/*
** Copyright (C) 2001-2025 Zabbix SIA
**
** This program is free software: you can redistribute it and/or modify it under the terms of
** the GNU Affero General Public License as published by the Free Software Foundation, version 3.
**
** This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
** without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
** See the GNU Affero General Public License for more details.
**
** You should have received a copy of the GNU Affero General Public License along with this program.
** If not, see <https://www.gnu.org/licenses/>.
**/

package tcpudp

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"math"
	"net"
	"net/url"
	"strconv"
	"strings"
	"time"

	"github.com/go-ldap/ldap"
	"golang.zabbix.com/agent2/pkg/web"
	"golang.zabbix.com/sdk/log"
	"golang.zabbix.com/sdk/plugin"
)

const (
	errorInvalidFirstParam  = "Invalid first parameter."
	errorInvalidSecondParam = "Invalid second parameter."
	errorInvalidThirdParam  = "Invalid third parameter."
	errorInvalidFourthParam = "Invalid fourth parameter."
	errorInvalidFifthParam  = "Invalid fifth parameter."
	errorTooManyParams      = "Too many parameters."
	errorUnsupportedMetric  = "Unsupported metric."
)

const (
	tcpExpectFail   = -1
	tcpExpectOk     = 0
	tcpExpectIgnore = 1
)

// Plugin -
type Plugin struct {
	plugin.Base
}

var impl Plugin

func (p *Plugin) exportNetTcpListen(params []string) (result interface{}, err error) {
	if len(params) > 1 {
		return nil, errors.New(errorTooManyParams)
	}
	if len(params) == 0 || params[0] == "" {
		return nil, errors.New(errorInvalidFirstParam)
	}
	port, err := strconv.ParseUint(params[0], 10, 16)
	if err != nil {
		return nil, errors.New(errorInvalidFirstParam)
	}

	return exportSystemTcpListen(uint16(port))
}

func (p *Plugin) exportNetTcpPort(params []string, timeout int) (result int, err error) {
	if len(params) > 2 {
		err = errors.New(errorTooManyParams)
		return
	}
	if len(params) < 2 || len(params[1]) == 0 {
		err = errors.New(errorInvalidSecondParam)
		return
	}

	port := params[1]

	if _, err = strconv.ParseUint(port, 10, 16); err != nil {
		err = errors.New(errorInvalidSecondParam)
		return
	}

	var address string

	if params[0] == "" {
		address = net.JoinHostPort("127.0.0.1", port)
	} else {
		address = net.JoinHostPort(params[0], port)
	}

	if _, err := net.DialTimeout("tcp", address, time.Duration(timeout)*time.Second); err != nil {
		return 0, nil
	}
	return 1, nil
}

func (p *Plugin) validateSsh(buf []byte, conn net.Conn) int {
	var major, minor int
	var sendBuf string
	ret := tcpExpectFail

	if _, err := fmt.Sscanf(string(buf), "SSH-%d.%d", &major, &minor); err == nil {
		sendBuf = fmt.Sprintf("SSH-%d.%d-zabbix_agent\r\n", major, minor)
		ret = tcpExpectOk
	}

	if ret == tcpExpectFail {
		sendBuf = fmt.Sprintf("0\n")
	}

	if _, err := conn.Write([]byte(sendBuf)); err != nil {
		log.Debugf("SSH check error: %s\n", err.Error())
	}

	return ret
}

func (p *Plugin) validateSmtp(buf []byte) int {
	if string(buf[:3]) == "220" {
		if string(buf[3]) == "-" {
			return tcpExpectIgnore
		}
		if string(buf[3]) == "" || string(buf[3]) == " " {
			return tcpExpectOk
		}
	}
	return tcpExpectFail
}

func (p *Plugin) validateFtp(buf []byte) int {
	sc := bufio.NewScanner(bytes.NewReader(buf))
	ok := []byte("220 ")
	for sc.Scan() {
		if bytes.Equal(sc.Bytes()[:4], ok) {
			return tcpExpectOk
		}
	}
	return tcpExpectIgnore
}

func (p *Plugin) validatePop(buf []byte) int {
	if string(buf[:3]) == "+OK" {
		return tcpExpectOk
	}
	return tcpExpectFail
}

func (p *Plugin) validateNntp(buf []byte) int {
	if string(buf[:3]) == "200" || string(buf[:3]) == "201" {
		return tcpExpectOk
	}
	return tcpExpectFail
}

func (p *Plugin) validateImap(buf []byte) int {
	if string(buf[:4]) == "* OK" {
		return tcpExpectOk
	}
	return tcpExpectFail
}

func telnetRead(rw *bufio.ReadWriter) (byte, error) {
	b, err := rw.ReadByte()
	if err != nil {
		return 0, err
	}

	return b, nil
}

func telnetWrite(b byte, rw *bufio.ReadWriter) error {
	err := rw.WriteByte(b)
	if err != nil {
		return fmt.Errorf("buffer write [%x] error: %s", b, err.Error())
	}
	return nil
}

