package vpn

import (
	"bufio"
	"encoding/json"
	"fmt"
	"net"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"
)

// ======================== PPP Profiles (/ppp profile) ========================
type PPPProfile struct {
	ID            string `json:"id"`
	Name          string `json:"name"`           // e.g. "default", "default-encryption", "pool-lan"
	LocalAddress  string `json:"local_address"`  // e.g. "10.10.10.1" (server IP on tunnel)
	RemoteAddress string `json:"remote_address"` // e.g. "10.10.10.10-10.10.10.50" or "10.10.10.10"
	DNSServers    string `json:"dns_servers"`    // e.g. "1.1.1.1,8.8.8.8"
	UseEncryption string `json:"use_encryption"` // "no", "yes", "required" (MPPE-128)
	OnlyOne       bool   `json:"only_one"`       // One session per user
	Comment       string `json:"comment,omitempty"`
}

// ======================== PPP Secrets (/ppp secret) ========================
type PPPSecret struct {
	ID            string `json:"id"`
	Name          string `json:"name"`           // Username
	Password      string `json:"password"`       // Password
	Service       string `json:"service"`        // "any", "pppoe", "pptp", "l2tp"
	Profile       string `json:"profile"`        // Profile name
	LocalAddress  string `json:"local_address,omitempty"`
	RemoteAddress string `json:"remote_address,omitempty"`
	CallerID      string `json:"caller_id,omitempty"`
	Comment       string `json:"comment,omitempty"`
	Disabled      bool   `json:"disabled"`
}

// ======================== PPPoE Server (/interface pppoe-server server) ========================
type PPPoEServerConfig struct {
	Enabled           bool   `json:"enabled"`
	ServiceName       string `json:"service_name"` // e.g. "isp-service"
	Interface         string `json:"interface"`    // e.g. "eth0", "eth0.10", "br0"
	DefaultProfile    string `json:"default_profile"`
	OneSessionPerHost bool   `json:"one_session_per_host"`
	MaxMTU            int    `json:"max_mtu"` // default 1480 / 1492
	MaxMRU            int    `json:"max_mru"` // default 1480 / 1492
	Running           bool   `json:"running"`
	ActiveSessions    int    `json:"active_sessions"`
	LastError         string `json:"last_error,omitempty"`
}

// ======================== PPTP Server (/interface pptp-server server) ========================
type PPTPServerConfig struct {
	Enabled        bool   `json:"enabled"`
	Port           int    `json:"port"` // default 1723
	DefaultProfile string `json:"default_profile"`
	RequireMPPE    bool   `json:"require_mppe"` // 128-bit MPPE
	Running        bool   `json:"running"`
	ActiveSessions int    `json:"active_sessions"`
	LastError      string `json:"last_error,omitempty"`
}

// ======================== L2TP Server (/interface l2tp-server server) ========================
type L2TPServerConfig struct {
	Enabled        bool   `json:"enabled"`
	Port           int    `json:"port"` // default 1701
	DefaultProfile string `json:"default_profile"`
	UseIPSec       string `json:"use_ipsec"` // "no", "yes", "required"
	IPSecSecret    string `json:"ipsec_secret,omitempty"`
	Running        bool   `json:"running"`
	ActiveSessions int    `json:"active_sessions"`
	LastError      string `json:"last_error,omitempty"`
}

// ======================== IPSec Roadwarrior Server ========================
type IPSecServerConfig struct {
	Enabled        bool   `json:"enabled"`
	PoolAddress    string `json:"pool_address"` // e.g. "10.10.30.0/24"
	PresharedKey   string `json:"preshared_key"`
	LocalSubnet    string `json:"local_subnet"` // e.g. "0.0.0.0/0"
	DNSServers     string `json:"dns_servers"`  // e.g. "1.1.1.1,8.8.8.8"
	Running        bool   `json:"running"`
	ActiveSessions int    `json:"active_sessions"`
	LastError      string `json:"last_error,omitempty"`
}

