/*
Copyright © The ESO 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

    https://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 vault

import (
	"context"
	"errors"
	"fmt"
	"time"

	vault "github.com/hashicorp/vault/api"
	"github.com/spf13/pflag"
	"k8s.io/client-go/kubernetes"
	typedcorev1 "k8s.io/client-go/kubernetes/typed/core/v1"
	ctrl "sigs.k8s.io/controller-runtime"
	kclient "sigs.k8s.io/controller-runtime/pkg/client"
	ctrlcfg "sigs.k8s.io/controller-runtime/pkg/client/config"

	esv1 "github.com/external-secrets/external-secrets/apis/externalsecrets/v1"
	vaultutil "github.com/external-secrets/external-secrets/providers/v1/vault/util"
	"github.com/external-secrets/external-secrets/runtime/cache"
	"github.com/external-secrets/external-secrets/runtime/esutils/resolvers"
	"github.com/external-secrets/external-secrets/runtime/feature"
)

var (
	_           esv1.Provider = &Provider{}
	enableCache bool
	logger      = ctrl.Log.WithName("provider").WithName("vault")
	clientCache *cache.Cache[vaultutil.Client]
)

const (
	errVaultStore    = "received invalid Vault SecretStore resource: %w"
	errVaultClient   = "cannot setup new vault client: %w"
	errVaultCert     = "cannot set Vault CA certificate: %w"
	errClientTLSAuth = "error from Client TLS Auth: %q"
	errCANamespace   = "missing namespace on caProvider secret"
)

const (
	defaultCacheSize = 2 << 17
)

// Provider implements the ESO Provider interface for Hashicorp Vault.
type Provider struct {
	// NewVaultClient is a function that returns a new Vault client.
	// This is used for testing to inject a fake client.
	NewVaultClient func(config *vault.Config) (vaultutil.Client, error)
}

// NewVaultClient returns a new Vault client.
func NewVaultClient(config *vault.Config) (vaultutil.Client, error) {
	vaultClient, err := vault.NewClient(config)
	if err != nil {
		return nil, err
	}
	return &vaultutil.VaultClient{
		SetTokenFunc:     vaultClient.SetToken,
		TokenFunc:        vaultClient.Token,
		ClearTokenFunc:   vaultClient.ClearToken,
		AuthField:        vaultClient.Auth(),
		AuthTokenField:   vaultClient.Auth().Token(),
		LogicalField:     vaultClient.Logical(),
		NamespaceFunc:    vaultClient.Namespace,
		SetNamespaceFunc: vaultClient.SetNamespace,
		AddHeaderFunc:    vaultClient.AddHeader,
	}, nil
}

// Capabilities return the provider supported capabilities (ReadOnly, WriteOnly, ReadWrite).
func (p *Provider) Capabilities() esv1.SecretStoreCapabilities {
	return esv1.SecretStoreReadWrite
}

// NewClient implements the Client interface.
func (p *Provider) NewClient(ctx context.Context, store esv1.GenericStore, kube kclient.Client, namespace string) (esv1.SecretsClient, error) {
	// controller-runtime/client does not support TokenRequest or other subresource APIs
	// so we need to construct our own client and use it to fetch tokens
	// (for Kubernetes service account token auth)
	restCfg, err := ctrlcfg.GetConfig()
	if err != nil {
		return nil, err
	}
	clientset, err := kubernetes.NewForConfig(restCfg)
	if err != nil {
		return nil, err
	}
	return p.newClient(ctx, store, kube, clientset.CoreV1(), namespace)
}

// NewGeneratorClient creates a new Vault client for the generator controller.
func (p *Provider) NewGeneratorClient(
	ctx context.Context,
	kube kclient.Client,
	corev1 typedcorev1.CoreV1Interface,
	vaultSpec *esv1.VaultProvider,
	namespace string,
	retrySettings *esv1.SecretStoreRetrySettings,
) (vaultutil.Client, error) {
	vStore, cfg, err := p.prepareConfig(ctx, kube, corev1, vaultSpec, retrySettings, namespace, resolvers.EmptyStoreKind)
	if err != nil {
		return nil, err
	}

	client, err := p.NewVaultClient(cfg)
	if err != nil {
		return nil, err
	}

	_, err = p.initClient(ctx, vStore, client, cfg, vaultSpec)
	if err != nil {
		return nil, err
	}

	return client, nil
}

func (p *Provider) newClient(ctx context.Context, store esv1.GenericStore, kube kclient.Client, corev1 typedcorev1.CoreV1Interface, namespace string) (esv1.SecretsClient, error) {
	storeSpec := store.GetSpec()
	if storeSpec == nil || storeSpec.Provider == nil || storeSpec.Provider.Vault == nil {
		return nil, errors.New(errVaultStore)
	}
	vaultSpec := storeSpec.Provider.Vault

