package sdwan

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"
)

const DefaultStorePath = "/etc/debtik/sdwan.json"

// Global resolver registered for firewall integration
var GlobalManager *Manager

// ResolvedRouteNexthop represents a target egress interface/gateway for routing.
type ResolvedRouteNexthop struct {
	Gateway   string `json:"gateway"`
	Interface string `json:"interface"`
	Weight    int    `json:"weight"`
}

var (
	stateChangeCallbacks []func()
	stateChangeMu        sync.Mutex
)

// RegisterStateChangeCallback registers a function to be invoked when SD-WAN link health or topology changes.
func RegisterStateChangeCallback(cb func()) {
	if cb == nil {
		return
	}
	stateChangeMu.Lock()
	defer stateChangeMu.Unlock()
	stateChangeCallbacks = append(stateChangeCallbacks, cb)
}

// NotifyStateChange invokes all registered state change callbacks.
func NotifyStateChange() {
	stateChangeMu.Lock()
	cbs := make([]func(), len(stateChangeCallbacks))
	copy(cbs, stateChangeCallbacks)
	stateChangeMu.Unlock()

	for _, cb := range cbs {
		go cb()
	}
}

// Manager coordinates SD-WAN group configurations, kernel routing, and SLA health monitoring.
type Manager struct {
	mu        sync.RWMutex
	storePath string
	groups    map[string]*SDWANGroup
	engine    *KernelEngine
	monitor   *HealthMonitor
}

// NewManager creates an SD-WAN manager with persistent storage.
func NewManager(customStore ...string) *Manager {
	store := DefaultStorePath
	if len(customStore) > 0 && customStore[0] != "" {
		store = customStore[0]
	}

	mgr := &Manager{
		storePath: store,
		groups:    make(map[string]*SDWANGroup),
		engine:    NewKernelEngine(),
	}

	mgr.monitor = NewHealthMonitor(func() {
		mgr.mu.RLock()
		groups := mgr.listLocked()
		mgr.mu.RUnlock()
		_ = mgr.engine.Sync(groups)
		NotifyStateChange()
	})

	mgr.load()
	mgr.SyncAll()
	mgr.monitor.Start(func() []*SDWANGroup {
		return mgr.List()
	})

	GlobalManager = mgr
	return mgr
}

func (m *Manager) Stop() {
	if m.monitor != nil {
		m.monitor.Stop()
	}
	if m.engine != nil {
		m.engine.mu.Lock()
		for dev := range m.engine.virtualDevices {
			m.engine.removeVirtualDevice(dev)
		}
		m.engine.virtualDevices = make(map[string]bool)
		m.engine.cleanupMangle()
		m.engine.cleanupIPRules()
		m.engine.mu.Unlock()
	}
}

// Has checks if an SD-WAN group exists by ID or name.
func (m *Manager) Has(idOrName string) bool {
	_, found := m.Get(idOrName)
	return found
}

func (m *Manager) load() {
	m.mu.Lock()
	defer m.mu.Unlock()

	data, err := os.ReadFile(m.storePath)
	if err != nil {
		return
	}
	var list []*SDWANGroup
	if err := json.Unmarshal(data, &list); err == nil {
		for _, g := range list {
			m.groups[g.ID] = g
		}
	}
}

func (m *Manager) save() error {
	_ = os.MkdirAll(filepath.Dir(m.storePath), 0755)

	list := make([]*SDWANGroup, 0, len(m.groups))
	for _, g := range m.groups {
		list = append(list, g)
	}

	data, err := json.MarshalIndent(list, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(m.storePath, data, 0644)
}

func (m *Manager) listLocked() []*SDWANGroup {
	list := make([]*SDWANGroup, 0, len(m.groups))
	for _, g := range m.groups {
		list = append(list, g)
	}
	sort.Slice(list, func(i, j int) bool {
		return list[i].Name < list[j].Name
	})
	return list
}

// List returns a sorted copy of all configured SD-WAN groups.
func (m *Manager) List() []*SDWANGroup {
	m.mu.RLock()
	defer m.mu.RUnlock()
	return m.listLocked()
}

// Get returns an SD-WAN group by ID or group name.
func (m *Manager) Get(idOrName string) (*SDWANGroup, bool) {
	m.mu.RLock()
	defer m.mu.RUnlock()

	if g, ok := m.groups[idOrName]; ok {
		return g, true
	}
	for _, g := range m.groups {
		if strings.EqualFold(g.Name, idOrName) {
			return g, true
		}
	}
	return nil, false
}

