game/server/net/server.go

package net

import (
	"slices"
	"encoding/json"
	"fmt"
	"log"
	"math"
	"math/rand"
	"net"
	"os"
	"sync"
	"time"
)

// Player represents a connected player
type Player struct {
	ID       uint32
	Username string
	Position Vec3
	Velocity Vec3
	Color    string
	Address  *net.UDPAddr
	LastSeen time.Time
}

// UserData represents persistent user data
type UserData struct {
	Username string `json:"username"`
	Color    string `json:"color"`
	Position Vec3   `json:"position"`
}

// Server manages the game state and networking
type Server struct {
	conn         *net.UDPConn
	players      map[uint32]*Player
	usersByName  map[string]*Player  // Track by username for preventing duplicates
	userData     map[string]*UserData // Persistent user data
	heightmap    [][]float32
	mutex        sync.RWMutex
	nextID       uint32
}

// NewServer creates a new game server
func NewServer(port string, heightmap [][]float32) (*Server, error) {
	addr, err := net.ResolveUDPAddr("udp", ":"+port)
	if err != nil {
		return nil, fmt.Errorf("failed to resolve UDP address: %w", err)
	}

	conn, err := net.ListenUDP("udp", addr)
	if err != nil {
		return nil, fmt.Errorf("failed to listen on UDP: %w", err)
	}

	server := &Server{
		conn:        conn,
		players:     make(map[uint32]*Player),
		usersByName: make(map[string]*Player),
		userData:    make(map[string]*UserData),
		heightmap:   heightmap,
		nextID:      0,
	}

	server.loadUserData()

	return server, nil
}

// Run starts the server main loop
func (s *Server) Run() error {
	defer s.conn.Close()

	// Start periodic save
	go func() {
		ticker := time.NewTicker(10 * time.Second)
		defer ticker.Stop()
		for range ticker.C {
			s.saveUserData()
		}
	}()

	// Start player timeout checker
	go func() {
		ticker := time.NewTicker(5 * time.Second)
		defer ticker.Stop()
		for range ticker.C {
			s.checkTimeouts()
		}
	}()

	buffer := make([]byte, 1024)
	log.Println("Server running...")

	for {
		n, addr, err := s.conn.ReadFromUDP(buffer)
		if err != nil {
			log.Printf("Error reading UDP: %v", err)
			continue
		}

		if n < 1 {
			continue
		}

		msgType := buffer[0]

		switch msgType {
		case MSG_LOGIN:
			s.handleLogin(buffer[:n], addr)
		case MSG_MOVE:
			s.handleMove(buffer[:n], addr)
		case MSG_CHANGE_COLOR:
			s.handleColorChange(buffer[:n], addr)
		case MSG_LOGOUT:
			s.handleLogout(buffer[:n], addr)
		}
	}
}

func (s *Server) handleLogin(data []byte, addr *net.UDPAddr) {
	username, ok := DecodeLoginPacket(data)
	if !ok || username == "" {
		// Invalid login packet
		log.Printf("Received invalid login packet from %s", addr)
		responseMsg := EncodeLoginResponsePacket(false, "Invalid username")
		s.conn.WriteToUDP(responseMsg, addr)
		return
	}
	
	log.Printf("Login attempt for username: %s from %s", username, addr)

	s.mutex.Lock()
	
	// Check if username is already logged in
	if existingPlayer, exists := s.usersByName[username]; exists {
		s.mutex.Unlock()
		responseMsg := EncodeLoginResponsePacket(false, "User already logged in")
		s.conn.WriteToUDP(responseMsg, addr)
		log.Printf("Login rejected for %s: already logged in (ID: %d)", username, existingPlayer.ID)
		return
	}

	s.nextID++
	playerID := s.nextID

	// Load saved user data or create new
	var userData *UserData
	var exists bool
	if userData, exists = s.userData[username]; !exists {
		// New user - assign default color and random position
		colors := []string{"red", "green", "orange", "purple", "white"}
		colorIndex := (playerID - 1) % uint32(len(colors))
		color := colors[colorIndex]
		
		x := rand.Float32()*100 - 50
		z := rand.Float32()*100 - 50
		y := s.getHeightAt(x, z) + 1.0
		
		userData = &UserData{
			Username: username,
			Color:    color,
			Position: Vec3{x, y, z},
		}
		s.userData[username] = userData
	}

	player := &Player{
		ID:       playerID,
		Username: username,
		Position: userData.Position,
		Color:    userData.Color,
		Address:  addr,
		LastSeen: time.Now(),
	}

