// Package kubernetes provides the kubernetes backend.
package kubernetes

import (
	"errors"
	"fmt"
	"log"
	"strconv"
	"strings"
	"time"

	"github.com/miekg/coredns/middleware"
	"github.com/miekg/coredns/middleware/etcd/msg"
	"github.com/miekg/coredns/middleware/kubernetes/nametemplate"
	"github.com/miekg/coredns/middleware/pkg/dnsutil"
	dnsstrings "github.com/miekg/coredns/middleware/pkg/strings"
	"github.com/miekg/coredns/middleware/proxy"
	"github.com/miekg/coredns/request"

	"github.com/miekg/dns"
	"k8s.io/client-go/1.5/kubernetes"
	"k8s.io/client-go/1.5/pkg/api"
	unversionedapi "k8s.io/client-go/1.5/pkg/api/unversioned"
	"k8s.io/client-go/1.5/pkg/labels"
	"k8s.io/client-go/1.5/rest"
	"k8s.io/client-go/1.5/tools/clientcmd"
	clientcmdapi "k8s.io/client-go/1.5/tools/clientcmd/api"
)

// Kubernetes implements a middleware that connects to a Kubernetes cluster.
type Kubernetes struct {
	Next          middleware.Handler
	Zones         []string
	Proxy         proxy.Proxy // Proxy for looking up names during the resolution process
	APIEndpoint   string
	APICertAuth   string
	APIClientCert string
	APIClientKey  string
	APIConn       *dnsController
	ResyncPeriod  time.Duration
	NameTemplate  *nametemplate.Template
	Namespaces    []string
	LabelSelector *unversionedapi.LabelSelector
	Selector      *labels.Selector
}

var errNoItems = errors.New("no items found")
var errNsNotExposed = errors.New("namespace is not exposed")

// Services implements the ServiceBackend interface.
func (k *Kubernetes) Services(state request.Request, exact bool, opt middleware.Options) ([]msg.Service, []msg.Service, error) {
	s, e := k.Records(state.Name(), exact)
	return s, nil, e // Haven't implemented debug queries yet.
}

// Reverse implements the ServiceBackend interface.
func (k *Kubernetes) Reverse(state request.Request, exact bool, opt middleware.Options) ([]msg.Service, []msg.Service, error) {
	ip := dnsutil.ExtractAddressFromReverse(state.Name())
	if ip == "" {
		return nil, nil, nil
	}

	records := k.getServiceRecordForIP(ip, state.Name())
	return records, nil, nil
}

// Lookup implements the ServiceBackend interface.
func (k *Kubernetes) Lookup(state request.Request, name string, typ uint16) (*dns.Msg, error) {
	return k.Proxy.Lookup(state, name, typ)
}

// IsNameError implements the ServiceBackend interface.
func (k *Kubernetes) IsNameError(err error) bool {
	return err == errNoItems || err == errNsNotExposed
}

// Debug implements the ServiceBackend interface.
func (k *Kubernetes) Debug() string {
	return "debug"
}

func (k *Kubernetes) getClientConfig() (*rest.Config, error) {
	// For a custom api server or running outside a k8s cluster
	// set URL in env.KUBERNETES_MASTER or set endpoint in Corefile
	loadingRules := clientcmd.NewDefaultClientConfigLoadingRules()
	overrides := &clientcmd.ConfigOverrides{}
	clusterinfo := clientcmdapi.Cluster{}
	authinfo := clientcmdapi.AuthInfo{}
	if len(k.APIEndpoint) > 0 {
		clusterinfo.Server = k.APIEndpoint
	} else {
		cc, err := rest.InClusterConfig()
		if err != nil {
			return nil, err
		}
		return cc, err
	}
	if len(k.APICertAuth) > 0 {
		clusterinfo.CertificateAuthority = k.APICertAuth
	}
	if len(k.APIClientCert) > 0 {
		authinfo.ClientCertificate = k.APIClientCert
	}
	if len(k.APIClientKey) > 0 {
		authinfo.ClientKey = k.APIClientKey
	}
	overrides.ClusterInfo = clusterinfo
	overrides.AuthInfo = authinfo
	clientConfig := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(loadingRules, overrides)
	return clientConfig.ClientConfig()
}

// InitKubeCache initializes a new Kubernetes cache.
func (k *Kubernetes) InitKubeCache() error {

	config, err := k.getClientConfig()
	if err != nil {
		return err
	}

	kubeClient, err := kubernetes.NewForConfig(config)
	if err != nil {
		return fmt.Errorf("Failed to create kubernetes notification controller: %v", err)
	}

	if k.LabelSelector != nil {
		var selector labels.Selector
		selector, err = unversionedapi.LabelSelectorAsSelector(k.LabelSelector)
		k.Selector = &selector
		if err != nil {
			return fmt.Errorf("Unable to create Selector for LabelSelector '%s'.Error was: %s", k.LabelSelector, err)
		}
	}

	if k.LabelSelector == nil {
		log.Printf("[INFO] Kubernetes middleware configured without a label selector. No label-based filtering will be performed.")
	} else {
		log.Printf("[INFO] Kubernetes middleware configured with the label selector '%s'. Only kubernetes objects matching this label selector will be exposed.", unversionedapi.FormatLabelSelector(k.LabelSelector))
	}

	k.APIConn = newdnsController(kubeClient, k.ResyncPeriod, k.Selector)

