go-cart-actor/synced-pool.go

package main

import (
	"context"
	"fmt"
	"log"
	"reflect"
	"sync"
	"time"

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

// SyncedPool coordinates cart grain ownership across nodes using gRPC control plane
// and cart actor services.
//
// Responsibilities:
//   - Local grain access (delegates to GrainLocalPool)
//   - Cluster membership (AddRemote via discovery + negotiation)
//   - Health/ping monitoring & remote removal
//   - (Legacy) ring-based ownership removed in first-touch model
//
// Thread-safety: public methods that mutate internal maps lock p.mu (RWMutex).
type SyncedPool struct {
	LocalHostname string
	local         *GrainLocalPool

	// New ownership tracking (first-touch / announcement model)
	// remoteOwners maps cart id -> owning host (excluding locally owned carts which live in local.grains)
	remoteOwners map[CartId]string

	mu sync.RWMutex

	// Remote host state (gRPC only)
	remoteHosts map[string]*RemoteHostGRPC // host -> remote host

	// Discovery handler for re-adding hosts after failures
	discardedHostHandler *DiscardedHostHandler
}

// RemoteHostGRPC tracks a remote host's clients & health.
type RemoteHostGRPC struct {
	Host          string
	Conn          *grpc.ClientConn
	ControlClient proto.ControlPlaneClient
	MissedPings   int
}

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

var (
	negotiationCount = promauto.NewCounter(prometheus.CounterOpts{
		Name: "cart_remote_negotiation_total",
		Help: "The total number of remote negotiations",
	})
	connectedRemotes = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_connected_remotes",
		Help: "The number of connected remotes",
	})
	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.",
	})
)

func NewSyncedPool(local *GrainLocalPool, hostname string, discovery Discovery) (*SyncedPool, error) {
	p := &SyncedPool{
		LocalHostname:        hostname,
		local:                local,
		remoteHosts:          make(map[string]*RemoteHostGRPC),
		remoteOwners:         make(map[CartId]string),
		discardedHostHandler: NewDiscardedHostHandler(1338),
	}
	p.discardedHostHandler.SetReconnectHandler(p.AddRemote)
	// Initialize empty ring (will be rebuilt after first AddRemote or discovery event)
	p.rebuildRing()

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

	return p, nil
}

// ------------------------- Remote Host Management -----------------------------

// AddRemote dials a remote host and initializes grain proxies.
func (p *SyncedPool) AddRemote(host string) {
	if host == "" || host == p.LocalHostname {
		return
	}

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

	target := fmt.Sprintf("%s:1337", host)
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	conn, err := grpc.DialContext(ctx, target, grpc.WithInsecure(), grpc.WithBlock())
	if err != nil {
		log.Printf("AddRemote: dial %s failed: %v", target, err)
		return
	}

	controlClient := proto.NewControlPlaneClient(conn)

	// Health check (Ping) with limited retries
	pings := 3
	for pings > 0 {
		ctxPing, cancelPing := context.WithTimeout(context.Background(), 1*time.Second)
		_, pingErr := controlClient.Ping(ctxPing, &proto.Empty{})
		cancelPing()
		if pingErr == nil {
			break
		}
		pings--
		time.Sleep(200 * time.Millisecond)
		if pings == 0 {
			log.Printf("AddRemote: ping %s failed after retries: %v", host, pingErr)
			conn.Close()
			return
		}
	}

	remote := &RemoteHostGRPC{
		Host: host,
		Conn: conn,

		ControlClient: controlClient,
		MissedPings:   0,
	}

	p.mu.Lock()
	p.remoteHosts[host] = remote
	p.mu.Unlock()
	connectedRemotes.Set(float64(p.RemoteCount()))
	// Rebuild consistent hashing ring including this new host
	p.rebuildRing()

