package agent

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"sync/atomic"
	"time"

	flockv1alpha1 "code.fritzlab.net/fritzlab/flock/pkg/api/v1alpha1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/client-go/dynamic"
	"k8s.io/client-go/dynamic/dynamicinformer"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/cache"
)

// nodeConfigGVR is the resource coordinate watched by the agent.
var nodeConfigGVR = schema.GroupVersionResource{
	Group:    flockv1alpha1.GroupName,
	Version:  flockv1alpha1.Version,
	Resource: "nodeconfigs",
}

// NodeConfigCache holds the latest observed NodeConfig for this node, or
// nil when none exists. Read with Load(); safe for concurrent use.
type NodeConfigCache struct {
	current atomic.Pointer[flockv1alpha1.NodeConfig]
}

// Load returns the currently-cached NodeConfig (nil if none).
func (c *NodeConfigCache) Load() *flockv1alpha1.NodeConfig {
	return c.current.Load()
}

func (c *NodeConfigCache) store(nc *flockv1alpha1.NodeConfig) {
	c.current.Store(nc)
}

// StartNodeConfigInformer runs a dynamic informer against the cluster that
// watches `nodeconfigs.flock.fritzlab.net` and caches the entry for `node`.
// It blocks until ctx is cancelled. All other NodeConfigs are ignored —
// each agent only cares about its own.
//
// The caller (agent.Server) passes in cfg so tests / out-of-cluster runs can
// supply a fake; NewServer resolves in-cluster config via rest.InClusterConfig.
func StartNodeConfigInformer(
	ctx context.Context,
	cfg *rest.Config,
	node string,
	cache_ *NodeConfigCache,
	logger *slog.Logger,
) error {
	dyn, err := dynamic.NewForConfig(cfg)
	if err != nil {
		return fmt.Errorf("dynamic client: %w", err)
	}

	factory := dynamicinformer.NewDynamicSharedInformerFactory(dyn, 10*time.Minute)
	inf := factory.ForResource(nodeConfigGVR).Informer()

	handle := func(event string, obj interface{}) {
		u, ok := obj.(*unstructured.Unstructured)
		if !ok {
			// Informer hands us DeletedFinalStateUnknown on replays; skip.
			return
		}
		if u.GetName() != node {
			return
		}
		switch event {
		case "delete":
			logger.Info("NodeConfig removed", "node", node)
			cache_.store(nil)
			return
		}
		nc, err := decode(u)
		if err != nil {
			logger.Warn("NodeConfig decode failed",
				"node", node, "event", event, "err", err)
			return
		}
		cache_.store(nc)
		logger.Info("NodeConfig observed",
			"event", event,
			"node", nc.Name,
			"asn", nc.Spec.BGP.ASN,
			"cidr6", nc.Spec.CIDR6,
			"cidr4", nc.Spec.CIDR4,
			"peers", len(nc.Spec.BGP.Peers))
	}

	_, err = inf.AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc:    func(obj interface{}) { handle("add", obj) },
		UpdateFunc: func(_, obj interface{}) { handle("update", obj) },
		DeleteFunc: func(obj interface{}) {
			// Unwrap DeletedFinalStateUnknown.
			if d, ok := obj.(cache.DeletedFinalStateUnknown); ok {
				obj = d.Obj
			}
			handle("delete", obj)
		},
	})
	if err != nil {
		return fmt.Errorf("add event handler: %w", err)
	}

	logger.Info("NodeConfig informer starting", "node", node, "gvr", nodeConfigGVR.String())
	factory.Start(ctx.Done())
	if synced := factory.WaitForCacheSync(ctx.Done()); !synced[nodeConfigGVR] {
		return fmt.Errorf("informer cache failed to sync for %s", nodeConfigGVR)
	}
	logger.Info("NodeConfig informer synced", "node", node)

	<-ctx.Done()
	return nil
}

// decode turns an Unstructured NodeConfig into the typed form. We do this by
// round-tripping through JSON, which is fine for the low-frequency updates
// here and keeps pkg/api/v1alpha1 free of scheme-registration boilerplate.
func decode(u *unstructured.Unstructured) (*flockv1alpha1.NodeConfig, error) {
	b, err := json.Marshal(u.Object)
	if err != nil {
		return nil, err
	}
	var nc flockv1alpha1.NodeConfig
	if err := json.Unmarshal(b, &nc); err != nil {
		return nil, err
	}
	// metav1.ObjectMeta lives on u; copy just the name for clarity.
	nc.Name = u.GetName()
	nc.TypeMeta = metav1.TypeMeta{Kind: u.GetKind(), APIVersion: u.GetAPIVersion()}
	return &nc, nil
}