// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

//go:build !plan9

package main

import (
	"context"
	_ "embed"
	"fmt"
	"os"
	"strings"

	"go.uber.org/zap"
	appsv1 "k8s.io/api/apps/v1"
	corev1 "k8s.io/api/core/v1"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	"sigs.k8s.io/controller-runtime/pkg/client"
	"sigs.k8s.io/yaml"
	"tailscale.com/client/tailscale"
	"tailscale.com/tailcfg"
	"tailscale.com/types/opt"
	"tailscale.com/util/dnsname"
)

const (
	LabelManaged         = "tailscale.com/managed"
	LabelParentType      = "tailscale.com/parent-resource-type"
	LabelParentName      = "tailscale.com/parent-resource"
	LabelParentNamespace = "tailscale.com/parent-resource-ns"

	FinalizerName = "tailscale.com/finalizer"

	// Annotations settable by users on services.
	AnnotationExpose   = "tailscale.com/expose"
	AnnotationTags     = "tailscale.com/tags"
	AnnotationHostname = "tailscale.com/hostname"

	// Annotations set by the operator on pods to trigger restarts when the
	// hostname or IP changes.
	podAnnotationLastSetIP       = "tailscale.com/operator-last-set-ip"
	podAnnotationLastSetHostname = "tailscale.com/operator-last-set-hostname"
)

type tailscaleSTSConfig struct {
	ParentResourceName  string
	ParentResourceUID   string
	ChildResourceLabels map[string]string

	TargetIP string

	Hostname string
	Tags     []string // if empty, use defaultTags
}

type tailscaleSTSReconciler struct {
	client.Client
	tsClient               tsClient
	defaultTags            []string
	operatorNamespace      string
	proxyImage             string
	proxyPriorityClassName string
}

// Provision ensures that the StatefulSet for the given service is running and
// up to date.
func (a *tailscaleSTSReconciler) Provision(ctx context.Context, logger *zap.SugaredLogger, sts *tailscaleSTSConfig) error {
	// Do full reconcile.
	hsvc, err := a.reconcileHeadlessService(ctx, logger, sts)
	if err != nil {
		return fmt.Errorf("failed to reconcile headless service: %w", err)
	}

	secretName, err := a.createOrGetSecret(ctx, logger, sts, hsvc)
	if err != nil {
		return fmt.Errorf("failed to create or get API key secret: %w", err)
	}
	_, err = a.reconcileSTS(ctx, logger, sts, hsvc, secretName)
	if err != nil {
		return fmt.Errorf("failed to reconcile statefulset: %w", err)
	}

	return nil
}

// Cleanup removes all resources associated that were created by Provision with
// the given labels. It returns true when all resources have been removed,
// otherwise it returns false and the caller should retry later.
func (a *tailscaleSTSReconciler) Cleanup(ctx context.Context, logger *zap.SugaredLogger, labels map[string]string) (done bool, _ error) {
	// Need to delete the StatefulSet first, and delete it with foreground
	// cascading deletion. That way, the pod that's writing to the Secret will
	// stop running before we start looking at the Secret's contents, and
	// assuming k8s ordering semantics don't mess with us, that should avoid
	// tailscale device deletion races where we fail to notice a device that
	// should be removed.
	sts, err := getSingleObject[appsv1.StatefulSet](ctx, a.Client, a.operatorNamespace, labels)
	if err != nil {
		return false, fmt.Errorf("getting statefulset: %w", err)
	}
	if sts != nil {
		if !sts.GetDeletionTimestamp().IsZero() {
			// Deletion in progress, check again later. We'll get another
			// notification when the deletion is complete.
			logger.Debugf("waiting for statefulset %s/%s deletion", sts.GetNamespace(), sts.GetName())
			return false, nil
		}
		err := a.DeleteAllOf(ctx, &appsv1.StatefulSet{}, client.InNamespace(a.operatorNamespace), client.MatchingLabels(labels), client.PropagationPolicy(metav1.DeletePropagationForeground))
		if err != nil {
			return false, fmt.Errorf("deleting statefulset: %w", err)
		}
		logger.Debugf("started deletion of statefulset %s/%s", sts.GetNamespace(), sts.GetName())
		return false, nil
	}

	id, _, err := a.DeviceInfo(ctx, labels)
	if err != nil {
		return false, fmt.Errorf("getting device info: %w", err)
	}
	if id != "" {
		// TODO: handle case where the device is already deleted, but the secret
		// is still around.
		if err := a.tsClient.DeleteDevice(ctx, string(id)); err != nil {
			return false, fmt.Errorf("deleting device: %w", err)
		}
	}

	types := []client.Object{
		&corev1.Service{},
		&corev1.Secret{},
	}
	for _, typ := range types {
		if err := a.DeleteAllOf(ctx, typ, client.InNamespace(a.operatorNamespace), client.MatchingLabels(labels)); err != nil {
			return false, err
		}
	}
	return true, nil
}