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

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

// initializeRemote fetches remote cart ids and sets up remote grain proxies.
func (p *SyncedPool) initializeRemote(remote *RemoteHostGRPC) {
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()
	reply, err := remote.ControlClient.GetCartIds(ctx, &proto.Empty{})
	if err != nil {
		log.Printf("Init remote %s: GetCartIds error: %v", remote.Host, err)
		return
	}
	count := 0
	// Record remote ownership (first-touch model) instead of spawning remote grain proxies.
	p.mu.Lock()
	for _, cid := range reply.CartIds {

		// Only set if not already claimed (first claim wins)
		if _, exists := p.remoteOwners[CartId(cid)]; !exists {
			p.remoteOwners[CartId(cid)] = remote.Host
		}
		count++
	}
	p.mu.Unlock()
	log.Printf("Remote %s reported %d remote-owned carts (ownership cached)", remote.Host, count)
}

// RemoveHost removes remote host and its grains.
func (p *SyncedPool) RemoveHost(host string) {
	p.mu.Lock()
	remote, exists := p.remoteHosts[host]
	if exists {
		delete(p.remoteHosts, host)
	}
	// purge remote ownership entries for this host
	for id, h := range p.remoteOwners {
		if h == host {
			delete(p.remoteOwners, id)
		}
	}
	p.mu.Unlock()

	if exists {
		remote.Conn.Close()
	}
	connectedRemotes.Set(float64(p.RemoteCount()))
	// Rebuild ring after host removal
	p.rebuildRing()
}

// RemoteCount returns number of tracked remote hosts.
func (p *SyncedPool) RemoteCount() int {
	p.mu.RLock()
	defer p.mu.RUnlock()
	return len(p.remoteHosts)
}

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

func (p *SyncedPool) ExcludeKnown(hosts []string) []string {
	ret := make([]string, 0, len(hosts))
	for _, h := range hosts {
		if !p.IsKnown(h) {
			ret = append(ret, h)
		}
	}
	return ret
}

// ------------------------- Health / Ping -------------------------------------

func (p *SyncedPool) pingLoop(remote *RemoteHostGRPC) {
	ticker := time.NewTicker(3 * time.Second)
	defer ticker.Stop()
	for range ticker.C {
		ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
		_, err := remote.ControlClient.Ping(ctx, &proto.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 *SyncedPool) IsHealthy() bool {
	p.mu.RLock()
	defer p.mu.RUnlock()
	for _, r := range p.remoteHosts {
		if !r.IsHealthy() {
			return false
		}
	}
	return true
}

// ------------------------- Negotiation ---------------------------------------

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

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

	for _, r := range remotes {
		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
		reply, err := r.ControlClient.Negotiate(ctx, &proto.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)
			}
		}
	}

	// Ring rebuild removed (first-touch ownership model no longer uses ring)
}

// ------------------------- Grain / Ring Ownership ----------------------------

// RemoveRemoteGrain obsolete in first-touch model (no remote grain proxies retained)

// SpawnRemoteGrain removed (remote grain proxies eliminated in first-touch model)

// GetHealthyRemotes retained (still useful for broadcasting ownership)
func (p *SyncedPool) GetHealthyRemotes() []*RemoteHostGRPC {
	p.mu.RLock()
	defer p.mu.RUnlock()
	ret := make([]*RemoteHostGRPC, 0, len(p.remoteHosts))
	for _, r := range p.remoteHosts {
		if r.IsHealthy() {
			ret = append(ret, r)
		}
	}
	return ret
}

// rebuildRing removed (ring no longer used in first-touch ownership model)
func (p *SyncedPool) rebuildRing() {}

// (All ring construction & metrics removed)

// ForceRingRefresh kept as no-op for backward compatibility.
func (p *SyncedPool) ForceRingRefresh() {}

// ownersFor removed (ring-based ownership deprecated)
func (p *SyncedPool) ownersFor(id CartId) []string {
	return []string{p.LocalHostname}
}

// ownerHostFor retained as wrapper to satisfy existing calls (always local)
func (p *SyncedPool) ownerHostFor(id CartId) string {
	return p.LocalHostname
}

