package lease

import (
	"context"
	"errors"
	"time"

	coordinationv1 "k8s.io/api/coordination/v1"
	k8serrors "k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/rest"
)

var ErrLocked = errors.New("lease is held by another holder")

// Locker manages a Kubernetes Lease object for distributed locking.
type Locker struct {
	client     kubernetes.Interface
	namespace  string
	leaseName  string
	holderID   string
	ttlSeconds int
}

// New builds an in-cluster Kubernetes client and returns a Locker.
func New(namespace, leaseName, holderID string, ttlSeconds int) (*Locker, error) {
	cfg, err := rest.InClusterConfig()
	if err != nil {
		return nil, err
	}
	client, err := kubernetes.NewForConfig(cfg)
	if err != nil {
		return nil, err
	}
	return &Locker{
		client:     client,
		namespace:  namespace,
		leaseName:  leaseName,
		holderID:   holderID,
		ttlSeconds: ttlSeconds,
	}, nil
}

// Acquire tries to create the Lease. If it already exists and is stale
// (renewTime + TTL is in the past) it deletes and recreates it. If held by
// another identity and not stale, it returns ErrLocked.
func (l *Locker) Acquire(ctx context.Context) error {
	now := metav1.NewMicroTime(time.Now())
	ttl := int32(l.ttlSeconds)

	desired := &coordinationv1.Lease{
		ObjectMeta: metav1.ObjectMeta{
			Name:      l.leaseName,
			Namespace: l.namespace,
		},
		Spec: coordinationv1.LeaseSpec{
			HolderIdentity:       &l.holderID,
			LeaseDurationSeconds: &ttl,
			AcquireTime:          &now,
			RenewTime:            &now,
		},
	}

	_, err := l.client.CoordinationV1().Leases(l.namespace).Create(ctx, desired, metav1.CreateOptions{})
	if err == nil {
		return nil
	}
	if !k8serrors.IsAlreadyExists(err) {
		return err
	}

	// Lease already exists — inspect it.
	existing, err := l.client.CoordinationV1().Leases(l.namespace).Get(ctx, l.leaseName, metav1.GetOptions{})
	if err != nil {
		return err
	}

	if isStale(existing, l.ttlSeconds) {
		// Delete the stale lease and recreate.
		if err := l.client.CoordinationV1().Leases(l.namespace).Delete(ctx, l.leaseName, metav1.DeleteOptions{}); err != nil && !k8serrors.IsNotFound(err) {
			return err
		}
		_, err = l.client.CoordinationV1().Leases(l.namespace).Create(ctx, desired, metav1.CreateOptions{})
		return err
	}

	return ErrLocked
}

// Release deletes the Lease if its holderIdentity matches our holderID.
func (l *Locker) Release(ctx context.Context) error {
	existing, err := l.client.CoordinationV1().Leases(l.namespace).Get(ctx, l.leaseName, metav1.GetOptions{})
	if err != nil {
		if k8serrors.IsNotFound(err) {
			return nil
		}
		return err
	}

	if existing.Spec.HolderIdentity == nil || *existing.Spec.HolderIdentity != l.holderID {
		return nil
	}

	err = l.client.CoordinationV1().Leases(l.namespace).Delete(ctx, l.leaseName, metav1.DeleteOptions{})
	if k8serrors.IsNotFound(err) {
		return nil
	}
	return err
}

// StartHeartbeat starts a goroutine that updates renewTime every ttl/3 seconds
// until ctx is cancelled, preventing the lock from going stale during long syncs.
func (l *Locker) StartHeartbeat(ctx context.Context) {
	interval := time.Duration(l.ttlSeconds) * time.Second / 3
	go func() {
		ticker := time.NewTicker(interval)
		defer ticker.Stop()
		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker.C:
				_ = l.updateRenewTime(ctx)
			}
		}
	}()
}

// updateRenewTime patches the Lease's renewTime to now, keeping the lock alive.
func (l *Locker) updateRenewTime(ctx context.Context) error {
	existing, err := l.client.CoordinationV1().Leases(l.namespace).Get(ctx, l.leaseName, metav1.GetOptions{})
	if err != nil {
		return err
	}

	if existing.Spec.HolderIdentity == nil || *existing.Spec.HolderIdentity != l.holderID {
		return ErrLocked
	}

	now := metav1.NewMicroTime(time.Now())
	existing.Spec.RenewTime = &now
	_, err = l.client.CoordinationV1().Leases(l.namespace).Update(ctx, existing, metav1.UpdateOptions{})
	return err
}

// isStale returns true if the lease's renewTime + TTL is in the past.
func isStale(lease *coordinationv1.Lease, ttlSeconds int) bool {
	if lease.Spec.RenewTime == nil {
		return true
	}
	expiry := lease.Spec.RenewTime.Time.Add(time.Duration(ttlSeconds) * time.Second)
	return time.Now().After(expiry)
}