package lb

import (
	"crypto/tls"
	"encoding/json"
	"fmt"
	"net"
	"sort"
	"strings"
	"time"

	coreapi "k8s.io/api/core/v1"
	discovery "k8s.io/api/discovery/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/labels"
)

// Gateways of a class this agent implements are served like LoadBalancer Services: a Gateway names one address a
// node holds (spec.addresses), and that node, the holder, serves all of it and writes its status. TCP listeners
// are forwarded in the kernel (the DNAT of LoadBalancer Services: the backend sees the client's own address);
// HTTP and HTTPS listeners are served by the agent itself on the holder (TLS terminated with the listener's
// certificate, requests routed by their HTTPRoutes). ComputeGateways is the whole policy as a pure function of
// what the API shows.

const (
	ProtocolHTTP  = "HTTP"
	ProtocolHTTPS = "HTTPS"
	ProtocolTCP   = "TCP"

	kindGateway   = "Gateway"
	kindHTTPRoute = "HTTPRoute"
	kindTCPRoute  = "TCPRoute"
	kindService   = "Service"
	kindSecret    = "Secret"

	condAccepted     = "Accepted"
	condProgrammed   = "Programmed"
	condResolvedRefs = "ResolvedRefs"
	condConflicted   = "Conflicted"

	filterRequestHeaderModifier  = "RequestHeaderModifier"
	filterResponseHeaderModifier = "ResponseHeaderModifier"
	filterRequestRedirect        = "RequestRedirect"
	filterURLRewrite             = "URLRewrite"

	pathExact  = "Exact"
	pathPrefix = "PathPrefix"
)

// GatewayInput is what the API shows that the gateway policy reads.
type GatewayInput struct {
	Classes    []*GatewayClass
	Gateways   []*Gateway
	HTTPRoutes []*HTTPRoute
	TCPRoutes  []*TCPRoute
	Grants     []*ReferenceGrant
	Namespaces []*coreapi.Namespace
	Services   []*coreapi.Service
	Slices     []*discovery.EndpointSlice
	// Secrets the agent can read, and the namespaces they come from: a certificate elsewhere cannot be served
	Secrets          []*coreapi.Secret
	SecretNamespaces map[string]bool
	// Unbound are the listeners ("namespace/gateway/listener") this node could not bind on its last try, and why
	Unbound map[string]string
	Now     metav1.Time
}

// GatewayDesired is what one node does for Gateways, and the statuses it writes.
type GatewayDesired struct {
	Forwards []Forward       // this node's TCP listeners, forwarded like LoadBalancer Services
	Holding  []string        // nodes forwarding some Gateway's TCP listener (other nodes steer replies back to them)
	Serve    []ServeListener // this node's HTTP and HTTPS listeners
	Classes  []ClassStatusWrite
	Gateways []GatewayStatusWrite
	Routes   []RouteStatusWrite
	Problems []string
}

// ServeListener is an HTTP or HTTPS listener this node serves.
type ServeListener struct {
	Gateway  string // namespace/name
	Name     string
	Address  net.IP
	Port     int32
	HTTPS    bool
	Hostname string          // "" takes any host
	Cert     *coreapi.Secret // HTTPS: the listener's certificate
	Routes   []ServeRoute
}

// ServeRoute is an HTTPRoute attached to a listener.
type ServeRoute struct {
	Key     string // namespace/name
	Created time.Time
	// Hostnames the route answers on this listener (its own, narrowed to the listener's); none: the listener's
	Hostnames []string
	Rules     []ServeRule
}

// ServeRule is one rule of an attached route.
type ServeRule struct {
	Matches  []HTTPRouteMatch // defaulted: a match without a path is a PathPrefix match on "/"
	Filters  []HTTPRouteFilter
	Backends []ServeBackend
	// Broken: some backend could not be resolved; requests the rule takes are answered 500, as the spec says
	Broken bool
}

// ServeBackend is a Service port a rule sends requests to, with its ready endpoints.
type ServeBackend struct {
	Key       string // namespace/name:port
	Weight    int32
	Endpoints []Endpoint
	Filters   []HTTPRouteFilter
}

type ClassStatusWrite struct {
	Name, ResourceVersion string
	Status                GatewayClassStatus
}

type GatewayStatusWrite struct {
	Namespace, Name, ResourceVersion string
	Status                           GatewayStatus
}

type RouteStatusWrite struct {
	Resource, Namespace, Name, ResourceVersion string
	Status                                     RouteStatus
}

// listener is a listener as the policy judges it.
type listener struct {
	spec       Listener
	kinds      []string // route kinds it takes
	usable     bool     // accepted, references resolved, port free: it can be served unless it conflicts
	unbound    bool     // served, but this node could not bind it on its last try
	conds      []metav1.Condition
	conflicted bool
	cert       *coreapi.Secret
	attached   int32
	tcpRoute   *TCPRoute // the TCPRoute a TCP listener forwards (the oldest of those attached)
	http       []ServeRoute
}

type gatewayView struct {
	gw        *Gateway
	address   net.IP
	addrErr   string
	holder    *Node
	holderErr string
	listeners []*listener
}

