package vpn

import (
	"encoding/json"
	"fmt"
	"net"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"sync"
	"syscall"

	"github.com/vishvananda/netlink"
)

const (
	L2TPInstancesStorePath = "/etc/debtik/vpn/l2tp_instances.json"
	Xl2tpdConfigPath       = "/etc/xl2tpd/xl2tpd.conf"
	L2TPControlFIFO        = "/var/run/xl2tpd/l2tp-control"
)

type L2TPManager struct {
	mu        sync.Mutex
	instances []L2TPInstance
	pppServer *PPPServerManager
}

func NewL2TPManager() *L2TPManager {
	m := &L2TPManager{
		instances: make([]L2TPInstance, 0),
	}
	m.load()
	return m
}

func (m *L2TPManager) SetPPPServer(ps *PPPServerManager) {
	m.pppServer = ps
}

func (m *L2TPManager) load() {
	data, err := os.ReadFile(L2TPInstancesStorePath)
	if err == nil {
		_ = json.Unmarshal(data, &m.instances)
	}
	if m.instances == nil {
		m.instances = make([]L2TPInstance, 0)
	}
}

func (m *L2TPManager) save() error {
	_ = os.MkdirAll(filepath.Dir(L2TPInstancesStorePath), 0755)
	data, err := json.MarshalIndent(m.instances, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(L2TPInstancesStorePath, data, 0600)
}

func (m *L2TPManager) List() []L2TPInstance {
	m.mu.Lock()
	defer m.mu.Unlock()

	m.refreshRuntimeStatus()

	res := make([]L2TPInstance, len(m.instances))
	copy(res, m.instances)
	return res
}

func (m *L2TPManager) Save(inst L2TPInstance) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	if inst.Name == "" {
		return fmt.Errorf("instance name is required (e.g. l2tp-out1)")
	}
	if inst.ConnectTo == "" {
		return fmt.Errorf("server address (connect-to) is required")
	}
	if inst.Profile == "" {
		inst.Profile = "default-encryption"
	}

	found := false
	for i, existing := range m.instances {
		if existing.Name == inst.Name {
			m.instances[i] = inst
			found = true
			break
		}
	}
	if !found {
		m.instances = append(m.instances, inst)
	}

	if err := m.save(); err != nil {
		return err
	}

	if err := m.regenerateXl2tpdConf(); err != nil {
		return err
	}

	if !inst.Disabled {
		return m.connectInstance(inst.Name)
	} else {
		return m.disconnectInstance(inst.Name)
	}
}

func (m *L2TPManager) Delete(name string) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	_ = m.disconnectInstance(name)

	updated := make([]L2TPInstance, 0)
	for _, inst := range m.instances {
		if inst.Name != name {
			updated = append(updated, inst)
		}
	}
	m.instances = updated

	if err := m.save(); err != nil {
		return err
	}
	return m.regenerateXl2tpdConf()
}

func (m *L2TPManager) SetEnabled(name string, enabled bool) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	for i, inst := range m.instances {
		if inst.Name == name {
			m.instances[i].Disabled = !enabled
			if err := m.save(); err != nil {
				return err
			}
			if enabled {
				return m.connectInstance(name)
			} else {
				return m.disconnectInstance(name)
			}
		}
	}
	return fmt.Errorf("instance %q not found", name)
}

func (m *L2TPManager) Connect(name string) error {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.connectInstance(name)
}

func (m *L2TPManager) Disconnect(name string) error {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.disconnectInstance(name)
}

func (m *L2TPManager) regenerateXl2tpdConf() error {
	_ = os.MkdirAll("/etc/xl2tpd", 0755)
	_ = os.MkdirAll("/var/run/xl2tpd", 0755)

	var sb strings.Builder
	sb.WriteString("[global]\n")
	sb.WriteString("port = 1701\n\n")

	for _, inst := range m.instances {
		prof := inst.Profile
		if prof == "" {
			prof = "default-encryption"
		}
		var profObj *PPPProfile
		if m.pppServer != nil {
			profObj = m.pppServer.GetProfile(prof)
		}

		optFile := fmt.Sprintf("/etc/ppp/options.l2tpd.%s", inst.Name)
		sb.WriteString(fmt.Sprintf("[lac %s]\n", inst.Name))
		sb.WriteString(fmt.Sprintf("lns = %s\n", inst.ConnectTo))
		sb.WriteString("ppp debug = yes\n")
		sb.WriteString(fmt.Sprintf("pppoptfile = %s\n", optFile))
		sb.WriteString("length bit = yes\n")
		sb.WriteString("redial = yes\n\n")

