package main

import (
	"fmt"
	"github.com/cevatbarisyilmaz/lossy"
	"log"
	"math/rand"
	"net"
	"time"
)

const packetSize = 64

func main() {
	// Create two connection endpoints over UDP
	packetConn, conn := createConnections()

	// Create a lossy packet connection
	bandwidth := 1048 // 8 Kbit/s
	minLatency := 100 * time.Millisecond
	maxLatency := time.Second
	packetLossRate := 0.33
	headerOverhead := lossy.UDPv4MinHeaderOverhead
	lossyPacketConn := lossy.NewPacketConn(packetConn, bandwidth, minLatency, maxLatency, packetLossRate, headerOverhead)

	// Write some packets via lossy
	var bytesWritten int
	const packetCount = 32
	go func() {
		for i := 0; i < packetCount; i++ {
			packet := createPacket()
			_, err := lossyPacketConn.WriteTo(packet, conn.LocalAddr())
			if err != nil {
				log.Fatal(err)
			}
			bytesWritten += len(packet) + headerOverhead
		}
		fmt.Println("Sent", packetCount, "packets with total size of", bytesWritten, "bytes")
		baseTransmissionDuration := time.Duration(float64(bytesWritten * int(time.Second)) / float64(bandwidth))
		earliestCompletion := baseTransmissionDuration + minLatency
		latestCompletion := baseTransmissionDuration + maxLatency
		fmt.Println("Expected transmission duration is between", earliestCompletion, "and", latestCompletion)
	}()

	// Read packets at the other side
	const timeout = 3 * time.Second
	var packets, bytesRead int
	startTime := time.Now()
	for {
		_ = conn.SetReadDeadline(time.Now().Add(timeout))
		buffer := make([]byte, packetSize)
		n, err := conn.Read(buffer)
		if err != nil {
			break
		}
		bytesRead += n + headerOverhead
		packets++
	}
	dur := time.Now().Sub(startTime) - timeout
	fmt.Println("Received", packets, "packets with total size of", bytesRead, "bytes in", dur)

	// Close the connections
	_ = lossyPacketConn.Close()
	_ = conn.Close()
}

func createConnections() (net.PacketConn, net.Conn) {
	packetConn, err := net.ListenUDP("udp", &net.UDPAddr{
		IP:   net.IPv4(127, 0, 0, 1),
		Port: 0,
	})
	if err != nil {
		log.Fatal(err)
	}
	conn, err := net.DialUDP("udp", nil, packetConn.LocalAddr().(*net.UDPAddr))
	if err != nil {
		log.Fatal(err)
	}
	return packetConn, conn
}

func createPacket() []byte {
	packet := make([]byte, packetSize)
	rand.Read(packet)
	return packet
}