// ComputeGateways decides what node self does for Gateways, given every node and what the API shows. taken are
// the address:protocol:port triples LoadBalancer Services already forward (a listener cannot share one).
func ComputeGateways(self string, nodes []Node, in GatewayInput) GatewayDesired {
	var d GatewayDesired
	sorted := append([]Node(nil), nodes...)
	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Name < sorted[j].Name })
	first := ""
	if len(sorted) > 0 {
		first = sorted[0].Name
	}
	holdersOf := func(ip net.IP) []Node {
		var hs []Node
		for _, n := range sorted {
			if n.Holds(ip) {
				hs = append(hs, n)
			}
		}
		return hs
	}

	ours := map[string]*GatewayClass{}
	classes := append([]*GatewayClass(nil), in.Classes...)
	sort.Slice(classes, func(i, j int) bool { return classes[i].Name < classes[j].Name })
	for _, c := range classes {
		if c.Spec.ControllerName != GatewayControllerName {
			continue
		}
		ours[c.Name] = c
		want := GatewayClassStatus{Conditions: []metav1.Condition{
			condition(c.Status.Conditions, condAccepted, true, "Accepted", "served by the reweave agent on the node holding each Gateway's address", c.Generation, in.Now),
		}}
		if self == first && !sameJSON(want, c.Status) {
			d.Classes = append(d.Classes, ClassStatusWrite{Name: c.Name, ResourceVersion: c.ResourceVersion, Status: want})
		}
	}

	nsLabels := map[string]labels.Set{}
	for _, n := range in.Namespaces {
		nsLabels[n.Name] = labels.Set(n.Labels)
	}
	secrets := map[string]*coreapi.Secret{}
	for _, s := range in.Secrets {
		secrets[s.Namespace+"/"+s.Name] = s
	}
	services := map[string]*coreapi.Service{}
	taken := map[string]string{}
	for _, s := range in.Services {
		services[s.Namespace+"/"+s.Name] = s
		if !eligible(s) {
			continue
		}
		if ip := net.ParseIP(s.Spec.LoadBalancerIP).To4(); ip != nil {
			for _, p := range s.Spec.Ports {
				proto := p.Protocol
				if proto == "" {
					proto = coreapi.ProtocolTCP
				}
				taken[fmt.Sprintf("%s:%s:%d", ip, proto, p.Port)] = key(s)
			}
		}
	}

	// the Gateways of our classes, judged listener by listener
	var views []*gatewayView
	byKey := map[string]*gatewayView{}
	gws := append([]*Gateway(nil), in.Gateways...)
	sort.Slice(gws, func(i, j int) bool { return objKey(&gws[i].ObjectMeta) < objKey(&gws[j].ObjectMeta) })
	for _, gw := range gws {
		if ours[gw.Spec.GatewayClassName] == nil {
			continue
		}
		v := &gatewayView{gw: gw}
		v.address, v.addrErr = gatewayAddress(gw)
		if v.address != nil {
			switch hs := holdersOf(v.address); len(hs) {
			case 0:
				v.holderErr = fmt.Sprintf("no node holds %s", v.address)
			case 1:
				v.holder = &hs[0]
			default:
				names := make([]string, len(hs))
				for i, h := range hs {
					names[i] = h.Name
				}
				v.holderErr = fmt.Sprintf("%s is held by several nodes (%s); serving it from none", v.address, strings.Join(names, ", "))
			}
		}
		v.listeners = judgeListeners(gw, v.address, in, secrets, taken)
		views = append(views, v)
		byKey[objKey(&gw.ObjectMeta)] = v
		if v.addrErr != "" {
			d.Problems = append(d.Problems, fmt.Sprintf("gateway %s: %s", objKey(&gw.ObjectMeta), v.addrErr))
		} else if v.holderErr != "" {
			d.Problems = append(d.Problems, fmt.Sprintf("gateway %s: %s", objKey(&gw.ObjectMeta), v.holderErr))
		}
	}

