package starnet

import (
	"bytes"
	"context"
	"crypto/tls"
	"errors"
	"io"
	"net"
	"sync"
	"time"

	"b612.me/starnet/internal/tlssniffercore"
)

// replayConn replays buffered bytes first, then reads from live conn.
type replayConn struct {
	reader io.Reader
	conn   net.Conn
}

func newReplayConn(buffered io.Reader, conn net.Conn) *replayConn {
	return &replayConn{
		reader: io.MultiReader(buffered, conn),
		conn:   conn,
	}
}

func (c *replayConn) Read(p []byte) (int, error)         { return c.reader.Read(p) }
func (c *replayConn) Write(p []byte) (int, error)        { return c.conn.Write(p) }
func (c *replayConn) Close() error                       { return c.conn.Close() }
func (c *replayConn) LocalAddr() net.Addr                { return c.conn.LocalAddr() }
func (c *replayConn) RemoteAddr() net.Addr               { return c.conn.RemoteAddr() }
func (c *replayConn) SetDeadline(t time.Time) error      { return c.conn.SetDeadline(t) }
func (c *replayConn) SetReadDeadline(t time.Time) error  { return c.conn.SetReadDeadline(t) }
func (c *replayConn) SetWriteDeadline(t time.Time) error { return c.conn.SetWriteDeadline(t) }

// SniffResult describes protocol sniffing result.
type SniffResult struct {
	IsTLS       bool
	ClientHello *ClientHelloMeta
	Buffer      *bytes.Buffer
}

// Sniffer detects protocol and metadata from initial bytes.
type Sniffer interface {
	Sniff(conn net.Conn, maxBytes int) (SniffResult, error)
}

// TLSSniffer is the default sniffer implementation.
type TLSSniffer struct{}

// Sniff detects TLS and extracts SNI when possible.
func (s TLSSniffer) Sniff(conn net.Conn, maxBytes int) (SniffResult, error) {
	res, err := (tlssniffercore.Sniffer{}).Sniff(conn, maxBytes)
	if err != nil {
		return SniffResult{}, err
	}
	return convertCoreSniffResult(res), nil
}

func convertCoreSniffResult(res tlssniffercore.SniffResult) SniffResult {
	out := SniffResult{
		IsTLS:  res.IsTLS,
		Buffer: res.Buffer,
	}
	if res.ClientHello != nil {
		out.ClientHello = convertCoreClientHelloMeta(res.ClientHello)
	}
	return out
}

func convertCoreClientHelloMeta(meta *tlssniffercore.ClientHelloMeta) *ClientHelloMeta {
	if meta == nil {
		return nil
	}
	return &ClientHelloMeta{
		ServerName:        meta.ServerName,
		LocalAddr:         meta.LocalAddr,
		RemoteAddr:        meta.RemoteAddr,
		SupportedProtos:   append([]string(nil), meta.SupportedProtos...),
		SupportedVersions: append([]uint16(nil), meta.SupportedVersions...),
		CipherSuites:      append([]uint16(nil), meta.CipherSuites...),
	}
}

// Conn wraps net.Conn with lazy protocol initialization.
type Conn struct {
	net.Conn

	once      sync.Once
	initErr   error
	closeOnce sync.Once

	isTLS     bool
	tlsConn   *tls.Conn
	plainConn net.Conn

	clientHello *ClientHelloMeta

	baseTLSConfig           *tls.Config
	getConfigForClient      GetConfigForClientFunc
	getConfigForClientHello GetConfigForClientHelloFunc
	allowNonTLS             bool
	sniffer                 Sniffer
	sniffTimeout            time.Duration
	maxClientHello          int
	logger                  Logger
	stats                   *Stats
	skipSniff               bool
}

func newConn(raw net.Conn, cfg ListenerConfig, stats *Stats) *Conn {
	return &Conn{
		Conn:                    raw,
		plainConn:               raw,
		baseTLSConfig:           cfg.BaseTLSConfig,
		getConfigForClient:      cfg.GetConfigForClient,
		getConfigForClientHello: cfg.GetConfigForClientHello,
		allowNonTLS:             cfg.AllowNonTLS,
		sniffer:                 TLSSniffer{},
		sniffTimeout:            cfg.SniffTimeout,
		maxClientHello:          cfg.MaxClientHelloBytes,
		logger:                  cfg.Logger,
		stats:                   stats,
	}
}

