package awgserver

import (
	"fmt"
	"log/slog"
	"strings"
	"sync"

	"github.com/amnezia-vpn/amneziawg-go/device"
	"github.com/amnezia-vpn/amneziawg-go/ipc"
	"github.com/amnezia-vpn/amneziawg-go/tun"
	"github.com/quic-go/quic-go/http3"

	"sourcecraft.dev/bigbes/shroud/internal/store"
)

// Config holds all settings for the AmneziaWG server.
type Config struct {
	ListenPort   int
	TUNName      string
	Address      string // server CIDR, e.g. "10.14.0.1/24"
	MTU          int
	PrivateKey   string // server interface key, base64
	Domain       string
	CertCache    string
	ACMEHTTPPort int

	// Obfuscation parameters.
	Jc, Jmin, Jmax int
	S1, S2, S3, S4 int
	H1, H2, H3, H4 HeaderRange
}

// Server wraps an AmneziaWG device with MuxBind + HTTP/3 multiplexing.
type Server struct {
	cfg     Config
	dev     *device.Device
	tunDev  tun.Device
	muxBind *MuxBind
	h3srv   *http3.Server
	logger  *slog.Logger

	mu sync.Mutex
}

// New creates a new AWG server (not yet started).
func New(cfg Config, logger *slog.Logger) *Server {
	return &Server{
		cfg:    cfg,
		logger: logger,
	}
}

// Start creates the TUN device, AWG device with MuxBind, and HTTP/3 server.
func (s *Server) Start() error {
	s.mu.Lock()
	defer s.mu.Unlock()

	// 1. Create TUN device.
	tunDev, err := tun.CreateTUN(s.cfg.TUNName, s.cfg.MTU)
	if err != nil {
		return fmt.Errorf("create TUN %q: %w", s.cfg.TUNName, err)
	}
	s.tunDev = tunDev
	s.logger.Info("TUN device created.", "name", s.cfg.TUNName, "mtu", s.cfg.MTU)

	// 2. Create MuxBind.
	quicCh := make(chan quicPacket, 1024)
	s.muxBind = NewMuxBind(&s.cfg, quicCh)

	// 3. Create AWG device.
	logLevel := device.LogLevelError
	devLogger := device.NewLogger(logLevel, "[awg] ")
	s.dev = device.NewDevice(tunDev, s.muxBind, devLogger)

	// 4. Configure via UAPI (interface only, peers added by SyncKeys).
	ifaceConf, err := s.buildInterfaceConfig()
	if err != nil {
		s.dev.Close()
		tunDev.Close()
		return fmt.Errorf("build UAPI interface config: %w", err)
	}
	if err := s.dev.IpcSet(ifaceConf); err != nil {
		s.dev.Close()
		tunDev.Close()
		return fmt.Errorf("IpcSet interface config: %w", err)
	}
	s.logger.Info("AWG device configured.")

	// 5. Bring up — triggers MuxBind.Open(), starts listening.
	s.dev.Up()
	s.logger.Info("AWG device is up.", "port", s.cfg.ListenPort)

	// 6. Set up UAPI socket for awg show/set.
	go s.setupUAPI()

	// 7. Get FilteredConn and start HTTP/3 server.
	fc := s.muxBind.FilteredConn()
	if s.cfg.Domain != "" {
		h3srv, err := startH3Server(fc, &s.cfg, s.logger)
		if err != nil {
			s.logger.Warn("HTTP/3 server failed to start (non-fatal).", "err", err)
		} else {
			s.h3srv = h3srv
		}
	}

	// 8. Configure TUN address.
	if s.cfg.Address != "" {
		if err := setTUNAddress(s.cfg.TUNName, s.cfg.Address, s.logger); err != nil {
			s.logger.Warn("Failed to configure TUN address (non-fatal).", "err", err)
		}
	}

	return nil
}

// SyncKeys rebuilds the AWG peer list from access keys that have AWG data.
func (s *Server) SyncKeys(keys []store.AccessKey) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.dev == nil {
		return fmt.Errorf("AWG device not started")
	}

	conf := s.buildPeerConfig(keys)
	if err := s.dev.IpcSet(conf); err != nil {
		return fmt.Errorf("IpcSet peers: %w", err)
	}

	count := 0
	for _, k := range keys {
		if k.AWG != nil {
			count++
		}
	}
	s.logger.Info("AWG peers synced.", "count", count)
	return nil
}

// Stop shuts down the AWG device, TUN, and HTTP/3 server.
func (s *Server) Stop() error {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.h3srv != nil {
		s.h3srv.Close()
	}
	if s.dev != nil {
		s.dev.Close()
	}
	if s.tunDev != nil {
		s.tunDev.Close()
	}
	s.logger.Info("AWG server stopped.")
	return nil
}

func (s *Server) buildInterfaceConfig() (string, error) {
	privHex, err := base64ToHex(s.cfg.PrivateKey)
	if err != nil {
		return "", fmt.Errorf("PrivateKey: %w", err)
	}

	var b strings.Builder
	fmt.Fprintf(&b, "private_key=%s\n", privHex)
	fmt.Fprintf(&b, "listen_port=%d\n", s.cfg.ListenPort)

	if s.cfg.Jc > 0 {
		fmt.Fprintf(&b, "jc=%d\n", s.cfg.Jc)
		fmt.Fprintf(&b, "jmin=%d\n", s.cfg.Jmin)
		fmt.Fprintf(&b, "jmax=%d\n", s.cfg.Jmax)
	}
	fmt.Fprintf(&b, "s1=%d\n", s.cfg.S1)
	fmt.Fprintf(&b, "s2=%d\n", s.cfg.S2)
	fmt.Fprintf(&b, "s3=%d\n", s.cfg.S3)
	fmt.Fprintf(&b, "s4=%d\n", s.cfg.S4)
	fmt.Fprintf(&b, "h1=%s\n", s.cfg.H1)
	fmt.Fprintf(&b, "h2=%s\n", s.cfg.H2)
	fmt.Fprintf(&b, "h3=%s\n", s.cfg.H3)
	fmt.Fprintf(&b, "h4=%s\n", s.cfg.H4)

	return b.String(), nil
}

func (s *Server) buildPeerConfig(keys []store.AccessKey) string {
	var b strings.Builder
	b.WriteString("replace_peers=true\n")

	for _, k := range keys {
		if k.AWG == nil {
			continue
		}
		pubHex, err := base64ToHex(k.AWG.PublicKey)
		if err != nil {
			s.logger.Warn("Skipping AWG peer: bad public key.", "keyID", k.ID, "err", err)
			continue
		}
		fmt.Fprintf(&b, "public_key=%s\n", pubHex)
		fmt.Fprintf(&b, "allowed_ip=%s\n", k.AWG.AllowedIP)
	}

	return b.String()
}

func (s *Server) setupUAPI() {
	fileUAPI, err := ipc.UAPIOpen(s.cfg.TUNName)
	if err != nil {
		s.logger.Debug("UAPI open (non-fatal).", "err", err)
		return
	}
	uapiListener, err := ipc.UAPIListen(s.cfg.TUNName, fileUAPI)
	if err != nil {
		s.logger.Debug("UAPI listen (non-fatal).", "err", err)
		return
	}
	s.logger.Info("UAPI listening.", "interface", s.cfg.TUNName)
	for {
		conn, err := uapiListener.Accept()
		if err != nil {
			return
		}
		go s.dev.IpcHandle(conn)
	}
}