	// routes, oldest first: that order decides which TCPRoute a TCP listener forwards, and HTTP precedence ties
	type routeRef struct {
		resource, kind string
		meta           *metav1.ObjectMeta
		parents        []ParentReference
		current        RouteStatus
		http           *HTTPRoute
		tcp            *TCPRoute
	}
	var routes []routeRef
	for _, r := range in.HTTPRoutes {
		routes = append(routes, routeRef{resource: HTTPRoutes, kind: kindHTTPRoute, meta: &r.ObjectMeta, parents: r.Spec.ParentRefs, current: r.Status, http: r})
	}
	for _, r := range in.TCPRoutes {
		routes = append(routes, routeRef{resource: TCPRoutes, kind: kindTCPRoute, meta: &r.ObjectMeta, parents: r.Spec.ParentRefs, current: r.Status, tcp: r})
	}
	sort.Slice(routes, func(i, j int) bool {
		a, b := routes[i], routes[j]
		if !a.meta.CreationTimestamp.Equal(&b.meta.CreationTimestamp) {
			return a.meta.CreationTimestamp.Before(&b.meta.CreationTimestamp)
		}
		if a.kind != b.kind {
			return a.kind < b.kind
		}
		return objKey(a.meta) < objKey(b.meta)
	})
	for _, r := range routes {
		var ourParents []RouteParentStatus
		for _, pr := range r.parents {
			if group(pr.Group, GatewayGroup) != GatewayGroup || kind(pr.Kind, kindGateway) != kindGateway {
				continue
			}
			v := byKey[ns(pr.Namespace, r.meta.Namespace)+"/"+pr.Name]
			if v == nil {
				continue // not one of ours (another implementation's, or none's)
			}
			var accepted metav1.Condition
			var resolved metav1.Condition
			if r.http != nil {
				accepted, resolved = attachHTTP(r.http, pr, v, in, nsLabels, services)
			} else {
				accepted, resolved = attachTCP(r.tcp, pr, v, in, nsLabels, services)
			}
			ourParents = append(ourParents, RouteParentStatus{
				ParentRef:      pr,
				ControllerName: GatewayControllerName,
				Conditions: []metav1.Condition{
					condition(currentParent(r.current, pr), condAccepted, accepted.Status == metav1.ConditionTrue, accepted.Reason, accepted.Message, r.meta.Generation, in.Now),
					condition(currentParent(r.current, pr), condResolvedRefs, resolved.Status == metav1.ConditionTrue, resolved.Reason, resolved.Message, r.meta.Generation, in.Now),
				},
			})
		}
		// our entries are rewritten whole; other controllers' entries are kept as they are
		var parents []RouteParentStatus
		hadOurs := false
		for _, p := range r.current.Parents {
			if p.ControllerName == GatewayControllerName {
				hadOurs = true
				continue
			}
			parents = append(parents, p)
		}
		parents = append(parents, ourParents...)
		if len(ourParents) == 0 && !hadOurs {
			continue
		}
		want := RouteStatus{Parents: parents}
		if want.Parents == nil {
			want.Parents = []RouteParentStatus{}
		}
		if self == first && !sameJSON(want, r.current) {
			d.Routes = append(d.Routes, RouteStatusWrite{Resource: r.resource, Namespace: r.meta.Namespace, Name: r.meta.Name, ResourceVersion: r.meta.ResourceVersion, Status: want})
		}
	}

	// what this node serves, and every Gateway's status from its writer
	holding := map[string]bool{}
	for _, v := range views {
		gw := v.gw
		served := v.holder != nil
		if served {
			for _, l := range v.listeners {
				if l.usable && !l.conflicted && l.spec.Protocol == ProtocolTCP && l.tcpRoute != nil {
					holding[v.holder.Name] = true
				}
			}
		}
		if served && v.holder.Name == self {
			for _, l := range v.listeners {
				if !l.usable || l.conflicted {
					continue
				}
				switch l.spec.Protocol {
				case ProtocolTCP:
					if l.tcpRoute == nil {
						continue
					}
					d.Forwards = append(d.Forwards, Forward{
						Namespace: gw.Namespace, Name: gw.Name + "/" + l.spec.Name, Address: v.address,
						Ports: []Port{{Protocol: coreapi.ProtocolTCP, Port: l.spec.Port, Endpoints: tcpEndpoints(l.tcpRoute, in, services)}},
					})
				case ProtocolHTTP, ProtocolHTTPS:
					d.Serve = append(d.Serve, ServeListener{
						Gateway: objKey(&gw.ObjectMeta), Name: l.spec.Name, Address: v.address, Port: l.spec.Port,
						HTTPS: l.spec.Protocol == ProtocolHTTPS, Hostname: str(l.spec.Hostname), Cert: l.cert, Routes: l.http,
					})
				}
			}
		}
		writer := first
		if v.holder != nil {
			writer = v.holder.Name
		}
		if writer != self {
			continue
		}
		want := gatewayStatus(v, in.Now)
		if !sameJSON(want, gw.Status) {
			d.Gateways = append(d.Gateways, GatewayStatusWrite{Namespace: gw.Namespace, Name: gw.Name, ResourceVersion: gw.ResourceVersion, Status: want})
		}
	}
	for n := range holding {
		d.Holding = append(d.Holding, n)
	}
	sort.Strings(d.Holding)
	return d
}

// gatewayAddress is the one IPv4 address a Gateway names, or why it names none this agent can serve.
func gatewayAddress(gw *Gateway) (net.IP, string) {
	if len(gw.Spec.Addresses) != 1 {
		return nil, fmt.Sprintf("spec.addresses must name exactly one IPv4 address a node holds (has %d)", len(gw.Spec.Addresses))
	}
	a := gw.Spec.Addresses[0]
	if t := str(a.Type); t != "" && t != "IPAddress" {
		return nil, fmt.Sprintf("address type %s is not supported (IPAddress only)", t)
	}
	ip := net.ParseIP(a.Value).To4()
	if ip == nil {
		return nil, fmt.Sprintf("%q is not an IPv4 address", a.Value)
	}
	return ip, ""
}

