	remote, exists := p.remoteHosts[host]
	if exists {
		delete(p.remoteHosts, host)
	}
	for id, owner := range p.remoteOwners {
		if owner.Host == host {
			delete(p.remoteOwners, id)
		}
	}
	p.remoteMu.Unlock()

	if exists {
		remote.Conn.Close()
	}
	connectedRemotes.Set(float64(p.RemoteCount()))
}

func (p *CartPool) RemoteCount() int {
	p.remoteMu.RLock()
	defer p.remoteMu.RUnlock()
	return len(p.remoteHosts)
}

// RemoteHostNames returns a snapshot of connected remote host identifiers.
func (p *CartPool) RemoteHostNames() []string {
	p.remoteMu.RLock()
	defer p.remoteMu.RUnlock()
	hosts := make([]string, 0, len(p.remoteHosts))
	for host := range p.remoteHosts {
		hosts = append(hosts, host)
	}
	return hosts
}

func (p *CartPool) IsKnown(host string) bool {
	if host == p.hostname {
		return true
	}
	p.remoteMu.RLock()
	defer p.remoteMu.RUnlock()
	_, ok := p.remoteHosts[host]
	return ok
}

func (p *CartPool) pingLoop(remote *RemoteHostGRPC) {
	ticker := time.NewTicker(3 * time.Second)
	defer ticker.Stop()
	for range ticker.C {
		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
		_, err := remote.ControlClient.Ping(ctx, &messages.Empty{})
		cancel()
		if err != nil {
			remote.MissedPings++
			log.Printf("Ping %s failed (%d)", remote.Host, remote.MissedPings)
			if !remote.IsHealthy() {
				log.Printf("Remote %s unhealthy, removing", remote.Host)
				p.RemoveHost(remote.Host)
				return
			}
			continue
		}
		remote.MissedPings = 0
	}
}

func (p *CartPool) IsHealthy() bool {
	p.remoteMu.RLock()
	defer p.remoteMu.RUnlock()
	for _, r := range p.remoteHosts {
		if !r.IsHealthy() {
			return false
		}
	}
	return true
}

func (p *CartPool) Negotiate() {
	negotiationCount.Inc()

	p.remoteMu.RLock()
	hosts := make([]string, 0, len(p.remoteHosts)+1)
	hosts = append(hosts, p.hostname)
	remotes := make([]*RemoteHostGRPC, 0, len(p.remoteHosts))
	for h, r := range p.remoteHosts {
		hosts = append(hosts, h)
		remotes = append(remotes, r)
	}
	p.remoteMu.RUnlock()

	for _, r := range remotes {
		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
		reply, err := r.ControlClient.Negotiate(ctx, &messages.NegotiateRequest{KnownHosts: hosts})
		cancel()
		if err != nil {
			log.Printf("Negotiate with %s failed: %v", r.Host, err)
			continue
		}
		for _, h := range reply.Hosts {
			if !p.IsKnown(h) {
				p.AddRemote(h)
			}
		}
	}
}

func (p *CartPool) broadcastOwnership(ids []CartId) {
	if len(ids) == 0 {
		return
	}
	uids := make([]uint64, len(ids))
	for i, id := range ids {
		uids[i] = uint64(id)
	}

	p.remoteMu.RLock()
	remotes := make([]*RemoteHostGRPC, 0, len(p.remoteHosts))
	for _, r := range p.remoteHosts {
		if r.IsHealthy() {
			remotes = append(remotes, r)
		}
	}
	p.remoteMu.RUnlock()

	for _, remote := range remotes {
		go func(rh *RemoteHostGRPC) {
			_, err := rh.ControlClient.AnnounceOwnership(context.Background(), &messages.OwnershipAnnounce{
				Host:    p.hostname,
				CartIds: uids,
			})
			if err != nil {
				log.Printf("ownership announce to %s failed: %v", rh.Host, err)
			}
		}(remote)
	}
}

func (p *CartPool) broadcastExpiry(ids []CartId) {
	if len(ids) == 0 {
		return
	}
	uids := make([]uint64, len(ids))
	for i, id := range ids {
		uids[i] = uint64(id)
	}

	p.remoteMu.RLock()
	remotes := make([]*RemoteHostGRPC, 0, len(p.remoteHosts))
	for _, r := range p.remoteHosts {
		if r.IsHealthy() {
			remotes = append(remotes, r)
		}
	}
	p.remoteMu.RUnlock()

