package ipstack

import (
	"fmt"
	ipv4header "github.com/brown-csci1680/iptcp-headers"
	"github.com/google/netstack/tcpip/header"
	"github.com/pkg/errors"
	"iptcp/pkg/lnxconfig"
	"log"
	"net"
	"net/netip"
	"time"
	"encoding/binary"
)

const (
	MAX_IP_PACKET_SIZE        = 1400
	LOCAL_COST         uint32 = 0
	STATIC_COST        uint32 = 4294967295 // 2^32 - 1
	MaxEntries = 64
	INFINITY   = 15
)

// STRUCTS ---------------------------------------------------------------------
type Interface struct {
	Name     string
	IpPrefix netip.Prefix
	UdpAddr  netip.AddrPort

	RecvSocket    net.UDPConn
	SocketChannel chan bool
	State         bool
}

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

	SendSocket    net.UDPConn
	SocketChannel chan bool
}

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

type RIPEntry struct {
	address uint32
	cost uint32
	mask uint32
}

type Hop struct {
	Cost     uint32
	VipAsStr string	
	Type    string
	// added this for printing purposes
}

// GLOBAL VARIABLES (data structures) ------------------------------------------
var myVIP Interface
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.UDPConn, isN bool) error {
	listenString := UdpAddr.String()
	listenAddr, err := net.ResolveUDPAddr("udp4", listenString)
	if err != nil {
		return errors.WithMessage(err, "Error resolving address->\t"+listenString)
	}
	if !isN {
		tmpConn, err := net.ListenUDP("udp4", listenAddr)
		if err != nil {
			return errors.WithMessage(err, "Could not bind to UDP port->\t"+listenString)
		}
		*conn = *tmpConn
	} else {
		tmpConn, err := net.DialUDP("udp4", nil, 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 {
	// 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
	// static := false
	interfaceToReturn := Interface{}
	for _, iface := range lnxConfig.Interfaces {
		prefix := netip.PrefixFrom(iface.AssignedIP, iface.AssignedPrefix.Bits())
		i := &Interface{
			Name:          iface.Name,
			IpPrefix:      prefix,
			UdpAddr:       iface.UDPAddr,
			RecvSocket:    net.UDPConn{},
			SocketChannel: make(chan bool),
			State:         true,
		}
		if interfaceToReturn == (Interface{}) {
			interfaceToReturn = *i
			myVIP = *i
		}
		// Added this for printing purposes for REPL FYI, if you have a better way lmk

		err := createUDPConn(iface.UDPAddr, &i.RecvSocket, false)
		if err != nil {
			return errors.WithMessage(err, "Error creating UDP socket for interface->\t"+iface.Name)
		}
		go InterfaceListenerRoutine(i.RecvSocket, i.SocketChannel)
		myInterfaces = append(myInterfaces, i)

		// TODO: (FOR HOSTS ONLY)
		// add STATIC to routing table
		// if !static {
		// 	ifacePrefix := netip.MustParsePrefix("0.0.0.0/0")
		// 	routingTable[ifacePrefix] = Hop{STATIC_COST, iface.Name, "S"}
		// 	static = true
		// }
		// Took this out for printing purposes for REPL FYI
	}

	// 2) initialize the neighbors connected to the node and into the routing table
	for _, neighbor := range lnxConfig.Neighbors {
		n := &Neighbor{
			VipAddr:       neighbor.DestAddr,
			UdpAddr:       neighbor.UDPAddr,
			SendSocket:    net.UDPConn{},
			SocketChannel: make(chan bool),
		}

		err := createUDPConn(neighbor.UDPAddr, &n.SendSocket, true)
		if err != nil {
			return errors.WithMessage(err, "Error creating UDP socket for neighbor->\t"+neighbor.DestAddr.String())
		}

		myNeighbors[neighbor.InterfaceName] = append(myNeighbors[neighbor.InterfaceName], n)