// judgeListeners checks each listener on its own (protocol, route kinds, certificate) and against the others on
// its port (conflicts), and against LoadBalancer Services forwarding the same address and port.
func judgeListeners(gw *Gateway, addr net.IP, in GatewayInput, secrets map[string]*coreapi.Secret, taken map[string]string) []*listener {
	gen := gw.Generation
	var out []*listener
	for _, spec := range gw.Spec.Listeners {
		l := &listener{spec: spec, usable: true}
		cur := currentListener(gw, spec.Name)
		resolved := condition(cur, condResolvedRefs, true, "ResolvedRefs", "", gen, in.Now)
		accepted := condition(cur, condAccepted, true, "Accepted", "", gen, in.Now)
		var supported []string
		switch spec.Protocol {
		case ProtocolHTTP, ProtocolHTTPS:
			supported = []string{kindHTTPRoute}
		case ProtocolTCP:
			supported = []string{kindTCPRoute}
		default:
			l.usable = false
			accepted = condition(cur, condAccepted, false, "UnsupportedProtocol", fmt.Sprintf("protocol %s is not supported (HTTP, HTTPS and TCP are)", spec.Protocol), gen, in.Now)
		}
		l.kinds = supported
		if spec.AllowedRoutes != nil && len(spec.AllowedRoutes.Kinds) > 0 {
			l.kinds = nil
			var bad []string
			for _, k := range spec.AllowedRoutes.Kinds {
				if group(k.Group, GatewayGroup) == GatewayGroup && contains(supported, k.Kind) {
					l.kinds = append(l.kinds, k.Kind)
				} else {
					bad = append(bad, k.Kind)
				}
			}
			if len(bad) > 0 {
				resolved = condition(cur, condResolvedRefs, false, "InvalidRouteKinds", fmt.Sprintf("route kinds %s cannot attach to a %s listener", strings.Join(bad, ", "), spec.Protocol), gen, in.Now)
			}
		}
		if spec.Protocol == ProtocolHTTPS && l.usable {
			cert, reason, msg := listenerCert(gw, spec, in, secrets)
			if cert == nil {
				// without its certificate the listener cannot be served (not programmed); an unsupported TLS mode
				// is not accepted at all, an unresolved certificate is a reference problem
				l.usable = false
				if reason == "UnsupportedValue" {
					accepted = condition(cur, condAccepted, false, reason, msg, gen, in.Now)
				} else {
					resolved = condition(cur, condResolvedRefs, false, reason, msg, gen, in.Now)
				}
			}
			l.cert = cert
		}
		if addr != nil && l.usable {
			if svc, ok := taken[fmt.Sprintf("%s:TCP:%d", addr, spec.Port)]; ok {
				l.usable = false
				accepted = condition(cur, condAccepted, false, "PortUnavailable", fmt.Sprintf("LoadBalancer Service %s already forwards %s:%d", svc, addr, spec.Port), gen, in.Now)
			} else if why, ok := in.Unbound[objKey(&gw.ObjectMeta)+"/"+spec.Name]; ok {
				// still served (each pass tries again), but not reported as working
				l.unbound = true
				accepted = condition(cur, condAccepted, false, "PortUnavailable", "binding "+addr.String()+": "+why, gen, in.Now)
			}
		}
		l.conds = []metav1.Condition{accepted, resolved}
		out = append(out, l)
	}
	// listeners sharing a port must agree on the protocol, and HTTP(S) ones must differ in hostname
	byPort := map[int32][]*listener{}
	for _, l := range out {
		byPort[l.spec.Port] = append(byPort[l.spec.Port], l)
	}
	for _, ls := range byPort {
		protos := map[string]bool{}
		for _, l := range ls {
			protos[l.spec.Protocol] = true
		}
		for _, l := range ls {
			reason := ""
			if len(protos) > 1 {
				reason = "ProtocolConflict"
			} else {
				for _, o := range ls {
					if o != l && (l.spec.Protocol == ProtocolTCP || str(o.spec.Hostname) == str(l.spec.Hostname)) {
						reason = "HostnameConflict"
					}
				}
			}
			if reason != "" {
				l.conflicted = true
			}
			cur := currentListener(gw, l.spec.Name)
			if reason != "" {
				l.conds = append(l.conds, condition(cur, condConflicted, true, reason, fmt.Sprintf("port %d is shared with listeners that cannot be told apart", l.spec.Port), gen, in.Now))
			} else {
				l.conds = append(l.conds, condition(cur, condConflicted, false, "NoConflicts", "", gen, in.Now))
			}
		}
	}
	return out
}