// DebugOwnerHost exposes (for tests) the currently computed primary owner host.
func (p *SyncedPool) DebugOwnerHost(id CartId) string {
	return p.ownerHostFor(id)
}

func (p *SyncedPool) removeLocalGrain(id CartId) {
	p.mu.Lock()
	delete(p.local.grains, uint64(id))
	p.mu.Unlock()
}

// ------------------------- First-Touch Ownership Resolution ------------------

// ErrNotOwner is returned when an operation is attempted on a cart that is
// owned by a different host (according to first-touch ownership mapping).
var ErrNotOwner = fmt.Errorf("not owner")

// resolveOwnerFirstTouch implements the new semantics:
//  1. If local grain exists -> local host owns it.
//  2. Else if remoteOwners has an entry -> return that host.
//  3. Else: claim locally (spawn), insert into remoteOwners map locally for
//     idempotency, and asynchronously announce ownership to all remotes.
//
// NOTE: This does NOT (yet) reconcile conflicting announcements; first claim
// wins. Later improvements can add tie-break via timestamp or host ordering.
func (p *SyncedPool) resolveOwnerFirstTouch(id CartId) (string, error) {
	// Fast local existence check
	p.local.mu.RLock()
	_, existsLocal := p.local.grains[uint64(id)]
	p.local.mu.RUnlock()
	if existsLocal {
		return p.LocalHostname, nil
	}

	// Remote ownership map lookup
	p.mu.RLock()
	remoteHost, foundRemote := p.remoteOwners[id]
	p.mu.RUnlock()
	if foundRemote && remoteHost != "" {
		return remoteHost, nil
	}

	// Claim: spawn locally
	_, err := p.local.GetGrain(id)
	if err != nil {
		return "", err
	}

	// Record (defensive) in remoteOwners pointing to self (not strictly needed
	// for local queries, but keeps a single lookup structure).
	p.mu.Lock()
	if _, stillMissing := p.remoteOwners[id]; !stillMissing {
		// Another goroutine inserted meanwhile; keep theirs (first claim wins).
	} else {
		p.remoteOwners[id] = p.LocalHostname
	}
	p.mu.Unlock()

	// Announce asynchronously
	go p.broadcastOwnership([]CartId{id})
	return p.LocalHostname, nil
}

// broadcastOwnership sends an AnnounceOwnership RPC to all healthy remotes.
// Best-effort: failures are logged and ignored.
func (p *SyncedPool) broadcastOwnership(ids []CartId) {
	if len(ids) == 0 {
		return
	}
	// Prepare payload (convert to string slice)
	payload := make([]string, 0, len(ids))
	for _, id := range ids {
		if id.String() != "" {
			payload = append(payload, id.String())
		}
	}
	if len(payload) == 0 {
		return
	}

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

	for _, r := range remotes {
		go func(rh *RemoteHostGRPC) {
			// AnnounceOwnership RPC not yet available (proto regeneration pending); no-op broadcast for now.
			// Intended announcement: host=p.LocalHostname ids=payload
			_ = rh
		}(r)
	}
}

// AdoptRemoteOwnership processes an incoming ownership announcement for cart ids.
func (p *SyncedPool) AdoptRemoteOwnership(host string, ids []string) {
	if host == "" || host == p.LocalHostname {
		return
	}
	p.mu.Lock()
	defer p.mu.Unlock()
	for _, s := range ids {
		if s == "" {
			continue
		}
		parsed, ok := ParseCartId(s)
		if !ok {
			continue // skip invalid cart id strings
		}
		id := parsed
		// Do not overwrite if already claimed by another host (first wins).
		if existing, ok := p.remoteOwners[id]; ok && existing != host {
			continue
		}
		// Skip if we own locally (local wins for our own process)
		p.local.mu.RLock()
		_, localHas := p.local.grains[uint64(id)]
		p.local.mu.RUnlock()
		if localHas {
			continue
		}
		p.remoteOwners[id] = host
	}
}

