package server

import (
	"fmt"
	"log"
	"net"
	"sort"
	"sync"
	"time"

	"github.com/urit/urit/internal/auth"
	"github.com/urit/urit/internal/config"
	"github.com/urit/urit/internal/menu"
	"github.com/urit/urit/internal/session"
	"github.com/urit/urit/internal/store"
)

// maxNodes is the fixed pool size for node numbers.
// Node numbers are recycled: when a user disconnects, their number
// goes back into the pool for the next connection. This provides a
// natural connection limit and keeps node numbers small and readable.
//
// The original TAG-BBS was single-node (serial port). Our pool of 256
// is generous for a retro BBS — even large boards rarely had more than
// a few dozen simultaneous callers.
const maxNodes = 256

// Server manages listener(s) and active connections.
type Server struct {
	cfg      *config.Config
	store    store.Store
	listener net.Listener

	// Session management — protected by mu.
	mu       sync.Mutex
	sessions map[int]*session.Session

	// Web access tokens — shared between telnet and HTTP.
	// Telnet users generate tokens; HTTP uses them for auth.
	Tokens *TokenStore

	// Chat — inter-node real-time messaging.
	Chat *ChatManager

	// StartedAt records when the server was created, used for uptime.
	StartedAt time.Time

	// Node number recycling pool. nodeBitmap tracks which node numbers
	// (1 through maxNodes) are currently assigned. AllocNode picks the
	// lowest free number; FreeNode returns it to the pool.
	//
	// This replaces the monotonically-incrementing connCount from earlier
	// versions. A bitmap is efficient and gives predictable, small node
	// numbers that are easy for sysops to reference.
	nodeBitmap [(maxNodes + 7) / 8]byte
}

// New creates a Server from the given configuration.
func New(cfg *config.Config, db store.Store) *Server {
	return &Server{
		cfg:      cfg,
		store:    db,
		sessions:  make(map[int]*session.Session),
		Tokens:    NewTokenStore(),
		Chat:      NewChatManager(),
		StartedAt: time.Now(),
	}
}

// ListenAndServe starts the telnet listener and blocks, accepting
// connections until the listener is closed. Each connection is handled
// in its own goroutine — this is the multi-user equivalent of the
// original TAG-BBS's single-caller Await_Logon() loop.
func (s *Server) ListenAndServe() error {
	if !s.cfg.Telnet.Enabled {
		return fmt.Errorf("telnet is not enabled in configuration")
	}

	ln, err := net.Listen("tcp", s.cfg.Telnet.Address)
	if err != nil {
		return fmt.Errorf("telnet listen %s: %w", s.cfg.Telnet.Address, err)
	}
	s.listener = ln

	log.Printf("Telnet listening on %s", s.cfg.Telnet.Address)

	for {
		conn, err := ln.Accept()
		if err != nil {
			// Listener was closed (shutdown)
			if opErr, ok := err.(*net.OpError); ok && !opErr.Temporary() {
				return nil
			}
			log.Printf("Accept error: %v", err)
			continue
		}

		go s.handleConnection(conn)
	}
}

// Close shuts down the listener and disconnects all active sessions.
func (s *Server) Close() error {
	s.mu.Lock()
	for _, sess := range s.sessions {
		sess.Close(session.DisconnectKicked)
	}
	s.mu.Unlock()

	if s.listener != nil {
		return s.listener.Close()
	}
	return nil
}

// --- WebTokenizer implementation ---
// These methods let the menu layer generate web access tokens for
// HTTP file downloads without coupling to the token store directly.

func (s *Server) GenerateWebToken(userID int64, userName string, secLibrary int) (string, error) {
	return s.Tokens.Generate(userID, userName, secLibrary)
}

func (s *Server) HTTPAddress() string {
	if s.cfg.HTTP.Enabled {
		return s.cfg.HTTP.Address
	}
	return ""
}

// --- ChatAgent implementation ---
// These methods let the menu layer manage chat sessions without
// coupling to the ChatManager directly.

func (s *Server) EnterChat(node int) <-chan string { return s.Chat.EnterChat(node) }
func (s *Server) LinkChat(a, b int) bool           { return s.Chat.LinkChat(a, b) }
func (s *Server) SendChat(from int, msg string) bool { return s.Chat.SendChat(from, msg) }
func (s *Server) EndChat(node int)                 { s.Chat.EndChat(node) }
func (s *Server) ChatPartner(node int) int         { return s.Chat.Partner(node) }
func (s *Server) IsInChat(node int) bool           { return s.Chat.IsInChat(node) }

// --- NodeManager interface implementation ---
// These methods allow the menu layer to list, message, and disconnect
// nodes without coupling to the server's internal session management.