		// Create individual options file
		var optSb strings.Builder
		optSb.WriteString(fmt.Sprintf("# L2TP Client: %s (Profile: %s)\n", inst.Name, prof))
		optSb.WriteString(fmt.Sprintf("name %q\n", inst.Username))
		optSb.WriteString(fmt.Sprintf("password %q\n", inst.Password))
		optSb.WriteString("ipcp-accept-local\n")
		optSb.WriteString("ipcp-accept-remote\n")
		optSb.WriteString("refuse-eap\n")
		optSb.WriteString("require-mschap-v2\n")

		if profObj != nil {
			switch strings.ToLower(profObj.UseEncryption) {
			case "no":
				optSb.WriteString("nomppe\n")
			case "yes":
				optSb.WriteString("mppe-128\n")
			default:
				optSb.WriteString("require-mppe-128\n")
			}
			if profObj.DNSServers != "" {
				for _, dns := range strings.Split(profObj.DNSServers, ",") {
					dns = strings.TrimSpace(dns)
					if dns != "" {
						optSb.WriteString(fmt.Sprintf("ms-dns %s\n", dns))
					}
				}
			}
			if profObj.LocalAddress != "" && profObj.RemoteAddress != "" {
				local := strings.TrimSpace(profObj.LocalAddress)
				remote := strings.TrimSpace(profObj.RemoteAddress)
				if strings.Contains(remote, "-") {
					remote = strings.TrimSpace(strings.Split(remote, "-")[0])
				}
				if local != "" && remote != "" {
					optSb.WriteString(fmt.Sprintf("%s:%s\n", local, remote))
				}
			}
		} else {
			if strings.EqualFold(prof, "default") {
				optSb.WriteString("nomppe\n")
			} else {
				optSb.WriteString("require-mppe-128\n")
			}
		}

		optSb.WriteString("noccp\n")
		optSb.WriteString("noauth\n")
		optSb.WriteString("mtu 1410\n")
		optSb.WriteString("mru 1410\n")
		if inst.DefaultRoute {
			optSb.WriteString("defaultroute\n")
			optSb.WriteString("replacedefaultroute\n")
		}
		_ = os.WriteFile(optFile, []byte(optSb.String()), 0600)
	}

	if err := os.WriteFile(Xl2tpdConfigPath, []byte(sb.String()), 0600); err != nil {
		return err
	}

	if err := exec.Command("systemctl", "restart", "xl2tpd").Run(); err != nil {
		return err
	}
	return nil
}

func writeL2TPControl(command, name string) error {
	f, err := os.OpenFile(L2TPControlFIFO, os.O_WRONLY|syscall.O_NONBLOCK, 0600)
	if err != nil {
		return fmt.Errorf("L2TP control unavailable: %w", err)
	}
	defer f.Close()
	_, err = fmt.Fprintf(f, "%s %s\n", command, name)
	return err
}
func (m *L2TPManager) connectInstance(name string) error    { return writeL2TPControl("c", name) }
func (m *L2TPManager) disconnectInstance(name string) error { return writeL2TPControl("d", name) }

func (m *L2TPManager) refreshRuntimeStatus() {
	psOut, _ := exec.Command("ps", "-ef").Output()
	psStr := string(psOut)

	links, _ := netlink.LinkList()

	for i := range m.instances {
		name := m.instances[i].Name
		if strings.Contains(psStr, name) || strings.Contains(psStr, "xl2tpd") {
			m.instances[i].Running = true
		} else {
			m.instances[i].Running = false
		}

		m.instances[i].AssignedIP = ""
		m.instances[i].PPPDevice = ""
		for _, l := range links {
			if strings.HasPrefix(l.Attrs().Name, "ppp") && l.Attrs().Flags&net.FlagUp != 0 {
				addrs, _ := netlink.AddrList(l, netlink.FAMILY_V4)
				if len(addrs) > 0 {
					m.instances[i].AssignedIP = addrs[0].IPNet.String()
					m.instances[i].PPPDevice = l.Attrs().Name
					m.instances[i].Running = true
					break
				}
			}
		}
	}
}