package k8s

import (
	"context"
	"encoding/base64"
	"fmt"
	"strings"
	"time"

	authenticationv1 "k8s.io/api/authentication/v1"
	corev1 "k8s.io/api/core/v1"
	rbacv1 "k8s.io/api/rbac/v1"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/clientcmd"
	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"

	"github.com/ocdp/cluster-service/internal/domain/entity"
	"github.com/ocdp/cluster-service/internal/domain/repository"
)

// TenantClient provisions namespace-scoped tenant Kubernetes resources.
type TenantClient struct {
	clientset kubernetes.Interface
}

// NewTenantClient creates a tenant provisioning client that builds Kubernetes
// clients from the supplied cluster entity for each call.
func NewTenantClient() repository.TenantKubeClient {
	return &TenantClient{}
}

// NewTenantClientForClientset creates a tenant provisioning client for tests or
// callers that already own a Kubernetes client.
func NewTenantClientForClientset(clientset kubernetes.Interface) repository.TenantKubeClient {
	return &TenantClient{clientset: clientset}
}

// EnsureTenant idempotently ensures Namespace, ServiceAccount, RoleBinding, and
// ResourceQuota resources for the tenant binding.
func (c *TenantClient) EnsureTenant(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding) error {
	binding = binding.WithDefaults()
	if err := binding.Validate(); err != nil {
		return err
	}
	clientset, _, err := c.clientsetForCluster(cluster)
	if err != nil {
		return err
	}
	if err := c.ensureNamespace(ctx, clientset, binding); err != nil {
		return err
	}
	if err := c.ensureServiceAccount(ctx, clientset, binding); err != nil {
		return err
	}
	if err := c.ensureRoleBinding(ctx, clientset, binding); err != nil {
		return err
	}
	if err := c.ensureResourceQuota(ctx, clientset, binding); err != nil {
		return err
	}
	return nil
}

// IssueKubeconfig returns a short-lived kubeconfig backed by a Kubernetes
// TokenRequest. The token exists only in the returned value and is never stored.
func (c *TenantClient) IssueKubeconfig(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding, ttl time.Duration) (*entity.TenantKubeconfig, error) {
	binding = binding.WithDefaults()
	if err := binding.Validate(); err != nil {
		return nil, err
	}
	clientset, restConfig, err := c.clientsetForCluster(cluster)
	if err != nil {
		return nil, err
	}

	cappedTTL := entity.TenantTokenTTL(ttl)
	expirationSeconds := int64(cappedTTL.Seconds())
	tokenRequest, err := clientset.CoreV1().
		ServiceAccounts(binding.Namespace).
		CreateToken(ctx, binding.ServiceAccountName, &authenticationv1.TokenRequest{
			Spec: authenticationv1.TokenRequestSpec{
				ExpirationSeconds: &expirationSeconds,
			},
		}, metav1.CreateOptions{})
	if err != nil {
		return nil, fmt.Errorf("failed to request tenant service account token: %w", err)
	}
	if tokenRequest.Status.Token == "" {
		return nil, entity.ErrInvalidTenantKubeconfigToken
	}

	expiresAt := tokenRequest.Status.ExpirationTimestamp.Time
	if expiresAt.IsZero() {
		expiresAt = time.Now().Add(cappedTTL)
	}
	kubeconfig, err := buildTenantKubeconfig(cluster, restConfig, binding, tokenRequest.Status.Token)
	if err != nil {
		return nil, err
	}
	return &entity.TenantKubeconfig{
		Kubeconfig: kubeconfig,
		ExpiresAt:  expiresAt,
	}, nil
}

func (c *TenantClient) GetResourceQuotaUsage(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding) (*repository.ResourceQuotaUsage, error) {
	binding = binding.WithDefaults()
	if err := binding.Validate(); err != nil {
		return nil, err
	}
	clientset, _, err := c.clientsetForCluster(cluster)
	if err != nil {
		return nil, err
	}
	quota, err := clientset.CoreV1().ResourceQuotas(binding.Namespace).Get(ctx, binding.ResourceQuotaName, metav1.GetOptions{})
	if err != nil {
		return nil, fmt.Errorf("failed to get tenant resource quota usage: %w", err)
	}
	return &repository.ResourceQuotaUsage{
		Hard: resourceVectorFromList(quota.Status.Hard),
		Used: resourceVectorFromList(quota.Status.Used),
	}, nil
}

