package main

import (
	"context"
	"encoding/binary"
	"fmt"
	"io"
	"log"
	"net"
	"strings"
	"time"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/kubernetes"
)

type Discovery interface {
	Discover() ([]string, error)
}

type K8sDiscovery struct {
	ctx    context.Context
	client *kubernetes.Clientset
}

func (k *K8sDiscovery) Discover() ([]string, error) {
	return k.DiscoverInNamespace("")
}
func (k *K8sDiscovery) DiscoverInNamespace(namespace string) ([]string, error) {
	pods, err := k.client.CoreV1().Pods(namespace).List(k.ctx, metav1.ListOptions{
		LabelSelector: "actor-pool=cart",
	})
	if err != nil {
		return nil, err
	}
	hosts := make([]string, 0, len(pods.Items))
	for _, pod := range pods.Items {
		hosts = append(hosts, pod.Status.PodIP)
	}
	return hosts, nil
}

func NewK8sDiscovery(client *kubernetes.Clientset) *K8sDiscovery {
	return &K8sDiscovery{
		ctx:    context.Background(),
		client: client,
	}
}

type Quorum interface {
	Negotiate(knownHosts []string) ([]string, error)
	OwnerChanged(CartId, host string) error
}

type RemoteHost struct {
	Host       string
	Pool       *RemoteGrainPool
	connection net.Conn
}

type SyncedPool struct {
	Discovery   Discovery
	listener    net.Listener
	Hostname    string
	local       *GrainLocalPool
	remotes     []RemoteHost
	remoteIndex map[CartId]*RemoteGrainPool
}

func NewSyncedPool(local *GrainLocalPool, hostname string, d Discovery) (*SyncedPool, error) {
	listen := fmt.Sprintf("%s:1338", hostname)
	l, err := net.Listen("tcp", listen)
	if err != nil {
		return nil, err
	}
	pool := &SyncedPool{
		Discovery:   d,
		Hostname:    hostname,
		local:       local,
		listener:    l,
		remotes:     make([]RemoteHost, 0),
		remoteIndex: make(map[CartId]*RemoteGrainPool),
	}
	if d != nil {
		discoveryTimer := time.NewTicker(time.Second * 5)
		go func() {
			<-discoveryTimer.C
			hosts, err := d.Discover()
			if err != nil {
				log.Printf("Error discovering hosts: %v\n", err)
				return
			}
			for _, h := range hosts {
				if h == hostname {
					continue
				}
				log.Printf("Discovered host %s\n", h)
				err := pool.AddRemote(h)
				if err != nil {
					log.Printf("Error adding remote %s: %v\n", h, err)
				}
			}
		}()
	}
	go func() {
		for {
			conn, err := l.Accept()
			if err != nil {
				log.Printf("Error accepting connection: %v\n", err)
				continue
			}
			log.Printf("Got connection from %s", conn.RemoteAddr().String())
			go pool.handleConnection(conn)
		}
	}()
	return pool, nil
}

const (
	RemoteNegotiate    = uint16(3)
	RemoteGrainChanged = uint16(4)
	AckChange          = uint16(5)
	AckError           = uint16(6)
)

func (p *SyncedPool) handleConnection(conn net.Conn) {
	defer conn.Close()
	var packet Packet
	for {
		err := binary.Read(conn, binary.LittleEndian, &packet)
		if err != nil {
			if err == io.EOF {
				break
			}
			log.Printf("Error in connection: %v\n", err)
		}
		// if packet.Version != 1 {
		// 	log.Printf("Invalid version %d\n", packet.Version)
		// 	return
		// }
		switch packet.MessageType {
		case RemoteNegotiate:
			data := make([]byte, packet.DataLength)
			conn.Read(data)
			knownHosts := strings.Split(string(data), ";")
			log.Printf("Negotiated with remote, found %v hosts\n", knownHosts)

			for _, h := range knownHosts {
				err = p.AddRemote(h)
				if err != nil {
					log.Printf("Error adding remote %s: %v\n", h, err)
				}
			}