	// Send existing players to new player before adding them
	existingPlayers := make([]*Player, 0)
	for _, p := range s.players {
		if p.ID != playerID {
			existingPlayers = append(existingPlayers, p)
		}
	}

	s.players[playerID] = player
	s.usersByName[username] = player
	s.mutex.Unlock()

	// Send login success response
	responseMsg := EncodeLoginResponsePacket(true, "Login successful")
	s.conn.WriteToUDP(responseMsg, addr)

	// Send spawn message with saved position and color
	spawnMsg := EncodeSpawnPacket(playerID, userData.Position, userData.Color)
	s.conn.WriteToUDP(spawnMsg, addr)

	// Send player list to new player
	if len(existingPlayers) > 0 {
		listMsg := EncodePlayerListPacket(existingPlayers)
		s.conn.WriteToUDP(listMsg, addr)
	}

	// Notify other players about new player
	s.broadcastPlayerJoined(player)

	log.Printf("Player %s (ID %d) logged in at (%.2f, %.2f, %.2f) with color %s",
		username, playerID, userData.Position.X, userData.Position.Y, userData.Position.Z, userData.Color)

	s.saveUserData()
}

func (s *Server) handleMove(data []byte, _ *net.UDPAddr) {
	playerID, delta, ok := DecodeMovePacket(data)
	if !ok {
		return
	}

	s.mutex.Lock()
	player, exists := s.players[playerID]
	if !exists {
		s.mutex.Unlock()
		return
	}

	// Server-authoritative movement
	deltaTime := float32(0.016) // 60fps
	newX := player.Position.X + delta.X*15.0*deltaTime
	newZ := player.Position.Z + delta.Z*15.0*deltaTime

	// Clamp to world bounds
	newX = float32(math.Max(-50, math.Min(50, float64(newX))))
	newZ = float32(math.Max(-50, math.Min(50, float64(newZ))))

	// Set Y to terrain height with smoothing
	targetY := s.getHeightAt(newX, newZ) + 1.0
	smoothFactor := float32(0.15)
	newY := player.Position.Y + (targetY-player.Position.Y)*smoothFactor

	player.Position.X = newX
	player.Position.Y = newY
	player.Position.Z = newZ
	player.LastSeen = time.Now()
	
	// Update persistent user data
	if userData, exists := s.userData[player.Username]; exists {
		userData.Position = player.Position
	}

	s.mutex.Unlock()

	// Broadcast position update to all players
	s.broadcastUpdate(player)
}

func (s *Server) handleLogout(data []byte, _ *net.UDPAddr) {
	playerID, ok := DecodeLogoutPacket(data)
	if !ok {
		log.Printf("Failed to decode logout packet")
		return
	}
	
	log.Printf("Received logout request for player ID %d", playerID)

	s.mutex.Lock()
	player, exists := s.players[playerID]
	if !exists {
		s.mutex.Unlock()
		log.Printf("Player ID %d not found in active players", playerID)
		return
	}

	// Save final position
	if userData, exists := s.userData[player.Username]; exists {
		userData.Position = player.Position
		userData.Color = player.Color
	}

	// Remove from active players
	username := player.Username
	delete(s.players, playerID)
	delete(s.usersByName, username)
	s.mutex.Unlock()

	// Notify other players
	s.broadcastPlayerLeft(playerID)
	
	log.Printf("Player %s (ID %d) successfully logged out", username, playerID)
	s.saveUserData()
}

func (s *Server) handleColorChange(data []byte, _ *net.UDPAddr) {
	playerID, newColor, ok := DecodeColorChangePacket(data)
	if !ok {
		return
	}