// SuspendTenant revokes tenant API access by deleting only the RoleBinding.
func (c *TenantClient) SuspendTenant(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding) error {
	binding = binding.WithDefaults()
	if err := binding.Validate(); err != nil {
		return err
	}
	clientset, _, err := c.clientsetForCluster(cluster)
	if err != nil {
		return err
	}
	err = clientset.RbacV1().
		RoleBindings(binding.Namespace).
		Delete(ctx, binding.RoleBindingName, metav1.DeleteOptions{})
	if apierrors.IsNotFound(err) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("failed to delete tenant role binding: %w", err)
	}
	return nil
}

func (c *TenantClient) DeleteTenant(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding) error {
	binding = binding.WithDefaults()
	if err := binding.Validate(); err != nil {
		return err
	}
	if isProtectedTenantNamespace(binding.Namespace) {
		return entity.ErrProtectedNamespace
	}
	clientset, _, err := c.clientsetForCluster(cluster)
	if err != nil {
		return err
	}
	if err := deleteIgnoringNotFound(ctx, func() error {
		return clientset.RbacV1().RoleBindings(binding.Namespace).Delete(ctx, binding.RoleBindingName, metav1.DeleteOptions{})
	}); err != nil {
		return fmt.Errorf("failed to delete tenant role binding: %w", err)
	}
	if err := deleteIgnoringNotFound(ctx, func() error {
		return clientset.CoreV1().ResourceQuotas(binding.Namespace).Delete(ctx, binding.ResourceQuotaName, metav1.DeleteOptions{})
	}); err != nil {
		return fmt.Errorf("failed to delete tenant resource quota: %w", err)
	}
	if err := deleteIgnoringNotFound(ctx, func() error {
		return clientset.CoreV1().ServiceAccounts(binding.Namespace).Delete(ctx, binding.ServiceAccountName, metav1.DeleteOptions{})
	}); err != nil {
		return fmt.Errorf("failed to delete tenant service account: %w", err)
	}
	namespace, err := clientset.CoreV1().Namespaces().Get(ctx, binding.Namespace, metav1.GetOptions{})
	if apierrors.IsNotFound(err) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("failed to get tenant namespace before deletion: %w", err)
	}
	if namespace.Labels["ocdp.io/managed-by"] != "ocdp" || namespace.Labels["ocdp.io/tenant"] != binding.Namespace {
		return fmt.Errorf("refusing to delete unmanaged namespace %q", binding.Namespace)
	}
	if err := deleteIgnoringNotFound(ctx, func() error {
		return clientset.CoreV1().Namespaces().Delete(ctx, binding.Namespace, metav1.DeleteOptions{})
	}); err != nil {
		return fmt.Errorf("failed to delete tenant namespace: %w", err)
	}
	return nil
}

func deleteIgnoringNotFound(ctx context.Context, deleteFn func() error) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	err := deleteFn()
	if apierrors.IsNotFound(err) {
		return nil
	}
	return err
}

func isProtectedTenantNamespace(namespace string) bool {
	switch strings.TrimSpace(namespace) {
	case "", "default", "kube-system", "kube-public", "kube-node-lease":
		return true
	default:
		return false
	}
}

func resourceVectorFromList(values corev1.ResourceList) repository.ResourceVector {
	gpu := values[corev1.ResourceName("requests.nvidia.com/gpu")]
	gpuMem := values[corev1.ResourceName("requests.nvidia.com/gpumem")]
	return repository.ResourceVector{
		CPU:         values[corev1.ResourceName("requests.cpu")],
		Memory:      values[corev1.ResourceName("requests.memory")],
		GPU:         gpu.Value(),
		GPUMemoryMB: gpuMem.Value(),
	}
}

func (c *TenantClient) clientsetForCluster(cluster *entity.Cluster) (kubernetes.Interface, *rest.Config, error) {
	if c.clientset != nil {
		config := &rest.Config{Host: "https://kubernetes.default.svc"}
		if cluster != nil {
			clusterConfig, err := restConfigFromCluster(cluster)
			if err == nil {
				config = clusterConfig
			}
		}
		return c.clientset, config, nil
	}

	config, err := restConfigFromCluster(cluster)
	if err != nil {
		return nil, nil, err
	}
	clientset, err := kubernetes.NewForConfig(config)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to create tenant kubernetes client: %w", err)
	}
	return clientset, config, nil
}

func restConfigFromCluster(cluster *entity.Cluster) (*rest.Config, error) {
	if cluster == nil {
		return nil, entity.ErrInvalidClusterHost
	}
	if looksLikeKubeconfig(cluster.CAData) {
		config, err := clientcmd.RESTConfigFromKubeConfig([]byte(cluster.CAData))
		if err != nil {
			return nil, fmt.Errorf("failed to parse tenant kubeconfig: %w", err)
		}
		return config, nil
	}
	if strings.TrimSpace(cluster.Host) == "" {
		return nil, entity.ErrInvalidClusterHost
	}
	return &rest.Config{
		Host: cluster.Host,
		TLSClientConfig: rest.TLSClientConfig{
			CAData:   decodePossiblyBase64(cluster.CAData),
			CertData: decodePossiblyBase64(cluster.CertData),
			KeyData:  decodePossiblyBase64(cluster.KeyData),
		},
		BearerToken: cluster.Token,
	}, nil
}