// listenerCert resolves an HTTPS listener's certificate (the first certificateRef: one certificate per listener).
func listenerCert(gw *Gateway, l Listener, in GatewayInput, secrets map[string]*coreapi.Secret) (*coreapi.Secret, string, string) {
	if l.TLS == nil || len(l.TLS.CertificateRefs) == 0 {
		return nil, "InvalidCertificateRef", "an HTTPS listener needs tls.certificateRefs"
	}
	if m := str(l.TLS.Mode); m != "" && m != "Terminate" {
		return nil, "UnsupportedValue", fmt.Sprintf("tls mode %s is not supported on HTTPS (Terminate is)", m)
	}
	ref := l.TLS.CertificateRefs[0]
	if group(ref.Group, "") != "" || kind(ref.Kind, kindSecret) != kindSecret {
		return nil, "InvalidCertificateRef", fmt.Sprintf("certificateRef %s/%s is not a Secret", group(ref.Group, ""), kind(ref.Kind, kindSecret))
	}
	target := ns(ref.Namespace, gw.Namespace)
	if target != gw.Namespace && !granted(in.Grants, GatewayGroup, kindGateway, gw.Namespace, "", kindSecret, target, ref.Name) {
		return nil, "RefNotPermitted", fmt.Sprintf("no ReferenceGrant in %s lets Gateways in %s use Secret %s", target, gw.Namespace, ref.Name)
	}
	if !in.SecretNamespaces[target] {
		return nil, "RefNotPermitted", fmt.Sprintf("this agent reads Secrets only in its gateway namespaces, not in %s", target)
	}
	s := secrets[target+"/"+ref.Name]
	if s == nil {
		return nil, "InvalidCertificateRef", fmt.Sprintf("Secret %s/%s not found", target, ref.Name)
	}
	if _, err := tls.X509KeyPair(s.Data[coreapi.TLSCertKey], s.Data[coreapi.TLSPrivateKeyKey]); err != nil {
		return nil, "InvalidCertificateRef", fmt.Sprintf("Secret %s/%s holds no usable certificate and key: %v", target, ref.Name, err)
	}
	return s, "", ""
}

// listenersFor are the listeners a parentRef names (all, or the one its sectionName and port pick).
func listenersFor(v *gatewayView, pr ParentReference) []*listener {
	var out []*listener
	for _, l := range v.listeners {
		if pr.SectionName != nil && *pr.SectionName != l.spec.Name {
			continue
		}
		if pr.Port != nil && *pr.Port != l.spec.Port {
			continue
		}
		out = append(out, l)
	}
	return out
}

// allows reports whether a listener takes routes of this kind from this namespace.
func allows(l *listener, gw *Gateway, routeKind, routeNS string, nsLabels map[string]labels.Set) bool {
	if !l.usable || l.conflicted || !contains(l.kinds, routeKind) {
		return false
	}
	from := "Same"
	var sel *metav1.LabelSelector
	if l.spec.AllowedRoutes != nil && l.spec.AllowedRoutes.Namespaces != nil {
		from = str(l.spec.AllowedRoutes.Namespaces.From)
		if from == "" {
			from = "Same"
		}
		sel = l.spec.AllowedRoutes.Namespaces.Selector
	}
	switch from {
	case "All":
		return true
	case "Same":
		return routeNS == gw.Namespace
	case "Selector":
		if sel == nil {
			return false
		}
		s, err := metav1.LabelSelectorAsSelector(sel)
		return err == nil && s.Matches(nsLabels[routeNS])
	}
	return false
}

func attachHTTP(r *HTTPRoute, pr ParentReference, v *gatewayView, in GatewayInput, nsLabels map[string]labels.Set, services map[string]*coreapi.Service) (metav1.Condition, metav1.Condition) {
	ls := listenersFor(v, pr)
	if len(ls) == 0 {
		return cond(false, "NoMatchingParent", "no listener matches the parentRef's sectionName and port"), cond(true, "ResolvedRefs", "")
	}
	if msg := unsupportedHTTP(r); msg != "" {
		return cond(false, "UnsupportedValue", msg), cond(true, "ResolvedRefs", "")
	}
	rules, resolved := serveRules(r, in, services)
	allowed, hostOK := false, false
	for _, l := range ls {
		if !allows(l, v.gw, kindHTTPRoute, r.Namespace, nsLabels) {
			continue
		}
		allowed = true
		hosts, ok := narrowHostnames(str(l.spec.Hostname), r.Spec.Hostnames)
		if !ok {
			continue
		}
		hostOK = true
		l.attached++
		l.http = append(l.http, ServeRoute{Key: objKey(&r.ObjectMeta), Created: r.CreationTimestamp.Time, Hostnames: hosts, Rules: rules})
	}
	switch {
	case !allowed:
		return cond(false, "NotAllowedByListeners", "no listener the parentRef names takes HTTPRoutes from this namespace"), resolved
	case !hostOK:
		return cond(false, "NoMatchingListenerHostname", "the route's hostnames intersect no listener's"), resolved
	}
	return cond(true, "Accepted", ""), resolved
}