		// add to routing table
		// TODO: REVISIT AND SEE IF "24" IS CORRECT
		neighborPrefix := netip.PrefixFrom(neighbor.DestAddr, 24)
		routingTable[neighborPrefix] = Hop{LOCAL_COST, neighbor.InterfaceName, "L"}
	}

	for _, route := range lnxConfig.StaticRoutes {
		// add to routing table
		prefix := netip.MustParsePrefix("0.0.0.0/0")
		routingTable[prefix] = Hop{LOCAL_COST, route.String(), "S"}
	}
	// added for printing purposes for REPL FYI

	return nil
}

func InterfaceListenerRoutine(socket net.UDPConn, signal <-chan bool) {
	isUp := true
	// testing purposes set to TRUE
	closed := false

	// go routine that hangs on the recv
	fmt.Println("MAKING GO ROUTINE TO LISTEN:\t", socket.LocalAddr().String())
	go func() {
		defer func() { // on close, set isUp to false
			fmt.Println("exiting go routine that listens on ", socket.LocalAddr().String())
		}()

		for {
			if closed { // stop this go routine if channel is closed
				return
			}
			if !isUp { // don't call the listeners if interface is down
				continue
			}
			// TODO: remove these "training wheels"
			time.Sleep(1 * time.Millisecond)
			err := RecvIP(socket, &isUp)
			if err != nil {
				fmt.Println("Error receiving IP packet", err)
				return
			}
		}
	}()

	for {
		select {
		case sig, ok := <-signal:
			if !ok {
				fmt.Println("channel closed, exiting")
				closed = true
				return
			}
			fmt.Println("received isUP SIGNAL with value", sig)
			isUp = sig
		default:
			continue
		}
	}
}

func InterfaceUp(iface *Interface) {
	iface.State = true
	iface.SocketChannel <- true
}

func InterfaceUpREPL(ifaceName string) {
	iface, err := GetInterfaceByName(ifaceName)
	if err != nil {
		fmt.Println("Error getting interface by name", err)
		return
	}
	iface.State = true
	iface.SocketChannel <- true
}

// we could do either of these but the REPL results in less work done in router and host

func InterfaceDown(iface *Interface) {
	iface.SocketChannel <- false
	iface.State = false
}

func InterfaceDownREPL(ifaceName string) {
	iface, err := GetInterfaceByName(ifaceName)
	if err != nil {
		fmt.Println("Error getting interface by name", err)
		return
	}
	iface.SocketChannel <- false
	iface.State = false
}
// same as above comment

func GetInterfaceByName(ifaceName string) (*Interface, error) {
	for _, iface := range myInterfaces {
		if iface.Name == ifaceName {
			return iface, nil
		}
	}

	return nil, errors.Errorf("No interface with name %s", ifaceName)
}

func GetNeighborByIP(ipAddr string) (*Neighbor, error) {
	for _, neighbors := range myNeighbors {
		for _, neighbor := range neighbors {
			if neighbor.VipAddr.String() == ipAddr {
				return neighbor, nil
			}
		}
	}

	return nil, errors.Errorf("No interface with ip %s", ipAddr)
}

func GetRouteByIP(ipAddr string) (*Neighbor, error) {
	for prefix, hop := range routingTable {
		netIP := net.ParseIP(prefix.Addr().String())
		if netIP.String() == ipAddr {
			fmt.Println("found route", hop.VipAsStr)
			neighbor, err := GetNeighborByIP(hop.VipAsStr)
			if err != nil {
				fmt.Println("Error getting neighbors to interface", err)
				continue // fix with longest prefix matching?
			}
			return neighbor, nil
		}
	}

	return nil, errors.Errorf("No interface with ip %s", ipAddr)
}

func GetNeighborsToInterface(ifaceName string) ([]*Neighbor, error) {
	if neighbors, ok := myNeighbors[ifaceName]; ok {
		return neighbors, nil
	}

	return nil, errors.Errorf("No interface with name %s", ifaceName)
}

func GetMyVIP() Interface {
	return myVIP
}

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

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

func SprintRoutingTable() {
	for prefix, hop := range routingTable {
		if hop.Type == "L" {
			fmt.Printf("%s\t%s\tLOCAL:%s\t%d\n", hop.Type, prefix.String(), hop.VipAsStr, 0)
		} else if hop.Type == "S" {
			fmt.Printf("%s\t%s\t%s\t%s\n", hop.Type, prefix.String(), hop.VipAsStr, "-")
		} else {
			fmt.Printf("%s\t%s\t%s\t%d\n", hop.Type, prefix.String(), hop.VipAsStr, hop.Cost)
		}
	}
}