	vStore, cfg, err := p.prepareConfig(
		ctx,
		kube,
		corev1,
		vaultSpec,
		storeSpec.RetrySettings,
		namespace,
		store.GetObjectKind().GroupVersionKind().Kind)
	if err != nil {
		return nil, err
	}

	client, err := getVaultClient(p, store, cfg, namespace)
	if err != nil {
		return nil, fmt.Errorf(errVaultClient, err)
	}

	return p.initClient(ctx, vStore, client, cfg, vaultSpec)
}

func (p *Provider) initClient(ctx context.Context, c *client, client vaultutil.Client, cfg *vault.Config, vaultSpec *esv1.VaultProvider) (esv1.SecretsClient, error) {
	if vaultSpec.Namespace != nil {
		client.SetNamespace(*vaultSpec.Namespace)
	}

	if vaultSpec.Headers != nil {
		for hKey, hValue := range vaultSpec.Headers {
			client.AddHeader(hKey, hValue)
		}
	}

	if vaultSpec.ReadYourWrites && vaultSpec.ForwardInconsistent {
		client.AddHeader("X-Vault-Inconsistent", "forward-active-node")
	}

	c.client = client
	c.auth = client.Auth()
	c.logical = client.Logical()
	c.token = client.AuthToken()

	// allow SecretStore controller validation to pass
	// when using referent namespace.
	if c.storeKind == esv1.ClusterSecretStoreKind && c.namespace == "" && isReferentSpec(vaultSpec) {
		return c, nil
	}
	// set auth also sets the token expiry value
	if err := c.setAuth(ctx, cfg); err != nil {
		return nil, err
	}

	return c, nil
}

func (p *Provider) prepareConfig(
	ctx context.Context,
	kube kclient.Client,
	corev1 typedcorev1.CoreV1Interface,
	vaultSpec *esv1.VaultProvider,
	retrySettings *esv1.SecretStoreRetrySettings,
	namespace, storeKind string,
) (*client, *vault.Config, error) {
	c := &client{
		kube:      kube,
		corev1:    corev1,
		store:     vaultSpec,
		log:       logger,
		namespace: namespace,
		storeKind: storeKind,
	}

	cfg, err := c.newConfig(ctx)
	if err != nil {
		return nil, nil, err
	}

	// Setup retry options if present
	if retrySettings != nil {
		if retrySettings.MaxRetries != nil {
			cfg.MaxRetries = int(*retrySettings.MaxRetries)
		} else {
			// By default we rely only on the reconciliation process for retrying
			cfg.MaxRetries = 0
		}

		if retrySettings.RetryInterval != nil {
			retryWait, err := time.ParseDuration(*retrySettings.RetryInterval)
			if err != nil {
				return nil, nil, err
			}
			cfg.MinRetryWait = retryWait
			cfg.MaxRetryWait = retryWait
		}
	}

	return c, cfg, nil
}

func getVaultClient(p *Provider, store esv1.GenericStore, cfg *vault.Config, namespace string) (vaultutil.Client, error) {
	vaultProvider := store.GetSpec().Provider.Vault
	auth := vaultProvider.Auth
	isStaticToken := auth != nil && auth.TokenSecretRef != nil
	useCache := enableCache && !isStaticToken

	keyNamespace := store.GetObjectMeta().Namespace
	// A single ClusterSecretStore may need to spawn separate vault clients for each namespace.
	if store.GetTypeMeta().Kind == esv1.ClusterSecretStoreKind && namespace != "" && isReferentSpec(vaultProvider) {
		keyNamespace = namespace
	}

	key := cache.Key{
		Name:      store.GetObjectMeta().Name,
		Namespace: keyNamespace,
		Kind:      store.GetTypeMeta().Kind,
	}
	if useCache {
		client, ok := clientCache.Get(store.GetObjectMeta().ResourceVersion, key)
		if ok {
			return client, nil
		}
	}

	client, err := p.NewVaultClient(cfg)
	if err != nil {
		return nil, fmt.Errorf(errVaultClient, err)
	}

	if useCache && !clientCache.Contains(key) {
		clientCache.Add(store.GetObjectMeta().ResourceVersion, key, client)
	}
	return client, nil
}

func isReferentSpec(prov *esv1.VaultProvider) bool {
	if prov.Auth == nil {
		return false
	}

