/*
Copyright 2018 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 controller

import (
	"fmt"
	"net/http"
	"sync"
	"time"

	"golang.org/x/oauth2"

	v1authenticationapi "k8s.io/api/authentication/v1"
	"k8s.io/apimachinery/pkg/util/clock"
	"k8s.io/apimachinery/pkg/util/wait"
	apiserverserviceaccount "k8s.io/apiserver/pkg/authentication/serviceaccount"
	clientset "k8s.io/client-go/kubernetes"
	v1core "k8s.io/client-go/kubernetes/typed/core/v1"
	restclient "k8s.io/client-go/rest"
	"k8s.io/client-go/transport"
	"k8s.io/klog"
	utilpointer "k8s.io/utils/pointer"
)

var (
	// defaultExpirationSeconds defines the duration of a TokenRequest in seconds.
	defaultExpirationSeconds = int64(3600)
	// defaultLeewayPercent defines the percentage of expiration left before the client trigger a token rotation.
	// range[0, 100]
	defaultLeewayPercent = 20
)

type DynamicControllerClientBuilder struct {
	// ClientConfig is a skeleton config to clone and use as the basis for each controller client
	ClientConfig *restclient.Config

	// CoreClient is used to provision service accounts if needed and watch for their associated tokens
	// to construct a controller client
	CoreClient v1core.CoreV1Interface

	// Namespace is the namespace used to host the service accounts that will back the
	// controllers.  It must be highly privileged namespace which normal users cannot inspect.
	Namespace string

	// roundTripperFuncMap is a cache stores the corresponding roundtripper func for each
	// service account
	roundTripperFuncMap map[string]func(http.RoundTripper) http.RoundTripper

	// expirationSeconds defines the token expiration seconds
	expirationSeconds int64

	// leewayPercent defines the percentage of expiration left before the client trigger a token rotation.
	leewayPercent int

	mutex sync.Mutex

	clock clock.Clock
}

func NewDynamicClientBuilder(clientConfig *restclient.Config, coreClient v1core.CoreV1Interface, ns string) ControllerClientBuilder {
	builder := &DynamicControllerClientBuilder{
		ClientConfig:        clientConfig,
		CoreClient:          coreClient,
		Namespace:           ns,
		roundTripperFuncMap: map[string]func(http.RoundTripper) http.RoundTripper{},
		expirationSeconds:   defaultExpirationSeconds,
		leewayPercent:       defaultLeewayPercent,
		clock:               clock.RealClock{},
	}
	return builder
}

// this function only for test purpose, don't call it
func NewTestDynamicClientBuilder(clientConfig *restclient.Config, coreClient v1core.CoreV1Interface, ns string, expirationSeconds int64, leewayPercent int) ControllerClientBuilder {
	builder := &DynamicControllerClientBuilder{
		ClientConfig:        clientConfig,
		CoreClient:          coreClient,
		Namespace:           ns,
		roundTripperFuncMap: map[string]func(http.RoundTripper) http.RoundTripper{},
		expirationSeconds:   expirationSeconds,
		leewayPercent:       leewayPercent,
		clock:               clock.RealClock{},
	}
	return builder
}

func (t *DynamicControllerClientBuilder) Config(saName string) (*restclient.Config, error) {
	_, err := getOrCreateServiceAccount(t.CoreClient, t.Namespace, saName)
	if err != nil {
		return nil, err
	}

	configCopy := constructClient(t.Namespace, saName, t.ClientConfig)

	t.mutex.Lock()
	defer t.mutex.Unlock()

	rt, ok := t.roundTripperFuncMap[saName]
	if ok {
		configCopy.WrapTransport = rt
	} else {
		cachedTokenSource := transport.NewCachedTokenSource(&tokenSourceImpl{
			namespace:          t.Namespace,
			serviceAccountName: saName,
			coreClient:         t.CoreClient,
			expirationSeconds:  t.expirationSeconds,
			leewayPercent:      t.leewayPercent,
		})
		configCopy.WrapTransport = transport.TokenSourceWrapTransport(cachedTokenSource)

		t.roundTripperFuncMap[saName] = configCopy.WrapTransport
	}

	return &configCopy, nil
}

func (t *DynamicControllerClientBuilder) ConfigOrDie(name string) *restclient.Config {
	clientConfig, err := t.Config(name)
	if err != nil {
		klog.Fatal(err)
	}
	return clientConfig
}

func (t *DynamicControllerClientBuilder) Client(name string) (clientset.Interface, error) {
	clientConfig, err := t.Config(name)
	if err != nil {
		return nil, err
	}
	return clientset.NewForConfig(clientConfig)
}

func (t *DynamicControllerClientBuilder) ClientOrDie(name string) clientset.Interface {
	client, err := t.Client(name)
	if err != nil {
		klog.Fatal(err)
	}
	return client
}

type tokenSourceImpl struct {
	namespace          string
	serviceAccountName string
	coreClient         v1core.CoreV1Interface
	expirationSeconds  int64
	leewayPercent      int
}

func (ts *tokenSourceImpl) Token() (*oauth2.Token, error) {
	var retTokenRequest *v1authenticationapi.TokenRequest

	backoff := wait.Backoff{
		Duration: 500 * time.Millisecond,
		Factor:   2, // double the timeout for every failure
		Steps:    4,
	}
	if err := wait.ExponentialBackoff(backoff, func() (bool, error) {
		if _, inErr := getOrCreateServiceAccount(ts.coreClient, ts.namespace, ts.serviceAccountName); inErr != nil {
			klog.Warningf("get or create service account failed: %v", inErr)
			return false, nil
		}

		tr, inErr := ts.coreClient.ServiceAccounts(ts.namespace).CreateToken(ts.serviceAccountName, &v1authenticationapi.TokenRequest{
			Spec: v1authenticationapi.TokenRequestSpec{
				ExpirationSeconds: utilpointer.Int64Ptr(ts.expirationSeconds),
			},
		})
		if inErr != nil {
			klog.Warningf("get token failed: %v", inErr)
			return false, nil
		}
		retTokenRequest = tr
		return true, nil
	}); err != nil {
		return nil, fmt.Errorf("failed to get token for %s/%s: %v", ts.namespace, ts.serviceAccountName, err)
	}

	if retTokenRequest.Spec.ExpirationSeconds == nil {
		return nil, fmt.Errorf("nil pointer of expiration in token request")
	}

	lifetime := retTokenRequest.Status.ExpirationTimestamp.Time.Sub(time.Now())
	if lifetime < time.Minute*10 {
		// possible clock skew issue, pin to minimum token lifetime
		lifetime = time.Minute * 10
	}

	leeway := time.Duration(int64(lifetime) * int64(ts.leewayPercent) / 100)
	expiry := time.Now().Add(lifetime).Add(-1 * leeway)

	return &oauth2.Token{
		AccessToken: retTokenRequest.Status.Token,
		TokenType:   "Bearer",
		Expiry:      expiry,
	}, nil
}

func constructClient(saNamespace, saName string, config *restclient.Config) restclient.Config {
	username := apiserverserviceaccount.MakeUsername(saNamespace, saName)
	ret := *restclient.AnonymousClientConfig(config)
	restclient.AddUserAgent(&ret, username)
	return ret
}