func (a *tailscaleSTSReconciler) reconcileHeadlessService(ctx context.Context, logger *zap.SugaredLogger, sts *tailscaleSTSConfig) (*corev1.Service, error) {
	hsvc := &corev1.Service{
		ObjectMeta: metav1.ObjectMeta{
			GenerateName: "ts-" + sts.ParentResourceName + "-",
			Namespace:    a.operatorNamespace,
			Labels:       sts.ChildResourceLabels,
		},
		Spec: corev1.ServiceSpec{
			ClusterIP: "None",
			Selector: map[string]string{
				"app": sts.ParentResourceUID,
			},
		},
	}
	logger.Debugf("reconciling headless service for StatefulSet")
	return createOrUpdate(ctx, a.Client, a.operatorNamespace, hsvc, func(svc *corev1.Service) { svc.Spec = hsvc.Spec })
}

func (a *tailscaleSTSReconciler) createOrGetSecret(ctx context.Context, logger *zap.SugaredLogger, stsC *tailscaleSTSConfig, hsvc *corev1.Service) (string, error) {
	secret := &corev1.Secret{
		ObjectMeta: metav1.ObjectMeta{
			// Hardcode a -0 suffix so that in future, if we support
			// multiple StatefulSet replicas, we can provision -N for
			// those.
			Name:      hsvc.Name + "-0",
			Namespace: a.operatorNamespace,
			Labels:    stsC.ChildResourceLabels,
		},
	}
	if err := a.Get(ctx, client.ObjectKeyFromObject(secret), secret); err == nil {
		logger.Debugf("secret %s/%s already exists", secret.GetNamespace(), secret.GetName())
		return secret.Name, nil
	} else if !apierrors.IsNotFound(err) {
		return "", err
	}

	// Secret doesn't exist yet, create one. Initially it contains
	// only the Tailscale authkey, but once Tailscale starts it'll
	// also store the daemon state.
	sts, err := getSingleObject[appsv1.StatefulSet](ctx, a.Client, a.operatorNamespace, stsC.ChildResourceLabels)
	if err != nil {
		return "", err
	}
	if sts != nil {
		// StatefulSet exists, so we have already created the secret.
		// If the secret is missing, they should delete the StatefulSet.
		logger.Errorf("Tailscale proxy secret doesn't exist, but the corresponding StatefulSet %s/%s already does. Something is wrong, please delete the StatefulSet.", sts.GetNamespace(), sts.GetName())
		return "", nil
	}
	// Create API Key secret which is going to be used by the statefulset
	// to authenticate with Tailscale.
	logger.Debugf("creating authkey for new tailscale proxy")
	tags := stsC.Tags
	if len(tags) == 0 {
		tags = a.defaultTags
	}
	authKey, err := a.newAuthKey(ctx, tags)
	if err != nil {
		return "", err
	}

	secret.StringData = map[string]string{
		"authkey": authKey,
	}
	if err := a.Create(ctx, secret); err != nil {
		return "", err
	}
	return secret.Name, nil
}

// DeviceInfo returns the device ID and hostname for the Tailscale device
// associated with the given labels.
func (a *tailscaleSTSReconciler) DeviceInfo(ctx context.Context, childLabels map[string]string) (id tailcfg.StableNodeID, hostname string, err error) {
	sec, err := getSingleObject[corev1.Secret](ctx, a.Client, a.operatorNamespace, childLabels)
	if err != nil {
		return "", "", err
	}
	if sec == nil {
		return "", "", nil
	}
	id = tailcfg.StableNodeID(sec.Data["device_id"])
	if id == "" {
		return "", "", nil
	}
	// Kubernetes chokes on well-formed FQDNs with the trailing dot, so we have
	// to remove it.
	hostname = strings.TrimSuffix(string(sec.Data["device_fqdn"]), ".")
	if hostname == "" {
		return "", "", nil
	}
	return id, hostname, nil
}

func (a *tailscaleSTSReconciler) newAuthKey(ctx context.Context, tags []string) (string, error) {
	caps := tailscale.KeyCapabilities{
		Devices: tailscale.KeyDeviceCapabilities{
			Create: tailscale.KeyDeviceCreateCapabilities{
				Reusable:      false,
				Preauthorized: true,
				Tags:          tags,
			},
		},
	}

	key, _, err := a.tsClient.CreateKey(ctx, caps)
	if err != nil {
		return "", err
	}
	return key, nil
}

//go:embed manifests/proxy.yaml
var proxyYaml []byte

func (a *tailscaleSTSReconciler) reconcileSTS(ctx context.Context, logger *zap.SugaredLogger, sts *tailscaleSTSConfig, headlessSvc *corev1.Service, authKeySecret string) (*appsv1.StatefulSet, error) {
	var ss appsv1.StatefulSet
	if err := yaml.Unmarshal(proxyYaml, &ss); err != nil {
		return nil, fmt.Errorf("failed to unmarshal proxy spec: %w", err)
	}
	container := &ss.Spec.Template.Spec.Containers[0]
	container.Image = a.proxyImage
	container.Env = append(container.Env,
		corev1.EnvVar{
			Name:  "TS_DEST_IP",
			Value: sts.TargetIP,
		},
		corev1.EnvVar{
			Name:  "TS_KUBE_SECRET",
			Value: authKeySecret,
		},
		corev1.EnvVar{
			Name:  "TS_HOSTNAME",
			Value: sts.Hostname,
		})
	ss.ObjectMeta = metav1.ObjectMeta{
		Name:      headlessSvc.Name,
		Namespace: a.operatorNamespace,
		Labels:    sts.ChildResourceLabels,
	}
	ss.Spec.ServiceName = headlessSvc.Name
	ss.Spec.Selector = &metav1.LabelSelector{
		MatchLabels: map[string]string{
			"app": sts.ParentResourceUID,
		},
	}

