package net

import (
	"context"
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"fmt"
	"log"
	"math/big"
	"net"
	"net/http"
	"sort"
	"sync"
	"sync/atomic"
	"time"

	"thehouseoficarus/internal/color"
	"thehouseoficarus/internal/config"
	"thehouseoficarus/internal/player"
)

type SessionState int

const (
	StateAccountName SessionState = iota
	StatePassword
	StateNewAccountPass
	StateNewAccount
	StateMenu
	StateNewCharName
	StateNewCharConfirm
	StateRenameAccount
	StateRenameChar
	StateRenameCharName
	StateDeleteChar
	StatePurgeAccount
	StateGame
	StateChangeDesc
	StateTalk
	StateTalkSequence
	StateDropAllConfirm
	StateRecipeChoice
	StateHowMany
	StateSmithProduct
	StateFletchProduct
	StateCraftProduct
	StateProductChoice
	StateColorChoice
	StateBank
	StateHacking
	StateDangerConfirm
	StateUndigConfirm
)

type Session struct {
	Conn              Conn
	State             SessionState
	Account           *player.Account
	Player            *player.Player
	PendingChar       string
	PendingPass       string
	PendingMenu       []map[string]string
	PendingItemID     string
	PendingSkill      string
	PendingLastFlag   string
	PendingBackground bool
	Disconnecting     bool
	DisconnectTicks   int
	PendingUndigDir   string
	PendingUndigRoom  int
	promptVisible     bool
	writeMu           sync.Mutex

	// Outbound queueing. Transport sessions (telnet/TLS/websocket) are put
	// into queued mode by startWriter before their input goroutine begins:
	// Write* then enqueues into outbox, and the dedicated writer goroutine
	// performs the network I/O with a per-message write deadline. A stalled
	// or slow client therefore blocks at most its own queue, never the
	// world; an overflowing queue disconnects only that client. Sessions
	// without a writer (tests, synthetic conns) keep the legacy synchronous
	// path so message construction is shared and behavior identical.
	outbox     chan string
	writerOnce sync.Once
	closeOnce  sync.Once
	writeDone  chan struct{}

	// seq is a monotonically increasing sequence number assigned when the
	// session is added to a Hub. Hub.AllSessions and Hub.PlayersInRoom sort
	// sessions by seq so per-tick consumers iterate players in a stable,
	// registration order instead of Go's randomized map iteration order.
	// Sessions constructed without being added (e.g. in tests) keep seq=0
	// and tie-break by map-append order, which is also deterministic.
	seq uint64
}

// sessionSeq is the source of Session.seq values. It is incremented under the
// adding Hub's mutex, so no extra atomicity is needed for correctness; atomic
// access keeps the package-level default counter safe if Hub.Add is ever
// called concurrently across hubs (it isn't today, but this is defensive).
var sessionSeq atomic.Uint64

type Server struct {
	config         *config.Config
	telnetLn       net.Listener
	telnetTLSLn    net.Listener
	httpServer     *http.Server
	httpsServer    *http.Server
	httpsTLSConfig *tls.Config
	hub            *Hub
	handler        func(*Session, string)

	done         chan struct{}
	shutdownOnce sync.Once
	listenErr    error
}

type Hub struct {
	mu           sync.Mutex
	sessions     map[*Session]bool
	rooms        map[int]map[*Session]bool
	onRemove     func(*Session)
	onDisconnect func(*Session)
}

// writeQueueBounds bound the outbound queue: maxQueuedMessages before a
// client is disconnected for falling behind, writeDeadline per message, and
// closeFlushTimeout to drain the queue when the session is closing.
const (
	maxQueuedMessages = 512
	writeDeadline     = 5 * time.Second
	closeFlushTimeout = 2 * time.Second
)

