package services

import (
	"context"
	"encoding/hex"
	"fmt"
	"net"
	"time"

	"github.com/shadow1ng/fscan/common"
)

type SNMPPlugin struct {
	name  string
	ports []int
}

func NewSNMPPlugin() *SNMPPlugin {
	return &SNMPPlugin{
		name:  "snmp",
		ports: []int{161, 162},
	}
}

func (p *SNMPPlugin) Name() string {
	return p.name
}

func (p *SNMPPlugin) GetPorts() []int {
	return p.ports
}

func (p *SNMPPlugin) Scan(ctx context.Context, info *common.HostInfo) *ScanResult {
	target := fmt.Sprintf("%s:%s", info.Host, info.Ports)

	if common.DisableBrute {
		return p.identifyService(ctx, info)
	}

	credentials := GenerateCredentials("snmp")
	if len(credentials) == 0 {
		return &ScanResult{
			Success: false,
			Service: "snmp",
			Error:   fmt.Errorf("没有可用的测试凭据"),
		}
	}

	for _, cred := range credentials {
		if p.testCredential(ctx, info, cred) {
			common.LogSuccess(fmt.Sprintf("SNMP %s %s", target, cred.Username))

			return &ScanResult{
				Success:  true,
				Service:  "snmp",
				Username: cred.Username,
				Password: "",
			}
		}
	}

	return &ScanResult{
		Success: false,
		Service: "snmp",
		Error:   fmt.Errorf("未发现弱团体字符串"),
	}
}

func (p *SNMPPlugin) testCredential(ctx context.Context, info *common.HostInfo, cred Credential) bool {
	target := fmt.Sprintf("%s:%s", info.Host, info.Ports)
	
	conn, err := net.DialTimeout("udp", target, time.Duration(common.Timeout)*time.Second)
	if err != nil {
		return false
	}
	defer conn.Close()

	packet := p.buildSNMPGetRequest(cred.Username, "1.3.6.1.2.1.1.1.0")
	
	conn.SetWriteDeadline(time.Now().Add(time.Duration(common.Timeout) * time.Second))
	if _, err := conn.Write(packet); err != nil {
		return false
	}

	conn.SetReadDeadline(time.Now().Add(time.Duration(common.Timeout) * time.Second))
	response := make([]byte, 1024)
	n, err := conn.Read(response)
	if err != nil {
		return false
	}

	return p.isValidSNMPResponse(response[:n])
}

func (p *SNMPPlugin) buildSNMPGetRequest(community, oid string) []byte {
	template := "302902010004067075626c6963a01c02020f7102010002010030113015060a2b060102010101000500"
	
	packet, err := hex.DecodeString(template)
	if err != nil {
		return nil
	}
	
	return packet
}

func (p *SNMPPlugin) isValidSNMPResponse(data []byte) bool {
	if len(data) < 10 {
		return false
	}
	
	return data[0] == 0x30
}


func (p *SNMPPlugin) identifyService(ctx context.Context, info *common.HostInfo) *ScanResult {
	target := fmt.Sprintf("%s:%s", info.Host, info.Ports)

	cred := Credential{Username: "public", Password: ""}
	if p.testCredential(ctx, info, cred) {
		banner := "SNMP网络管理服务 (public团体可访问)"
		common.LogSuccess(fmt.Sprintf("SNMP %s %s", target, banner))
		
		return &ScanResult{
			Success: true,
			Service: "snmp",
			Banner:  banner,
		}
	}

	conn, err := net.DialTimeout("udp", target, time.Duration(common.Timeout)*time.Second)
	if err != nil {
		return &ScanResult{
			Success: false,
			Service: "snmp",
			Error:   err,
		}
	}
	defer conn.Close()

	banner := "SNMP网络管理服务"
	common.LogSuccess(fmt.Sprintf("SNMP %s %s", target, banner))

	return &ScanResult{
		Success: true,
		Service: "snmp",
		Banner:  banner,
	}
}

func init() {
	// 使用高效注册方式：直接传递端口信息，避免实例创建
	RegisterPluginWithPorts("snmp", func() Plugin {
		return NewSNMPPlugin()
	}, []int{161, 162})
}