func attachTCP(r *TCPRoute, pr ParentReference, v *gatewayView, in GatewayInput, nsLabels map[string]labels.Set, services map[string]*coreapi.Service) (metav1.Condition, metav1.Condition) {
	ls := listenersFor(v, pr)
	if len(ls) == 0 {
		return cond(false, "NoMatchingParent", "no listener matches the parentRef's sectionName and port"), cond(true, "ResolvedRefs", "")
	}
	resolved := cond(true, "ResolvedRefs", "")
	for _, rule := range r.Spec.Rules {
		for _, b := range rule.BackendRefs {
			if _, why, reason := resolveBackend(b, kindTCPRoute, r.Namespace, in, services); why != "" {
				resolved = cond(false, reason, why)
			}
		}
	}
	allowed, attached := false, false
	busy := ""
	for _, l := range ls {
		if !allows(l, v.gw, kindTCPRoute, r.Namespace, nsLabels) {
			continue
		}
		allowed = true
		if l.tcpRoute != nil {
			// a TCP listener forwards one route: the oldest attached keeps it
			busy = objKey(&l.tcpRoute.ObjectMeta)
			continue
		}
		l.tcpRoute = r
		l.attached++
		attached = true
	}
	switch {
	case !allowed:
		return cond(false, "NotAllowedByListeners", "no listener the parentRef names takes TCPRoutes from this namespace"), resolved
	case !attached:
		return cond(false, "NotAllowedByListeners", fmt.Sprintf("the listener already forwards TCPRoute %s", busy)), resolved
	}
	return cond(true, "Accepted", ""), resolved
}

// unsupportedHTTP names what in an HTTPRoute this agent does not implement ("" if nothing).
func unsupportedHTTP(r *HTTPRoute) string {
	okFilter := func(fs []HTTPRouteFilter) string {
		for _, f := range fs {
			switch f.Type {
			case filterRequestHeaderModifier, filterResponseHeaderModifier, filterRequestRedirect, filterURLRewrite:
			default:
				return fmt.Sprintf("filter %s is not supported", f.Type)
			}
		}
		return ""
	}
	for _, rule := range r.Spec.Rules {
		for _, m := range rule.Matches {
			if m.Path != nil && m.Path.Type != nil && *m.Path.Type != pathExact && *m.Path.Type != pathPrefix {
				return fmt.Sprintf("path match type %s is not supported", *m.Path.Type)
			}
			for _, h := range m.Headers {
				if t := str(h.Type); t != "" && t != "Exact" {
					return fmt.Sprintf("header match type %s is not supported", t)
				}
			}
			for _, q := range m.QueryParams {
				if t := str(q.Type); t != "" && t != "Exact" {
					return fmt.Sprintf("query parameter match type %s is not supported", t)
				}
			}
		}
		if msg := okFilter(rule.Filters); msg != "" {
			return msg
		}
		for _, b := range rule.BackendRefs {
			if msg := okFilter(b.Filters); msg != "" {
				return msg
			}
		}
	}
	return ""
}

// serveRules resolves an HTTPRoute's rules into what the proxy runs, and whether all its backends resolved.
func serveRules(r *HTTPRoute, in GatewayInput, services map[string]*coreapi.Service) ([]ServeRule, metav1.Condition) {
	resolved := cond(true, "ResolvedRefs", "")
	var rules []ServeRule
	for _, rule := range r.Spec.Rules {
		sr := ServeRule{Filters: rule.Filters}
		for _, m := range rule.Matches {
			if m.Path == nil {
				m.Path = &HTTPPathMatch{}
			}
			if m.Path.Type == nil {
				t := pathPrefix
				m.Path.Type = &t
			}
			if m.Path.Value == nil {
				v := "/"
				m.Path.Value = &v
			}
			sr.Matches = append(sr.Matches, m)
		}
		if len(sr.Matches) == 0 {
			t, v := pathPrefix, "/"
			sr.Matches = []HTTPRouteMatch{{Path: &HTTPPathMatch{Type: &t, Value: &v}}}
		}
		for _, b := range rule.BackendRefs {
			eps, why, reason := resolveBackend(b.BackendRef, kindHTTPRoute, r.Namespace, in, services)
			if why != "" {
				resolved = cond(false, reason, why)
				sr.Broken = true
				continue
			}
			w := int32(1)
			if b.Weight != nil {
				w = *b.Weight
			}
			sr.Backends = append(sr.Backends, ServeBackend{
				Key: fmt.Sprintf("%s/%s:%d", ns(b.Namespace, r.Namespace), b.Name, *b.Port), Weight: w, Endpoints: eps, Filters: b.Filters,
			})
		}
		rules = append(rules, sr)
	}
	return rules, resolved
}

// resolveBackend finds a backendRef's ready endpoints, or why it cannot be used and the reason to report.
func resolveBackend(b BackendRef, routeKind, routeNS string, in GatewayInput, services map[string]*coreapi.Service) ([]Endpoint, string, string) {
	if group(b.Group, "") != "" || kind(b.Kind, kindService) != kindService {
		return nil, fmt.Sprintf("backend %s %s is not a Service", kind(b.Kind, kindService), b.Name), "InvalidKind"
	}
	target := ns(b.Namespace, routeNS)
	if target != routeNS && !granted(in.Grants, GatewayGroup, routeKind, routeNS, "", kindService, target, b.Name) {
		return nil, fmt.Sprintf("no ReferenceGrant in %s lets %ss in %s use Service %s", target, routeKind, routeNS, b.Name), "RefNotPermitted"
	}
	s := services[target+"/"+b.Name]
	if s == nil {
		return nil, fmt.Sprintf("Service %s/%s not found", target, b.Name), "BackendNotFound"
	}
	if b.Port == nil {
		return nil, fmt.Sprintf("backend Service %s/%s needs a port", target, b.Name), "BackendNotFound"
	}
	for _, p := range ports(s, in.Slices) {
		if p.Port == *b.Port && p.Protocol == coreapi.ProtocolTCP {
			return p.Endpoints, "", ""
		}
	}
	return nil, fmt.Sprintf("Service %s/%s has no TCP port %d", target, b.Name, *b.Port), "BackendNotFound"
}