func loginReceived(buf []byte) bool {
	return strings.HasSuffix(strings.TrimRight(string(buf), " "), ":")
}

func (p *Plugin) validateTelnet(conn net.Conn) error {
	var err error
	var buf []byte

	cmdIAC := byte(255)
	cmdWILL := byte(251)
	cmdWONT := byte(252)
	cmdDO := byte(253)
	cmdDONT := byte(254)
	optSGA := byte(3)
	rw := bufio.NewReadWriter(bufio.NewReader(conn), bufio.NewWriter(conn))
	for {
		if loginReceived(buf) {
			return nil
		}

		var c, c1, c2, c3 byte
		c1, err = telnetRead(rw)
		if err != nil {
			return fmt.Errorf("c1 network read error: %s", err.Error())
		}

		if cmdIAC == c1 {
			c2, err = telnetRead(rw)
			if nil != err {
				return fmt.Errorf("c2 read error: %s", err.Error())
			}

			switch c2 {
			case cmdWILL, cmdWONT, cmdDO, cmdDONT:
				c3, err = telnetRead(rw)
				if nil != err {
					return fmt.Errorf("c3 read error: %s", err.Error())
				}

				c = cmdIAC
				err := telnetWrite(c, rw)
				if err != nil {
					return err
				}

				if c2 == cmdWONT {
					c = cmdDONT
				} else if c2 == cmdDONT {
					c = cmdWONT
				} else if c3 == optSGA {
					if c2 == cmdDO {
						c = cmdWILL
					} else {
						c = cmdDO
					}
				} else {
					if c2 == cmdDO {
						c = cmdWONT
					} else {
						c = cmdDONT
					}
				}

				err = telnetWrite(c, rw)
				if err != nil {
					return err
				}
				err = telnetWrite(c3, rw)
				if err != nil {
					return err
				}
				err = rw.Flush()
				if err != nil {
					return fmt.Errorf("buffer flush error: %s", err.Error())
				}
			case cmdIAC:
				buf = append(buf, c1)
			default:
				return fmt.Errorf("malformed telnet response")
			}
		} else {
			buf = append(buf, c1)
		}
	}
}

func removeScheme(in string) (scheme string, host string, err error) {
	parts := strings.Split(in, "://")
	switch len(parts) {
	case 1:
		return "", in, nil
	case 2:
		return parts[0], parts[1], nil
	default:
		return "", in, errors.New("malformed url")
	}
}

func encloseIPv6(in string) string {
	parsedIP := net.ParseIP(in)
	if parsedIP != nil {
		ipv6 := parsedIP.To16()
		if ipv6 != nil {
			out := ipv6.String()
			return fmt.Sprintf("[%s]", out)
		}
	}

	return in
}

func (p *Plugin) httpsExpect(ip string, port string, timeout int) int {
	scheme, host, err := removeScheme(ip)
	if err != nil {
		log.Debugf("https error: cannot parse the url [%s]: %s", ip, err.Error())
		return 0
	}
	if scheme != "" && scheme != "https" {
		log.Debugf("https error: incorrect scheme '%s' in url [%s]", scheme, ip)
		return 0
	}

	rawURL := fmt.Sprintf("%s://%s", "https", encloseIPv6(host))
	u, err := url.Parse(rawURL)
	if err != nil {
		log.Debugf("https error: cannot parse the combined url [%s]: %s", rawURL, err.Error())
		return 0
	}

	// does NOT return an error on >=400 status codes same as C agent
	_, err = web.Get(fmt.Sprintf("%s://%s:%s%s", u.Scheme, u.Hostname(), port, u.Path),
		time.Second*time.Duration(timeout), false)
	if err != nil {
		log.Debugf("https network error: cannot connect to [%s]: %s", u, err.Error())
		return 0
	}

	return 1
}

func (p *Plugin) validateLdap(conn *ldap.Conn, address string) (result int) {
	res, err := conn.Search(&ldap.SearchRequest{Scope: ldap.ScopeBaseObject, Filter: "(objectClass=*)",
		Attributes: []string{"namingContexts"}})
	if err != nil {
		log.Debugf("TCP expect search error: searching failed for [%s]: %s", address, err.Error())
		return
	}

	if len(res.Entries) < 1 {
		log.Debugf("TCP expect response error: empty search result for [%s]", address)
		return
	}

	if len(res.Entries[0].Attributes) < 1 {
		log.Debugf("TCP expect response error: no attributes in first entry for [%s]", address)
		return
	}

	return 1
}

func (p *Plugin) tcpExpect(service string, address string, timeout int) (result int) {
	var conn net.Conn
	var err error

	if conn, err = net.DialTimeout("tcp", address, time.Second*time.Duration(timeout)); err != nil {
		log.Debugf("TCP expect network error: cannot connect to [%s]: %s", address, err.Error())
		return
	}
	defer conn.Close()