func (c *TenantClient) ensureNamespace(ctx context.Context, clientset kubernetes.Interface, binding entity.TenantBinding) error {
	namespace := &corev1.Namespace{
		ObjectMeta: metav1.ObjectMeta{
			Name:        binding.Namespace,
			Labels:      copyStringMap(binding.Labels),
			Annotations: copyStringMap(binding.Annotations),
		},
	}
	_, err := clientset.CoreV1().Namespaces().Create(ctx, namespace, metav1.CreateOptions{})
	if apierrors.IsAlreadyExists(err) {
		current, getErr := clientset.CoreV1().Namespaces().Get(ctx, binding.Namespace, metav1.GetOptions{})
		if getErr != nil {
			return fmt.Errorf("failed to get tenant namespace: %w", getErr)
		}
		mergeObjectMetadata(&current.ObjectMeta, binding.Labels, binding.Annotations)
		if _, updateErr := clientset.CoreV1().Namespaces().Update(ctx, current, metav1.UpdateOptions{}); updateErr != nil {
			return fmt.Errorf("failed to update tenant namespace: %w", updateErr)
		}
		return nil
	}
	if err != nil {
		return fmt.Errorf("failed to create tenant namespace: %w", err)
	}
	return nil
}

func (c *TenantClient) ensureServiceAccount(ctx context.Context, clientset kubernetes.Interface, binding entity.TenantBinding) error {
	serviceAccount := &corev1.ServiceAccount{
		ObjectMeta: metav1.ObjectMeta{
			Name:        binding.ServiceAccountName,
			Namespace:   binding.Namespace,
			Labels:      copyStringMap(binding.Labels),
			Annotations: copyStringMap(binding.Annotations),
		},
	}
	_, err := clientset.CoreV1().ServiceAccounts(binding.Namespace).Create(ctx, serviceAccount, metav1.CreateOptions{})
	if apierrors.IsAlreadyExists(err) {
		current, getErr := clientset.CoreV1().ServiceAccounts(binding.Namespace).Get(ctx, binding.ServiceAccountName, metav1.GetOptions{})
		if getErr != nil {
			return fmt.Errorf("failed to get tenant service account: %w", getErr)
		}
		mergeObjectMetadata(&current.ObjectMeta, binding.Labels, binding.Annotations)
		if _, updateErr := clientset.CoreV1().ServiceAccounts(binding.Namespace).Update(ctx, current, metav1.UpdateOptions{}); updateErr != nil {
			return fmt.Errorf("failed to update tenant service account: %w", updateErr)
		}
		return nil
	}
	if err != nil {
		return fmt.Errorf("failed to create tenant service account: %w", err)
	}
	return nil
}

func (c *TenantClient) ensureRoleBinding(ctx context.Context, clientset kubernetes.Interface, binding entity.TenantBinding) error {
	roleBinding := desiredRoleBinding(binding)
	_, err := clientset.RbacV1().RoleBindings(binding.Namespace).Create(ctx, roleBinding, metav1.CreateOptions{})
	if apierrors.IsAlreadyExists(err) {
		current, getErr := clientset.RbacV1().RoleBindings(binding.Namespace).Get(ctx, binding.RoleBindingName, metav1.GetOptions{})
		if getErr != nil {
			return fmt.Errorf("failed to get tenant role binding: %w", getErr)
		}
		mergeObjectMetadata(&current.ObjectMeta, binding.Labels, binding.Annotations)
		current.Subjects = roleBinding.Subjects
		current.RoleRef = roleBinding.RoleRef
		if _, updateErr := clientset.RbacV1().RoleBindings(binding.Namespace).Update(ctx, current, metav1.UpdateOptions{}); updateErr != nil {
			return fmt.Errorf("failed to update tenant role binding: %w", updateErr)
		}
		return nil
	}
	if err != nil {
		return fmt.Errorf("failed to create tenant role binding: %w", err)
	}
	return nil
}

