// Local demonstration receiver/query tool. It never changes device settings.
package main

import (
	"bufio"
	"fmt"
	"net"
	"os"
	"time"

	"github.com/gosnmp/gosnmp"
)

func main() {
	if len(os.Args) != 2 {
		fmt.Fprintln(os.Stderr, "Usage: probe get|trap|syslog|getv3|trapv3|syslogtcp")
		os.Exit(2)
	}
	switch os.Args[1] {
	case "get", "getv3":
		client := &gosnmp.GoSNMP{Target: "192.168.0.223", Port: 161, Community: "TERA_DEMO_RO", Version: gosnmp.Version2c, Timeout: 3 * time.Second, Retries: 1}
		if os.Args[1] == "getv3" {
			useV3(client, false)
		}
		if err := client.Connect(); err != nil {
			fail(err)
		}
		defer client.Conn.Close()
		packet, err := client.Get([]string{"1.3.6.1.2.1.1.6.0", "1.3.6.1.2.1.1.3.0"})
		if err != nil {
			fail(err)
		}
		if packet.Error != gosnmp.NoError {
			fail(fmt.Errorf("SNMP error: %v index=%v", packet.Error, packet.ErrorIndex))
		}
		fmt.Printf("Response from 192.168.0.223 (SNMP %v)\n", client.Version)
		for _, variable := range packet.Variables {
			show(variable)
		}
	case "trap", "trapv3":
		listener := gosnmp.NewTrapListener()
		listener.Params = &gosnmp.GoSNMP{Version: gosnmp.Version2c}
		v3 := os.Args[1] == "trapv3"
		if v3 {
			useV3(listener.Params, true)
		}
		listener.OnNewTrap = func(packet *gosnmp.SnmpPacket, source *net.UDPAddr) {
			if source.IP.String() != "192.168.0.223" {
				return
			}
			if v3 && packet.Version != gosnmp.Version3 {
				return
			}
			if !v3 && (packet.Version != gosnmp.Version2c || packet.Community != "TERA_DEMO_TRAP") {
				return
			}
			fmt.Printf("%s Trap from %s\n", time.Now().Format(time.RFC3339), source)
			for _, variable := range packet.Variables {
				show(variable)
			}
		}
		fmt.Printf("Waiting on 192.168.0.100:2162 UDP, SNMP %v. Ctrl+C stops.\n", listener.Params.Version)
		if err := listener.Listen("192.168.0.100:2162"); err != nil {
			fail(err)
		}
	case "syslog":
		connection, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.ParseIP("192.168.0.100"), Port: 1514})
		if err != nil {
			fail(err)
		}
		defer connection.Close()
		fmt.Println("Waiting on 192.168.0.100:1514 UDP. Ctrl+C stops.")
		buffer := make([]byte, 65535)
		for {
			size, source, err := connection.ReadFromUDP(buffer)
			if err != nil {
				fail(err)
			}
			if source.IP.String() == "192.168.0.223" {
				fmt.Printf("%s %s %s\n", time.Now().Format(time.RFC3339), source, buffer[:size])
			}
		}
	case "syslogtcp":
		listener, err := net.Listen("tcp", "192.168.0.100:1514")
		if err != nil {
			fail(err)
		}
		defer listener.Close()
		fmt.Println("Waiting on 192.168.0.100:1514 TCP. Ctrl+C stops.")
		for {
			connection, err := listener.Accept()
			if err != nil {
				fail(err)
			}
			go func() {
				defer connection.Close()
				host, _, _ := net.SplitHostPort(connection.RemoteAddr().String())
				if host != "192.168.0.223" {
					return
				}
				scanner := bufio.NewScanner(connection)
				scanner.Buffer(make([]byte, 4096), 1024*1024)
				for scanner.Scan() {
					fmt.Printf("%s %s %s\n", time.Now().Format(time.RFC3339), host, scanner.Text())
				}
				if err := scanner.Err(); err != nil {
					fmt.Fprintln(os.Stderr, err)
				}
			}()
		}
	default:
		fail(fmt.Errorf("unknown mode: %s", os.Args[1]))
	}
}

func useV3(client *gosnmp.GoSNMP, trap bool) {
	client.Version = gosnmp.Version3
	client.SecurityModel = gosnmp.UserSecurityModel
	client.MsgFlags = gosnmp.AuthPriv
	security := &gosnmp.UsmSecurityParameters{UserName: "TERA_DEMO_V3", AuthenticationProtocol: gosnmp.SHA, AuthenticationPassphrase: "TeraDemoAuth0910", PrivacyProtocol: gosnmp.AES, PrivacyPassphrase: "TeraDemoPriv0910"}
	if trap {
		security.AuthoritativeEngineID = "TERA-DEMO-0910"
	}
	client.SecurityParameters = security
}

func show(variable gosnmp.SnmpPDU) {
	if data, ok := variable.Value.([]byte); ok {
		fmt.Printf("%s = %s\n", variable.Name, data)
	} else {
		fmt.Printf("%s = %v (%v)\n", variable.Name, variable.Value, variable.Type)
	}
}
func fail(err error) { fmt.Fprintln(os.Stderr, "ERROR:", err); os.Exit(1) }