package main

import (
	"crypto/tls"
	"encoding/binary"
	kademlia "gitlab.lrz.de/netintum/teaching/p2psec_projects_2024/DHT-6/pkg"
	"io"
	"log"
	"net"
	"strconv"
	"time"
)

type P2PServer struct {
	dhtInstance *kademlia.DHT
}

func initializeP2PServer(config *kademlia.Config, dht *kademlia.DHT) {

	// Get the certificate ready to accept connections via TLS
	cert, err := tls.LoadX509KeyPair(config.CertFile, config.KeyFile)
	if err != nil {
		log.Fatal(err)
	}

	tlsConfig := &tls.Config{Certificates: []tls.Certificate{cert}}
	listener, err := tls.Listen("tcp", config.P2PAddress+":"+strconv.Itoa(int(config.P2PPort)), tlsConfig)

	if err != nil {
		log.Fatalln("[P2P Server] Error starting server: ", err)
	}
	defer listener.Close()
	server := &P2PServer{dhtInstance: dht}

	lastUpdated := time.Now()

	for {
		connection, err := listener.Accept()

		// Expire and republish entries periodically
		if time.Since(lastUpdated) > config.RepublishInterval {
			go server.dhtInstance.Housekeeping(time.Now().Sub(lastUpdated))
			lastUpdated = time.Now()
		}

		if err != nil {
			log.Println("[P2P Server] Error accepting connection: ", err)
			continue
		}

		// Handle in separate thread and close when done
		go func() {
			server.handleP2PMessage(connection)
			connection.Close()
		}()
	}
}

func (p *P2PServer) handleP2PMessage(connection net.Conn) {
	// Add a lenient timeout so connections cannot be held open forever.
	err := connection.SetDeadline(time.Now().Add(10 * time.Second))
	if err != nil {
		log.Println("[P2P Server] Error setting deadline: ", err)
		return
	}

	buf := make([]byte, 4)
	_, err = io.ReadFull(connection, buf)
	if err != nil {
		log.Println("[P2P Server] Error reading message: ", err)
		return
	}
	size := binary.BigEndian.Uint16(buf[:2])
	messageType := binary.BigEndian.Uint16(buf[2:])

	// Subtract 4 bytes used for size and message type
	buf2 := make([]byte, size-4)
	_, err = io.ReadFull(connection, buf2)
	if err != nil {
		log.Println("[P2P Server] Error reading message: ", err)
		return
	}

	// combine header and body to get the full message again
	data := append(buf, buf2...)

	switch messageType {
	case kademlia.STORE:
		packet, err := kademlia.ParseStorePacket(data)
		if err != nil {
			log.Println("[P2P Server] Error parsing store packet: ", err)
			return
		}
		p.handleStore(packet)
	case kademlia.PING:
		packet, err := kademlia.ParsePingPacket(data)
		if err != nil {
			log.Println("[P2P Server] Error parsing ping packet: ", err)
			return
		}
		p.handlePing(packet, connection)
	case kademlia.FINDNODE:
		packet, err := kademlia.ParseFindNodePacket(data)
		if err != nil {
			log.Println("[P2P Server] Error parsing find node packet: ", err)
			return
		}
		p.handleFindNode(packet, connection)
	case kademlia.FINDVALUE:
		packet, err := kademlia.ParseFindValuePacket(data)
		if err != nil {
			log.Println("[P2P Server] Error parsing find value packet: ", err)
			return
		}
		p.handleFindValue(packet, connection)
	default:
		log.Println("[P2P Server] Invalid message type")
	}
}

func (p *P2PServer) handleStore(packet *kademlia.P2PStorePacket) {
	// Always add the sender to the routing table
	senderNode := kademlia.NodeFromIpPort(packet.SourceIP, uint64(packet.SourcePort), packet.Certificate)
	go p.dhtInstance.RoutingTable.Insert(senderNode)

	nodes := p.dhtInstance.RoutingTable.FindClosest(packet.Key, int(packet.RepCount))

	if len(*nodes) < int(packet.RepCount) || kademlia.ContainsID((*nodes)[:packet.RepCount], p.dhtInstance.SelfNode.NodeID) {
		log.Printf("Storing value...")
		value := packet.Value
		p.dhtInstance.Storage.Put(packet.Key, value, packet.TTL, packet.RepCount)
	} else {
		log.Printf("Stored at enough other nodes, no need to.")
	}
}

func (p *P2PServer) handlePing(packet *kademlia.P2PPingPacket, connection net.Conn) {
	// Always add the sender to the routing table
	senderNode := kademlia.NodeFromIpPort(packet.SourceIP, uint64(packet.SourcePort), packet.Certificate)
	go p.dhtInstance.RoutingTable.Insert(senderNode)

	reply := kademlia.SerialisePongPacket(&kademlia.P2PPongPacket{})
	_, _ = connection.Write(reply)
}

func (p *P2PServer) handleFindNode(packet *kademlia.P2PFindNodePacket, connection net.Conn) {
	// Always add the sender to the routing table
	senderNode := kademlia.NodeFromIpPort(packet.SourceIP, uint64(packet.SourcePort), packet.Certificate)
	go p.dhtInstance.RoutingTable.Insert(senderNode)

	nodes := p.dhtInstance.RoutingTable.FindClosest(packet.Key, int(packet.Amount))

	reply := kademlia.SerialiseFoundNodePacket(&kademlia.P2PFoundNodePacket{Nodes: *nodes})

	_, _ = connection.Write(reply)
}

func (p *P2PServer) handleFindValue(packet *kademlia.P2PFindValuePacket, connection net.Conn) {
	// Always add the sender to the routing table
	senderNode := kademlia.NodeFromIpPort(packet.SourceIP, uint64(packet.SourcePort), packet.Certificate)
	go p.dhtInstance.RoutingTable.Insert(senderNode)

	val, exists := p.dhtInstance.Storage.GetValue(packet.Key)

	if exists {
		reply := kademlia.P2PFoundValuePacket{
			Value: val,
		}
		_, _ = connection.Write(kademlia.SerialiseFoundValuePacket(&reply))
	} else {
		reply := kademlia.SerialiseNotFoundValuePacket(&kademlia.P2PNotFoundPValuePacket{})
		_, _ = connection.Write(reply)
	}

}