func (c *TenantClient) ensureResourceQuota(ctx context.Context, clientset kubernetes.Interface, binding entity.TenantBinding) error {
	resourceQuota := &corev1.ResourceQuota{
		ObjectMeta: metav1.ObjectMeta{
			Name:        binding.ResourceQuotaName,
			Namespace:   binding.Namespace,
			Labels:      copyStringMap(binding.Labels),
			Annotations: copyStringMap(binding.Annotations),
		},
		Spec: corev1.ResourceQuotaSpec{
			Hard: binding.ResourceQuotaHard.DeepCopy(),
		},
	}
	_, err := clientset.CoreV1().ResourceQuotas(binding.Namespace).Create(ctx, resourceQuota, metav1.CreateOptions{})
	if apierrors.IsAlreadyExists(err) {
		current, getErr := clientset.CoreV1().ResourceQuotas(binding.Namespace).Get(ctx, binding.ResourceQuotaName, metav1.GetOptions{})
		if getErr != nil {
			return fmt.Errorf("failed to get tenant resource quota: %w", getErr)
		}
		mergeObjectMetadata(&current.ObjectMeta, binding.Labels, binding.Annotations)
		current.Spec.Hard = binding.ResourceQuotaHard.DeepCopy()
		if _, updateErr := clientset.CoreV1().ResourceQuotas(binding.Namespace).Update(ctx, current, metav1.UpdateOptions{}); updateErr != nil {
			return fmt.Errorf("failed to update tenant resource quota: %w", updateErr)
		}
		return nil
	}
	if err != nil {
		return fmt.Errorf("failed to create tenant resource quota: %w", err)
	}
	return nil
}

func desiredRoleBinding(binding entity.TenantBinding) *rbacv1.RoleBinding {
	return &rbacv1.RoleBinding{
		ObjectMeta: metav1.ObjectMeta{
			Name:        binding.RoleBindingName,
			Namespace:   binding.Namespace,
			Labels:      copyStringMap(binding.Labels),
			Annotations: copyStringMap(binding.Annotations),
		},
		Subjects: []rbacv1.Subject{{
			Kind:      rbacv1.ServiceAccountKind,
			Name:      binding.ServiceAccountName,
			Namespace: binding.Namespace,
		}},
		RoleRef: rbacv1.RoleRef{
			APIGroup: rbacv1.GroupName,
			Kind:     "ClusterRole",
			Name:     binding.ClusterRoleName,
		},
	}
}

func buildTenantKubeconfig(cluster *entity.Cluster, restConfig *rest.Config, binding entity.TenantBinding, token string) (string, error) {
	host := ""
	var caData []byte
	if restConfig != nil {
		host = restConfig.Host
		caData = append([]byte{}, restConfig.CAData...)
	}
	if host == "" && cluster != nil {
		host = cluster.Host
	}
	if len(caData) == 0 && cluster != nil {
		caData = decodePossiblyBase64(cluster.CAData)
	}
	if host == "" {
		return "", entity.ErrInvalidClusterHost
	}

	clusterName := "tenant-cluster"
	if cluster != nil && cluster.Name != "" {
		clusterName = cluster.Name
	}
	userName := binding.ServiceAccountName
	contextName := fmt.Sprintf("%s/%s", clusterName, binding.Namespace)
	config := clientcmdapi.NewConfig()
	config.Clusters[clusterName] = &clientcmdapi.Cluster{
		Server:                   host,
		CertificateAuthorityData: caData,
	}
	config.AuthInfos[userName] = &clientcmdapi.AuthInfo{
		Token: token,
	}
	config.Contexts[contextName] = &clientcmdapi.Context{
		Cluster:   clusterName,
		AuthInfo:  userName,
		Namespace: binding.Namespace,
	}
	config.CurrentContext = contextName

	bytes, err := clientcmd.Write(*config)
	if err != nil {
		return "", fmt.Errorf("failed to build tenant kubeconfig: %w", err)
	}
	return string(bytes), nil
}

func mergeObjectMetadata(meta *metav1.ObjectMeta, labels, annotations map[string]string) {
	if len(labels) > 0 && meta.Labels == nil {
		meta.Labels = map[string]string{}
	}
	for key, value := range labels {
		meta.Labels[key] = value
	}
	if len(annotations) > 0 && meta.Annotations == nil {
		meta.Annotations = map[string]string{}
	}
	for key, value := range annotations {
		meta.Annotations[key] = value
	}
}

func copyStringMap(values map[string]string) map[string]string {
	if len(values) == 0 {
		return nil
	}
	copied := make(map[string]string, len(values))
	for key, value := range values {
		copied[key] = value
	}
	return copied
}

func decodePossiblyBase64(value string) []byte {
	decoded, err := base64.StdEncoding.DecodeString(value)
	if err == nil {
		return decoded
	}
	return []byte(value)
}

func looksLikeKubeconfig(value string) bool {
	trimmed := strings.TrimSpace(value)
	return strings.HasPrefix(trimmed, "apiVersion:") || strings.HasPrefix(trimmed, "kind: Config")
}