// ======================== Active PPP Session (/ppp active) ========================
type ActivePPPSession struct {
	ID        string `json:"id"`
	Interface string `json:"interface"` // e.g. "ppp0"
	Username  string `json:"username"`
	Service   string `json:"service"` // "pppoe", "pptp", "l2tp"
	CallerID  string `json:"caller_id,omitempty"`
	Address   string `json:"address"` // client assigned IP
	Uptime    string `json:"uptime"`
	RxBytes   uint64 `json:"rx_bytes"`
	TxBytes   uint64 `json:"tx_bytes"`
	RxHuman   string `json:"rx_human,omitempty"`
	TxHuman   string `json:"tx_human,omitempty"`
}

// ======================== Central PPP & Server Manager ========================
type PPPServerManager struct {
	mu           sync.RWMutex
	baseDir      string
	profiles     map[string]*PPPProfile
	secrets      map[string]*PPPSecret
	pppoeServer  PPPoEServerConfig
	pptpServer   PPTPServerConfig
	l2tpServer   L2TPServerConfig
	ipsecServer  IPSecServerConfig
	pppoePIDFile string
}

func NewPPPServerManager() *PPPServerManager {
	mgr := &PPPServerManager{
		baseDir:      "/etc/debtik/vpn",
		profiles:     make(map[string]*PPPProfile),
		secrets:      make(map[string]*PPPSecret),
		pppoePIDFile: "/var/run/debtik-pppoe-server.pid",
		pppoeServer: PPPoEServerConfig{
			Enabled:        false,
			ServiceName:    "debtik-pppoe",
			Interface:      "eth0",
			DefaultProfile: "default",
			MaxMTU:         1480,
			MaxMRU:         1480,
		},
		pptpServer: PPTPServerConfig{
			Enabled:        false,
			Port:           1723,
			DefaultProfile: "default-encryption",
			RequireMPPE:    true,
		},
		l2tpServer: L2TPServerConfig{
			Enabled:        false,
			Port:           1701,
			DefaultProfile: "default",
			UseIPSec:       "no",
		},
		ipsecServer: IPSecServerConfig{
			Enabled:      false,
			PoolAddress:  "10.10.30.0/24",
			PresharedKey: "DebTikSecret123",
			LocalSubnet:  "0.0.0.0/0",
			DNSServers:   "1.1.1.1,8.8.8.8",
		},
	}

	mgr.initDefaults()
	mgr.loadAll()
	mgr.SyncSecretsToSystem()
	mgr.applyAll()
	return mgr
}

func (m *PPPServerManager) initDefaults() {
	m.profiles["default"] = &PPPProfile{
		ID:            "default",
		Name:          "default",
		LocalAddress:  "10.10.10.1",
		RemoteAddress: "10.10.10.10-10.10.10.50",
		DNSServers:    "1.1.1.1,8.8.8.8",
		UseEncryption: "no",
		OnlyOne:       true,
		Comment:       "Default PPP profile for unencrypted/standard tunnels",
	}
	m.profiles["default-encryption"] = &PPPProfile{
		ID:            "default-encryption",
		Name:          "default-encryption",
		LocalAddress:  "10.10.20.1",
		RemoteAddress: "10.10.20.10-10.10.20.50",
		DNSServers:    "1.1.1.1,8.8.8.8",
		UseEncryption: "required",
		OnlyOne:       true,
		Comment:       "Default PPP profile with required MPPE-128 encryption",
	}
}

func (m *PPPServerManager) loadAll() {
	_ = os.MkdirAll(m.baseDir, 0755)

	// Profiles
	if data, err := os.ReadFile(filepath.Join(m.baseDir, "ppp_profiles.json")); err == nil {
		var list []*PPPProfile
		if err := json.Unmarshal(data, &list); err == nil {
			for _, p := range list {
				m.profiles[p.Name] = p
			}
		}
	}

	// Secrets
	if data, err := os.ReadFile(filepath.Join(m.baseDir, "ppp_secrets.json")); err == nil {
		var list []*PPPSecret
		if err := json.Unmarshal(data, &list); err == nil {
			for _, s := range list {
				m.secrets[s.ID] = s
			}
		}
	}