// startWriter puts the session into queued mode: writes are enqueued and a
// dedicated goroutine drains the queue to the network with per-message write
// deadlines. The goroutine closes the transport after the queue drains, so a
// Close() during shutdown flushes pending output before the socket drops.
// Must be called before the session's input goroutine starts.
func (sess *Session) StartWriter() {
	sess.writerOnce.Do(func() {
		sess.outbox = make(chan string, maxQueuedMessages)
		sess.writeDone = make(chan struct{})
		go func() {
			defer close(sess.writeDone)
			for msg := range sess.outbox {
				if dl, ok := sess.Conn.(interface {
					SetWriteDeadline(time.Time) error
				}); ok {
					_ = dl.SetWriteDeadline(time.Now().Add(writeDeadline))
				}
				if _, err := sess.Conn.Write([]byte(msg)); err != nil {
					log.Printf("session write error: %v", err)
					// Abandon the queue and drop the transport; the input
					// goroutine notices the closed connection on its next
					// read and performs normal removal.
					sess.Conn.Close()
					return
				}
			}
			// Queue closed and drained: flush any final bytes and close.
			if dl, ok := sess.Conn.(interface {
				SetWriteDeadline(time.Time) error
			}); ok {
				_ = dl.SetWriteDeadline(time.Now().Add(closeFlushTimeout))
			}
			sess.Conn.Close()
		}()
	})
}

// enqueue appends msg to the outbound queue. When the client's queue is full
// the session is disconnected instead of blocking the caller: the world must
// never wait on a single slow client.
func (sess *Session) enqueue(msg string) {
	select {
	case sess.outbox <- msg:
	default:
		log.Printf("session write queue overflow; disconnecting slow client")
		sess.Close()
	}
}

func NewHub() *Hub {
	return &Hub{
		sessions: make(map[*Session]bool),
		rooms:    make(map[int]map[*Session]bool),
	}
}

func (h *Hub) OnRemove(cb func(*Session)) {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.onRemove = cb
}

func (h *Hub) OnDisconnect(cb func(*Session)) {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.onDisconnect = cb
}

func (h *Hub) Add(s *Session) {
	h.mu.Lock()
	defer h.mu.Unlock()
	s.seq = sessionSeq.Add(1)
	h.sessions[s] = true
}

func (h *Hub) Remove(s *Session) {
	h.mu.Lock()
	if s.Player != nil && !s.Disconnecting {
		s.Disconnecting = true
		s.DisconnectTicks = 10
		onDisconnect := h.onDisconnect
		h.mu.Unlock()
		if onDisconnect != nil {
			onDisconnect(s)
		}
		return
	}
	callback := h.hardRemoveLocked(s)
	h.mu.Unlock()
	// The removal callback runs outside the Hub mutex: it performs saves
	// and game-state cleanup, and must never serialize behind (or hold up)
	// Hub membership operations.
	if callback != nil {
		callback(s)
	}
}

func (h *Hub) HardRemove(s *Session) {
	h.mu.Lock()
	callback := h.hardRemoveLocked(s)
	h.mu.Unlock()
	if callback != nil {
		callback(s)
	}
}

// hardRemoveLocked removes the session from all membership structures and
// returns the removal callback for the caller to invoke AFTER releasing the
// Hub mutex (nil when none is registered).
func (h *Hub) hardRemoveLocked(s *Session) func(*Session) {
	delete(h.sessions, s)
	for _, room := range h.rooms {
		delete(room, s)
	}
	return h.onRemove
}

func (h *Hub) EnterRoom(s *Session, roomID int) {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.leaveRoomLocked(s)
	if h.rooms[roomID] == nil {
		h.rooms[roomID] = make(map[*Session]bool)
	}
	h.rooms[roomID][s] = true
}

func (h *Hub) LeaveRoom(s *Session) {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.leaveRoomLocked(s)
}

func (h *Hub) leaveRoomLocked(s *Session) {
	for _, room := range h.rooms {
		delete(room, s)
	}
}