func (c *Conn) init() {
	c.once.Do(func() {
		if c.skipSniff {
			return
		}
		if c.baseTLSConfig == nil && c.getConfigForClient == nil && c.getConfigForClientHello == nil {
			c.isTLS = false
			return
		}

		if c.sniffTimeout > 0 {
			_ = c.Conn.SetReadDeadline(time.Now().Add(c.sniffTimeout))
		}
		res, err := c.sniffer.Sniff(c.Conn, c.maxClientHello)
		if c.sniffTimeout > 0 {
			_ = c.Conn.SetReadDeadline(time.Time{})
		}
		if err != nil {
			c.initErr = errors.Join(ErrTLSSniffFailed, err)
			c.failSniff(err)
			return
		}

		c.isTLS = res.IsTLS
		c.clientHello = res.ClientHello

		if c.isTLS {
			if c.stats != nil {
				c.stats.incTLSDetected()
			}
			tlsCfg, errCfg := c.selectTLSConfig()
			if errCfg != nil {
				c.initErr = errors.Join(ErrTLSConfigSelectionFailed, errCfg)
				c.failTLSConfigSelection(errCfg)
				return
			}
			rc := newReplayConn(bytes.NewBuffer(res.Buffer.Bytes()), c.Conn)
			c.tlsConn = tls.Server(rc, tlsCfg)
			return
		}

		if c.stats != nil {
			c.stats.incPlainDetected()
		}
		if !c.allowNonTLS {
			c.initErr = ErrNonTLSNotAllowed
			c.failPlainRejected()
			return
		}
		c.plainConn = newReplayConn(bytes.NewBuffer(res.Buffer.Bytes()), c.Conn)
	})
}

func (c *Conn) failAndClose(format string, v ...interface{}) {
	if c.logger != nil {
		c.logger.Printf("starnet: "+format, v...)
	}
	_ = c.Close()
}

func (c *Conn) failSniff(err error) {
	if c.stats != nil {
		c.stats.incSniffFailures()
	}
	c.failAndClose("tls sniff failed: %v", err)
}

func (c *Conn) failTLSConfigSelection(err error) {
	if c.stats != nil {
		c.stats.incTLSConfigFailures()
	}
	c.failAndClose("tls config selection failed: %v", err)
}

func (c *Conn) failPlainRejected() {
	if c.stats != nil {
		c.stats.incPlainRejected()
	}
	c.failAndClose("plain tcp rejected")
}

func (c *Conn) selectTLSConfig() (*tls.Config, error) {
	var selected *tls.Config
	if c.getConfigForClientHello != nil {
		cfg, err := c.getConfigForClientHello(c.clientHello.Clone())
		if err != nil {
			return nil, err
		}
		if cfg != nil {
			selected = cfg
		}
	}
	if selected == nil && c.getConfigForClient != nil {
		cfg, err := c.getConfigForClient(c.serverName())
		if err != nil {
			return nil, err
		}
		if cfg != nil {
			selected = cfg
		}
	}

	composed := composeServerTLSConfig(c.baseTLSConfig, selected)
	if composed != nil {
		return composed, nil
	}
	return nil, ErrNoTLSConfig
}

// Hostname returns sniffed SNI hostname (if any).
func (c *Conn) Hostname() string {
	c.init()
	return c.serverName()
}

// ClientHello returns sniffed TLS metadata (if any).
func (c *Conn) ClientHello() *ClientHelloMeta {
	c.init()
	return c.clientHello.Clone()
}

func (c *Conn) serverName() string {
	if c.clientHello == nil {
		return ""
	}
	return c.clientHello.ServerName
}

func composeServerTLSConfig(base, selected *tls.Config) *tls.Config {
	return tlssniffercore.ComposeServerTLSConfig(base, selected)
}

func applyServerTLSOverrides(dst, src *tls.Config) {
	tlssniffercore.ApplyServerTLSOverrides(dst, src)
}