	// PPPoE Server
	if data, err := os.ReadFile(filepath.Join(m.baseDir, "pppoe_server.json")); err == nil {
		_ = json.Unmarshal(data, &m.pppoeServer)
	}

	// PPTP Server
	if data, err := os.ReadFile(filepath.Join(m.baseDir, "pptp_server.json")); err == nil {
		_ = json.Unmarshal(data, &m.pptpServer)
	}

	// L2TP Server
	if data, err := os.ReadFile(filepath.Join(m.baseDir, "l2tp_server.json")); err == nil {
		_ = json.Unmarshal(data, &m.l2tpServer)
	}

	// IPSec Server
	if data, err := os.ReadFile(filepath.Join(m.baseDir, "ipsec_server.json")); err == nil {
		_ = json.Unmarshal(data, &m.ipsecServer)
	}
}

func (m *PPPServerManager) save(filename string, v any) error {
	_ = os.MkdirAll(m.baseDir, 0755)
	data, err := json.MarshalIndent(v, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(filepath.Join(m.baseDir, filename), data, 0644)
}

// ======================== PPP Profiles CRUD ========================
func (m *PPPServerManager) ListProfiles() []*PPPProfile {
	m.mu.RLock()
	defer m.mu.RUnlock()
	list := make([]*PPPProfile, 0)
	for _, p := range m.profiles {
		list = append(list, p)
	}
	sort.Slice(list, func(i, j int) bool {
		return list[i].Name < list[j].Name
	})
	return list
}

func (m *PPPServerManager) GetProfile(name string) *PPPProfile {
	m.mu.RLock()
	defer m.mu.RUnlock()
	return m.profiles[name]
}

func (m *PPPServerManager) SaveProfile(p *PPPProfile) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	if p.Name == "" {
		return fmt.Errorf("profile name is required")
	}
	if p.LocalAddress == "" {
		p.LocalAddress = "10.10.10.1"
	}
	if p.RemoteAddress == "" {
		p.RemoteAddress = "10.10.10.10-10.10.10.50"
	}
	if p.ID == "" {
		p.ID = p.Name
	}

	m.profiles[p.Name] = p

	var list []*PPPProfile
	for _, pr := range m.profiles {
		list = append(list, pr)
	}
	return m.save("ppp_profiles.json", list)
}

func (m *PPPServerManager) DeleteProfile(name string) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	if name == "default" || name == "default-encryption" {
		return fmt.Errorf("cannot delete default profile")
	}
	delete(m.profiles, name)

	var list []*PPPProfile
	for _, pr := range m.profiles {
		list = append(list, pr)
	}
	return m.save("ppp_profiles.json", list)
}

// ======================== PPP Secrets CRUD ========================
func (m *PPPServerManager) ListSecrets() []*PPPSecret {
	m.mu.RLock()
	defer m.mu.RUnlock()
	list := make([]*PPPSecret, 0)
	for _, s := range m.secrets {
		list = append(list, s)
	}
	sort.Slice(list, func(i, j int) bool {
		return list[i].Name < list[j].Name
	})
	return list
}

func (m *PPPServerManager) SaveSecret(s *PPPSecret) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	if s.Name == "" || s.Password == "" {
		return fmt.Errorf("username and password are required")
	}
	if s.Service == "" {
		s.Service = "any"
	}
	if s.Profile == "" {
		s.Profile = "default"
	}
	if s.ID == "" {
		s.ID = fmt.Sprintf("secret-%d", time.Now().UnixNano())
	}

	m.secrets[s.ID] = s

	var list []*PPPSecret
	for _, sc := range m.secrets {
		list = append(list, sc)
	}
	if err := m.save("ppp_secrets.json", list); err != nil {
		return err
	}

	return m.SyncSecretsToSystem()
}

func (m *PPPServerManager) SetSecretState(id string, disabled bool) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	s, ok := m.secrets[id]
	if !ok {
		return fmt.Errorf("secret not found")
	}
	s.Disabled = disabled

	var list []*PPPSecret
	for _, sc := range m.secrets {
		list = append(list, sc)
	}
	_ = m.save("ppp_secrets.json", list)
	return m.SyncSecretsToSystem()
}

func (m *PPPServerManager) DeleteSecret(id string) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	delete(m.secrets, id)
	var list []*PPPSecret
	for _, sc := range m.secrets {
		list = append(list, sc)
	}
	_ = m.save("ppp_secrets.json", list)
	return m.SyncSecretsToSystem()
}

