/*
Copyright 2016 The Kubernetes 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 app

import (
	"fmt"
	"io/ioutil"
	_ "net/http/pprof"
	"os"
	"path/filepath"

	"github.com/golang/glog"

	"k8s.io/apimachinery/pkg/types"
	restclient "k8s.io/client-go/rest"
	"k8s.io/client-go/tools/clientcmd"
	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"
	certutil "k8s.io/client-go/util/cert"
	certificates "k8s.io/kubernetes/pkg/client/clientset_generated/clientset/typed/certificates/v1beta1"
	"k8s.io/kubernetes/pkg/kubelet/util/csr"
)

const (
	defaultKubeletClientCertificateFile = "kubelet-client.crt"
	defaultKubeletClientKeyFile         = "kubelet-client.key"
)

// bootstrapClientCert requests a client cert for kubelet if the kubeconfigPath file does not exist.
// The kubeconfig at bootstrapPath is used to request a client certificate from the API server.
// On success, a kubeconfig file referencing the generated key and obtained certificate is written to kubeconfigPath.
// The certificate and key file are stored in certDir.
func bootstrapClientCert(kubeconfigPath string, bootstrapPath string, certDir string, nodeName types.NodeName) error {
	// Short-circuit if the kubeconfig file already exists.
	// TODO: inspect the kubeconfig, ensure a rest client can be built from it, verify client cert expiration, etc.
	_, err := os.Stat(kubeconfigPath)
	if err == nil {
		glog.V(2).Infof("Kubeconfig %s exists, skipping bootstrap", kubeconfigPath)
		return nil
	}
	if !os.IsNotExist(err) {
		glog.Errorf("Error reading kubeconfig %s, skipping bootstrap: %v", kubeconfigPath, err)
		return err
	}

	glog.V(2).Info("Using bootstrap kubeconfig to generate TLS client cert, key and kubeconfig file")

	bootstrapClientConfig, err := loadRESTClientConfig(bootstrapPath)
	if err != nil {
		return fmt.Errorf("unable to load bootstrap kubeconfig: %v", err)
	}
	bootstrapClient, err := certificates.NewForConfig(bootstrapClientConfig)
	if err != nil {
		return fmt.Errorf("unable to create certificates signing request client: %v", err)
	}

	success := false

	// Get the private key.
	keyPath, err := filepath.Abs(filepath.Join(certDir, defaultKubeletClientKeyFile))
	if err != nil {
		return fmt.Errorf("unable to build bootstrap key path: %v", err)
	}
	keyData, generatedKeyFile, err := loadOrGenerateKeyFile(keyPath)
	if err != nil {
		return err
	}
	if generatedKeyFile {
		defer func() {
			if !success {
				if err := os.Remove(keyPath); err != nil {
					glog.Warningf("Cannot clean up the key file %q: %v", keyPath, err)
				}
			}
		}()
	}

	// Get the cert.
	certPath, err := filepath.Abs(filepath.Join(certDir, defaultKubeletClientCertificateFile))
	if err != nil {
		return fmt.Errorf("unable to build bootstrap client cert path: %v", err)
	}
	certData, err := csr.RequestNodeCertificate(bootstrapClient.CertificateSigningRequests(), keyData, nodeName)
	if err != nil {
		return err
	}
	if err := certutil.WriteCert(certPath, certData); err != nil {
		return err
	}
	defer func() {
		if !success {
			if err := os.Remove(certPath); err != nil {
				glog.Warningf("Cannot clean up the cert file %q: %v", certPath, err)
			}
		}
	}()

	// Get the CA data from the bootstrap client config.
	caFile, caData := bootstrapClientConfig.CAFile, []byte{}
	if len(caFile) == 0 {
		caData = bootstrapClientConfig.CAData
	}

	// Build resulting kubeconfig.
	kubeconfigData := clientcmdapi.Config{
		// Define a cluster stanza based on the bootstrap kubeconfig.
		Clusters: map[string]*clientcmdapi.Cluster{"default-cluster": {
			Server:                   bootstrapClientConfig.Host,
			InsecureSkipTLSVerify:    bootstrapClientConfig.Insecure,
			CertificateAuthority:     caFile,
			CertificateAuthorityData: caData,
		}},
		// Define auth based on the obtained client cert.
		AuthInfos: map[string]*clientcmdapi.AuthInfo{"default-auth": {
			ClientCertificate: certPath,
			ClientKey:         keyPath,
		}},
		// Define a context that connects the auth info and cluster, and set it as the default
		Contexts: map[string]*clientcmdapi.Context{"default-context": {
			Cluster:   "default-cluster",
			AuthInfo:  "default-auth",
			Namespace: "default",
		}},
		CurrentContext: "default-context",
	}

	// Marshal to disk
	if err := clientcmd.WriteToFile(kubeconfigData, kubeconfigPath); err != nil {
		return err
	}

	success = true
	return nil
}

func loadRESTClientConfig(kubeconfig string) (*restclient.Config, error) {
	// Load structured kubeconfig data from the given path.
	loader := &clientcmd.ClientConfigLoadingRules{ExplicitPath: kubeconfig}
	loadedConfig, err := loader.Load()
	if err != nil {
		return nil, err
	}
	// Flatten the loaded data to a particular restclient.Config based on the current context.
	return clientcmd.NewNonInteractiveClientConfig(
		*loadedConfig,
		loadedConfig.CurrentContext,
		&clientcmd.ConfigOverrides{},
		loader,
	).ClientConfig()
}

func loadOrGenerateKeyFile(keyPath string) (data []byte, wasGenerated bool, err error) {
	loadedData, err := ioutil.ReadFile(keyPath)
	if err == nil {
		return loadedData, false, err
	}
	if !os.IsNotExist(err) {
		return nil, false, fmt.Errorf("error loading key from %s: %v", keyPath, err)
	}

	generatedData, err := certutil.MakeEllipticPrivateKeyPEM()
	if err != nil {
		return nil, false, fmt.Errorf("error generating key: %v", err)
	}
	if err := certutil.WriteKey(keyPath, generatedData); err != nil {
		return nil, false, fmt.Errorf("error writing key to %s: %v", keyPath, err)
	}
	return generatedData, true, nil
}