	if service == "http" || service == "tcp" {
		return 1
	}

	if err = conn.SetReadDeadline(time.Now().Add(time.Second * time.Duration(timeout))); err != nil {
		return
	}

	if service == "ldap" {
		l := ldap.NewConn(conn, false)
		l.Start()
		defer l.Close()
		return p.validateLdap(l, address)
	}

	if service == "telnet" {
		err := p.validateTelnet(conn)
		if err != nil {
			log.Debugf("TCP telnet network error: %s", err.Error())
			return tcpExpectFail
		}

		return 1
	}

	var sendToClose string
	var checkResult int
	buf := make([]byte, 2048)
	for {
		if _, err = conn.Read(buf); err == nil {
			switch service {
			case "ssh":
				checkResult = p.validateSsh(buf, conn)
			case "smtp":
				checkResult = p.validateSmtp(buf)
				sendToClose = fmt.Sprintf("%s", "QUIT\r\n")
			case "ftp":
				checkResult = p.validateFtp(buf)
				sendToClose = fmt.Sprintf("%s", "QUIT\r\n")
			case "pop":
				checkResult = p.validatePop(buf)
				sendToClose = fmt.Sprintf("%s", "QUIT\r\n")
			case "nntp":
				checkResult = p.validateNntp(buf)
				sendToClose = fmt.Sprintf("%s", "QUIT\r\n")
			case "imap":
				checkResult = p.validateImap(buf)
				sendToClose = fmt.Sprintf("%s", "a1 LOGOUT\r\n")
			}

			if checkResult == tcpExpectOk {
				break
			}
		} else {
			log.Debugf("TCP expect network error: cannot read from [%s]: %s", address, err.Error())
			return 0
		}
	}

	if checkResult == tcpExpectOk {
		if sendToClose != "" {
			conn.Write([]byte(sendToClose))
		}
		result = 1
	}

	if checkResult == tcpExpectFail {
		log.Debugf("TCP expect content error, received [%s]", buf)
	}

	return
}

func (p *Plugin) exportNetService(params []string, timeout int) int {
	var ip, port string
	service := params[0]

	if len(params) > 1 && params[1] != "" {
		ip = params[1]
	} else {
		ip = "127.0.0.1"
	}
	if len(params) == 3 && params[2] != "" {
		port = params[2]
	} else {
		switch service {
		case "pop":
			port = "pop3"
		case "https":
			port = "443"
		default:
			port = service
		}
	}
	if service == "https" {
		return p.httpsExpect(ip, port, timeout)
	}

	return p.tcpExpect(service, net.JoinHostPort(ip, port), timeout)
}

func toFixed(num float64, precision int) float64 {
	output := math.Pow(10, float64(precision))
	return math.Round(num*output) / output
}

func (p *Plugin) exportNetServicePerf(params []string, timeout int) float64 {
	const floatPrecision = 0.0001

	start := time.Now()
	ret := p.exportNetService(params, timeout)

	if ret == 1 {
		elapsedTime := toFixed(time.Since(start).Seconds(), 6)

		if elapsedTime < floatPrecision {
			elapsedTime = floatPrecision
		}
		return elapsedTime
	}
	return 0.0
}

// Export -
func (p *Plugin) Export(key string, params []string, ctx plugin.ContextProvider) (result interface{}, err error) {
	switch key {
	case "net.tcp.listen":
		return p.exportNetTcpListen(params)
	case "net.tcp.port":
		return p.exportNetTcpPort(params, ctx.Timeout())
	case "net.tcp.service", "net.tcp.service.perf":
		if len(params) > 3 {
			err = errors.New(errorTooManyParams)
			return
		}
		if len(params) < 1 || (len(params) == 1 && len(params[0]) == 0) {
			err = errors.New(errorInvalidFirstParam)
			return
		}

		switch params[0] {
		case "tcp":
			if len(params) != 3 || len(params[2]) == 0 {
				err = errors.New(errorInvalidThirdParam)
				return
			}
		case "ssh", "smtp", "ftp", "pop", "nntp", "imap", "http", "https", "ldap", "telnet":
		default:
			err = errors.New(errorInvalidFirstParam)
			return
		}

		if len(params) == 3 && len(params[2]) != 0 {
			if _, err = strconv.ParseUint(params[2], 10, 16); err != nil {
				err = errors.New(errorInvalidThirdParam)
				return
			}
		}

		if key == "net.tcp.service" {
			return p.exportNetService(params, ctx.Timeout()), nil
		} else if key == "net.tcp.service.perf" {
			return p.exportNetServicePerf(params, ctx.Timeout()), nil
		}
	case "net.tcp.socket.count":
		return p.exportNetTcpSocketCount(params)
	}

	/* SHOULD_NEVER_HAPPEN */
	return nil, errors.New(errorUnsupportedMetric)
}