// SyncSecretsToSystem synchronizes all enabled secrets into /etc/ppp/chap-secrets and /etc/ppp/pap-secrets
func (m *PPPServerManager) SyncSecretsToSystem() error {
	var lines []string
	lines = append(lines, "# Autogenerated by DebTik - DO NOT EDIT MANUALLY")
	lines = append(lines, "# client\tserver\tsecret\tIP addresses")

	for _, s := range m.secrets {
		if s.Disabled {
			continue
		}
		serviceName := "*"
		if s.Service != "any" && s.Service != "" {
			serviceName = s.Service
		}
		ipAddr := "*"
		if s.RemoteAddress != "" {
			ipAddr = s.RemoteAddress
		}
		lines = append(lines, fmt.Sprintf("\"%s\"\t%s\t\"%s\"\t%s", s.Name, serviceName, s.Password, ipAddr))
	}

	content := strings.Join(lines, "\n") + "\n"
	_ = os.WriteFile("/etc/ppp/chap-secrets", []byte(content), 0600)
	_ = os.WriteFile("/etc/ppp/pap-secrets", []byte(content), 0600)
	return nil
}

// ======================== PPPoE Server Management ========================
func (m *PPPServerManager) GetPPPoEServer() PPPoEServerConfig {
	m.mu.Lock()
	defer m.mu.Unlock()

	// Check if running
	m.pppoeServer.Running = m.isProcessRunning(m.pppoePIDFile)
	m.pppoeServer.ActiveSessions = m.countPPPSessions("pppoe")
	return m.pppoeServer
}

func (m *PPPServerManager) SetPPPoEServer(cfg PPPoEServerConfig) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	m.pppoeServer.Enabled = cfg.Enabled
	if cfg.ServiceName != "" {
		m.pppoeServer.ServiceName = cfg.ServiceName
	}
	if cfg.Interface != "" {
		m.pppoeServer.Interface = cfg.Interface
	}
	if cfg.DefaultProfile != "" {
		m.pppoeServer.DefaultProfile = cfg.DefaultProfile
	}
	m.pppoeServer.OneSessionPerHost = cfg.OneSessionPerHost
	if cfg.MaxMTU > 0 {
		m.pppoeServer.MaxMTU = cfg.MaxMTU
	}
	if cfg.MaxMRU > 0 {
		m.pppoeServer.MaxMRU = cfg.MaxMRU
	}

	_ = m.save("pppoe_server.json", m.pppoeServer)
	return m.applyPPPoEServer()
}

func (m *PPPServerManager) applyPPPoEServer() error {
	m.stopPPPoEServer()

	if !m.pppoeServer.Enabled {
		m.pppoeServer.Running = false
		m.pppoeServer.LastError = ""
		return nil
	}

	// Prepare pppoe-server-options
	profile := m.profiles[m.pppoeServer.DefaultProfile]
	if profile == nil {
		profile = m.profiles["default"]
	}

	localIP := "10.10.10.1"
	if profile != nil && profile.LocalAddress != "" {
		localIP = profile.LocalAddress
	}

	startIP := "10.10.10.10"
	poolCount := 50
	if profile != nil && profile.RemoteAddress != "" {
		if strings.Contains(profile.RemoteAddress, "-") {
			parts := strings.Split(profile.RemoteAddress, "-")
			startIP = strings.TrimSpace(parts[0])
		} else {
			startIP = profile.RemoteAddress
		}
	}

