package ipstack

import (
	"fmt"
	"github.com/pkg/errors"
	"iptcp/pkg/lnxconfig"
	"net"
	"net/netip"
)

const (
	MAX_IP_PACKET_SIZE        = 1400
	LOCAL_COST         uint32 = 4294967295 // 2^32 - 1
	STATIC_COST        uint32 = 1
)

// STRUCTS ---------------------------------------------------------------------
type Interface struct {
	Name      string
	IpAddress netip.Addr
	IpPrefix  netip.Prefix

	RecvSocket    net.Conn
	SocketChannel chan<- bool
	State         bool
}

type Neighbor struct {
	VipAddr netip.Addr
	UdpAddr netip.AddrPort

	SendSocket    net.Conn
	SocketChannel chan<- bool
}

type RIPMessage struct {
	command    uint8
	numEntries uint8
	entries    []RIPEntry
}

type RIPEntry struct {
	addr netip.Addr
	cost uint32
	mask netip.Prefix
}

type Hop struct {
	Cost     uint32
	VipAsStr string
}

// GLOBAL VARIABLES (data structures) ------------------------------------------
var myInterfaces []Interface
var myNeighbors = make(map[string]Neighbor)

// var myRIPNeighbors = make(map[string]Neighbor)
type HandlerFunc func(int, string, *[]byte) error

var protocolHandlers = make(map[uint16]HandlerFunc)

// var routingTable = routingtable.New()
var routingTable = make(map[netip.Prefix]Hop)

// reference: https://github.com/brown-csci1680/lecture-examples/blob/main/ip-demo/cmd/udp-ip-recv/main.go
func createUDPConn(UdpAddr netip.AddrPort, conn *net.Conn) error {
	listenString := UdpAddr.String()
	listenAddr, err := net.ResolveUDPAddr("udp4", listenString)
	if err != nil {
		return errors.WithMessage(err, "Error resolving address->\t"+listenString)
	}
	tmpConn, err := net.ListenUDP("udp4", listenAddr)
	if err != nil {
		return errors.WithMessage(err, "Could not bind to UDP port->\t"+listenString)
	}
	*conn = tmpConn

	return nil
}

func Initialize(lnxFilePath string) error {
	//if len(os.Args) != 2 {
	//	fmt.Printf("Usage:  %s <configFile>\n", os.Args[0])
	//	os.Exit(1)
	//}
	//lnxFilePath := os.Args[1]

	// Parse the file
	lnxConfig, err := lnxconfig.ParseConfig(lnxFilePath)
	if err != nil {
		return errors.WithMessage(err, "Error parsing config file->\t"+lnxFilePath)
	}

	// 1) initialize the interfaces on this node here and into the routing table
	for _, iface := range lnxConfig.Interfaces {
		i := &Interface{
			Name:          iface.Name,
			IpAddress:     iface.AssignedIP,
			IpPrefix:      iface.AssignedPrefix,
			RecvSocket:    nil,
			SocketChannel: nil,
			State:         false,
		}
		err := createUDPConn(iface.UDPAddr, &i.RecvSocket)
		if err != nil {
			return errors.WithMessage(err, "Error creating UDP socket for interface->\t"+iface.Name)
		}
		myInterfaces = append(myInterfaces, *i)

		// add to routing table
		ifacePrefix := netip.PrefixFrom(iface.AssignedIP, iface.AssignedPrefix.Bits())
		routingTable[ifacePrefix] = Hop{STATIC_COST, iface.Name}
	}

	// 2) initialize the neighbors connected to the node
	for _, neighbor := range lnxConfig.Neighbors {
		n := &Neighbor{
			VipAddr:    neighbor.DestAddr,
			UdpAddr:    neighbor.UDPAddr,
			SendSocket: nil,
		}
		err := createUDPConn(neighbor.UDPAddr, &n.SendSocket)
		if err != nil {
			return errors.WithMessage(err, "Error creating UDP socket for neighbor->\t"+neighbor.DestAddr.String())
		}
		// TODO: make a hash map
		myNeighbors[neighbor.InterfaceName] = *n

		// add to routing table
		neighborPrefix := netip.PrefixFrom(neighbor.DestAddr, 24)
		routingTable[neighborPrefix] = Hop{LOCAL_COST, neighbor.InterfaceName}
	}

	return nil
}

/*

func ListerToInterfaces() {
	for _, iface := range myInterfaces {
		go RecvIp(iface)
	}
}

func RecvIp(iface Interface) error {
	for {
		buffer := make([]byte, MAX_IP_PACKET_SIZE)
		_, sourceAddr, err := iface.udp.ReadFrom(buffer)
		if err != nil {
			log.Panicln("Error reading from UDP socket ", err)
		}

		hdr, err := ipv4header.ParseHeader(buffer)

		if err != nil {
			fmt.Println("Error parsing header", err)
			continue
		}

		headerSize := hdr.Len
		headerBytes := buffer[:headerSize]

		checksumFromHeader := uint16(hdr.Checksum)
		computedChecksum := ValidateChecksum(headerBytes, checksumFromHeader)

		var checksumState string
		if computedChecksum == checksumFromHeader {
			checksumState = "OK"
		} else {
			checksumState = "FAIL"
			continue
		}