	return err
}

// getZoneForName returns the zone string that matches the name and a
// list of the DNS labels from name that are within the zone.
// For example, if "coredns.local" is a zone configured for the
// Kubernetes middleware, then getZoneForName("a.b.coredns.local")
// will return ("coredns.local", ["a", "b"]).
func (k *Kubernetes) getZoneForName(name string) (string, []string) {
	var zone string
	var serviceSegments []string

	for _, z := range k.Zones {
		if dns.IsSubDomain(z, name) {
			zone = z

			serviceSegments = dns.SplitDomainName(name)
			serviceSegments = serviceSegments[:len(serviceSegments)-dns.CountLabel(zone)]
			break
		}
	}

	return zone, serviceSegments
}

// Records looks up services in kubernetes. If exact is true, it will lookup
// just this name. This is used when find matches when completing SRV lookups
// for instance.
func (k *Kubernetes) Records(name string, exact bool) ([]msg.Service, error) {
	var (
		serviceName string
		namespace   string
		typeName    string
	)

	zone, serviceSegments := k.getZoneForName(name)

	// TODO: Implementation above globbed together segments for the serviceName if
	//       multiple segments remained. Determine how to do similar globbing using
	//		 the template-based implementation.
	namespace = k.NameTemplate.NamespaceFromSegmentArray(serviceSegments)
	serviceName = k.NameTemplate.ServiceFromSegmentArray(serviceSegments)
	typeName = k.NameTemplate.TypeFromSegmentArray(serviceSegments)

	if namespace == "" {
		err := errors.New("Parsing query string did not produce a namespace value. Assuming wildcard namespace.")
		log.Printf("[WARN] %v\n", err)
		namespace = "*"
	}

	if serviceName == "" {
		err := errors.New("Parsing query string did not produce a serviceName value. Assuming wildcard serviceName.")
		log.Printf("[WARN] %v\n", err)
		serviceName = "*"
	}

	nsWildcard := symbolContainsWildcard(namespace)
	serviceWildcard := symbolContainsWildcard(serviceName)

	// Abort if the namespace does not contain a wildcard, and namespace is not published per CoreFile
	// Case where namespace contains a wildcard is handled in Get(...) method.
	if (!nsWildcard) && (len(k.Namespaces) > 0) && (!dnsstrings.StringInSlice(namespace, k.Namespaces)) {
		return nil, errNsNotExposed
	}

	k8sItems, err := k.Get(namespace, nsWildcard, serviceName, serviceWildcard, typeName)
	if err != nil {
		return nil, err
	}
	if len(k8sItems) == 0 {
		// Did not find item in k8s
		return nil, errNoItems
	}

	records := k.getRecordsForServiceItems(k8sItems, zone)
	return records, nil
}

func (k *Kubernetes) getRecordsForServiceItems(serviceItems []*api.Service, zone string) []msg.Service {
	var records []msg.Service

	for _, item := range serviceItems {
		clusterIP := item.Spec.ClusterIP

		// Create records for each exposed port...
		key := k.NameTemplate.RecordNameFromNameValues(nametemplate.NameValues{TypeName: "svc", ServiceName: item.ObjectMeta.Name, Namespace: item.ObjectMeta.Namespace, Zone: zone})
		key = strings.Replace(key, ".", "/", -1)

		for i, p := range item.Spec.Ports {
			s := msg.Service{Key: msg.Path(strconv.Itoa(i)+"."+key, "coredns"), Host: clusterIP, Port: int(p.Port)}
			records = append(records, s)
		}
	}

	return records
}

// Get performs the call to the Kubernetes http API.
func (k *Kubernetes) Get(namespace string, nsWildcard bool, servicename string, serviceWildcard bool, typeName string) ([]*api.Service, error) {
	switch {
	case typeName == "pod":
		return nil, fmt.Errorf("pod not implemented")
	default:
		return k.getServices(namespace, nsWildcard, servicename, serviceWildcard)
	}
}

func (k *Kubernetes) getServices(namespace string, nsWildcard bool, servicename string, serviceWildcard bool) ([]*api.Service, error) {
	serviceList := k.APIConn.ServiceList()

	var resultItems []*api.Service

	for _, item := range serviceList {
		if symbolMatches(namespace, item.Namespace, nsWildcard) && symbolMatches(servicename, item.Name, serviceWildcard) {
			// If namespace has a wildcard, filter results against Corefile namespace list.
			// (Namespaces without a wildcard were filtered before the call to this function.)
			if nsWildcard && (len(k.Namespaces) > 0) && (!dnsstrings.StringInSlice(item.Namespace, k.Namespaces)) {
				continue
			}
			resultItems = append(resultItems, item)
		}
	}

	return resultItems, nil
}

func symbolMatches(queryString string, candidateString string, wildcard bool) bool {
	result := false
	switch {
	case !wildcard:
		result = (queryString == candidateString)
	case queryString == "*":
		result = true
	case queryString == "any":
		result = true
	}
	return result
}

func (k *Kubernetes) getServiceRecordForIP(ip, name string) []msg.Service {
	svcList, err := k.APIConn.svcLister.List(labels.Everything())
	if err != nil {
		return nil
	}
	for _, service := range svcList {
		if service.Spec.ClusterIP == ip {
			return []msg.Service{{Host: ip}}
		}
	}

	return nil
}

// symbolContainsWildcard checks whether symbol contains a wildcard value
func symbolContainsWildcard(symbol string) bool {
	return (strings.Contains(symbol, "*") || (symbol == "any"))
}