	// Write /etc/ppp/pppoe-server-options
	dns1 := "1.1.1.1"
	dns2 := "8.8.8.8"
	if profile != nil && profile.DNSServers != "" {
		parts := strings.Split(profile.DNSServers, ",")
		if len(parts) > 0 {
			dns1 = strings.TrimSpace(parts[0])
		}
		if len(parts) > 1 {
			dns2 = strings.TrimSpace(parts[1])
		}
	}

	opts := fmt.Sprintf(`auth
require-chap
login
lcp-echo-interval 10
lcp-echo-failure 2
ms-dns %s
ms-dns %s
netmask 255.255.255.0
default-mru
default-asyncmap
proxyarp
`, dns1, dns2)
	_ = os.WriteFile("/etc/ppp/pppoe-server-options", []byte(opts), 0644)

	// Launch pppoe-server
	// pppoe-server -I <if> -L <local_ip> -R <start_ip> -N <count> -S <service> -O /etc/ppp/pppoe-server-options -X <pidfile>
	args := []string{
		"-I", m.pppoeServer.Interface,
		"-L", localIP,
		"-R", startIP,
		"-N", strconv.Itoa(poolCount),
		"-S", m.pppoeServer.ServiceName,
		"-O", "/etc/ppp/pppoe-server-options",
		"-X", m.pppoePIDFile,
	}
	if m.pppoeServer.OneSessionPerHost {
		args = append(args, "-x", "1")
	}

	cmd := exec.Command("/usr/sbin/pppoe-server", args...)
	if out, err := cmd.CombinedOutput(); err != nil {
		m.pppoeServer.LastError = fmt.Sprintf("start failed: %s - %v", strings.TrimSpace(string(out)), err)
		m.pppoeServer.Running = false
		return fmt.Errorf("%s", m.pppoeServer.LastError)
	}

	time.Sleep(300 * time.Millisecond)
	m.pppoeServer.Running = m.isProcessRunning(m.pppoePIDFile)
	m.pppoeServer.LastError = ""
	return nil
}

func (m *PPPServerManager) stopPPPoEServer() {
	if data, err := os.ReadFile(m.pppoePIDFile); err == nil {
		pid, _ := strconv.Atoi(strings.TrimSpace(string(data)))
		if pid > 0 {
			_ = syscall.Kill(pid, syscall.SIGTERM)
			time.Sleep(200 * time.Millisecond)
			_ = syscall.Kill(pid, syscall.SIGKILL)
		}
		_ = os.Remove(m.pppoePIDFile)
	}
	_ = exec.Command("pkill", "-f", "/usr/sbin/pppoe-server").Run()
}

// ======================== PPTP Server Management ========================
func (m *PPPServerManager) GetPPTPServer() PPTPServerConfig {
	m.mu.Lock()
	defer m.mu.Unlock()

	out, _ := exec.Command("systemctl", "is-active", "pptpd").Output()
	m.pptpServer.Running = strings.TrimSpace(string(out)) == "active"
	m.pptpServer.ActiveSessions = m.countPPPSessions("pptp")
	return m.pptpServer
}

func (m *PPPServerManager) SetPPTPServer(cfg PPTPServerConfig) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	m.pptpServer.Enabled = cfg.Enabled
	if cfg.Port > 0 {
		m.pptpServer.Port = cfg.Port
	}
	if cfg.DefaultProfile != "" {
		m.pptpServer.DefaultProfile = cfg.DefaultProfile
	}
	m.pptpServer.RequireMPPE = cfg.RequireMPPE

	_ = m.save("pptp_server.json", m.pptpServer)
	return m.applyPPTPServer()
}

func (m *PPPServerManager) applyPPTPServer() error {
	if !m.pptpServer.Enabled {
		_ = exec.Command("systemctl", "stop", "pptpd").Run()
		m.pptpServer.Running = false
		m.pptpServer.LastError = ""
		return nil
	}

	profile := m.profiles[m.pptpServer.DefaultProfile]
	if profile == nil {
		profile = m.profiles["default-encryption"]
	}

	localIP := "10.10.20.1"
	if profile != nil && profile.LocalAddress != "" {
		localIP = profile.LocalAddress
	}

	remotePool := "10.10.20.10-50"
	if profile != nil && profile.RemoteAddress != "" {
		remotePool = profile.RemoteAddress
	}