func (c *Conn) IsTLS() bool {
	c.init()
	return c.initErr == nil && c.isTLS
}

func (c *Conn) TLSConn() (*tls.Conn, error) {
	c.init()
	if c.initErr != nil {
		return nil, c.initErr
	}
	if !c.isTLS || c.tlsConn == nil {
		return nil, ErrNotTLS
	}
	return c.tlsConn, nil
}

func (c *Conn) Read(b []byte) (int, error) {
	c.init()
	if c.initErr != nil {
		return 0, c.initErr
	}
	if c.isTLS {
		return c.tlsConn.Read(b)
	}
	return c.plainConn.Read(b)
}

func (c *Conn) Write(b []byte) (int, error) {
	c.init()
	if c.initErr != nil {
		return 0, c.initErr
	}
	if c.isTLS {
		return c.tlsConn.Write(b)
	}
	return c.plainConn.Write(b)
}

func (c *Conn) Close() error {
	var err error
	c.closeOnce.Do(func() {
		if c.tlsConn != nil {
			err = c.tlsConn.Close()
		} else {
			err = c.Conn.Close()
		}
		if c.stats != nil {
			c.stats.incClosed()
		}
	})
	return err
}

func (c *Conn) SetDeadline(t time.Time) error {
	c.init()
	if c.initErr != nil {
		return c.initErr
	}
	if c.isTLS && c.tlsConn != nil {
		return c.tlsConn.SetDeadline(t)
	}
	return c.plainConn.SetDeadline(t)
}

func (c *Conn) SetReadDeadline(t time.Time) error {
	c.init()
	if c.initErr != nil {
		return c.initErr
	}
	if c.isTLS && c.tlsConn != nil {
		return c.tlsConn.SetReadDeadline(t)
	}
	return c.plainConn.SetReadDeadline(t)
}

func (c *Conn) SetWriteDeadline(t time.Time) error {
	c.init()
	if c.initErr != nil {
		return c.initErr
	}
	if c.isTLS && c.tlsConn != nil {
		return c.tlsConn.SetWriteDeadline(t)
	}
	return c.plainConn.SetWriteDeadline(t)
}

// Listener wraps net.Listener and returns starnet.Conn from Accept.
type Listener struct {
	net.Listener

	mu    sync.RWMutex
	cfg   ListenerConfig
	stats Stats
}

// Listen creates a plain listener config (no TLS detection).
func Listen(network, address string) (*Listener, error) {
	ln, err := net.Listen(network, address)
	if err != nil {
		return nil, err
	}
	cfg := DefaultListenerConfig()
	cfg.AllowNonTLS = true
	cfg.BaseTLSConfig = nil
	cfg.GetConfigForClient = nil
	return &Listener{Listener: ln, cfg: cfg}, nil
}

// ListenWithConfig creates a listener with full config.
func ListenWithConfig(network, address string, cfg ListenerConfig) (*Listener, error) {
	ln, err := net.Listen(network, address)
	if err != nil {
		return nil, err
	}
	return &Listener{Listener: ln, cfg: normalizeConfig(cfg)}, nil
}

// ListenWithListenConfig creates listener using net.ListenConfig.
func ListenWithListenConfig(lc net.ListenConfig, network, address string, cfg ListenerConfig) (*Listener, error) {
	ln, err := lc.Listen(context.Background(), network, address)
	if err != nil {
		return nil, err
	}
	return &Listener{Listener: ln, cfg: normalizeConfig(cfg)}, nil
}

// ListenTLS creates TLS listener from cert/key paths.
func ListenTLS(network, address, certFile, keyFile string, allowNonTLS bool) (*Listener, error) {
	cert, err := tls.LoadX509KeyPair(certFile, keyFile)
	if err != nil {
		return nil, err
	}
	cfg := DefaultListenerConfig()
	cfg.AllowNonTLS = allowNonTLS
	cfg.BaseTLSConfig = TLSDefaults()
	cfg.BaseTLSConfig.Certificates = []tls.Certificate{cert}
	return ListenWithConfig(network, address, cfg)
}

func normalizeConfig(cfg ListenerConfig) ListenerConfig {
	out := DefaultListenerConfig()
	out.AllowNonTLS = cfg.AllowNonTLS
	out.SniffTimeout = cfg.SniffTimeout
	out.MaxClientHelloBytes = cfg.MaxClientHelloBytes
	out.BaseTLSConfig = cfg.BaseTLSConfig
	out.GetConfigForClient = cfg.GetConfigForClient
	out.GetConfigForClientHello = cfg.GetConfigForClientHello
	out.Logger = cfg.Logger
	if out.MaxClientHelloBytes <= 0 {
		out.MaxClientHelloBytes = 64 * 1024
	}
	return out
}

