/*
Copyright 2023 The Karmada Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package metricsadapter

import (
	"context"
	"time"

	corev1 "k8s.io/api/core/v1"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/util/wait"
	"k8s.io/client-go/informers"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/cache"
	"k8s.io/client-go/util/workqueue"
	"k8s.io/klog/v2"

	clusterV1alpha1 "github.com/karmada-io/karmada/pkg/apis/cluster/v1alpha1"
	informerfactory "github.com/karmada-io/karmada/pkg/generated/informers/externalversions"
	clusterlister "github.com/karmada-io/karmada/pkg/generated/listers/cluster/v1alpha1"
	"github.com/karmada-io/karmada/pkg/metricsadapter/multiclient"
	"github.com/karmada-io/karmada/pkg/metricsadapter/provider"
	"github.com/karmada-io/karmada/pkg/util"
	"github.com/karmada-io/karmada/pkg/util/fedinformer/genericmanager"
	"github.com/karmada-io/karmada/pkg/util/gclient"
)

var (
	// NamespacesGVR is the gvr of namespaces
	NamespacesGVR = corev1.SchemeGroupVersion.WithResource("namespaces")
)

// MetricsController is a controller for metrics, control the lifecycle of multi-clusters informer
type MetricsController struct {
	InformerFactory       informerfactory.SharedInformerFactory
	ClusterLister         clusterlister.ClusterLister
	InformerManager       genericmanager.MultiClusterInformerManager
	MultiClusterDiscovery multiclient.MultiClusterDiscoveryInterface
	queue                 workqueue.RateLimitingInterface
	restConfig            *rest.Config
}

// NewMetricsController creates a new metrics controller
func NewMetricsController(restConfig *rest.Config, factory informerfactory.SharedInformerFactory, kubeFactory informers.SharedInformerFactory) *MetricsController {
	clusterLister := factory.Cluster().V1alpha1().Clusters().Lister()
	controller := &MetricsController{
		InformerFactory:       factory,
		ClusterLister:         clusterLister,
		MultiClusterDiscovery: multiclient.NewMultiClusterDiscoveryClient(clusterLister, kubeFactory),
		InformerManager:       genericmanager.GetInstance(),
		restConfig:            restConfig,
		queue:                 workqueue.NewNamedRateLimitingQueue(workqueue.DefaultControllerRateLimiter(), "metrics-adapter"),
	}
	controller.addEventHandler()

	return controller
}

// addEventHandler adds event handler for cluster
func (m *MetricsController) addEventHandler() {
	clusterInformer := m.InformerFactory.Cluster().V1alpha1().Clusters().Informer()
	_, err := clusterInformer.AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc: m.addCluster,
		// Update event and delete event will be handled by the same handler
		UpdateFunc: m.updateCluster,
	})
	if err != nil {
		klog.Errorf("Failed to add cluster event handler for cluster: %v", err)
	}
}

// addCluster adds cluster to queue
func (m *MetricsController) addCluster(obj interface{}) {
	cluster := obj.(*clusterV1alpha1.Cluster)
	m.queue.Add(cluster.GetName())
}

// updateCluster updates cluster in queue
func (m *MetricsController) updateCluster(oldObj, curObj interface{}) {
	curCluster := curObj.(*clusterV1alpha1.Cluster)
	oldCluster := oldObj.(*clusterV1alpha1.Cluster)
	if curCluster.ResourceVersion == oldCluster.ResourceVersion {
		// no change, do nothing.
		return
	}

	if oldCluster.DeletionTimestamp.IsZero() != curCluster.DeletionTimestamp.IsZero() {
		// cluster is being deleted.
		m.queue.Add(curCluster.GetName())
	}

	if util.ClusterAccessCredentialChanged(curCluster.Spec, oldCluster.Spec) ||
		util.IsClusterReady(&curCluster.Status) != util.IsClusterReady(&oldCluster.Status) {
		// Cluster.Spec or Cluster health state is changed, rebuild informer.
		m.InformerManager.Stop(curCluster.GetName())
		m.queue.Add(curCluster.GetName())
	}
}

// startController starts controller
func (m *MetricsController) startController(stopCh <-chan struct{}) {
	m.InformerFactory.WaitForCacheSync(stopCh)

	go wait.Until(m.worker, time.Second, stopCh)

	go func() {
		<-stopCh
		genericmanager.StopInstance()
		klog.Infof("Shutting down karmada-metrics-adapter")
	}()
}

// worker is a worker for handle the data in queue
func (m *MetricsController) worker() {
	for m.handleClusters() {
	}
}

// handleClusters handles clusters changes
func (m *MetricsController) handleClusters() bool {
	key, shutdown := m.queue.Get()
	if shutdown {
		klog.Errorf("Fail to pop item from queue")
		return false
	}
	defer m.queue.Done(key)

	clusterName := key.(string)
	cls, err := m.ClusterLister.Get(clusterName)
	if err != nil {
		if apierrors.IsNotFound(err) {
			klog.Infof("try to stop cluster informer %s", clusterName)
			m.InformerManager.Stop(clusterName)
			m.MultiClusterDiscovery.Remove(clusterName)
			return true
		}
		return false
	}

	if !cls.DeletionTimestamp.IsZero() {
		klog.Infof("try to stop cluster informer %s", clusterName)
		m.InformerManager.Stop(clusterName)
		m.MultiClusterDiscovery.Remove(clusterName)
		return true
	}

	if !util.IsClusterReady(&cls.Status) {
		klog.Warningf("cluster %s is notReady try to stop this cluster informer", clusterName)
		m.InformerManager.Stop(clusterName)
		m.MultiClusterDiscovery.Remove(clusterName)
		return false
	}

	if !m.InformerManager.IsManagerExist(clusterName) {
		klog.Info("Try to build informer manager for cluster ", clusterName)
		controlPlaneClient := gclient.NewForConfigOrDie(m.restConfig)
		clusterDynamicClient, err := util.NewClusterDynamicClientSet(clusterName, controlPlaneClient)
		if err != nil {
			return false
		}
		// Note: For pull mode clusters, users need to provide a method to connect the network between the Karmada control plane and the member cluster,
		// so that `karmada-metrics-adapter` can access this member cluster.
		if _, err = clusterDynamicClient.DynamicClientSet.Resource(NamespacesGVR).Get(context.Background(), "kube-system", metav1.GetOptions{}); err != nil {
			klog.Warningf("unable to access cluster %s, Error: %+v", clusterName, err)
			return true
		}
		_ = m.InformerManager.ForCluster(clusterName, clusterDynamicClient.DynamicClientSet, 0)
	}
	err = m.MultiClusterDiscovery.Set(clusterName)
	if err != nil {
		klog.Warningf("failed to build discoveryClient for cluster(%s), Error: %+v", clusterName, err)
		return true
	}
	sci := m.InformerManager.GetSingleClusterManager(clusterName)
	// Just trigger the informer to work
	_ = sci.Lister(provider.PodsGVR)
	_ = sci.Lister(provider.NodesGVR)

	sci.Start()
	_ = sci.WaitForCacheSync()

	return true
}