package client

import (
	"context"
	"fmt"
	"net"

	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/util/intstr"
	"k8s.io/client-go/kubernetes"
)

// ResolveCluster parses Service resource content by itself.
// Fixes Issue https://github.com/karmada-io/karmada/issues/2487
// Modified from "k8s.io/apiserver/pkg/util/proxy/proxy.go:92 => func ResolveCluster"
func resolveCluster(kubeClient kubernetes.Interface, namespace, id string, port int32) (string, error) {
	svc, err := kubeClient.CoreV1().Services(namespace).Get(context.TODO(), id, metav1.GetOptions{})
	if err != nil {
		if apierrors.IsNotFound(err) {
			/*
			 * When Deploying Karmada in Host Kubernetes Cluster, the kubeClient will connect kube-apiserver
			 * of Karmada Control Plane, rather than of host cluster.
			 * But the Service resource is defined in Host Kubernetes Cluster. So we cannot get its content here.
			 * The best thing we can do is just glue host:port together, and try to connect to it.
			 */
			return net.JoinHostPort(id, fmt.Sprintf("%d", port)), nil
		}

		return "", err
	}

	if svc.Spec.Type != corev1.ServiceTypeExternalName {
		// We only support ExternalName type here.
		// See discussions in PR: https://github.com/karmada-io/karmada/pull/2574#discussion_r979539389
		return "", fmt.Errorf("unsupported service type %q", svc.Spec.Type)
	}

	svcPort, err := findServicePort(svc, port)
	if err != nil {
		return "", err
	}
	if svcPort.TargetPort.Type != intstr.Int {
		return "", fmt.Errorf("ExternalName service type should have int target port, "+
			"current target port: %v", svcPort.TargetPort)
	}
	return net.JoinHostPort(svc.Spec.ExternalName, fmt.Sprintf("%d", svcPort.TargetPort.IntVal)), nil
}

// findServicePort finds the service port by name or numerically.
func findServicePort(svc *corev1.Service, port int32) (*corev1.ServicePort, error) {
	for _, svcPort := range svc.Spec.Ports {
		if svcPort.Port == port {
			return &svcPort, nil
		}
	}
	return nil, apierrors.NewServiceUnavailable(fmt.Sprintf("no service port %d found for service %q", port, svc.Name))
}