	// containerboot currently doesn't have a way to re-read the hostname/ip as
	// it is passed via an environment variable. So we need to restart the
	// container when the value changes. We do this by adding an annotation to
	// the pod template that contains the last value we set.
	ss.Spec.Template.Annotations = map[string]string{
		"tailscale.com/operator-last-set-hostname": sts.Hostname,
	}
	if sts.TargetIP != "" {
		ss.Spec.Template.Annotations["tailscale.com/operator-last-set-ip"] = sts.TargetIP
	}
	ss.Spec.Template.Labels = map[string]string{
		"app": sts.ParentResourceUID,
	}
	ss.Spec.Template.Spec.PriorityClassName = a.proxyPriorityClassName
	logger.Debugf("reconciling statefulset %s/%s", ss.GetNamespace(), ss.GetName())
	return createOrUpdate(ctx, a.Client, a.operatorNamespace, &ss, func(s *appsv1.StatefulSet) { s.Spec = ss.Spec })
}

// ptrObject is a type constraint for pointer types that implement
// client.Object.
type ptrObject[T any] interface {
	client.Object
	*T
}

// createOrUpdate adds obj to the k8s cluster, unless the object already exists,
// in which case update is called to make changes to it. If update is nil, the
// existing object is returned unmodified.
//
// obj is looked up by its Name and Namespace if Name is set, otherwise it's
// looked up by labels.
func createOrUpdate[T any, O ptrObject[T]](ctx context.Context, c client.Client, ns string, obj O, update func(O)) (O, error) {
	var (
		existing O
		err      error
	)
	if obj.GetName() != "" {
		existing = new(T)
		existing.SetName(obj.GetName())
		existing.SetNamespace(obj.GetNamespace())
		err = c.Get(ctx, client.ObjectKeyFromObject(obj), existing)
	} else {
		existing, err = getSingleObject[T, O](ctx, c, ns, obj.GetLabels())
	}
	if err == nil && existing != nil {
		if update != nil {
			update(existing)
			if err := c.Update(ctx, existing); err != nil {
				return nil, err
			}
		}
		return existing, nil
	}
	if err != nil && !apierrors.IsNotFound(err) {
		return nil, fmt.Errorf("failed to get object: %w", err)
	}
	if err := c.Create(ctx, obj); err != nil {
		return nil, err
	}
	return obj, nil
}

// getSingleObject searches for k8s objects of type T
// (e.g. corev1.Service) with the given labels, and returns
// it. Returns nil if no objects match the labels, and an error if
// more than one object matches.
func getSingleObject[T any, O ptrObject[T]](ctx context.Context, c client.Client, ns string, labels map[string]string) (O, error) {
	ret := O(new(T))
	kinds, _, err := c.Scheme().ObjectKinds(ret)
	if err != nil {
		return nil, err
	}
	if len(kinds) != 1 {
		// TODO: the runtime package apparently has a "pick the best
		// GVK" function somewhere that might be good enough?
		return nil, fmt.Errorf("more than 1 GroupVersionKind for %T", ret)
	}

	gvk := kinds[0]
	gvk.Kind += "List"
	lst := unstructured.UnstructuredList{}
	lst.SetGroupVersionKind(gvk)
	if err := c.List(ctx, &lst, client.InNamespace(ns), client.MatchingLabels(labels)); err != nil {
		return nil, err
	}

	if len(lst.Items) == 0 {
		return nil, nil
	}
	if len(lst.Items) > 1 {
		return nil, fmt.Errorf("found multiple matching %T objects", ret)
	}
	if err := c.Scheme().Convert(&lst.Items[0], ret, nil); err != nil {
		return nil, err
	}
	return ret, nil
}

func defaultBool(envName string, defVal bool) bool {
	vs := os.Getenv(envName)
	if vs == "" {
		return defVal
	}
	v, _ := opt.Bool(vs).Get()
	return v
}

func defaultEnv(envName, defVal string) string {
	v := os.Getenv(envName)
	if v == "" {
		return defVal
	}
	return v
}

func nameForService(svc *corev1.Service) (string, error) {
	if h, ok := svc.Annotations[AnnotationHostname]; ok {
		if err := dnsname.ValidLabel(h); err != nil {
			return "", fmt.Errorf("invalid Tailscale hostname %q: %w", h, err)
		}
		return h, nil
	}
	return svc.Namespace + "-" + svc.Name, nil
}