package icmp

import (
	"fmt"
	"net"
	"time"

	"golang.org/x/net/icmp"
	"golang.org/x/net/ipv4"
)

// NewMessage create a new ICMP message
func NewMessage(message string, id int) icmp.Message {
	return icmp.Message{
		Type: ipv4.ICMPTypeEcho,
		Code: 0,
		Body: &icmp.Echo{
			ID:   id,
			Seq:  0,
			Data: []byte(message),
		},
	}
}

// NewPacketConnection create a new ICMP packet connection
func NewPacketConnection(timeout time.Duration) (*icmp.PacketConn, error) {
	packetconn, err := icmp.ListenPacket("ip4:icmp", "0.0.0.0")
	if err != nil {
		return nil, fmt.Errorf("error making packet connection: %w", err)
	}

	deadline := time.Now().Add(timeout)
	err = packetconn.SetReadDeadline(deadline)
	if err != nil {
		return nil, fmt.Errorf("failed to set read deadline on connection: %w", err)
	}
	return packetconn, nil
}

// SendRequest writes the icmp message to the packet connection
func SendRequest(packetconn *icmp.PacketConn, im icmp.Message, dst net.Addr) error {
	ib, err := im.Marshal(nil)
	if err != nil {
		return fmt.Errorf("failure to marshall ICMP message: %w", err)
	}

	_, err = packetconn.WriteTo(ib, dst)
	if err != nil {
		return fmt.Errorf("failed to write ICMP bytes to packet connection: %w", err)
	}
	return nil
}

// ReceiveReply tries reading from the packet connection.
//
// There are three possible outcomes of this operation:
//
// - If the read operation errors, most likely due to a deadline exceeded error
// then the function returns false, as this constitutes a detection failure.
//
// - If the received packet doesn't parse or conform to the echo reply type,
// this function skips to the next iteration of the for-loop and reads the next packet.
//
// - Finally, if the icmp message's ID correctly identifies it, the functions returns true.
func ReceiveReply(packetconn *icmp.PacketConn, id int) bool {
	for {
		rb := make([]byte, 1500)
		n, _, err := packetconn.ReadFrom(rb)
		if err != nil {
			return false
		}

		rm, err := icmp.ParseMessage(1, rb[:n])
		if err != nil {
			continue
		}

		if rm.Type != ipv4.ICMPTypeEchoReply {
			continue
		}

		mes, ok := rm.Body.(*icmp.Echo)
		if !ok {
			continue
		}

		if id == mes.ID {
			return true
		}
	}
}