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

// func RemoveNeighbor(neighbor Neighbor) {
// 	// TODO: remove from routing table
// 	myRoutes := GetRoutes()
// 	for prefix, hop := range myRoutes {
// 		if hop.VipAsStr == neighbor.VipAddr.String() {
// 			delete(myRoutes, prefix)
// 		}
// 	}
	
// 	// TODO: remove from myNeighbors
// 	myNeighbors[neighbor.VipAddr.String()] = nil

// 	// TODO: close the UDP socket
// 	err := neighbor.SendSocket.Close()
// 	if err != nil {
// 		fmt.Println("Error closing UDP socket", err)
// 	}

// }
// untested function above

func CleanUp() {
	fmt.Print("Cleaning up...\n")
	// go through the interfaces, pop thread & close the UDP FDs
	for _, iface := range myInterfaces {
		if iface.SocketChannel != nil {
			close(iface.SocketChannel)
		}
		err := iface.RecvSocket.Close()
		if err != nil {
			continue
		}
	}

	// go through the neighbors, pop thread & close the UDP FDs
	for _, neighbor := range myNeighbors {
		for _, n := range neighbor {
			if n.SocketChannel != nil {
				close(n.SocketChannel)
			}
			err := n.SendSocket.Close()
			if err != nil {
				continue
			}
		}
	}

	// delete all the neighbors
	myNeighbors = make(map[string][]*Neighbor)
	// delete all the interfaces
	myInterfaces = nil
	// delete the routing table
	routingTable = make(map[netip.Prefix]Hop)

	time.Sleep(5 * time.Millisecond)
}

// TODO: have it take TTL so we can decrement it when forwarding
func SendIP(src Interface, dest *Neighbor, protocolNum int, message []byte, destIP string) error {
	hdr := ipv4header.IPv4Header{
		Version:  4,
		Len:      20, // Header length is always 20 when no IP options
		TOS:      0,
		TotalLen: ipv4header.HeaderLen + len(message),
		ID:       0,
		Flags:    0,
		FragOff:  0,
		TTL:      32,
		Protocol: protocolNum,
		Checksum: 0, // Should be 0 until checksum is computed
		Src:      src.IpPrefix.Addr(),
		Dst:      netip.MustParseAddr(destIP),
		Options:  []byte{},
	}

	// Assemble the header into a byte array
	headerBytes, err := hdr.Marshal()
	if err != nil {
		return 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
	listenAddr, err := net.ResolveUDPAddr("udp4", dest.UdpAddr.String())
	if err != nil {
		return err
	}
	// idk that this is ^^
	bytesWritten, err := dest.SendSocket.Write(bytesToSend)
	if err != nil {
		return err
	}

	// send to the dest.UdpAddr without the SendSocket
	// conn, err := net.DialUDP("udp4", nil, listenAddr)
	// if err != nil {
	// 	fmt.Println(err, "here5")
	// 	return err
	// }

	// bytesWritten, err := conn.Write(bytesToSend)
	// if err != nil {
	// 	fmt.Println(err, "here6")
	// 	return err
	// }
	
	// what we had previously just in case
	fmt.Printf("Sent %d bytes to %s\n", bytesWritten, listenAddr.String())

	return nil
}

func RecvIP(conn net.UDPConn, isOpen *bool) error {
	buffer := make([]byte, MAX_IP_PACKET_SIZE) // TODO: fix wordking

	// Read on the UDP port
	// fmt.Println("wating to read from UDP socket")
	_, _, err := conn.ReadFromUDP(buffer)
	if err != nil {
		return err
	}

	if !*isOpen {
		return errors.New("interface is down")
	}

	// Marshal the received byte array into a UDP header
	// NOTE:  This does not validate the checksum or check any fields
	// (You'll need to do this part yourself)
	hdr, err := ipv4header.ParseHeader(buffer)
	if err != nil {
		// What should you if the message fails to parse?
		// Your node should not crash or exit when you get a bad message.
		// Instead, simply drop the packet and return to processing.
		fmt.Println("Error parsing header", err)
		return err
	}

	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"
	}

	// Next, get the message, which starts after the header
	message := buffer[headerSize:]