// Save validates, stores, and synchronizes an SD-WAN group.
func (m *Manager) Save(g *SDWANGroup) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	if g.Name == "" {
		g.Name = fmt.Sprintf("sdwan%d", len(m.groups))
	}
	if g.ID == "" {
		g.ID = fmt.Sprintf("sdwan-%d", time.Now().UnixNano())
	}
	if g.Mode == "" {
		g.Mode = ModeWeighted
	}
	if g.ProbeInterval <= 0 {
		g.ProbeInterval = 3
	}

	// Validate name collisions
	for _, existing := range m.groups {
		if existing.ID != g.ID && strings.EqualFold(existing.Name, g.Name) {
			return fmt.Errorf("sd-wan group with name %q already exists", g.Name)
		}
	}

	// Preserve existing members if not specified in update payload
	if existing, ok := m.groups[g.ID]; ok {
		if g.Members == nil && existing.Members != nil {
			g.Members = existing.Members
		}
	}

	// Ensure member IDs and initial statuses
	for _, mem := range g.Members {
		if mem.ID == "" {
			mem.ID = fmt.Sprintf("mem-%d-%s", time.Now().UnixNano(), mem.Interface)
		}
		if mem.Weight <= 0 {
			mem.Weight = 50
		}
		if mem.Priority <= 0 {
			mem.Priority = 1
		}
		if mem.Status == "" {
			mem.Status = StatusHealthy
		}
	}

	m.groups[g.ID] = g
	if err := m.save(); err != nil {
		return err
	}

	return m.syncLocked()
}

func (m *Manager) syncLocked() error {
	err := m.engine.Sync(m.listLocked())
	_ = m.save()
	NotifyStateChange()
	return err
}

// SetState enables or disables an SD-WAN group.
func (m *Manager) SetState(idOrName string, disabled bool) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	g := m.findLocked(idOrName)
	if g == nil {
		return fmt.Errorf("sd-wan group %q not found", idOrName)
	}

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

	return m.syncLocked()
}

// Delete removes an SD-WAN group.
func (m *Manager) Delete(idOrName string) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	g := m.findLocked(idOrName)
	if g == nil {
		return fmt.Errorf("sd-wan group %q not found", idOrName)
	}

	delete(m.groups, g.ID)
	if err := m.save(); err != nil {
		return err
	}

	return m.syncLocked()
}

// AddMember adds an interface member to a group.
func (m *Manager) AddMember(groupIDOrName string, mem *SDWANMember) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	g := m.findLocked(groupIDOrName)
	if g == nil {
		return fmt.Errorf("sd-wan group %q not found", groupIDOrName)
	}

	if mem.Interface == "" {
		return fmt.Errorf("member interface is required")
	}

	// Check duplicates
	for _, existing := range g.Members {
		if existing.Interface == mem.Interface {
			return fmt.Errorf("interface %s already a member of %s", mem.Interface, g.Name)
		}
	}

	if mem.ID == "" {
		mem.ID = fmt.Sprintf("mem-%d-%s", time.Now().UnixNano(), mem.Interface)
	}
	if mem.Weight <= 0 {
		mem.Weight = 50
	}
	if mem.Priority <= 0 {
		mem.Priority = 1
	}
	if mem.TargetProbe == "" {
		mem.TargetProbe = "1.1.1.1"
	}
	mem.Status = StatusHealthy

	g.Members = append(g.Members, mem)
	if err := m.save(); err != nil {
		return err
	}

	return m.syncLocked()
}

// UpdateMember modifies a member's configuration.
func (m *Manager) UpdateMember(groupIDOrName string, mem *SDWANMember) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	g := m.findLocked(groupIDOrName)
	if g == nil {
		return fmt.Errorf("sd-wan group %q not found", groupIDOrName)
	}

	idx := -1
	for i, existing := range g.Members {
		if (mem.ID != "" && existing.ID == mem.ID) || (mem.Interface != "" && existing.Interface == mem.Interface) {
			idx = i
			break
		}
	}

	if idx == -1 {
		return fmt.Errorf("member %s not found in group %s", mem.Interface, g.Name)
	}

	// Preserve existing ID & Interface if not specified
	if mem.ID == "" {
		mem.ID = g.Members[idx].ID
	}
	if mem.Interface == "" {
		mem.Interface = g.Members[idx].Interface
	}
	if mem.Weight <= 0 {
		mem.Weight = g.Members[idx].Weight
	}
	if mem.Priority <= 0 {
		mem.Priority = g.Members[idx].Priority
	}
	if mem.TargetProbe == "" {
		mem.TargetProbe = g.Members[idx].TargetProbe
	}
	if mem.MaxLatency <= 0 {
		mem.MaxLatency = g.Members[idx].MaxLatency
	}
	if mem.MaxLoss <= 0 {
		mem.MaxLoss = g.Members[idx].MaxLoss
	}