// RekeyRooms remaps Hub room membership buckets per idMap (oldID -> newID).
// Uses delete-all-then-set-all so a swap (A<->B) cannot clobber an entry
// mid-rekey. Sessions' own player state is migrated by the game layer; this
// only moves the membership buckets.
func (h *Hub) RekeyRooms(idMap map[int]int) {
	h.mu.Lock()
	defer h.mu.Unlock()
	if len(idMap) == 0 {
		return
	}
	moved := make(map[int]map[*Session]bool, len(h.rooms))
	for id, set := range h.rooms {
		if newID, ok := idMap[id]; ok && newID != id {
			moved[newID] = set
			delete(h.rooms, id)
		}
	}
	for newID, set := range moved {
		h.rooms[newID] = set
	}
}

func (h *Hub) AllSessions() []*Session {
	h.mu.Lock()
	defer h.mu.Unlock()
	var out []*Session
	for s := range h.sessions {
		out = append(out, s)
	}
	sort.SliceStable(out, func(i, j int) bool { return out[i].seq < out[j].seq })
	return out
}

func (h *Hub) PlayersInRoom(roomID int) []*Session {
	h.mu.Lock()
	defer h.mu.Unlock()
	var out []*Session
	if room, ok := h.rooms[roomID]; ok {
		for s := range room {
			out = append(out, s)
		}
	}
	sort.SliceStable(out, func(i, j int) bool { return out[i].seq < out[j].seq })
	return out
}

func NewServer(cfg *config.Config) (*Server, error) {
	s := &Server{
		config: cfg,
		hub:    NewHub(),
		done:   make(chan struct{}),
	}

	if cfg.Telnet.Enabled {
		addr := fmt.Sprintf(":%d", cfg.Telnet.Port)
		ln, err := net.Listen("tcp", addr)
		if err != nil {
			return nil, fmt.Errorf("telnet listen: %w", err)
		}
		s.telnetLn = ln
	}

	if cfg.TelnetTLS.Enabled {
		cert, err := loadOrGenerateCert(cfg, "telnet_tls")
		if err != nil {
			return nil, fmt.Errorf("telnet_tls cert: %w", err)
		}
		tlsCfg := &tls.Config{
			Certificates: []tls.Certificate{cert},
			MinVersion:   tls.VersionTLS12,
		}
		addr := fmt.Sprintf(":%d", cfg.TelnetTLS.Port)
		ln, err := net.Listen("tcp", addr)
		if err != nil {
			return nil, fmt.Errorf("telnet_tls listen: %w", err)
		}
		s.telnetTLSLn = tls.NewListener(ln, tlsCfg)
	}

	if cfg.HTTP.Enabled {
		s.httpServer = &http.Server{
			Addr:    fmt.Sprintf(":%d", cfg.HTTP.Port),
			Handler: newHTTPMux(s),
		}
	}

	if cfg.HTTPS.Enabled {
		cert, err := loadOrGenerateCert(cfg, "https")
		if err != nil {
			return nil, fmt.Errorf("https cert: %w", err)
		}
		s.httpsTLSConfig = &tls.Config{
			Certificates: []tls.Certificate{cert},
			MinVersion:   tls.VersionTLS12,
		}
		s.httpsServer = &http.Server{
			Addr:    fmt.Sprintf(":%d", cfg.HTTPS.Port),
			Handler: newHTTPMux(s),
		}
	}

	return s, nil
}

func loadOrGenerateCert(cfg *config.Config, service string) (tls.Certificate, error) {
	if cfg.TLS.CertFile != "" && cfg.TLS.KeyFile != "" {
		return tls.LoadX509KeyPair(cfg.TLS.CertFile, cfg.TLS.KeyFile)
	}
	log.Printf("%s: using self-signed certificate (no shared tls cert configured)", service)
	return generateSelfSignedCert()
}