	// TODO:  handle the message
	// 1) check if the TTL & checksum is valid
	TTL := hdr.TTL
	if TTL == 0 {
		// drop the packet
		return nil
	}
	
	// check if the checksum is valid
	if checksumState == "FAIL" {
		// drop the packet
		return nil
	}
	if hdr.Protocol == 12 {
		// RIP
		// 1) check if the message is for me, if so, sendUP (aka call the correct handler)
		command := message[0]
		if command == 1 {
			// request
			// SendUpdates()
		} else if command == 2 {
			numEntries := message[1]

			entries := make([]RIPEntry, 0, numEntries)
			for i := 0; i < int(numEntries); i++ {
				offset := 4 + 2 + i*12
				address := binary.BigEndian.Uint32(message[offset : offset+4])
				mask := binary.BigEndian.Uint32(message[offset+4 : offset+8])
				cost := binary.BigEndian.Uint32(message[offset+8 : offset+12])
				entries = append(entries, RIPEntry{address: address, mask: mask, cost: cost})
			}

			// add to routing table
			for _, entry := range entries {
				address := fmt.Sprintf("%d.%d.%d.%d", byte(entry.address>>24), byte(entry.address>>16), byte(entry.address>>8), byte(entry.address))
				mask := fmt.Sprintf("%d.%d.%d.%d", byte(entry.mask>>24), byte((entry.mask>>16)&0xff), byte((entry.mask>>8)&0xff), byte(entry.mask&0xff))

				// check if the entry is already in the routing table
				if _, ok := routingTable[netip.MustParsePrefix(address+"/24")]; ok {
					// if so, check if the cost is the same
					// if routingTable[netip.MustParsePrefix(address+"/24")].Cost == entry.cost {
					// 	// if so, do nothing
					// 	continue
					// } else {
					// 	// if not, update the cost
					// 	routingTable[netip.MustParsePrefix(address+"/24")] = Hop{entry.cost, mask, "R"}
					// }
					continue
				}
				// fmt.Println(entry.cost)
				routingTable[netip.MustParsePrefix(address+"/24")] = Hop{entry.cost + 1, mask, "R"}
			}
		}
	} else {
		// 2) check if the message is for me, if so, sendUP (aka call the correct handler)
		if hdr.Dst.String() == myVIP.IpPrefix.Addr().String() {

			fmt.Println("for me")
			if hdr.Protocol == 0 {
				fmt.Printf("Received test packet:  Src: %s, Dst: %s, TTL: %d, Data:  %s\n",
				hdr.Src.String(), hdr.Dst.String(), hdr.TTL, string(message))
				return nil
			}
			
		}
		// if not, need to forward the packer to a neighbor or check the table
		// after decrementing TTL and updating checksum
		hdr.TTL--
		// update checksum
		headerBytes, err = hdr.Marshal()
		if err != nil {
			log.Fatalln("Error marshalling header:  ", err)
		}
		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)...)


		// 3) check if message is for a neighbor, if so, sendIP there
		for _, neighbors := range myNeighbors {
			// fmt.Println(neighbors)
			for _, neighbor := range neighbors {
				if hdr.Dst.String() == neighbor.VipAddr.String() {
					fmt.Println("for neighbor")
					// send the packet to the neighbor
					err := SendIP(myVIP, neighbor, hdr.Protocol, bytesToSend, hdr.Dst.String())
					if err != nil {
						fmt.Println("Error sending IP packet", err)
						return err
					}
					return nil
				}
			}
		}
		// fmt.Println("No neighbors, checking Routes")
		// 4) check forwarding table. if so, forward to the neighbor with that VIP

		for prefix, hop := range routingTable {
			netIP := net.ParseIP(prefix.Addr().String())
			if netIP.String() == hdr.Dst.String() {
				// send the packet to next hop
				neighbors, err := GetNeighborByIP(hop.VipAsStr)
				if err != nil {
					fmt.Println("Error getting neighbor by IP", err)
					return err
				}
				err = SendIP(myVIP, neighbors, hdr.Protocol, bytesToSend, hdr.Dst.String())
				if err != nil {
					fmt.Println("Error sending IP packet", err)
					return err
				}
				return nil
			}
		}
		// send 10.2.0.3 hello
		// 5) if not, drop the packet
		return nil
	}

