package vpn

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

	"github.com/vishvananda/netlink"
)

const (
	PPTPInstancesStorePath = "/etc/proxmox-router/vpn/pptp_instances.json"
)

type PPTPManager struct {
	mu        sync.Mutex
	instances []PPTPInstance
}

func NewPPTPManager() *PPTPManager {
	m := &PPTPManager{
		instances: make([]PPTPInstance, 0),
	}
	m.load()
	return m
}

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

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

func (m *PPTPManager) List() []PPTPInstance {
	m.mu.Lock()
	defer m.mu.Unlock()

	m.refreshRuntimeStatus()

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

func (m *PPTPManager) Save(inst PPTPInstance) error {
	m.mu.Lock()
	defer m.mu.Unlock()

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

	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.generatePeerConfig(inst); err != nil {
		return err
	}

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

	return nil
}

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

	_ = m.disconnectInstance(name)
	_ = os.Remove(fmt.Sprintf("/etc/ppp/peers/%s", name))

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

func (m *PPTPManager) 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
			_ = m.save()
			if enabled {
				go m.connectInstance(name)
			} else {
				go m.disconnectInstance(name)
			}
			return nil
		}
	}
	return fmt.Errorf("instance %q not found", name)
}

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

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

func (m *PPTPManager) connectInstance(name string) error {
	_ = exec.Command("poff", name).Run()
	time.Sleep(300 * time.Millisecond)

	cmd := exec.Command("pon", name)
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("failed to start PPTP %s: %s: %w", name, string(out), err)
	}
	return nil
}

func (m *PPTPManager) disconnectInstance(name string) error {
	cmd := exec.Command("poff", name)
	_ = cmd.Run()
	return nil
}

func (m *PPTPManager) generatePeerConfig(inst PPTPInstance) error {
	_ = os.MkdirAll("/etc/ppp/peers", 0755)

	var sb strings.Builder
	sb.WriteString(fmt.Sprintf("# MikroTik-Style PPTP Client: %s\n", inst.Name))
	sb.WriteString(fmt.Sprintf("pty \"pptp %s --nolaunchpppd\"\n", inst.ConnectTo))
	sb.WriteString(fmt.Sprintf("name %q\n", inst.Username))
	sb.WriteString("remotename PPTP\n")
	if inst.RequireMPPE {
		sb.WriteString("require-mppe-128\n")
	}
	if inst.DefaultRoute {
		sb.WriteString("defaultroute\n")
		sb.WriteString("replacedefaultroute\n")
	}
	if inst.AutoReconnect {
		sb.WriteString("persist\n")
		sb.WriteString("maxfail 0\n")
	}
	sb.WriteString("file /etc/ppp/options.pptp\n")
	sb.WriteString(fmt.Sprintf("ipparam %q\n", inst.Name))

	peerPath := fmt.Sprintf("/etc/ppp/peers/%s", inst.Name)
	if err := os.WriteFile(peerPath, []byte(sb.String()), 0600); err != nil {
		return err
	}

	if inst.Username != "" && inst.Password != "" {
		line := fmt.Sprintf("%q PPTP %q *\n", inst.Username, inst.Password)
		content, _ := os.ReadFile(ChapSecretsPath)
		str := string(content)
		if !strings.Contains(str, fmt.Sprintf("%q PPTP", inst.Username)) {
			str += "\n" + line
			_ = os.WriteFile(ChapSecretsPath, []byte(str), 0600)
		}
	}

	return nil
}

func (m *PPTPManager) 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) {
			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
				}
			}
		}
	}
}