	if prov.Auth.TokenSecretRef != nil && prov.Auth.TokenSecretRef.Namespace == nil {
		return true
	}
	if prov.Auth.AppRole != nil && prov.Auth.AppRole.SecretRef.Namespace == nil {
		return true
	}
	if prov.Auth.Kubernetes != nil && prov.Auth.Kubernetes.SecretRef != nil && prov.Auth.Kubernetes.SecretRef.Namespace == nil {
		return true
	}
	if prov.Auth.Kubernetes != nil && prov.Auth.Kubernetes.ServiceAccountRef != nil && prov.Auth.Kubernetes.ServiceAccountRef.Namespace == nil {
		return true
	}
	if prov.Auth.Ldap != nil && prov.Auth.Ldap.SecretRef.Namespace == nil {
		return true
	}
	if prov.Auth.UserPass != nil && prov.Auth.UserPass.SecretRef.Namespace == nil {
		return true
	}
	if prov.Auth.Jwt != nil && prov.Auth.Jwt.SecretRef != nil && prov.Auth.Jwt.SecretRef.Namespace == nil {
		return true
	}
	if prov.Auth.Jwt != nil && prov.Auth.Jwt.KubernetesServiceAccountToken != nil && prov.Auth.Jwt.KubernetesServiceAccountToken.ServiceAccountRef.Namespace == nil {
		return true
	}
	if prov.Auth.Cert != nil && prov.Auth.Cert.SecretRef.Namespace == nil {
		return true
	}
	if prov.Auth.Iam != nil && prov.Auth.Iam.JWTAuth != nil && prov.Auth.Iam.JWTAuth.ServiceAccountRef != nil && prov.Auth.Iam.JWTAuth.ServiceAccountRef.Namespace == nil {
		return true
	}
	if prov.Auth.Iam != nil && prov.Auth.Iam.SecretRef != nil &&
		(prov.Auth.Iam.SecretRef.AccessKeyID.Namespace == nil ||
			prov.Auth.Iam.SecretRef.SecretAccessKey.Namespace == nil ||
			(prov.Auth.Iam.SecretRef.SessionToken != nil && prov.Auth.Iam.SecretRef.SessionToken.Namespace == nil)) {
		return true
	}
	return false
}

func initCache(size int) {
	logger.Info("initializing vault cache", "size", size)
	clientCache = cache.Must(size, func(client vaultutil.Client) {
		err := revokeTokenIfValid(context.Background(), client)
		if err != nil {
			logger.Error(err, "unable to revoke cached token on eviction")
		}
	})
}

func init() {
	var (
		vaultTokenCacheSize     int
		experimentalEnableCache bool
		experimentalCacheSize   int
	)

	fs := pflag.NewFlagSet("vault", pflag.ExitOnError)
	fs.BoolVar(
		&enableCache,
		"enable-vault-token-cache",
		false,
		"Enable Vault token cache. External secrets will reuse the Vault token without creating a new one on each request.",
	)
	// max. 265k vault leases with 30bytes each ~= 7MB
	fs.IntVar(
		&vaultTokenCacheSize,
		"vault-token-cache-size",
		defaultCacheSize,
		"Maximum size of Vault token cache. Only used if --enable-vault-token-cache is set.",
	)
	fs.BoolVar(
		&experimentalEnableCache,
		"experimental-enable-vault-token-cache",
		false,
		"Enable Vault token cache. External secrets will reuse the Vault token without creating a new one on each request.",
	)
	// max. 265k vault leases with 30bytes each ~= 7MB
	fs.IntVar(
		&experimentalCacheSize,
		"experimental-vault-token-cache-size",
		defaultCacheSize,
		"Maximum size of Vault token cache. Only used if --experimental-enable-vault-token-cache is set.",
	)
	feature.Register(feature.Feature{
		Flags: fs,
		Initialize: func() {
			// Check for deprecated experimental flags and warn users
			if experimentalEnableCache {
				logger.Info("DEPRECATION WARNING: --experimental-enable-vault-token-cache is deprecated. Please use --enable-vault-token-cache instead. This flag will be removed in a future release.")
				enableCache = true
			}
			if experimentalCacheSize > 0 {
				logger.Info("DEPRECATION WARNING: --experimental-vault-token-cache-size is deprecated. Please use --vault-token-cache-size instead. This flag will be removed in a future release.")
				vaultTokenCacheSize = experimentalCacheSize
			}
			initCache(vaultTokenCacheSize)
		},
	})
}

// NewProvider creates a new Provider instance.
func NewProvider() esv1.Provider {
	return &Provider{
		NewVaultClient: NewVaultClient,
	}
}

// ProviderSpec returns the provider specification for registration.
func ProviderSpec() *esv1.SecretStoreProvider {
	return &esv1.SecretStoreProvider{
		Vault: &esv1.VaultProvider{},
	}
}

// MaintenanceStatus returns the maintenance status of the provider.
func MaintenanceStatus() esv1.MaintenanceStatus {
	return esv1.MaintenanceStatusMaintained
}