package dhcp

import (
	"encoding/json"
	"fmt"
	"net"
	"os"
	"os/exec"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/vishvananda/netlink"
)

const (
	DHCPConfigFile = "/etc/proxmox-router/dhcp_clients.json"
	DHCPRunDir     = "/run"
	DHCPLeaseDir   = "/var/lib/dhcp"
	DHCPConfDir    = "/etc/dhcp"
)

var (
	leaseBlockRegex     = regexp.MustCompile(`(?s)lease\s+\{([^}]+)\}`)
	fixedAddrRegex      = regexp.MustCompile(`fixed-address\s+([0-9.]+);`)
	subnetMaskRegex     = regexp.MustCompile(`option subnet-mask\s+([0-9.]+);`)
	routersRegex        = regexp.MustCompile(`option routers\s+([0-9.]+);`)
	dhcpServerRegex     = regexp.MustCompile(`option dhcp-server-identifier\s+([0-9.]+);`)
	dnsServersRegex     = regexp.MustCompile(`option domain-name-servers\s+([^;]+);`)
	domainNameRegex     = regexp.MustCompile(`option domain-name\s+"([^"]+)";`)
	leaseTimeRegex      = regexp.MustCompile(`option dhcp-lease-time\s+(\d+);`)
	expireTimeRegex     = regexp.MustCompile(`expire\s+\d+\s+([0-9/]+ [0-9:]+);`)
	renewTimeRegex      = regexp.MustCompile(`renew\s+\d+\s+([0-9/]+ [0-9:]+);`)
	validInterfaceRegex = regexp.MustCompile(`^[a-zA-Z0-9.:_-]+$`)
)

// DHCPConfigStore wraps the persisted configuration.
type DHCPConfigStore struct {
	Clients []*DHCPClient `json:"clients"`
}

// Manager orchestrates all DHCP client instances.
type Manager struct {
	mu        sync.RWMutex
	storePath string
	clients   map[string]*DHCPClient
}

// NewManager initializes the DHCP Manager and restores saved clients.
func NewManager() *Manager {
	_ = os.MkdirAll("/etc/proxmox-router", 0755)
	_ = os.MkdirAll(DHCPLeaseDir, 0755)
	_ = os.MkdirAll(DHCPConfDir, 0755)

	m := &Manager{
		storePath: DHCPConfigFile,
		clients:   make(map[string]*DHCPClient),
	}

	_ = m.Load()
	return m
}

// Load loads saved clients from disk and ensures enabled clients are started.
func (m *Manager) Load() error {
	m.mu.Lock()
	defer m.mu.Unlock()

	data, err := os.ReadFile(m.storePath)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return err
	}

	var store DHCPConfigStore
	if err := json.Unmarshal(data, &store); err != nil {
		return err
	}

	for _, c := range store.Clients {
		if c.ID == "" {
			c.ID = "dhcp-" + c.Interface
		}
		m.clients[c.ID] = c
	}

	// Startup active clients
	go func() {
		time.Sleep(1 * time.Second)
		m.SyncAll()
	}()

	return nil
}

// Save persists the current DHCP clients to disk.
func (m *Manager) Save() error {
	store := DHCPConfigStore{
		Clients: make([]*DHCPClient, 0, len(m.clients)),
	}
	for _, c := range m.clients {
		store.Clients = append(store.Clients, c)
	}

	data, err := json.MarshalIndent(store, "", "  ")
	if err != nil {
		return err
	}

	tmpFile := m.storePath + ".tmp"
	if err := os.WriteFile(tmpFile, data, 0644); err != nil {
		return err
	}
	return os.Rename(tmpFile, m.storePath)
}

// SyncAll refreshes status and launches any enabled clients that aren't running.
func (m *Manager) SyncAll() {
	m.mu.Lock()
	defer m.mu.Unlock()

	for _, c := range m.clients {
		m.updateStatus(c)
		if c.Enabled && c.Status != "bound" && c.Status != "searching" {
			_ = m.startClient(c)
			m.updateStatus(c)
		}
	}
}

// ListClients returns all DHCP clients with real-time lease info.
func (m *Manager) ListClients() []*DHCPClient {
	m.mu.Lock()
	defer m.mu.Unlock()

	res := make([]*DHCPClient, 0, len(m.clients))
	for _, c := range m.clients {
		m.updateStatus(c)
		res = append(res, c)
	}