	// Preserve live telemetry
	mem.Status = g.Members[idx].Status
	if mem.Status == "" {
		mem.Status = StatusHealthy
	}
	mem.LiveLatency = g.Members[idx].LiveLatency
	mem.PacketLoss = g.Members[idx].PacketLoss
	mem.Jitter = g.Members[idx].Jitter
	mem.ConsecutiveFails = g.Members[idx].ConsecutiveFails

	g.Members[idx] = mem
	if err := m.save(); err != nil {
		return err
	}

	return m.syncLocked()
}

// DeleteMember removes a member from a group.
func (m *Manager) DeleteMember(groupIDOrName, memberIDOrIface string) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	g := m.findLocked(groupIDOrName)
	if g == nil {
		return fmt.Errorf("sd-wan group %q not found", groupIDOrName)
	}

	idx := -1
	for i, mem := range g.Members {
		if mem.ID == memberIDOrIface || mem.Interface == memberIDOrIface {
			idx = i
			break
		}
	}

	if idx == -1 {
		return fmt.Errorf("member %s not found in group %s", memberIDOrIface, g.Name)
	}

	g.Members = append(g.Members[:idx], g.Members[idx+1:]...)
	if err := m.save(); err != nil {
		return err
	}

	return m.syncLocked()
}

// ResolveGroupInterfaces resolves an SD-WAN group to its member interfaces (used by Firewall).
func (m *Manager) ResolveGroupInterfaces(groupName string) []string {
	m.mu.RLock()
	defer m.mu.RUnlock()

	var res []string
	for _, g := range m.groups {
		if strings.EqualFold(g.Name, groupName) && !g.Disabled {
			for _, mem := range g.Members {
				if !mem.Disabled && mem.Interface != "" {
					res = append(res, mem.Interface)
				}
			}
			break
		}
	}
	sort.Strings(res)
	return res
}

// ResolveAllSDWANGroups returns a mapping of all group names to their member interfaces.
func (m *Manager) ResolveAllSDWANGroups() map[string][]string {
	m.mu.RLock()
	defer m.mu.RUnlock()

	res := make(map[string][]string)
	for _, g := range m.groups {
		if !g.Disabled {
			var members []string
			for _, mem := range g.Members {
				if !mem.Disabled && mem.Interface != "" {
					members = append(members, mem.Interface)
				}
			}
			sort.Strings(members)
			res[g.Name] = members
		}
	}
	return res
}

// GetSummary returns high-level telemetry across all SD-WAN groups.
func (m *Manager) GetSummary() TelemetrySummary {
	return m.GetTelemetrySummary()
}

// GetTelemetrySummary returns high-level telemetry across all SD-WAN groups.
func (m *Manager) GetTelemetrySummary() TelemetrySummary {
	m.mu.RLock()
	defer m.mu.RUnlock()

	sum := TelemetrySummary{
		TotalGroups: len(m.groups),
	}

	for _, g := range m.groups {
		if !g.Disabled {
			sum.ActiveGroups++
		}
		for _, mem := range g.Members {
			sum.TotalMembers++
			switch mem.Status {
			case StatusHealthy:
				sum.HealthyMembers++
			case StatusDegraded:
				sum.DegradedMembers++
			case StatusDown:
				sum.DownMembers++
			}
		}
	}
	return sum
}

// SyncAll reconciles kernel routing and iptables for all groups.
func (m *Manager) SyncAll() {
	m.mu.Lock()
	defer m.mu.Unlock()
	_ = m.engine.Sync(m.listLocked())
}

func (m *Manager) findLocked(idOrName string) *SDWANGroup {
	if g, ok := m.groups[idOrName]; ok {
		return g
	}
	for _, g := range m.groups {
		if strings.EqualFold(g.Name, idOrName) {
			return g
		}
	}
	return nil
}

// RenameInterface updates SD-WAN member references when an interface is renamed.
func (m *Manager) RenameInterface(oldName, newName string) {
	m.mu.Lock()
	defer m.mu.Unlock()

	modified := false
	for _, g := range m.groups {
		for _, mem := range g.Members {
			if mem.Interface == oldName {
				mem.Interface = newName
				modified = true
			}
		}
	}
	if modified {
		_ = m.save()
		_ = m.engine.Sync(m.listLocked())
		NotifyStateChange()
	}
}