	return nil
}

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

	return checksumInv
}

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

	return checksum
}

func GetInterfaces() []*Interface {
	return myInterfaces
}

func GetNeighbors() map[string][]*Neighbor {
	return myNeighbors
}

func GetRoutes() map[netip.Prefix]Hop {
	return routingTable
}

func NewRIPMessage(command uint8, entries []RIPEntry) *RIPMessage {
	return &RIPMessage{
		command: command,
		numEntries: uint8(len(entries)),
		entries: entries,
	}
}

func SendRIPMessage(src Interface, dest *Neighbor, message *RIPMessage) error {
	hdr := ipv4header.IPv4Header{
		Version:  4,
		Len:      20, // Header length is always 20 when no IP options
		TOS:      0,
		TotalLen: ipv4header.HeaderLen + 4 + 1 + 1 + len(message.entries)*12,
		ID:       0,
		Flags:    0,
		FragOff:  0,
		TTL:      32,
		Protocol: 12,
		Checksum: 0, // Should be 0 until checksum is computed
		Src:      src.IpPrefix.Addr(),
		Dst:      netip.MustParseAddr(dest.VipAddr.String()),
		Options:  []byte{},
	}

	headerBytes, err := hdr.Marshal()
	if err != nil {
		return err
	}

	hdr.Checksum = int(ComputeChecksum(headerBytes))

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

	bytesToSend := make([]byte, 0, len(headerBytes)+4+1+1+len(message.entries)*12)
	bytesToSend = append(bytesToSend, headerBytes...)
	

	buf := make([]byte, 4+1+1+len(message.entries)*12)
	buf[0] = message.command
	buf[1] = message.numEntries

	for i, entry := range message.entries {
		offset := 4 + 2 + i*12
		binary.BigEndian.PutUint32(buf[offset:offset+4], entry.address)
		binary.BigEndian.PutUint32(buf[offset+4:offset+8], entry.mask)
		binary.BigEndian.PutUint32(buf[offset+8:offset+12], entry.cost)
	}

	bytesToSend = append(bytesToSend, buf...)

	_, err = dest.SendSocket.Write(bytesToSend)
	if err != nil {
		return err
	}
	
	// what we had previously just in case
	// lots of printing
	// fmt.Printf("Sent %d bytes to %s\n", bytesWritten, dest.UdpAddr.String())

	return nil
}

func SendUpdates() {
	entries := make([]RIPEntry, len(routingTable))
	for prefix, hop := range routingTable {
		netIP := net.ParseIP(prefix.Addr().String())
		ipBytes := netIP.To4()
		ipUint32 := uint32(ipBytes[0]) << 24 | uint32(ipBytes[1]) << 16 | uint32(ipBytes[2]) << 8 | uint32(ipBytes[3])

		if netIP.String() == "0.0.0.0" {
			continue
		}

		if hop.Type == "S" {
			continue
		}

		for _, neighbors := range myNeighbors {
			for _, neighbor := range neighbors {
				neighborBits := net.ParseIP(myVIP.IpPrefix.Addr().String())
				neighborBits = neighborBits.To4()
				neighborUint32 := uint32(neighborBits[0]) << 24 | uint32(neighborBits[1]) << 16 | uint32(neighborBits[2]) << 8 | uint32(neighborBits[3])
				cost := hop.Cost
				if hop.Type == "R" {
					cost = INFINITY
				}
				entry := &RIPEntry{
					address: ipUint32,
					cost: cost,
					mask: neighborUint32,
				}
				entries = append(entries, *entry)
				message := NewRIPMessage(2, entries)

				err := SendRIPMessage(myVIP, neighbor, message)
				if err != nil {
					// fmt.Println("Error sending RIP packet")
					continue
				}
			}
		}

	}
}

func CheckAndUpdateRoutingTable() {
	for {
	time.Sleep(12 * time.Second)
	for prefix, hop := range routingTable {
		// delete route if not refreshed in 12 seconds
		// not sure if there is a better way to do this
		if hop.Type == "R" {
			delete(routingTable, prefix)
			SendUpdates()
		}
	}
	}
}