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

	return res
}

// GetSummary returns summary KPIs.
func (m *Manager) GetSummary() DHCPSummary {
	clients := m.ListClients()
	sum := DHCPSummary{
		TotalClients: len(clients),
	}
	for _, c := range clients {
		switch c.Status {
		case "bound":
			sum.BoundClients++
		case "searching":
			sum.Searching++
		case "disabled":
			sum.Disabled++
		}
	}
	return sum
}

// GetClient retrieves a single client by ID.
func (m *Manager) GetClient(id string) (*DHCPClient, error) {
	m.mu.Lock()
	defer m.mu.Unlock()

	c, ok := m.clients[id]
	if !ok {
		return nil, fmt.Errorf("dhcp client %s not found", id)
	}
	m.updateStatus(c)
	return c, nil
}

// AddClient creates and optionally starts a DHCP client on an interface.
func (m *Manager) AddClient(req CreateDHCPClientRequest) (*DHCPClient, error) {
	iface := strings.TrimSpace(req.Interface)
	if iface == "" || !validInterfaceRegex.MatchString(iface) {
		return nil, fmt.Errorf("invalid interface name")
	}

	// Verify interface exists on system
	if _, err := net.InterfaceByName(iface); err != nil {
		return nil, fmt.Errorf("interface %s does not exist on host", iface)
	}

	m.mu.Lock()
	defer m.mu.Unlock()

	id := "dhcp-" + iface
	if _, exists := m.clients[id]; exists {
		return nil, fmt.Errorf("dhcp client already exists for interface %s", iface)
	}

	dist := req.DefaultRouteDistance
	if dist <= 0 {
		dist = 1
	}

	c := &DHCPClient{
		ID:                   id,
		Interface:            iface,
		Enabled:              req.Enabled,
		AddDefaultRoute:      req.AddDefaultRoute,
		DefaultRouteDistance: dist,
		UsePeerDNS:           req.UsePeerDNS,
		UsePeerNTP:           req.UsePeerNTP,
		Comment:              req.Comment,
		Status:               "stopped",
		DNSServers:           []string{},
	}

	if c.Enabled {
		if err := m.startClient(c); err != nil {
			c.Status = "error"
		}
	} else {
		c.Status = "disabled"
	}

	m.updateStatus(c)
	m.clients[id] = c
	_ = m.Save()

	return c, nil
}

// UpdateClient modifies client settings and restarts if needed.
func (m *Manager) UpdateClient(id string, req UpdateDHCPClientRequest) (*DHCPClient, error) {
	m.mu.Lock()
	defer m.mu.Unlock()

	c, ok := m.clients[id]
	if !ok {
		return nil, fmt.Errorf("dhcp client %s not found", id)
	}

	needsRestart := false

	if req.AddDefaultRoute != nil && *req.AddDefaultRoute != c.AddDefaultRoute {
		c.AddDefaultRoute = *req.AddDefaultRoute
		needsRestart = true
	}
	if req.DefaultRouteDistance != nil && *req.DefaultRouteDistance != c.DefaultRouteDistance {
		c.DefaultRouteDistance = *req.DefaultRouteDistance
		needsRestart = true
	}
	if req.UsePeerDNS != nil && *req.UsePeerDNS != c.UsePeerDNS {
		c.UsePeerDNS = *req.UsePeerDNS
		needsRestart = true
	}
	if req.UsePeerNTP != nil && *req.UsePeerNTP != c.UsePeerNTP {
		c.UsePeerNTP = *req.UsePeerNTP
		needsRestart = true
	}
	if req.Comment != nil {
		c.Comment = *req.Comment
	}
	if req.Enabled != nil {
		if *req.Enabled != c.Enabled {
			c.Enabled = *req.Enabled
			if c.Enabled {
				_ = m.startClient(c)
			} else {
				_ = m.stopClient(c)
				c.Status = "disabled"
			}
			needsRestart = false
		}
	}

	if needsRestart && c.Enabled {
		_ = m.stopClient(c)
		_ = m.startClient(c)
	}

	m.updateStatus(c)
	_ = m.Save()
	return c, nil
}

// ToggleState enables or disables a DHCP client.
func (m *Manager) ToggleState(id string, enabled bool) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	c, ok := m.clients[id]
	if !ok {
		return fmt.Errorf("dhcp client %s not found", id)
	}

	c.Enabled = enabled
	if enabled {
		if err := m.startClient(c); err != nil {
			c.Status = "error"
		}
	} else {
		_ = m.stopClient(c)
		c.Status = "disabled"
	}

	m.updateStatus(c)
	return m.Save()
}

// RenewLease forces dhclient to renew its lease.
func (m *Manager) RenewLease(id string) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	c, ok := m.clients[id]
	if !ok {
		return fmt.Errorf("dhcp client %s not found", id)
	}

	if !c.Enabled {
		return fmt.Errorf("cannot renew disabled dhcp client")
	}

	_ = m.stopClient(c)
	time.Sleep(200 * time.Millisecond)
	err := m.startClient(c)
	m.updateStatus(c)
	return err
}