// ResolveGroupForRouting resolves an SD-WAN group name or ID to active egress nexthops for kernel routing.
func (m *Manager) ResolveGroupForRouting(groupNameOrID string) ([]ResolvedRouteNexthop, bool) {
	m.mu.RLock()
	defer m.mu.RUnlock()

	g := m.findLocked(groupNameOrID)
	if g == nil || g.Disabled || len(g.Members) == 0 {
		return nil, false
	}

	var candidates []*SDWANMember
	for _, mem := range g.Members {
		if !mem.Disabled && mem.Interface != "" {
			candidates = append(candidates, mem)
		}
	}
	if len(candidates) == 0 {
		return nil, false
	}

	var online []*SDWANMember
	for _, mem := range candidates {
		if mem.Status != StatusDown {
			online = append(online, mem)
		}
	}
	// Fallback to all enabled candidates if all are down so traffic isn't completely blackholed
	if len(online) == 0 {
		online = candidates
	}

	switch g.Mode {
	case ModeFailover:
		// Sort by priority (1 is highest priority)
		sort.Slice(online, func(i, j int) bool {
			p1, p2 := online[i].Priority, online[j].Priority
			if p1 <= 0 {
				p1 = 100
			}
			if p2 <= 0 {
				p2 = 100
			}
			return p1 < p2
		})
		primary := online[0]
		gw := primary.Gateway
		if gw == "" {
			gw = m.engine.detectInterfaceGateway(primary.Interface)
		}
		return []ResolvedRouteNexthop{{
			Gateway:   gw,
			Interface: primary.Interface,
			Weight:    1,
		}}, true

	case ModeLowestLatency:
		best := online[0]
		for _, mem := range online[1:] {
			if mem.LiveLatency > 0 && (best.LiveLatency <= 0 || mem.LiveLatency < best.LiveLatency) {
				best = mem
			}
		}
		gw := best.Gateway
		if gw == "" {
			gw = m.engine.detectInterfaceGateway(best.Interface)
		}
		return []ResolvedRouteNexthop{{
			Gateway:   gw,
			Interface: best.Interface,
			Weight:    1,
		}}, true

	case ModeLowestLoss:
		best := online[0]
		for _, mem := range online[1:] {
			if mem.PacketLoss < best.PacketLoss {
				best = mem
			}
		}
		gw := best.Gateway
		if gw == "" {
			gw = m.engine.detectInterfaceGateway(best.Interface)
		}
		return []ResolvedRouteNexthop{{
			Gateway:   gw,
			Interface: best.Interface,
			Weight:    1,
		}}, true

	case ModeWeighted, ModePCC:
		fallthrough
	default:
		var res []ResolvedRouteNexthop
		for _, mem := range online {
			gw := mem.Gateway
			if gw == "" {
				gw = m.engine.detectInterfaceGateway(mem.Interface)
			}
			w := mem.Weight
			if w <= 0 {
				w = 1
			}
			res = append(res, ResolvedRouteNexthop{
				Gateway:   gw,
				Interface: mem.Interface,
				Weight:    w,
			})
		}
		return res, true
	}
}

// ResolveGroupForRouting resolves an SD-WAN group name or ID via GlobalManager or file fallback.
func ResolveGroupForRouting(groupNameOrID string) ([]ResolvedRouteNexthop, bool) {
	if GlobalManager != nil {
		return GlobalManager.ResolveGroupForRouting(groupNameOrID)
	}

	// Fallback to reading file if GlobalManager is not yet initialized
	data, err := os.ReadFile(DefaultStorePath)
	if err != nil {
		return nil, false
	}
	var groups []*SDWANGroup
	if err := json.Unmarshal(data, &groups); err != nil {
		return nil, false
	}
	for _, g := range groups {
		if strings.EqualFold(g.Name, groupNameOrID) || g.ID == groupNameOrID {
			if g.Disabled || len(g.Members) == 0 {
				return nil, false
			}
			var res []ResolvedRouteNexthop
			for _, m := range g.Members {
				if !m.Disabled && m.Interface != "" {
					res = append(res, ResolvedRouteNexthop{
						Gateway:   m.Gateway,
						Interface: m.Interface,
						Weight:    m.Weight,
					})
				}
			}
			return res, len(res) > 0
		}
	}
	return nil, false
}

// IsSDWANGroup reports whether the given name corresponds to an active or configured SD-WAN group.
func IsSDWANGroup(name string) bool {
	clean := strings.TrimSpace(name)
	if clean == "" {
		return false
	}
	if GlobalManager != nil {
		return GlobalManager.Has(clean)
	}

	data, err := os.ReadFile(DefaultStorePath)
	if err != nil {
		return false
	}
	var groups []*SDWANGroup
	if err := json.Unmarshal(data, &groups); err != nil {
		return false
	}
	for _, g := range groups {
		if strings.EqualFold(g.Name, clean) || g.ID == clean {
			return true
		}
	}
	return false
}