package core

import (
	"fmt"
	"io"
	"net"
	"os"
	"time"

	"go.uber.org/zap"
	"golang.zx2c4.com/wireguard/wgctrl"
	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"

	"riasc.eu/wice/pkg/crypto"
	"riasc.eu/wice/pkg/device"
	"riasc.eu/wice/pkg/util"
	"riasc.eu/wice/pkg/util/buildinfo"
	"riasc.eu/wice/pkg/wg"

	proto "riasc.eu/wice/pkg/proto"
	coreproto "riasc.eu/wice/pkg/proto/core"
	pdiscproto "riasc.eu/wice/pkg/proto/feat/pdisc"
)

type Interface struct {
	// WireGuard handle of device
	*wg.Device

	// OS abstractions for kernel device
	KernelDevice device.Device

	Peers map[crypto.Key]*Peer

	LastSync time.Time

	client *wgctrl.Client

	onModified []InterfaceHandler
	onPeer     []PeerHandler

	logger *zap.Logger
}

func (i *Interface) OnModified(h InterfaceHandler) {
	i.onModified = append(i.onModified, h)
}

func (i *Interface) OnPeer(h PeerHandler) {
	i.onPeer = append(i.onPeer, h)
}

// Name returns the WireGuard interface name
func (i *Interface) Name() string {
	return i.Device.Name
}

// PublicKey returns the Curve25519 public key of the WireGuard interface
func (i *Interface) PublicKey() crypto.Key {
	return crypto.Key(i.Device.PublicKey)
}

// PublicKey returns the Curve25519 private key of the WireGuard interface
func (i *Interface) PrivateKey() crypto.Key {
	return crypto.Key(i.Device.PrivateKey)
}

func (i *Interface) WireGuardConfig() *wgtypes.Config {
	cfg := &wgtypes.Config{
		PrivateKey:   (*wgtypes.Key)(i.PrivateKey().Bytes()),
		ListenPort:   &i.ListenPort,
		FirewallMark: &i.FirewallMark,
	}

	for _, peer := range i.Peers {
		cfg.Peers = append(cfg.Peers, *peer.WireGuardConfig())
	}

	return cfg
}

func (i *Interface) DumpConfig(wr io.Writer) error {
	cfg := wg.Config{
		Config: *i.WireGuardConfig(),
	}
	return cfg.Dump(wr)
}

func (i *Interface) Sync(new *wgtypes.Device) (InterfaceModifier, []wgtypes.Peer, []wgtypes.Peer) {
	old := i.Device
	mod := InterfaceModifiedNone

	// Compare device properties
	if new.Name != old.Name {
		i.logger.Info("Name has changed",
			zap.Any("old", old.Name),
			zap.Any("new", new.Name),
		)

		mod |= InterfaceModifiedName
	}

	// Compare device properties
	if new.Type != old.Type {
		i.logger.Info("Type has changed",
			zap.Any("old", old.Type),
			zap.Any("new", new.Type),
		)

		mod |= InterfaceModifiedType
	}

	if new.FirewallMark != old.FirewallMark {
		i.logger.Info("Firewall mark has changed",
			zap.Any("old", old.FirewallMark),
			zap.Any("new", new.FirewallMark),
		)

		mod |= InterfaceModifiedFirewallMark
	}

	if new.PrivateKey != old.PrivateKey {
		i.logger.Info("PrivateKey has changed",
			zap.Any("old", old.PrivateKey),
			zap.Any("new", new.PrivateKey),
		)

		mod |= InterfaceModifiedPrivateKey
	}

	if new.ListenPort != old.ListenPort {
		i.logger.Info("ListenPort has changed",
			zap.Any("old", old.ListenPort),
			zap.Any("new", new.ListenPort),
		)

		mod |= InterfaceModifiedListenPort
	}

	peersAdded, peersRemoved, peersKept := util.DiffSliceFunc(old.Peers, new.Peers, wg.CmpPeers)
	if len(peersAdded) > 0 || len(peersRemoved) > 0 {
		mod |= InterfaceModifiedPeers
	}

	// Call handlers

	i.Device = (*wg.Device)(new)
	i.LastSync = time.Now()

	if mod != InterfaceModifiedNone {
		i.logger.Info("Interface has been modified", zap.Strings("changes", mod.Strings()))

		for _, h := range i.onModified {
			h.OnInterfaceModified(i, old, mod)
		}
	}

	for j := range peersRemoved {
		wgp := peersRemoved[j]
		pk := crypto.Key(wgp.PublicKey)

		p, ok := i.Peers[pk]
		if !ok {
			i.logger.Warn("Failed to find matching peer", zap.Any("peer", wgp.PublicKey))
			continue
		}

		i.logger.Info("Removed peer", zap.Any("peer", p.PublicKey()))

		delete(i.Peers, pk)

		for _, h := range i.onPeer {
			h.OnPeerRemoved(p)
		}
	}

	for j := range peersAdded {
		wgp := &peersAdded[j]

		i.logger.Info("Added peer", zap.Any("peer", wgp.PublicKey))

		p, err := NewPeer(wgp, i)
		if err != nil {
			i.logger.Fatal("Failed to setup peer",
				zap.Error(err),
				zap.Any("peer", p.PublicKey),
			)
		}

		i.Peers[p.PublicKey()] = p

		for _, h := range i.onPeer {
			h.OnPeerAdded(p)
		}

		p.Sync(wgp)
	}

	for j := range peersKept {
		wgp := &peersKept[j]

		p, ok := i.Peers[crypto.Key(wgp.PublicKey)]
		if !ok {
			i.logger.Warn("Failed to find matching peer", zap.Any("peer", wgp.PublicKey))
			continue
		}