	// Write /etc/pptpd.conf
	pptpdConf := fmt.Sprintf(`option /etc/ppp/pptpd-options
logwtmp
localip %s
remoteip %s
`, localIP, remotePool)
	_ = os.WriteFile("/etc/pptpd.conf", []byte(pptpdConf), 0644)

	// Write /etc/ppp/pptpd-options
	dns1 := "1.1.1.1"
	dns2 := "8.8.8.8"
	if profile != nil && profile.DNSServers != "" {
		parts := strings.Split(profile.DNSServers, ",")
		if len(parts) > 0 {
			dns1 = strings.TrimSpace(parts[0])
		}
		if len(parts) > 1 {
			dns2 = strings.TrimSpace(parts[1])
		}
	}

	mppeRule := "require-mppe-128"
	if !m.pptpServer.RequireMPPE {
		mppeRule = "# require-mppe-128"
	}

	pptpdOpts := fmt.Sprintf(`name pptpd
refuse-pap
refuse-chap
refuse-mschap
require-mschap-v2
%s
ms-dns %s
ms-dns %s
proxyarp
nodefaultroute
lock
nobsdcomp
novj
novjccomp
nologfd
`, mppeRule, dns1, dns2)
	_ = os.WriteFile("/etc/ppp/pptpd-options", []byte(pptpdOpts), 0644)

	_ = exec.Command("systemctl", "restart", "pptpd").Run()
	time.Sleep(300 * time.Millisecond)

	out, _ := exec.Command("systemctl", "is-active", "pptpd").Output()
	m.pptpServer.Running = strings.TrimSpace(string(out)) == "active"
	m.pptpServer.LastError = ""
	return nil
}

// ======================== L2TP Server Management ========================
func (m *PPPServerManager) GetL2TPServer() L2TPServerConfig {
	m.mu.Lock()
	defer m.mu.Unlock()

	out, _ := exec.Command("systemctl", "is-active", "xl2tpd").Output()
	m.l2tpServer.Running = strings.TrimSpace(string(out)) == "active"
	m.l2tpServer.ActiveSessions = m.countPPPSessions("l2tp")
	return m.l2tpServer
}

func (m *PPPServerManager) SetL2TPServer(cfg L2TPServerConfig) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	m.l2tpServer.Enabled = cfg.Enabled
	if cfg.Port > 0 {
		m.l2tpServer.Port = cfg.Port
	}
	if cfg.DefaultProfile != "" {
		m.l2tpServer.DefaultProfile = cfg.DefaultProfile
	}
	if cfg.UseIPSec != "" {
		m.l2tpServer.UseIPSec = cfg.UseIPSec
	}
	m.l2tpServer.IPSecSecret = cfg.IPSecSecret

	_ = m.save("l2tp_server.json", m.l2tpServer)
	return m.applyL2TPServer()
}

func (m *PPPServerManager) applyL2TPServer() error {
	if !m.l2tpServer.Enabled {
		// When disabled, don't stop xl2tpd completely as client may need it, just reload without LNS
		_ = os.WriteFile("/etc/ppp/options.xl2tpd.server", []byte("# disabled\n"), 0644)
		_ = exec.Command("systemctl", "reload-or-restart", "xl2tpd").Run()
		m.l2tpServer.Running = false
		m.l2tpServer.LastError = ""
		return nil
	}

	profile := m.profiles[m.l2tpServer.DefaultProfile]
	if profile == nil {
		profile = m.profiles["default"]
	}

	localIP := "10.10.40.1"
	if profile != nil && profile.LocalAddress != "" {
		localIP = profile.LocalAddress
	}

	remotePool := "10.10.40.10-10.10.40.50"
	if profile != nil && profile.RemoteAddress != "" {
		remotePool = profile.RemoteAddress
	}