	for _, remote := range remotes {
		go func(rh *RemoteHostGRPC) {
			_, err := rh.ControlClient.AnnounceExpiry(context.Background(), &messages.ExpiryAnnounce{
				Host:    p.hostname,
				CartIds: uids,
			})
			if err != nil {
				log.Printf("expiry announce to %s failed: %v", rh.Host, err)
			}
		}(remote)
	}
}

func (p *CartPool) AdoptRemoteOwnership(host string, ids []string) {
	if host == "" || host == p.hostname {
		return
	}
	remoteHost, ok := p.remoteHosts[host]
	if !ok {
		log.Printf("AdoptRemoteOwnership: unknown host %s", host)
	}
	p.remoteMu.Lock()
	defer p.remoteMu.Unlock()
	for _, s := range ids {
		if s == "" {
			continue
		}
		parsed, ok := ParseCartId(s)
		if !ok {
			continue
		}
		if existing, ok := p.remoteOwners[parsed]; ok && existing != remoteHost {
			continue
		}
		p.localMu.RLock()
		_, localHas := p.grains[uint64(parsed)]
		p.localMu.RUnlock()
		if localHas {
			continue
		}
		p.remoteOwners[parsed] = remoteHost
	}
}

func (p *CartPool) HandleRemoteExpiry(host string, ids []uint64) {
	if host == "" || host == p.hostname {
		return
	}
	p.remoteMu.Lock()
	defer p.remoteMu.Unlock()
	for _, raw := range ids {
		id := CartId(raw)
		if owner, ok := p.remoteOwners[id]; ok && owner.Host == host {
			delete(p.remoteOwners, id)
		}
	}
}

func (p *CartPool) getOrClaimGrain(id CartId) (*CartGrain, error) {
	p.localMu.RLock()
	grain, exists := p.grains[uint64(id)]
	p.localMu.RUnlock()
	if exists && grain != nil {
		return grain, nil
	}

	p.remoteMu.RLock()
	remoteHost, found := p.remoteOwners[id]
	p.remoteMu.RUnlock()
	if found && remoteHost != nil && remoteHost.Host != "" {
		return nil, ErrNotOwner
	}

	grain, err := p.getLocalGrain(id)
	if err != nil {
		return nil, err
	}
	go p.broadcastOwnership([]CartId{id})
	return grain, nil
}

// ErrNotOwner is returned when a cart belongs to another host.
var ErrNotOwner = fmt.Errorf("not owner")

// Apply applies a mutation to a grain.
func (p *CartPool) Apply(id CartId, mutation interface{}) (*CartGrain, error) {
	grain, err := p.getOrClaimGrain(id)
	if err != nil {
		return nil, err
	}
	start := time.Now()
	result, applyErr := grain.Apply(mutation, false)
	mutationType := "unknown"
	if mutation != nil {
		if t := reflect.TypeOf(mutation); t != nil {
			if t.Kind() == reflect.Ptr {
				t = t.Elem()
			}
			if t.Name() != "" {
				mutationType = t.Name()
			}
		}
	}
	cartMutationLatencySeconds.WithLabelValues(mutationType).Observe(time.Since(start).Seconds())

	if applyErr == nil && result != nil {
		cartMutationsTotal.Inc()
		p.RefreshExpiry(id)
		cartActiveGrains.Set(float64(p.DebugGrainCount()))
	} else if applyErr != nil {
		cartMutationFailuresTotal.Inc()
	}

	return result, applyErr
}

// Get returns the current state of a grain.
func (p *CartPool) Get(id CartId) (*CartGrain, error) {
	grain, err := p.getOrClaimGrain(id)
	if err != nil {
		return nil, err
	}
	return grain.GetCurrentState()
}

// OwnerHost reports the remote owner (if any) for the supplied cart id.
func (p *CartPool) OwnerHost(id CartId) (Host, bool) {
	p.remoteMu.RLock()
	defer p.remoteMu.RUnlock()
	owner, ok := p.remoteOwners[id]
	return owner, ok
}

// Hostname returns the local hostname (pod IP).
func (p *CartPool) Hostname() string {
	return p.hostname
}

// Close notifies remotes that this host is shutting down.
func (p *CartPool) Close() {
	p.remoteMu.Lock()
	defer p.remoteMu.Unlock()
	for _, r := range p.remoteHosts {
		go func(rh *RemoteHostGRPC) {
			_, err := rh.ControlClient.Closing(context.Background(), &messages.ClosingNotice{Host: p.hostname})
			if err != nil {
				log.Printf("Close notify to %s failed: %v", rh.Host, err)
			}
		}(r)
	}
	if p.purgeTicker != nil {
		p.purgeTicker.Stop()
	}
}