		// check ttl
		ttl := data[8]
		if ttl == 0 {
			fmt.Println("TTL is 0")
			continue
		}

		destAddr := netip.AddrFrom(data[16:20])
		protocolNum := data[9]

		if destAddr == iface.addr {
			// send to handler
			protocolHandlers[protocolNum](data)
			// message := buffer[headerSize:]

			// fmt.Printf("Received IP packet from %s\nHeader:  %v\nChecksum:  %s\nMessage:  %s\n",
			// sourceAddr.String(), hdr, checksumState, string(message))
		} else {
			// decrement ttl and update checksum
			data[8] = ttl - 1
			data[10] = 0
			data[11] = 0
			newChecksum := int(ComputeChecksum(data[:headerSize]))
			data[10] = newChecksum >> 8
			data[11] = newChecksum & 0xff

			// check neighbors
			for _, neighbor := range iface.neighbors {
				if neighbor == destAddr {
					// send to neighbor
					// SendIp(destAddr, protocolNum, data)
				}
			}

			// check forwarding table

		}

	}
}

func ValidateChecksum(b []byte, fromHeader uint16) uint16 {
	checksum := header.Checksum(b, fromHeader)

	return checksum
}

func SendIp(dst netip.Addr, port uint16, protocolNum uint16, data []byte, iface Interface) error {
	bindLocalAddr, err := net.ResolveUDPAddr("udp4", iface.UDPAddr.String())
	if err != nil {
		log.Panicln("Error resolving address:  ", err)
	}

	addrString := fmt.Sprintf("%s:%s", dst, port)
	remoteAddr, err := net.ResolveUDPAddr("udp4", addrString)
	if err != nil {
		log.Panicln("Error resolving address:  ", err)
	}

	fmt.Printf("Sending to %s:%d\n",
		remoteAddr.IP.String(), remoteAddr.Port)

	// Bind on the local UDP port:  this sets the source port
	// and creates a conn
	conn, err := net.ListenUDP("udp4", bindLocalAddr)
	if err != nil {
		log.Panicln("Dial: ", err)
	}

	// Start filling in the header
	message := data[20:]
	hdr := ipv4header.IPv4Header{
		Version:  data[0] >> 4,
		Len:      20, // Header length is always 20 when no IP options
		TOS:      data[1],
		TotalLen: ipv4header.HeaderLen + len(message),
		ID:       data[4],
		Flags:    data[6] >> 5,
		FragOff:  data[6] & 0x1f,
		TTL:      data[8],
		Protocol: data[9],
		Checksum: 0, // Should be 0 until checksum is computed
		Src:      netip.MustParseAddr(iface.addr.String()),
		Dst:      netip.MustParseAddr(dst.String()),
		Options:  []byte{},
	}

	// Assemble the header into a byte array
	headerBytes, err := hdr.Marshal()
	if err != nil {
		log.Fatalln("Error marshalling header:  ", err)
	}

	// Compute the checksum (see below)
	// Cast back to an int, which is what the Header structure expects
	hdr.Checksum = int(ComputeChecksum(headerBytes))

	headerBytes, err = hdr.Marshal()
	if err != nil {
		log.Fatalln("Error marshalling header:  ", err)
	}

	bytesToSend := make([]byte, 0, len(headerBytes)+len(message))
	bytesToSend = append(bytesToSend, headerBytes...)
	bytesToSend = append(bytesToSend, []byte(message)...)

	// Send the message to the "link-layer" addr:port on UDP
	bytesWritten, err := conn.WriteToUDP(bytesToSend, remoteAddr)
	if err != nil {
		log.Panicln("Error writing to socket: ", err)
	}
	fmt.Printf("Sent %d bytes\n", bytesWritten)
}

func ComputeChecksum(b []byte) uint16 {
	checksum := header.Checksum(b, 0)
	checksumInv := checksum ^ 0xffff

	return checksumInv
}

func ForwardIP(data []byte) error {
}

func AddRecvHandler(protocolNum uint8, callbackFunc HandlerFunc) error {
	if protocolHandlers[protocolNum] != nil {
		fmt.Printf("Warning: Handler for protocol %d already exists", protocolNum)
	}
	protocolHandlers[protocolNum] = callbackFunc
	return nil
}

func RemoveRecvHandler(protocolNum uint8) error {
	// consider error
	if protocolHandlers[protocolNum] == nil {
		return errors.Errorf("No handler for protocol %d", protocolNum)
	}
	delete(protocolHandlers, protocolNum)
	return nil
}

// func routeRip(data []byte) (error) {
// 	// deconstruct packet
// 	newRIPMessage := RIPMessage{}
// 	newRIPMessage.command = data[0]
// 	newRIPMessage.numEntries = data[1]
// 	newRIPMessage.entries = make([]RIPEntry, newRIPMessage.numEntries)
// }

func GetNeighbors() []netip.Addr {
	return myNeighbors
}
*/

func PrintInterfaces() {
	for _, iface := range myInterfaces {
		fmt.Printf("%s\t%s\t%t\n", iface.Name, iface.IpPrefix.String(), iface.State)
	}
}

func PrintNeighbors() {
	for ifaceName, neighbor := range myNeighbors {
		fmt.Printf("%s\t%s\t%s\n", ifaceName, neighbor.IpAddress.String(), neighbor.UdpAddr.String())
	}
}

func SprintRoutingTable() string {
	message := ""
	for prefix, hop := range routingTable {
		message += fmt.Sprintf("%s\t%s\t%d\n", prefix.String(), hop.VipAsStr, hop.Cost)
	}

	return message
}