	// Write /etc/xl2tpd/xl2tpd.conf with [lns default]
	_ = os.MkdirAll("/etc/xl2tpd", 0755)
	xl2tpdConf := fmt.Sprintf(`[global]
port = %d

[lns default]
ip range = %s
local ip = %s
require chap = yes
refuse pap = yes
require authentication = yes
name = l2tpd
pppoptfile = /etc/ppp/options.xl2tpd.server
length bit = yes
`, m.l2tpServer.Port, remotePool, localIP)
	_ = os.WriteFile("/etc/xl2tpd/xl2tpd.conf", []byte(xl2tpdConf), 0644)

	// Write /etc/ppp/options.xl2tpd.server
	dns1 := "1.1.1.1"
	dns2 := "8.8.8.8"
	if profile != nil && profile.DNSServers != "" {
		parts := strings.Split(profile.DNSServers, ",")
		if len(parts) > 0 {
			dns1 = strings.TrimSpace(parts[0])
		}
		if len(parts) > 1 {
			dns2 = strings.TrimSpace(parts[1])
		}
	}

	opts := fmt.Sprintf(`require-mschap-v2
ms-dns %s
ms-dns %s
auth
mtu 1400
mru 1400
proxyarp
nodefaultroute
`, dns1, dns2)
	_ = os.WriteFile("/etc/ppp/options.xl2tpd.server", []byte(opts), 0644)

	_ = exec.Command("systemctl", "restart", "xl2tpd").Run()
	time.Sleep(300 * time.Millisecond)

	out, _ := exec.Command("systemctl", "is-active", "xl2tpd").Output()
	m.l2tpServer.Running = strings.TrimSpace(string(out)) == "active"
	m.l2tpServer.LastError = ""
	return nil
}

// ======================== IPSec Server Management ========================
func (m *PPPServerManager) GetIPSecServer() IPSecServerConfig {
	m.mu.Lock()
	defer m.mu.Unlock()

	out, _ := exec.Command("swanctl", "--list-conns").Output()
	m.ipsecServer.Running = strings.Contains(string(out), "rw-server")
	m.ipsecServer.ActiveSessions = m.countIPSecSessions()
	return m.ipsecServer
}

func (m *PPPServerManager) SetIPSecServer(cfg IPSecServerConfig) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	m.ipsecServer.Enabled = cfg.Enabled
	if cfg.PoolAddress != "" {
		m.ipsecServer.PoolAddress = cfg.PoolAddress
	}
	if cfg.PresharedKey != "" {
		m.ipsecServer.PresharedKey = cfg.PresharedKey
	}
	if cfg.LocalSubnet != "" {
		m.ipsecServer.LocalSubnet = cfg.LocalSubnet
	}
	if cfg.DNSServers != "" {
		m.ipsecServer.DNSServers = cfg.DNSServers
	}

	_ = m.save("ipsec_server.json", m.ipsecServer)
	return m.applyIPSecServer()
}

func (m *PPPServerManager) applyIPSecServer() error {
	confFile := "/etc/swanctl/conf.d/rw-server.conf"
	if !m.ipsecServer.Enabled {
		_ = os.Remove(confFile)
		_ = exec.Command("swanctl", "--load-all").Run()
		m.ipsecServer.Running = false
		m.ipsecServer.LastError = ""
		return nil
	}

	_ = os.MkdirAll("/etc/swanctl/conf.d", 0755)
	swanConf := fmt.Sprintf(`connections {
    rw-server {
        local_addrs = %%any
        pools = rw-pool
        local {
            auth = psk
            id = %%any
        }
        remote {
            auth = psk
        }
        children {
            rw-net {
                local_ts = %s
                esp_proposals = aes256gcm128-sha256-modp2048,aes256-sha256-modp2048
            }
        }
    }
}
pools {
    rw-pool {
        addrs = %s
        dns = %s
    }
}
secrets {
    ike-rw {
        secret = "%s"
    }
}
`, m.ipsecServer.LocalSubnet, m.ipsecServer.PoolAddress, m.ipsecServer.DNSServers, m.ipsecServer.PresharedKey)

	if err := os.WriteFile(confFile, []byte(swanConf), 0600); err != nil {
		m.ipsecServer.LastError = err.Error()
		return err
	}

	if out, err := exec.Command("swanctl", "--load-all").CombinedOutput(); err != nil {
		m.ipsecServer.LastError = strings.TrimSpace(string(out))
		return err
	}

	m.ipsecServer.Running = true
	m.ipsecServer.LastError = ""
	return nil
}

// ======================== Active Connections & Kill ========================
func (m *PPPServerManager) ListActiveSessions() []ActivePPPSession {
	list := make([]ActivePPPSession, 0)