		p.Sync(wgp)
	}

	return mod, peersAdded, peersRemoved
}

func (i *Interface) SyncConfig(cfgFilename string) error {
	//#nosec G304 -- Filenames are limited to WireGuard config directory
	cfgFile, err := os.Open(cfgFilename)
	if err != nil {
		return fmt.Errorf("failed to open config file %s: %w", cfgFilename, err)
	}

	cfg, err := wg.ParseConfig(cfgFile, i.Name())
	if err != nil {
		return fmt.Errorf("failed to parse configuration: %s", err)
	}

	if err := i.Configure(cfg); err != nil {
		return fmt.Errorf("failed to configure interface: %w", err)
	}

	i.logger.Info("Synchronized configuration", zap.String("config_file", cfgFilename))

	return nil
}

func (i *Interface) Configure(cfg *wg.Config) error {
	if err := i.client.ConfigureDevice(i.Name(), cfg.Config); err != nil {
		return fmt.Errorf("failed to sync interface config: %s", err)
	}

	// TODO: remove old addresses?

	for _, addr := range cfg.Address {
		addr := addr
		if err := i.KernelDevice.AddAddress(&addr); err != nil {
			return err
		}
	}

	if cfg.MTU != nil {
		if err := i.KernelDevice.SetMTU(*cfg.MTU); err != nil {
			return err
		}
	}

	// TODO: Emulate more wg-quick behavior here
	//       E.g. Pre/Post-Up/Down scripts, Table, DNS

	return nil
}

func (i *Interface) AddPeer(pcfg *wgtypes.PeerConfig) error {
	return i.client.ConfigureDevice(i.Name(), wgtypes.Config{
		Peers: []wgtypes.PeerConfig{*pcfg},
	})
}

func (i *Interface) UpdatePeer(pcfg *wgtypes.PeerConfig) error {
	pcfg2 := *pcfg
	pcfg2.UpdateOnly = true

	return i.AddPeer(&pcfg2)
}

func (i *Interface) RemovePeer(pk crypto.Key) error {
	cfg := wgtypes.Config{
		Peers: []wgtypes.PeerConfig{
			{
				PublicKey: wgtypes.Key(pk),
				Remove:    true,
			},
		},
	}

	return i.client.ConfigureDevice(i.Name(), cfg)
}

func NewInterface(wgDev *wgtypes.Device, client *wgctrl.Client) (*Interface, error) {
	var err error

	i := &Interface{
		Device: (*wg.Device)(wgDev),
		client: client,
		Peers:  map[crypto.Key]*Peer{},

		onModified: []InterfaceHandler{},
		onPeer:     []PeerHandler{},

		logger: zap.L().Named("interface").With(
			zap.String("intf", wgDev.Name),
		),
	}

	if i.KernelDevice, err = device.FindDevice(wgDev.Name); err != nil {
		return nil, fmt.Errorf("failed to find kernel device: %w", err)
	}

	i.logger.Info("Added interface",
		zap.String("pk", i.PrivateKey().PublicKey().String()),
		zap.String("type", i.Type.String()),
		zap.Int("num_peers", len(i.Peers)),
	)

	return i, nil
}

func (i *Interface) Marshal() *coreproto.Interface {
	return i.MarshalWithPeers(func(p *Peer) *coreproto.Peer {
		return p.Marshal()
	})
}

func (i *Interface) MarshalWithPeers(cb func(p *Peer) *coreproto.Peer) *coreproto.Interface {
	q := &coreproto.Interface{
		Name:         i.Name(),
		Type:         coreproto.InterfaceType(i.Type),
		ListenPort:   uint32(i.ListenPort),
		FirewallMark: uint32(i.FirewallMark),
		Mtu:          uint32(i.KernelDevice.MTU()),
		Ifindex:      uint32(i.KernelDevice.Index()),
	}

	if cb == nil {
		cb = func(p *Peer) *coreproto.Peer {
			return p.Marshal()
		}
	}

	for _, p := range i.Peers {
		if qp := cb(p); qp != nil {
			q.Peers = append(q.Peers, qp)
		}
	}

	if !i.LastSync.IsZero() {
		q.LastSyncTimestamp = proto.Time(i.LastSync)
	}

	if i.PrivateKey().IsSet() {
		q.PrivateKey = i.PrivateKey().Bytes()
		q.PublicKey = i.PublicKey().Bytes()
	}

	return q
}

func (i *Interface) MarshalDescription(chg pdiscproto.PeerDescriptionChange, pkOld *crypto.Key) (*pdiscproto.PeerDescription, error) {
	allowedIPs := []*net.IPNet{
		i.PublicKey().IPv6Address(),
		i.PublicKey().IPv4Address(),
	}

	// Only allow a single IP from the network
	for _, allowedIP := range allowedIPs {
		for i := range allowedIP.Mask {
			allowedIP.Mask[i] = 0xff
		}
	}

	hn, err := os.Hostname()
	if err != nil {
		return nil, fmt.Errorf("failed to get hostname: %w", err)
	}

	pd := &pdiscproto.PeerDescription{
		Change:     chg,
		Hostname:   hn,
		AllowedIps: util.StringSlice(allowedIPs),
		BuildInfo:  buildinfo.BuildInfo(),
	}

	if pkOld != nil {
		if pd.Change != pdiscproto.PeerDescriptionChange_PEER_UPDATE {
			return nil, fmt.Errorf("can not change public key in non-update message")
		}

		pd.PublicKeyNew = i.PublicKey().Bytes()
		pd.PublicKey = pkOld.Bytes()
	} else {
		pd.PublicKey = i.PublicKey().Bytes()
	}

	return pd, nil
}