// ActiveNodes returns info about all currently connected sessions.
// Results are sorted by node number for stable display.
func (s *Server) ActiveNodes() []menu.NodeInfo {
	s.mu.Lock()
	defer s.mu.Unlock()

	nodes := make([]menu.NodeInfo, 0, len(s.sessions))
	for _, sess := range s.sessions {
		nodes = append(nodes, menu.NodeInfo{
			Node:        sess.Node,
			RemoteAddr:  sess.RemoteAddr(),
			UserName:    sess.UserName,
			UserID:      sess.UserID,
			ConnectedAt: sess.ConnectedAt,
		})
	}

	sort.Slice(nodes, func(i, j int) bool {
		return nodes[i].Node < nodes[j].Node
	})
	return nodes
}

// DisconnectNode forcibly disconnects the given node number.
func (s *Server) DisconnectNode(node int) error {
	s.mu.Lock()
	sess, ok := s.sessions[node]
	s.mu.Unlock()

	if !ok {
		return fmt.Errorf("node %d not found", node)
	}

	// Send a courtesy message before disconnecting
	sess.Color(session.AnsiFgRed, session.AnsiBold)
	sess.WriteString("\r\n*** Disconnected by sysop ***\r\n")
	sess.Color(session.AnsiReset)

	sess.Close(session.DisconnectKicked)
	return nil
}

// SendToNode sends a message string to the given node's terminal.
func (s *Server) SendToNode(node int, msg string) error {
	s.mu.Lock()
	sess, ok := s.sessions[node]
	s.mu.Unlock()

	if !ok {
		return fmt.Errorf("node %d not found", node)
	}

	return sess.WriteString(msg)
}

// --- Node number recycling ---

// allocNode assigns the lowest available node number (1-maxNodes).
// Returns 0 if all nodes are in use.
// Must be called with s.mu held.
func (s *Server) allocNode() int {
	for i := 1; i <= maxNodes; i++ {
		byteIdx := (i - 1) / 8
		bitIdx := uint((i - 1) % 8)
		if s.nodeBitmap[byteIdx]&(1<<bitIdx) == 0 {
			s.nodeBitmap[byteIdx] |= 1 << bitIdx
			return i
		}
	}
	return 0 // All nodes in use
}

// freeNode returns a node number to the pool.
// Must be called with s.mu held.
func (s *Server) freeNode(node int) {
	if node < 1 || node > maxNodes {
		return
	}
	byteIdx := (node - 1) / 8
	bitIdx := uint((node - 1) % 8)
	s.nodeBitmap[byteIdx] &^= 1 << bitIdx
}

// --- Connection handling ---

// handleConnection manages a single telnet session from connect to
// disconnect. In the original TAG-BBS, this entire flow was the main
// loop body — Reset_System, Await_Logon, Logon_Sequence, Menu, logoff.
// Here each connection gets its own goroutine and Session.
func (s *Server) handleConnection(conn net.Conn) {
	s.mu.Lock()
	nodeNum := s.allocNode()
	if nodeNum == 0 {
		s.mu.Unlock()
		// All nodes in use — reject the connection.
		conn.Write([]byte("All nodes are busy. Please try again later.\r\n"))
		conn.Close()
		log.Printf("Connection rejected (all %d nodes in use): %s",
			maxNodes, conn.RemoteAddr())
		return
	}
	s.mu.Unlock()

	// Create the session — this replaces the global User struct,
	// IO_Flags array, and jmp_buf Environment from the original.
	sess := session.New(conn, nodeNum)

	s.mu.Lock()
	s.sessions[nodeNum] = sess
	s.mu.Unlock()

	log.Printf("[Node %d] Connected: %s", nodeNum, sess.RemoteAddr())

	defer func() {
		reason := sess.Reason()
		sess.Close(reason)

		// Clean up any active chat session for this node
		s.Chat.EndChat(nodeNum)

		s.mu.Lock()
		delete(s.sessions, nodeNum)
		s.freeNode(nodeNum)
		s.mu.Unlock()

		log.Printf("[Node %d] Disconnected: %s (%s)",
			nodeNum, sess.RemoteAddr(), reason)
	}()