// tcpEndpoints is the union of a TCPRoute's resolved backends' endpoints (the kernel forward does not weigh them).
func tcpEndpoints(r *TCPRoute, in GatewayInput, services map[string]*coreapi.Service) []Endpoint {
	seen := map[string]bool{}
	var out []Endpoint
	for _, rule := range r.Spec.Rules {
		for _, b := range rule.BackendRefs {
			if b.Weight != nil && *b.Weight == 0 {
				continue
			}
			eps, why, _ := resolveBackend(b, kindTCPRoute, r.Namespace, in, services)
			if why != "" {
				continue
			}
			for _, e := range eps {
				if !seen[e.String()] {
					seen[e.String()] = true
					out = append(out, e)
				}
			}
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].String() < out[j].String() })
	return out
}

// granted reports whether a ReferenceGrant in the target namespace lets (fromGroup, fromKind) objects in fromNS
// refer to the (toGroup, toKind) object named name there.
func granted(grants []*ReferenceGrant, fromGroup, fromKind, fromNS, toGroup, toKind, toNS, name string) bool {
	for _, g := range grants {
		if g.Namespace != toNS {
			continue
		}
		from := false
		for _, f := range g.Spec.From {
			if f.Group == fromGroup && f.Kind == fromKind && f.Namespace == fromNS {
				from = true
			}
		}
		if !from {
			continue
		}
		for _, t := range g.Spec.To {
			if t.Group == toGroup && t.Kind == toKind && (t.Name == nil || *t.Name == name) {
				return true
			}
		}
	}
	return false
}

// narrowHostnames: the route's hostnames that a listener with this hostname takes (narrowed to it), and whether
// the route attaches at all. A route without hostnames takes the listener's (an empty result: any host).
func narrowHostnames(listener string, route []string) ([]string, bool) {
	if len(route) == 0 {
		if listener == "" {
			return nil, true
		}
		return []string{listener}, true
	}
	if listener == "" {
		return append([]string(nil), route...), true
	}
	var out []string
	for _, h := range route {
		switch {
		case hostMatches(listener, h):
			out = append(out, h) // the route's is as narrow or narrower
		case hostMatches(h, listener):
			out = append(out, listener) // the listener's is narrower
		}
	}
	return out, len(out) > 0
}

// hostMatches reports whether a hostname pattern (exact, or "*." for any non-empty prefix) covers name, which may
// itself be a wildcard (then the pattern must cover its whole suffix).
func hostMatches(pattern, name string) bool {
	pattern, name = strings.ToLower(pattern), strings.ToLower(name)
	if !strings.HasPrefix(pattern, "*.") {
		return pattern == name
	}
	suffix := pattern[1:] // ".example.com"
	if strings.HasPrefix(name, "*.") {
		return strings.HasSuffix(name[1:], suffix) && len(name[1:]) >= len(suffix)
	}
	return strings.HasSuffix(name, suffix) && len(name) > len(suffix)
}

// gatewayStatus is what a Gateway's status should say.
func gatewayStatus(v *gatewayView, now metav1.Time) GatewayStatus {
	gw := v.gw
	gen := gw.Generation
	var st GatewayStatus
	invalid := 0
	for _, l := range v.listeners {
		if !l.usable || l.conflicted || l.unbound {
			invalid++
		}
	}
	switch {
	case v.addrErr != "":
		st.Conditions = append(st.Conditions, condition(gw.Status.Conditions, condAccepted, false, "UnsupportedAddress", v.addrErr, gen, now))
	case invalid > 0:
		st.Conditions = append(st.Conditions, condition(gw.Status.Conditions, condAccepted, true, "ListenersNotValid", fmt.Sprintf("%d of %d listeners are not valid", invalid, len(v.listeners)), gen, now))
	default:
		st.Conditions = append(st.Conditions, condition(gw.Status.Conditions, condAccepted, true, "Accepted", "", gen, now))
	}
	programmed := v.addrErr == "" && v.holder != nil
	switch {
	case v.addrErr != "":
		st.Conditions = append(st.Conditions, condition(gw.Status.Conditions, condProgrammed, false, "Invalid", v.addrErr, gen, now))
	case v.holder == nil:
		st.Conditions = append(st.Conditions, condition(gw.Status.Conditions, condProgrammed, false, "AddressNotUsable", v.holderErr, gen, now))
	default:
		st.Conditions = append(st.Conditions, condition(gw.Status.Conditions, condProgrammed, true, "Programmed", "served by "+v.holder.Name, gen, now))
		ipType := "IPAddress"
		st.Addresses = []GatewayAddress{{Type: &ipType, Value: v.address.String()}}
	}
	for _, l := range v.listeners {
		cur := currentListener(gw, l.spec.Name)
		ls := ListenerStatus{Name: l.spec.Name, AttachedRoutes: l.attached, SupportedKinds: []RouteGroupKind{}}
		for _, k := range l.kinds {
			g := GatewayGroup
			ls.SupportedKinds = append(ls.SupportedKinds, RouteGroupKind{Group: &g, Kind: k})
		}
		ls.Conditions = append(ls.Conditions, l.conds...)
		switch {
		case !programmed:
			ls.Conditions = append(ls.Conditions, condition(cur, condProgrammed, false, "Pending", "the Gateway is not served", gen, now))
		case !l.usable || l.conflicted:
			ls.Conditions = append(ls.Conditions, condition(cur, condProgrammed, false, "Invalid", "the listener is not valid", gen, now))
		case l.unbound:
			ls.Conditions = append(ls.Conditions, condition(cur, condProgrammed, false, "Invalid", "its port could not be bound", gen, now))
		default:
			ls.Conditions = append(ls.Conditions, condition(cur, condProgrammed, true, "Programmed", "", gen, now))
		}
		st.Listeners = append(st.Listeners, ls)
	}
	return st
}