	// Read network interfaces matching ppp*
	ifaces, err := net.Interfaces()
	if err != nil {
		return list
	}

	for _, iface := range ifaces {
		if !strings.HasPrefix(iface.Name, "ppp") {
			continue
		}

		addrs, _ := iface.Addrs()
		var assignedIP string
		for _, a := range addrs {
			if ipNet, ok := a.(*net.IPNet); ok && !ipNet.IP.IsLoopback() && ipNet.IP.To4() != nil {
				assignedIP = ipNet.IP.String()
				break
			}
		}

		sess := ActivePPPSession{
			ID:        iface.Name,
			Interface: iface.Name,
			Address:   assignedIP,
			Uptime:    "active",
		}

		// Try to detect service from process or default
		sess.Service = "ppp"
		sess.Username = "client-" + iface.Name

		m.populateIfaceTraffic(iface.Name, &sess)
		list = append(list, sess)
	}

	sort.Slice(list, func(i, j int) bool {
		return list[i].Interface < list[j].Interface
	})

	return list
}

func (m *PPPServerManager) DisconnectSession(ifaceName string) error {
	if !strings.HasPrefix(ifaceName, "ppp") {
		return fmt.Errorf("invalid ppp interface")
	}
	_ = exec.Command("ip", "link", "set", ifaceName, "down").Run()
	_ = exec.Command("pkill", "-f", ifaceName).Run()
	return nil
}

func (m *PPPServerManager) populateIfaceTraffic(ifaceName string, sess *ActivePPPSession) {
	file, err := os.Open("/proc/net/dev")
	if err != nil {
		return
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := scanner.Text()
		if strings.Contains(line, ifaceName+":") {
			parts := strings.Fields(line)
			if len(parts) >= 10 {
				rxBytes, _ := strconv.ParseUint(parts[1], 10, 64)
				txBytes, _ := strconv.ParseUint(parts[9], 10, 64)
				sess.RxBytes = rxBytes
				sess.TxBytes = txBytes
				sess.RxHuman = formatBytes(rxBytes)
				sess.TxHuman = formatBytes(txBytes)
			}
			break
		}
	}
}

func (m *PPPServerManager) countPPPSessions(service string) int {
	ifaces, err := net.Interfaces()
	if err != nil {
		return 0
	}
	count := 0
	for _, i := range ifaces {
		if strings.HasPrefix(i.Name, "ppp") {
			count++
		}
	}
	return count
}

func (m *PPPServerManager) countIPSecSessions() int {
	out, err := exec.Command("swanctl", "--list-sas").Output()
	if err != nil {
		return 0
	}
	return strings.Count(string(out), "ESTABLISHED")
}

func (m *PPPServerManager) isProcessRunning(pidFile string) bool {
	data, err := os.ReadFile(pidFile)
	if err != nil {
		return false
	}
	pid, err := strconv.Atoi(strings.TrimSpace(string(data)))
	if err != nil || pid <= 0 {
		return false
	}
	return syscall.Kill(pid, 0) == nil
}

func (m *PPPServerManager) applyAll() {
	if m.pppoeServer.Enabled {
		_ = m.applyPPPoEServer()
	}
	if m.pptpServer.Enabled {
		_ = m.applyPPTPServer()
	}
	if m.l2tpServer.Enabled {
		_ = m.applyL2TPServer()
	}
	if m.ipsecServer.Enabled {
		_ = m.applyIPSecServer()
	}
}