			SendPacket(conn, RemoteNegotiate, func(w io.Writer) error {
				hostnames := make([]string, 0, len(p.remotes))
				for _, r := range p.remotes {
					hostnames = append(hostnames, r.Host)
				}
				w.Write([]byte(strings.Join(hostnames, ";")))
				return nil
			})
		case RemoteGrainChanged:
			// remote grain changed
			log.Printf("Remote grain changed\n")
			for err == nil {
				idAndHost := make([]byte, packet.DataLength)
				_, err = conn.Read(idAndHost)
				log.Printf("Remote grain %s changed\n", idAndHost)
				if err != nil {
					break
				}
				idAndHostParts := strings.Split(string(idAndHost), ";")
				if len(idAndHostParts) != 2 {
					log.Printf("Invalid remote grain change message\n")
					break
				}
				found := false
				for _, r := range p.remotes {
					if r.Host == string(idAndHostParts[1]) {
						found = true
						log.Printf("Remote grain %s changed to %s\n", idAndHostParts[0], idAndHostParts[1])
						p.remoteIndex[ToCartId(idAndHostParts[0])] = r.Pool
					}
				}

				if !found {
					log.Printf("Remote host %s not found\n", idAndHostParts[1])
					SendPacket(conn, AckError, func(w io.Writer) error {
						w.Write([]byte("remote host not found"))
						return nil
					})
				} else {
					SendPacket(conn, AckChange, func(w io.Writer) error {
						w.Write([]byte("ok"))
						return nil
					})
				}
			}
		}
	}
}

func (h *RemoteHost) Negotiate(knownHosts []string) ([]string, error) {
	SendPacket(h.connection, RemoteNegotiate, func(w io.Writer) error {
		w.Write([]byte(strings.Join(knownHosts, ";")))
		return nil
	})
	t, data, err := ReceivePacket(h.connection)
	if err != nil {
		return nil, err
	}
	if t != RemoteNegotiate {
		return nil, fmt.Errorf("unexpected message type %d", t)
	}
	return strings.Split(string(data), ";"), nil
}

func (p *SyncedPool) Negotiate(knownHosts []string) ([]string, error) {
	allHosts := make(map[string]struct{}, 0)
	for _, r := range p.remotes {
		hosts, err := r.Negotiate(knownHosts)
		if err != nil {
			return nil, err
		}
		for _, h := range hosts {
			allHosts[h] = struct{}{}
		}
	}
	ret := make([]string, 0, len(allHosts))
	for h := range allHosts {
		ret = append(ret, h)
	}
	return ret, nil
}

func (r *RemoteHost) ConfirmChange(id CartId, host string) error {
	SendPacket(r.connection, RemoteGrainChanged, func(w io.Writer) error {

		w.Write([]byte(fmt.Sprintf("%s;%s", id, host)))
		return nil
	})
	t, _, err := ReceivePacket(r.connection)
	if err != nil {
		return err
	}
	if t != AckChange {
		return fmt.Errorf("unexpected message type %d", t)
	}
	return nil
}

func (p *SyncedPool) OwnerChanged(id CartId, host string) error {
	for _, r := range p.remotes {
		err := r.ConfirmChange(id, host)

		if err != nil {
			log.Printf("Error confirming change: %v\n", err)
			return err
		}
	}
	return nil
}

func (p *SyncedPool) AddRemote(address string) error {
	for _, r := range p.remotes {
		if r.Host == address {
			log.Printf("Remote %s already exists\n", address)
			return fmt.Errorf("remote %s already exists", address)
		}
	}
	connection, err := net.Dial("tcp", fmt.Sprintf("%s:1338", address))
	if err != nil {
		return err
	}

	pool := NewRemoteGrainPool(fmt.Sprintf(address, 1337))
	remote := RemoteHost{
		connection: connection,
		Pool:       pool,
		Host:       address,
	}
	p.remotes = append(p.remotes, remote)
	log.Printf("Added remote %s\n", remote.Host)

	return nil
}

func (p *SyncedPool) Process(id CartId, messages ...Message) ([]byte, error) {
	// check if local grain exists
	_, ok := p.local.grains[id]
	if !ok {
		// check if remote grain exists
		remoteGrain, ok := p.remoteIndex[id]
		if ok {
			return remoteGrain.Process(id, messages...)
		}
	}
	err := p.OwnerChanged(id, p.Hostname)
	if err != nil {
		return nil, err
	}
	return p.local.Process(id, messages...)
}

func (p *SyncedPool) Get(id CartId) ([]byte, error) {
	// check if local grain exists
	_, ok := p.local.grains[id]
	if !ok {
		// check if remote grain exists
		remoteGrain, ok := p.remoteIndex[id]
		if ok {
			return remoteGrain.Get(id)
		}
	}
	return p.local.Get(id)
}