// ReleaseLease sends DHCPRELEASE and removes the IP address.
func (m *Manager) ReleaseLease(id string) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	c, ok := m.clients[id]
	if !ok {
		return fmt.Errorf("dhcp client %s not found", id)
	}

	pidFile := fmt.Sprintf("%s/dhclient.%s.pid", DHCPRunDir, c.Interface)
	leaseFile := fmt.Sprintf("%s/dhclient.%s.leases", DHCPLeaseDir, c.Interface)

	cmd := exec.Command("dhclient", "-4", "-r", "-pf", pidFile, "-lf", leaseFile, c.Interface)
	_ = cmd.Run()

	_ = m.stopClient(c)
	c.Status = "stopped"
	c.IPAddress = ""
	c.Gateway = ""
	c.ExpiresIn = ""
	return m.Save()
}

// DeleteClient stops the client and removes it from configuration.
func (m *Manager) DeleteClient(id string) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	c, ok := m.clients[id]
	if !ok {
		return fmt.Errorf("dhcp client %s not found", id)
	}

	_ = m.stopClient(c)

	// Clean up conf & lease files
	_ = os.Remove(fmt.Sprintf("%s/dhclient.%s.pid", DHCPRunDir, c.Interface))
	_ = os.Remove(fmt.Sprintf("%s/dhclient-%s.conf", DHCPConfDir, c.Interface))

	delete(m.clients, id)
	return m.Save()
}

func (m *Manager) startClient(c *DHCPClient) error {
	pidFile := fmt.Sprintf("%s/dhclient.%s.pid", DHCPRunDir, c.Interface)
	leaseFile := fmt.Sprintf("%s/dhclient.%s.leases", DHCPLeaseDir, c.Interface)
	confFile := fmt.Sprintf("%s/dhclient-%s.conf", DHCPConfDir, c.Interface)

	// Generate custom dhclient config
	var sb strings.Builder
	sb.WriteString("# RouterOS-style dhclient configuration\n")
	sb.WriteString("send host-name = gethostname();\n")
	sb.WriteString("request subnet-mask, broadcast-address, time-offset")
	if c.AddDefaultRoute {
		sb.WriteString(", routers")
	}
	if c.UsePeerDNS {
		sb.WriteString(", domain-name, domain-name-servers, domain-search, host-name")
	}
	if c.UsePeerNTP {
		sb.WriteString(", ntp-servers")
	}
	sb.WriteString(";\n")

	_ = os.WriteFile(confFile, []byte(sb.String()), 0644)

	// If already running, kill first
	_ = m.stopClient(c)

	// Launch dhclient in background
	cmd := exec.Command("dhclient", "-4", "-nw", "-pf", pidFile, "-lf", leaseFile, "-cf", confFile, c.Interface)
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("failed to start dhclient: %w", err)
	}

	c.Status = "searching"
	return nil
}

func (m *Manager) stopClient(c *DHCPClient) error {
	pidFile := fmt.Sprintf("%s/dhclient.%s.pid", DHCPRunDir, c.Interface)

	// Check PID file
	if pidBytes, err := os.ReadFile(pidFile); err == nil {
		if pid, err := strconv.Atoi(strings.TrimSpace(string(pidBytes))); err == nil && pid > 0 {
			_ = syscall.Kill(pid, syscall.SIGTERM)
			time.Sleep(100 * time.Millisecond)
			if err := syscall.Kill(pid, 0); err == nil {
				_ = syscall.Kill(pid, syscall.SIGKILL)
			}
		}
	}

	_ = os.Remove(pidFile)
	c.PID = 0
	return nil
}

func (m *Manager) updateStatus(c *DHCPClient) {
	pidFile := fmt.Sprintf("%s/dhclient.%s.pid", DHCPRunDir, c.Interface)
	leaseFile := fmt.Sprintf("%s/dhclient.%s.leases", DHCPLeaseDir, c.Interface)