	// Send telnet negotiation — puts client into character mode with
	// server-side echo. This replaces the modem handshake/baud detection
	// that Await_Logon() did in the original.
	if err := sess.Negotiate(); err != nil {
		log.Printf("[Node %d] Negotiation error: %v", nodeNum, err)
		return
	}

	// Run the BBS session: banner → login → menu → logoff.
	// This is the modernized equivalent of the original's
	// MenuSend(Logon.Text) → Logon_Sequence() → Menu() → logoff flow.
	s.runSession(sess)
}

// runSession is the main BBS session handler. It runs the full
// lifecycle: welcome banner → authentication → main menu → logoff.
//
// In the original TAG-BBS, this was the body of the FOREVER loop in
// TAG.C: Reset_System → Await_Logon → Logon_Sequence → Menu → logoff.
func (s *Server) runSession(sess *session.Session) {
	sess.ClearScreen()

	// Welcome banner
	sess.Color(session.AnsiFgCyan, session.AnsiBold)
	sess.WriteString("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━\r\n")
	sess.Color(session.AnsiFgBrightWhite)
	sess.Printf("  %s\r\n", s.cfg.System.Name)
	sess.Color(session.AnsiFgCyan)
	sess.WriteString("  Running URIT BBS v0.2.0\r\n")
	sess.Printf("  Operated by %s\r\n", s.cfg.System.Sysop)
	sess.Color(session.AnsiFgCyan, session.AnsiBold)
	sess.WriteString("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━\r\n")
	sess.Color(session.AnsiReset)
	sess.NewLine()

	// Welcome screen file (optional)
	sess.SendFile(s.cfg.System.Screens + "welcome.ans")

	// Authentication
	result, err := auth.Login(sess, s.store, s.cfg)
	if err != nil {
		log.Printf("[Node %d] Auth error: %v", sess.Node, err)
		return
	}

	user := result.User
	log.Printf("[Node %d] Logged in: %s (ID=%d, Status=%s)",
		sess.Node, user.Name, user.ID, user.StatusLabel())

	// Update session identity — makes this info available via NodeManager
	// so cmdWho and the sysop console can show who's logged in.
	sess.UserName = user.Name
	sess.UserID = user.ID

	// --- Login event logging and stats ---
	// This replaces Append_Stat(STAT_LOGON) and the per-type call
	// counters from the original TAG-BBS.
	s.store.LogEvent("login", user.ID, user.Name, sess.Node,
		sess.RemoteAddr(), user.StatusLabel())
	s.store.IncrementStat("total_calls", 1)
	switch {
	case user.IsGuest():
		s.store.IncrementStat("guest_calls", 1)
	case user.IsNew():
		s.store.IncrementStat("new_calls", 1)
	default:
		s.store.IncrementStat("valid_calls", 1)
	}
	if result.IsNew {
		s.store.IncrementStat("new_accounts", 1)
	}

	// Deferred logoff tracking — runs when the session ends for any
	// reason (normal logoff, timeout, kick, disconnect). This replaces
	// Append_Stat(STAT_LOGOFF) and the time accounting from TAG.C.
	defer func() {
		reason := sess.Reason()
		elapsed := time.Since(sess.ConnectedAt)
		s.store.LogEvent("logoff", user.ID, user.Name, sess.Node,
			sess.RemoteAddr(), reason.String())
		s.store.IncrementStat("total_time_secs", int64(elapsed.Seconds()))

		// Update user's time tracking in the database.
		// TimeUsed is per-session; TimeTotal is cumulative.
		if !result.IsGuest && user.ID > 0 {
			secs := int64(elapsed.Seconds())
			user.TimeUsed = secs
			user.TimeTotal += secs
			now := time.Now()
			user.LastOn = &now
			if err := s.store.UpdateUser(user); err != nil {
				log.Printf("[Node %d] Error updating user time: %v", sess.Node, err)
			}
		}
	}()

	// --- Logon sequence (replaces TAG.C post-login and MENU.C preamble) ---

	// 1. Time reset logic (matches original MENU.C)
	//    Must happen first — if the user has no time, we disconnect them
	//    immediately rather than showing informational screens.
	//    Original: if >12 hours since last login or sysop, reset TimeUsed;
	//    otherwise carry forward remaining time from previous session.
	if !result.IsGuest && user.ID > 0 {
		resetTime := user.SecStatus == 255 // Sysop always gets full time
		if user.LastOn != nil {
			elapsed := time.Since(*user.LastOn)
			if elapsed >= 12*time.Hour {
				resetTime = true
			}
		} else {
			resetTime = true // First login ever
		}