func generateSelfSignedCert() (tls.Certificate, error) {
	key, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("rsa key generation: %w", err)
	}
	serial, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("serial number: %w", err)
	}
	now := time.Now()
	template := &x509.Certificate{
		SerialNumber: serial,
		Subject: pkix.Name{
			CommonName: "THOI Self-Signed Certificate",
		},
		NotBefore:             now.Add(-1 * time.Hour),
		NotAfter:              now.Add(365 * 24 * time.Hour),
		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
		IsCA:                  true,
		DNSNames:              []string{"localhost"},
		IPAddresses:           []net.IP{net.ParseIP("127.0.0.1"), net.ParseIP("::1")},
	}
	certDER, err := x509.CreateCertificate(rand.Reader, template, template, &key.PublicKey, key)
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("x509 creation: %w", err)
	}
	return tls.Certificate{
		Certificate: [][]byte{certDER},
		PrivateKey:  key,
	}, nil
}

func (s *Server) Hub() *Hub {
	return s.hub
}

func (s *Server) ListenAndServe(handler func(*Session, string)) error {
	s.handler = handler

	if s.telnetLn != nil {
		go s.serveTelnet()
	}

	if s.telnetTLSLn != nil {
		go s.serveTelnetTLS()
	}

	if s.httpServer != nil {
		go s.serveHTTP()
	}

	if s.httpsServer != nil {
		go s.serveHTTPS()
	}

	if s.telnetLn == nil && s.telnetTLSLn == nil && s.httpServer == nil && s.httpsServer == nil {
		return fmt.Errorf("no listeners configured")
	}

	// Block until Shutdown is called (or a fatal listener error occurs).
	<-s.done
	return s.listenErr
}

// Shutdown stops all transports: HTTP(S) servers drain, listeners close, and
// every session is closed (its outbound queue drains first). ListenAndServe
// returns after Shutdown completes. It is safe to call more than once.
func (s *Server) Shutdown() {
	s.shutdownOnce.Do(func() {
		if s.httpServer != nil {
			ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
			defer cancel()
			_ = s.httpServer.Shutdown(ctx)
		}
		if s.httpsServer != nil {
			ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
			defer cancel()
			_ = s.httpsServer.Shutdown(ctx)
		}
		if s.telnetLn != nil {
			s.telnetLn.Close()
		}
		if s.telnetTLSLn != nil {
			s.telnetTLSLn.Close()
		}
		for _, sess := range s.hub.AllSessions() {
			sess.Close()
		}
		close(s.done)
	})
	<-s.done
}

func (s *Server) serveTelnet() {
	for {
		conn, err := s.telnetLn.Accept()
		if err != nil {
			return
		}
		sess := &Session{
			Conn:  newTCPConn(conn),
			State: StateAccountName,
		}
		s.hub.Add(sess)
		go s.handleSession(sess, s.handler)
	}
}

func (s *Server) serveTelnetTLS() {
	for {
		conn, err := s.telnetTLSLn.Accept()
		if err != nil {
			return
		}
		sess := &Session{
			Conn:  newTCPConn(conn),
			State: StateAccountName,
		}
		s.hub.Add(sess)
		go s.handleSession(sess, s.handler)
	}
}

func (s *Server) serveHTTP() {
	err := s.httpServer.ListenAndServe()
	if err != nil && err != http.ErrServerClosed {
		log.Printf("http server error: %v", err)
	}
}

func (s *Server) serveHTTPS() {
	addr := fmt.Sprintf(":%d", s.config.HTTPS.Port)
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		log.Printf("https server error: %v", err)
		return
	}
	tlsLn := tls.NewListener(ln, s.httpsTLSConfig)
	if err := s.httpsServer.Serve(tlsLn); err != nil && err != http.ErrServerClosed {
		log.Printf("https server error: %v", err)
	}
}

func (s *Server) handleSession(sess *Session, handler func(*Session, string)) {
	defer func() {
		if r := recover(); r != nil {
			log.Printf("session panic: %v", r)
		}
		s.hub.Remove(sess)
		sess.Close()
	}()

	sess.Write("\033[2J\033[H")

	sess.Write(WelcomeBanner())
	sess.Write("What's your account name? ")

	for {
		line, err := sess.Conn.ReadMessage()
		if err != nil {
			log.Printf("session read error: %v", err)
			return
		}
		if len(line) > 1024 {
			line = line[:1024]
		}
		handler(sess, line)
	}
}