	// Check if process is alive
	isRunning := false
	if pidBytes, err := os.ReadFile(pidFile); err == nil {
		if pid, err := strconv.Atoi(strings.TrimSpace(string(pidBytes))); err == nil && pid > 0 {
			if err := syscall.Kill(pid, 0); err == nil {
				isRunning = true
				c.PID = pid
			}
		}
	}

	if !isRunning {
		c.PID = 0
		if !c.Enabled {
			c.Status = "disabled"
		} else {
			c.Status = "stopped"
		}
	} else {
		c.Status = "searching"
	}

	// Read interface IPv4 addresses via netlink
	if link, err := netlink.LinkByName(c.Interface); err == nil {
		if addrs, err := netlink.AddrList(link, netlink.FAMILY_V4); err == nil && len(addrs) > 0 {
			for _, a := range addrs {
				ip := a.IPNet.IP.String()
				if !strings.HasPrefix(ip, "127.") && !strings.HasPrefix(ip, "169.254.") {
					c.IPAddress = a.IPNet.String()
					if isRunning {
						c.Status = "bound"
					}
					break
				}
			}
		}
	}

	// Parse lease file for rich metadata (gateway, dns, lease times)
	m.parseLeaseFile(leaseFile, c)
}

func (m *Manager) parseLeaseFile(leaseFile string, c *DHCPClient) {
	data, err := os.ReadFile(leaseFile)
	if err != nil {
		return
	}

	// Find the last lease block in the file
	matches := leaseBlockRegex.FindAllStringSubmatch(string(data), -1)
	if len(matches) == 0 {
		return
	}
	lastLease := matches[len(matches)-1][1]

	if m := fixedAddrRegex.FindStringSubmatch(lastLease); len(m) > 1 {
		ip := m[1]
		mask := "24"
		if sm := subnetMaskRegex.FindStringSubmatch(lastLease); len(sm) > 1 {
			mask = subnetToCIDR(sm[1])
		}
		if c.IPAddress == "" {
			c.IPAddress = fmt.Sprintf("%s/%s", ip, mask)
		}
	}

	if m := routersRegex.FindStringSubmatch(lastLease); len(m) > 1 {
		c.Gateway = m[1]
	}

	if m := dhcpServerRegex.FindStringSubmatch(lastLease); len(m) > 1 {
		c.DHCPServer = m[1]
	}

	if m := dnsServersRegex.FindStringSubmatch(lastLease); len(m) > 1 {
		raw := strings.Split(m[1], ",")
		dns := make([]string, 0, len(raw))
		for _, s := range raw {
			trimmed := strings.TrimSpace(s)
			if trimmed != "" {
				dns = append(dns, trimmed)
			}
		}
		c.DNSServers = dns
	}

	if m := domainNameRegex.FindStringSubmatch(lastLease); len(m) > 1 {
		c.Domain = m[1]
	}

	if m := leaseTimeRegex.FindStringSubmatch(lastLease); len(m) > 1 {
		c.LeaseTime, _ = strconv.Atoi(m[1])
	}

	if m := expireTimeRegex.FindStringSubmatch(lastLease); len(m) > 1 {
		// e.g. "2026/10/26 18:30:00"
		if t, err := time.Parse("2006/01/02 15:04:05", m[1]); err == nil {
			c.ExpiresAt = t
			rem := time.Until(t)
			if rem > 0 {
				hours := int(rem.Hours())
				mins := int(rem.Minutes()) % 60
				if hours > 24 {
					c.ExpiresIn = fmt.Sprintf("%dd %dh", hours/24, hours%24)
				} else if hours > 0 {
					c.ExpiresIn = fmt.Sprintf("%dh %dm", hours, mins)
				} else {
					c.ExpiresIn = fmt.Sprintf("%dm %ds", mins, int(rem.Seconds())%60)
				}
			} else {
				c.ExpiresIn = "Expired"
			}
		}
	}
}

func subnetToCIDR(mask string) string {
	parts := strings.Split(mask, ".")
	if len(parts) != 4 {
		return "24"
	}
	var count int
	for _, p := range parts {
		n, _ := strconv.Atoi(p)
		for n > 0 {
			count += n & 1
			n >>= 1
		}
	}
	return strconv.Itoa(count)
}