package netpol

import (
	"context"
	"fmt"
	"log/slog"
	"net"
	"sync"
	"time"

	corev1 "k8s.io/api/core/v1"
	netv1 "k8s.io/api/networking/v1"
	"k8s.io/client-go/informers"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/cache"
)

// World aggregates the cluster-wide caches the reconciler queries on
// every pass: NetworkPolicies, Namespaces, and all Pods (for peer
// resolution). Each field is safe for concurrent reads.
type World struct {
	logger *slog.Logger

	mu       sync.RWMutex
	policies map[string]netv1.NetworkPolicy // key = ns/name
	namespaces map[string]Namespace
	peerPods   map[string]PeerPod // key = ns/name

	onChange []func()
}

// NewWorld returns an empty World. Callers should call Start to populate
// it; before Start, the snapshot accessors return empty slices.
func NewWorld(logger *slog.Logger) *World {
	return &World{
		logger:     logger,
		policies:   map[string]netv1.NetworkPolicy{},
		namespaces: map[string]Namespace{},
		peerPods:   map[string]PeerPod{},
	}
}

// OnChange registers a callback fired (synchronously, inside the informer
// event handler) whenever any watched object changes. The reconciler
// uses this to debounce policy reloads.
func (w *World) OnChange(f func()) {
	w.mu.Lock()
	defer w.mu.Unlock()
	w.onChange = append(w.onChange, f)
}

func (w *World) fireChange() {
	w.mu.RLock()
	cbs := append([]func(){}, w.onChange...)
	w.mu.RUnlock()
	for _, f := range cbs {
		f()
	}
}

// Start launches three informers (NetworkPolicy, Namespace, Pod) against
// the cluster API. It blocks until each cache reports synced. The caller
// is responsible for cancelling ctx on shutdown.
func (w *World) Start(ctx context.Context, cfg *rest.Config) error {
	cs, err := kubernetes.NewForConfig(cfg)
	if err != nil {
		return fmt.Errorf("kubernetes client: %w", err)
	}
	factory := informers.NewSharedInformerFactory(cs, 10*time.Minute)

	npInformer := factory.Networking().V1().NetworkPolicies().Informer()
	nsInformer := factory.Core().V1().Namespaces().Informer()
	podInformer := factory.Core().V1().Pods().Informer()

	if _, err := npInformer.AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc:    func(obj interface{}) { w.onPolicy(obj, false) },
		UpdateFunc: func(_, n interface{}) { w.onPolicy(n, false) },
		DeleteFunc: func(obj interface{}) { w.onPolicy(obj, true) },
	}); err != nil {
		return fmt.Errorf("add netpol handler: %w", err)
	}
	if _, err := nsInformer.AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc:    func(obj interface{}) { w.onNamespace(obj, false) },
		UpdateFunc: func(_, n interface{}) { w.onNamespace(n, false) },
		DeleteFunc: func(obj interface{}) { w.onNamespace(obj, true) },
	}); err != nil {
		return fmt.Errorf("add ns handler: %w", err)
	}
	if _, err := podInformer.AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc:    func(obj interface{}) { w.onPod(obj, false) },
		UpdateFunc: func(_, n interface{}) { w.onPod(n, false) },
		DeleteFunc: func(obj interface{}) { w.onPod(obj, true) },
	}); err != nil {
		return fmt.Errorf("add pod handler: %w", err)
	}

	w.logger.Info("netpol informers starting")
	factory.Start(ctx.Done())
	if !cache.WaitForCacheSync(ctx.Done(),
		npInformer.HasSynced, nsInformer.HasSynced, podInformer.HasSynced) {
		return fmt.Errorf("netpol informer caches failed to sync")
	}
	w.logger.Info("netpol informers synced",
		"netpols", len(w.snapshotPolicies()),
		"namespaces", len(w.snapshotNamespaces()),
		"peer_pods", len(w.snapshotPeerPods()))
	return nil
}

// unwrapDFSU lifts a DeletedFinalStateUnknown wrapper if present.
func unwrapDFSU(obj interface{}) interface{} {
	if d, ok := obj.(cache.DeletedFinalStateUnknown); ok {
		return d.Obj
	}
	return obj
}

func (w *World) onPolicy(obj interface{}, deleted bool) {
	p, ok := unwrapDFSU(obj).(*netv1.NetworkPolicy)
	if !ok || p == nil {
		return
	}
	key := p.Namespace + "/" + p.Name
	w.mu.Lock()
	if deleted {
		delete(w.policies, key)
	} else {
		w.policies[key] = *p
	}
	w.mu.Unlock()
	w.fireChange()
}

func (w *World) onNamespace(obj interface{}, deleted bool) {
	ns, ok := unwrapDFSU(obj).(*corev1.Namespace)
	if !ok || ns == nil {
		return
	}
	w.mu.Lock()
	if deleted {
		delete(w.namespaces, ns.Name)
	} else {
		w.namespaces[ns.Name] = Namespace{Name: ns.Name, Labels: ns.Labels}
	}
	w.mu.Unlock()
	w.fireChange()
}

func (w *World) onPod(obj interface{}, deleted bool) {
	pod, ok := unwrapDFSU(obj).(*corev1.Pod)
	if !ok || pod == nil {
		return
	}
	key := pod.Namespace + "/" + pod.Name
	w.mu.Lock()
	if deleted {
		delete(w.peerPods, key)
	} else {
		w.peerPods[key] = PeerPod{
			Namespace: pod.Namespace,
			Name:      pod.Name,
			Labels:    pod.Labels,
			IPs:       podIPs(pod),
		}
	}
	w.mu.Unlock()
	w.fireChange()
}

// podIPs extracts every PodIP from the status. Pods without status (still
// scheduling) yield nil — safe for the translator.
func podIPs(p *corev1.Pod) []net.IP {
	out := make([]net.IP, 0, len(p.Status.PodIPs))
	for _, addr := range p.Status.PodIPs {
		ip := net.ParseIP(addr.IP)
		if ip == nil {
			continue
		}
		out = append(out, ip)
	}
	if len(out) == 0 && p.Status.PodIP != "" {
		// Older clusters may populate PodIP but not PodIPs; tolerate both.
		if ip := net.ParseIP(p.Status.PodIP); ip != nil {
			out = append(out, ip)
		}
	}
	return out
}

// snapshotPolicies returns a defensive copy of the policy map's values.
func (w *World) snapshotPolicies() []netv1.NetworkPolicy {
	w.mu.RLock()
	defer w.mu.RUnlock()
	out := make([]netv1.NetworkPolicy, 0, len(w.policies))
	for _, p := range w.policies {
		out = append(out, p)
	}
	return out
}

// snapshotNamespaces returns a defensive copy of the namespace map.
func (w *World) snapshotNamespaces() []Namespace {
	w.mu.RLock()
	defer w.mu.RUnlock()
	out := make([]Namespace, 0, len(w.namespaces))
	for _, n := range w.namespaces {
		out = append(out, n)
	}
	return out
}

// snapshotPeerPods returns a defensive copy of the peer-pod map.
func (w *World) snapshotPeerPods() []PeerPod {
	w.mu.RLock()
	defer w.mu.RUnlock()
	out := make([]PeerPod, 0, len(w.peerPods))
	for _, p := range w.peerPods {
		out = append(out, p)
	}
	return out
}