// wrap applies the player's wrap_width option to outgoing text. It is a no-op
// before login (no Player) so the welcome banner is never reflowed. The width
// is clamped to a minimum of 80 columns.
func (sess *Session) wrap(msg string) string {
	if sess.Player == nil {
		return msg
	}
	width := sess.Player.OptionInt("wrap_width")
	if width < 80 {
		width = 80
	}
	return color.WrapANSI(msg, width)
}

// ClearPrompt marks the prompt as consumed so the next Write/WriteLine does not
// emit a leading \r\n. Useful for clients that locally advance the line on Enter.
func (sess *Session) ClearPrompt() {
	sess.writeMu.Lock()
	defer sess.writeMu.Unlock()
	sess.promptVisible = false
}

// dispatch delivers a fully-formatted message to the transport: enqueued in
// queued mode (the writer goroutine owns the network), written synchronously
// in direct mode (tests, synthetic conns). Caller holds writeMu.
func (sess *Session) dispatch(msg string) {
	if sess.outbox != nil {
		sess.enqueue(msg)
		return
	}
	sess.Conn.Write([]byte(msg))
}

// Write sends raw text with no wrapping. Used for prompts and partial lines.
func (sess *Session) Write(msg string) {
	sess.writeMu.Lock()
	defer sess.writeMu.Unlock()
	if sess.promptVisible {
		sess.dispatch("\r\n")
		sess.promptVisible = false
	}
	sess.dispatch(msg)
}

func (sess *Session) WriteLine(msg string) {
	msg = sess.wrap(msg)
	sess.writeMu.Lock()
	defer sess.writeMu.Unlock()
	if sess.promptVisible {
		sess.dispatch("\r\n")
		sess.promptVisible = false
	}
	sess.dispatch(msg + "\r\n")
}

func (sess *Session) WriteLines(lines ...string) {
	sess.writeMu.Lock()
	defer sess.writeMu.Unlock()
	for i, l := range lines {
		if i == 0 && sess.promptVisible {
			sess.dispatch("\r\n")
			sess.promptVisible = false
		}
		sess.dispatch(sess.wrap(l) + "\r\n")
	}
}

func (sess *Session) Writef(format string, args ...interface{}) {
	msg := sess.wrap(fmt.Sprintf(format, args...))
	sess.writeMu.Lock()
	defer sess.writeMu.Unlock()
	if sess.promptVisible {
		sess.dispatch("\r\n")
		sess.promptVisible = false
	}
	sess.dispatch(msg)
}

func (sess *Session) WritePrompt(prompt string) {
	sess.writeMu.Lock()
	defer sess.writeMu.Unlock()
	if sess.promptVisible {
		return
	}
	sess.dispatch(prompt)
	sess.promptVisible = true
}

func (sess *Session) Reprompt(prompt string) {
	sess.writeMu.Lock()
	defer sess.writeMu.Unlock()
	sess.dispatch(prompt)
	sess.promptVisible = true
}

// Close stops the session. In queued mode it closes the queue so the writer
// goroutine drains pending messages and then closes the transport; in direct
// mode it closes the transport immediately. Idempotent.
func (sess *Session) Close() error {
	if sess.outbox != nil {
		sess.closeOnce.Do(func() { close(sess.outbox) })
		return nil
	}
	var err error
	sess.closeOnce.Do(func() { err = sess.Conn.Close() })
	return err
}