		if resetTime {
			user.TimeUsed = 0
		}

		// Apply user's time limit to the session, accounting for time
		// already used (carried forward from a recent session).
		limit := time.Duration(user.TimeLimit) * time.Second
		used := time.Duration(user.TimeUsed) * time.Second
		remaining := limit - used
		if remaining <= 0 {
			// No time left — show the "no time" screen and disconnect.
			// Matches original: MenuSend("Logon24hrs.Text") then longjmp.
			sess.SendFile(s.cfg.System.Screens + "notime.ans")
			sess.Color(session.AnsiFgRed)
			sess.WriteString("  You have no time remaining. Try again later.\r\n")
			sess.Color(session.AnsiReset)
			sess.NewLine()
			log.Printf("[Node %d] No time remaining for %s, disconnecting",
				sess.Node, user.Name)
			return
		}
		sess.TimeLimit = remaining
	}

	// 2. Post-login screen files
	//    The original had separate files: Logon.Text, GuestLogon.Text.
	//    We add newuser.ans for first-time registrations.
	if result.IsGuest {
		sess.SendFile(s.cfg.System.Screens + "guest.ans")
	} else if result.IsNew {
		sess.SendFile(s.cfg.System.Screens + "newuser.ans")
	} else {
		sess.SendFile(s.cfg.System.Screens + "logon.ans")
	}

	// 3. Last caller display
	//    Not in the original (single-node Amiga), but a classic BBS feature.
	//    Shows who was the last person to log in before the current user.
	if lastCaller, err := s.store.GetLastCaller(user.ID); err == nil && lastCaller != nil {
		sess.Color(session.AnsiFgBrightBlack)
		sess.Printf("  Last caller: %s on %s\r\n",
			lastCaller.UserName,
			lastCaller.CreatedAt.Format("Jan 02 at 3:04 PM"))
		sess.Color(session.AnsiReset)
	}

	// 4. Unread mail check
	if !result.IsGuest && user.ID > 0 {
		unread, _ := s.store.CountUnreadMail(user.ID)
		if unread > 0 {
			sess.Color(session.AnsiFgBrightYellow)
			sess.Printf("*** You have %d unread mail message(s) ***\r\n", unread)
			sess.Color(session.AnsiReset)
			sess.NewLine()
		}
	}

	// 5. New user validation notice
	//    The original had security levels: 0=guest, 1=new/unvalidated,
	//    2+=validated. New users could use the BBS but with restricted
	//    board/library access until the sysop validated them (which
	//    bumped their security levels up).
	if !result.IsGuest && user.IsNew() {
		sess.Color(session.AnsiFgYellow)
		sess.WriteString("  Your account is awaiting validation by the sysop.\r\n")
		sess.WriteString("  Some areas may have restricted access.\r\n")
		sess.Color(session.AnsiReset)
		sess.NewLine()
	}

	// 6. System call count and session info
	totalCalls, _ := s.store.GetStat("total_calls")
	if totalCalls > 0 {
		sess.Color(session.AnsiFgBrightBlack)
		sess.Printf("  Call #%d", totalCalls)
		if !result.IsGuest && user.LastOn != nil {
			sess.Printf(" | Last on: %s", user.LastOn.Format("Jan 02 at 3:04 PM"))
		}
		sess.WriteString("\r\n")
		sess.Color(session.AnsiReset)
	}

	// Post-login info
	sess.Color(session.AnsiFgBrightBlack)
	width, height := sess.TerminalSize()
	sess.Printf("  Node %d | %s | Terminal %dx%d | Time limit %s\r\n",
		sess.Node, user.StatusLabel(), width, height,
		fmtDuration(sess.TimeRemaining()))
	sess.Color(session.AnsiReset)
	sess.NewLine()

	// Hand off to the main menu loop — replaces the original's Menu() call.
	ctx := &menu.Context{
		Sess:   sess,
		User:   user,
		Store:  s.store,
		Cfg:    s.cfg,
		Auth:   result,
		Nodes:  s, // Server implements NodeManager
		Tokens: s, // Server implements WebTokenizer
		Chat:   s, // Server implements ChatAgent
	}

	menu.Run(ctx)
}

// fmtDuration formats a time.Duration as "Xh Ym" for display.
func fmtDuration(d time.Duration) string {
	mins := int(d.Minutes())
	hours := mins / 60
	mins = mins % 60
	if hours > 0 {
		return fmt.Sprintf("%dh %dm", hours, mins)
	}
	return fmt.Sprintf("%dm", mins)
}