// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you 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 kubernetes

import (
	"fmt"
	"io/ioutil"
	"os"
	"strings"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/tools/clientcmd"

	"github.com/elastic/beats/v7/libbeat/logp"
)

const defaultNode = "localhost"

func getKubeConfigEnvironmentVariable() string {
	envKubeConfig := os.Getenv("KUBECONFIG")
	if _, err := os.Stat(envKubeConfig); !os.IsNotExist(err) {
		return envKubeConfig
	}
	return ""
}

// GetKubernetesClient returns a kubernetes client. If inCluster is true, it returns an
// in cluster configuration based on the secrets mounted in the Pod. If kubeConfig is passed,
// it parses the config file to get the config required to build a client.
func GetKubernetesClient(kubeconfig string) (kubernetes.Interface, error) {
	if kubeconfig == "" {
		kubeconfig = getKubeConfigEnvironmentVariable()
	}

	cfg, err := clientcmd.BuildConfigFromFlags("", kubeconfig)
	if err != nil {
		return nil, fmt.Errorf("unable to build kube config due to error: %+v", err)
	}

	client, err := kubernetes.NewForConfig(cfg)
	if err != nil {
		return nil, fmt.Errorf("unable to build kubernetes clientset: %+v", err)
	}

	return client, nil
}

// IsInCluster takes a kubeconfig file path as input and deduces if Beats is running in cluster or not,
// taking into consideration the existence of KUBECONFIG variable
func IsInCluster(kubeconfig string) bool {
	if kubeconfig != "" || getKubeConfigEnvironmentVariable() != "" {
		return false
	}
	return true
}

// DiscoverKubernetesNode figures out the Kubernetes node to use.
// If host is provided in the config use it directly.
// If beat is deployed in k8s cluster, use hostname of pod which is pod name to query pod meta for node name.
// If beat is deployed outside k8s cluster, use machine-id to match against k8s nodes for node name.
func DiscoverKubernetesNode(log *logp.Logger, host string, inCluster bool, client kubernetes.Interface) (node string) {
	if host != "" {
		log.Infof("kubernetes: Using node %s provided in the config", host)
		return host
	}

	if inCluster {
		ns, err := inClusterNamespace()
		if err != nil {
			log.Errorf("kubernetes: Couldn't get namespace when beat is in cluster with error: %+v", err.Error())
			return defaultNode
		}
		podName, err := os.Hostname()
		if err != nil {
			log.Errorf("kubernetes: Couldn't get hostname as beat pod name in cluster with error: %+v", err.Error())
			return defaultNode
		}
		log.Infof("kubernetes: Using pod name %s and namespace %s to discover kubernetes node", podName, ns)
		pod, err := client.CoreV1().Pods(ns).Get(podName, metav1.GetOptions{})
		if err != nil {
			log.Errorf("kubernetes: Querying for pod failed with error: %+v", err)
			return defaultNode
		}
		log.Info("kubernetes: Using node %s discovered by in cluster pod node query", pod.Spec.NodeName)
		return pod.Spec.NodeName
	}

	mid := machineID()
	if mid == "" {
		log.Error("kubernetes: Couldn't collect info from any of the files in /etc/machine-id /var/lib/dbus/machine-id")
		return defaultNode
	}

	nodes, err := client.CoreV1().Nodes().List(metav1.ListOptions{})
	if err != nil {
		log.Errorf("kubernetes: Querying for nodes failed with error: %+v", err)
		return defaultNode
	}
	for _, n := range nodes.Items {
		if n.Status.NodeInfo.MachineID == mid {
			name := n.GetObjectMeta().GetName()
			log.Infof("kubernetes: Using node %s discovered by machine-id matching", name)
			return name
		}
	}

	log.Warn("kubernetes: Couldn't discover node, using localhost as default")
	return defaultNode
}

// machineID borrowed from cadvisor.
func machineID() string {
	for _, file := range []string{
		"/etc/machine-id",
		"/var/lib/dbus/machine-id",
	} {
		id, err := ioutil.ReadFile(file)
		if err == nil {
			return strings.TrimSpace(string(id))
		}
	}
	return ""
}

// inClusterNamespace gets namespace from serviceaccount when beat is in cluster.
// code borrowed from client-go with some changes.
func inClusterNamespace() (string, error) {
	// get namespace associated with the service account token, if available
	data, err := ioutil.ReadFile("/var/run/secrets/kubernetes.io/serviceaccount/namespace")
	if err != nil {
		return "", err
	}
	return strings.TrimSpace(string(data)), nil
}