func currentListener(gw *Gateway, name string) []metav1.Condition {
	for _, l := range gw.Status.Listeners {
		if l.Name == name {
			return l.Conditions
		}
	}
	return nil
}

func currentParent(st RouteStatus, pr ParentReference) []metav1.Condition {
	for _, p := range st.Parents {
		if p.ControllerName == GatewayControllerName && sameJSON(p.ParentRef, pr) {
			return p.Conditions
		}
	}
	return nil
}

// condition builds a condition, keeping the current one's transition time while its status stays the same (so an
// unchanged status reads back equal, and nothing is rewritten).
func condition(current []metav1.Condition, typ string, ok bool, reason, message string, gen int64, now metav1.Time) metav1.Condition {
	status := metav1.ConditionFalse
	if ok {
		status = metav1.ConditionTrue
	}
	c := metav1.Condition{Type: typ, Status: status, Reason: reason, Message: message, ObservedGeneration: gen, LastTransitionTime: now}
	for _, o := range current {
		if o.Type == typ && o.Status == status {
			c.LastTransitionTime = o.LastTransitionTime
		}
	}
	return c
}

// cond is a condition's verdict before it is dated (attach functions decide; the caller dates).
func cond(ok bool, reason, message string) metav1.Condition {
	s := metav1.ConditionFalse
	if ok {
		s = metav1.ConditionTrue
	}
	return metav1.Condition{Status: s, Reason: reason, Message: message}
}

func sameJSON(a, b interface{}) bool {
	x, err1 := json.Marshal(a)
	y, err2 := json.Marshal(b)
	return err1 == nil && err2 == nil && string(x) == string(y)
}

func objKey(m *metav1.ObjectMeta) string { return m.Namespace + "/" + m.Name }

func str(p *string) string {
	if p == nil {
		return ""
	}
	return *p
}

func group(p *string, def string) string {
	if p == nil {
		return def
	}
	return *p
}

func kind(p *string, def string) string {
	if p == nil || *p == "" {
		return def
	}
	return *p
}

func ns(p *string, def string) string {
	if p == nil || *p == "" {
		return def
	}
	return *p
}

func contains(xs []string, x string) bool {
	for _, y := range xs {
		if y == x {
			return true
		}
	}
	return false
}

// MergeGateways folds what a node does for Gateways into what it does for LoadBalancer Services: one set of
// forwards, one set of holders whose replies are steered back (marks over both), and the ports it serves itself.
func MergeGateways(d Desired, g GatewayDesired, self string, nodes []Node) Desired {
	d.Forwards = append(d.Forwards, g.Forwards...)
	holding := map[string]bool{}
	for _, h := range d.Holders {
		holding[h.Node.Name] = true
	}
	for _, n := range g.Holding {
		holding[n] = true
	}
	sorted := append([]Node(nil), nodes...)
	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Name < sorted[j].Name })
	var others []Node
	for _, n := range sorted {
		if !holding[n.Name] || n.Name == self {
			continue
		}
		if n.WeaveIP == nil {
			d.Problems = append(d.Problems, fmt.Sprintf("node %s holds an address but has not published its weave bridge; replies to its forwards cannot reach it", n.Name))
			continue
		}
		others = append(others, n)
	}
	d.Holders = assignMarks(others)
	seen := map[string]bool{}
	for _, l := range g.Serve {
		k := fmt.Sprintf("%s:%d", l.Address, l.Port)
		if seen[k] {
			continue
		}
		seen[k] = true
		d.Accept = append(d.Accept, Accept{Address: l.Address, Port: l.Port, Comment: "gateway " + l.Gateway + " " + l.Name})
	}
	d.Problems = append(d.Problems, g.Problems...)
	return d
}