// getGrain returns a local grain if this host is (or becomes) the owner under
// the first-touch model. If another host owns the cart, ErrNotOwner is returned.
// Remote grain proxy logic and ring-based spawning have been removed.
func (p *SyncedPool) getGrain(id CartId) (Grain, error) {
	owner, err := p.resolveOwnerFirstTouch(id)
	if err != nil {
		return nil, err
	}
	if owner != p.LocalHostname {
		// Another host owns it; signal caller to proxy / forward.
		return nil, ErrNotOwner
	}

	// Owner is local (either existing or just claimed), fetch/create grain.
	grain, err := p.local.GetGrain(id)
	if err != nil {
		return nil, err
	}
	return grain, nil
}

// Apply applies a single mutation to a grain (local or remote).
// Replication (RF>1) scaffolding: future enhancement will fan-out mutations
// to replica owners (best-effort) and reconcile quorum on read.
func (p *SyncedPool) Apply(id CartId, mutation interface{}) (*CartGrain, error) {
	grain, err := p.getGrain(id)
	if err == ErrNotOwner {
		// Remote owner reported but either unreachable or failed earlier in stack.
		// Takeover strategy: remove remote mapping (first-touch override) and claim locally.
		p.mu.Lock()
		delete(p.remoteOwners, id)
		p.mu.Unlock()
		if owner, terr := p.resolveOwnerFirstTouch(id); terr != nil {
			return nil, terr
		} else if owner == p.LocalHostname {
			// Fetch (now-local) grain
			grain, err = p.local.GetGrain(id)
			if err != nil {
				return nil, err
			}
		} else {
			// Another host reclaimed before us; treat as not owner.
			return nil, ErrNotOwner
		}
	} else if err != nil {
		return nil, err
	}

	start := time.Now()
	result, applyErr := grain.Apply(mutation, false)

	// Derive mutation type label (strip pointer)
	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()
		if p.ownerHostFor(id) == p.LocalHostname {
			// Update active grains gauge only for local ownership
			cartActiveGrains.Set(float64(p.local.DebugGrainCount()))
		}
	} else if applyErr != nil {
		cartMutationFailuresTotal.Inc()
	}
	return result, applyErr
}

// Get returns current state of a grain (local or remote).
// Future replication hook: Read-repair or quorum read can be added here.
func (p *SyncedPool) Get(id CartId) (*CartGrain, error) {
	grain, err := p.getGrain(id)
	if err == ErrNotOwner {
		// Attempt takeover on read as well (e.g. owner dead).
		p.mu.Lock()
		delete(p.remoteOwners, id)
		p.mu.Unlock()
		if owner, terr := p.resolveOwnerFirstTouch(id); terr != nil {
			return nil, terr
		} else if owner == p.LocalHostname {
			grain, err = p.local.GetGrain(id)
			if err != nil {
				return nil, err
			}
		} else {
			return nil, ErrNotOwner
		}
	} else if err != nil {
		return nil, err
	}
	return grain.GetCurrentState()
}

// Close notifies remotes this host is terminating.
func (p *SyncedPool) Close() {
	p.mu.RLock()
	remotes := make([]*RemoteHostGRPC, 0, len(p.remoteHosts))
	for _, r := range p.remoteHosts {
		remotes = append(remotes, r)
	}
	p.mu.RUnlock()

	for _, r := range remotes {
		go func(rh *RemoteHostGRPC) {
			ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
			_, err := rh.ControlClient.Closing(ctx, &proto.ClosingNotice{Host: p.LocalHostname})
			cancel()
			if err != nil {
				log.Printf("Close notify to %s failed: %v", rh.Host, err)
			}
		}(r)
	}
}

// Hostname implements the GrainPool interface, returning this node's hostname.
func (p *SyncedPool) Hostname() string {
	return p.LocalHostname
}

// OwnerHost returns the primary owning host for a given cart id (ring lookup).
func (p *SyncedPool) OwnerHost(id CartId) string {
	return p.ownerHostFor(id)
}