// SetConfig atomically replaces listener config for new accepted connections.
func (l *Listener) SetConfig(cfg ListenerConfig) {
	l.mu.Lock()
	l.cfg = normalizeConfig(cfg)
	l.mu.Unlock()
}

// Config returns a copy of current config.
func (l *Listener) Config() ListenerConfig {
	l.mu.RLock()
	cfg := l.cfg
	l.mu.RUnlock()
	return cfg
}

// Stats returns current counters snapshot.
func (l *Listener) Stats() StatsSnapshot {
	return l.stats.Snapshot()
}

func (l *Listener) Accept() (net.Conn, error) {
	raw, err := l.Listener.Accept()
	if err != nil {
		return nil, err
	}
	l.stats.incAccepted()

	l.mu.RLock()
	cfg := l.cfg
	l.mu.RUnlock()

	return newConn(raw, cfg, &l.stats), nil
}

// AcceptContext supports cancellation by closing accepted conn when ctx is done early.
func (l *Listener) AcceptContext(ctx context.Context) (net.Conn, error) {
	type result struct {
		c   net.Conn
		err error
	}
	ch := make(chan result, 1)
	go func() {
		c, err := l.Accept()
		ch <- result{c: c, err: err}
	}()

	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case r := <-ch:
		return r.c, r.err
	}
}

// Dial creates a plain TCP starnet.Conn.
func Dial(network, address string) (*Conn, error) {
	raw, err := net.Dial(network, address)
	if err != nil {
		return nil, err
	}
	cfg := DefaultListenerConfig()
	cfg.AllowNonTLS = true
	cfg.BaseTLSConfig = nil
	cfg.GetConfigForClient = nil
	c := newConn(raw, cfg, nil)
	c.isTLS = false
	return c, nil
}

// DialWithConfig dials with net.Dialer options.
func DialWithConfig(network, address string, dc DialConfig) (*Conn, error) {
	d := net.Dialer{
		Timeout:   dc.Timeout,
		LocalAddr: dc.LocalAddr,
	}
	raw, err := d.Dial(network, address)
	if err != nil {
		return nil, err
	}
	cfg := DefaultListenerConfig()
	cfg.AllowNonTLS = true
	c := newConn(raw, cfg, nil)
	c.isTLS = false
	return c, nil
}

// DialTLSWithConfig creates a TLS client connection wrapper.
func DialTLSWithConfig(network, address string, tlsCfg *tls.Config, timeout time.Duration) (*Conn, error) {
	d := net.Dialer{Timeout: timeout}
	raw, err := d.Dial(network, address)
	if err != nil {
		return nil, err
	}
	tc := tls.Client(raw, tlsCfg)
	return &Conn{
		Conn:        raw,
		plainConn:   raw,
		isTLS:       true,
		tlsConn:     tc,
		initErr:     nil,
		allowNonTLS: false,
		skipSniff:   true,
	}, nil
}

// DialTLS creates TLS client conn from cert/key paths.
func DialTLS(network, address, certFile, keyFile string) (*Conn, error) {
	cert, err := tls.LoadX509KeyPair(certFile, keyFile)
	if err != nil {
		return nil, err
	}
	cfg := TLSDefaults()
	cfg.Certificates = []tls.Certificate{cert}
	return DialTLSWithConfig(network, address, cfg, 0)
}

func WrapListener(listener net.Listener, cfg ListenerConfig) (*Listener, error) {
	if listener == nil {
		return nil, ErrNilConn
	}
	return &Listener{
		Listener: listener,
		cfg:      normalizeConfig(cfg),
	}, nil
}