	// Validate color
	validColors := []string{"red", "green", "orange", "purple", "white"}
	isValid := slices.Contains(validColors, newColor)

	if !isValid {
		return
	}

	s.mutex.Lock()
	player, exists := s.players[playerID]
	if !exists {
		s.mutex.Unlock()
		return
	}

	player.Color = newColor
	
	// Update persistent user data
	if userData, exists := s.userData[player.Username]; exists {
		userData.Color = newColor
	}
	
	s.mutex.Unlock()

	// Broadcast color change to all players
	s.broadcastColorChanged(playerID, newColor)
}

func (s *Server) getHeightAt(x, z float32) float32 {
	// Convert world coords to heightmap coords with bilinear interpolation
	size := float32(len(s.heightmap))
	fx := (x/100 + 0.5) * (size - 1)
	fz := (z/100 + 0.5) * (size - 1)

	// Get integer coordinates
	x0 := int(math.Floor(float64(fx)))
	z0 := int(math.Floor(float64(fz)))
	x1 := x0 + 1
	z1 := z0 + 1

	// Clamp to bounds
	if x0 < 0 || x1 >= len(s.heightmap) || z0 < 0 || z1 >= len(s.heightmap) {
		return 0
	}

	// Get fractional parts
	tx := fx - float32(x0)
	tz := fz - float32(z0)

	// Bilinear interpolation
	h00 := s.heightmap[z0][x0]
	h10 := s.heightmap[z0][x1]
	h01 := s.heightmap[z1][x0]
	h11 := s.heightmap[z1][x1]

	h0 := h00*(1-tx) + h10*tx
	h1 := h01*(1-tx) + h11*tx

	return h0*(1-tz) + h1*tz
}

func (s *Server) broadcastUpdate(player *Player) {
	msg := EncodeUpdatePacket(player.ID, player.Position)

	s.mutex.RLock()
	for _, p := range s.players {
		if p.Address != nil {
			s.conn.WriteToUDP(msg, p.Address)
		}
	}
	s.mutex.RUnlock()
}

func (s *Server) broadcastPlayerJoined(newPlayer *Player) {
	msg := EncodePlayerJoinedPacket(newPlayer.ID, newPlayer.Position, newPlayer.Color)

	s.mutex.RLock()
	for _, p := range s.players {
		if p.ID != newPlayer.ID && p.Address != nil {
			s.conn.WriteToUDP(msg, p.Address)
		}
	}
	s.mutex.RUnlock()
}

func (s *Server) broadcastPlayerLeft(playerID uint32) {
	msg := EncodePlayerLeftPacket(playerID)

	s.mutex.RLock()
	for _, p := range s.players {
		if p.ID != playerID && p.Address != nil {
			s.conn.WriteToUDP(msg, p.Address)
		}
	}
	s.mutex.RUnlock()
}

func (s *Server) broadcastColorChanged(playerID uint32, color string) {
	msg := EncodeColorChangedPacket(playerID, color)

	s.mutex.RLock()
	for _, p := range s.players {
		if p.Address != nil {
			s.conn.WriteToUDP(msg, p.Address)
		}
	}
	s.mutex.RUnlock()
}

func (s *Server) checkTimeouts() {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	now := time.Now()
	for id, player := range s.players {
		if now.Sub(player.LastSeen) > 30*time.Second {
			// Save final position before removing
			if userData, exists := s.userData[player.Username]; exists {
				userData.Position = player.Position
				userData.Color = player.Color
			}
			
			delete(s.players, id)
			delete(s.usersByName, player.Username)
			go s.broadcastPlayerLeft(id)
			log.Printf("Player %s (ID %d) timed out", player.Username, id)
			go s.saveUserData()
		}
	}
}

func (s *Server) loadUserData() {
	data, err := os.ReadFile("players.json")
	if err != nil {
		log.Printf("No existing user data found: %v", err)
		return
	}

	var savedUsers map[string]*UserData
	if err := json.Unmarshal(data, &savedUsers); err != nil {
		log.Printf("Failed to parse user data: %v", err)
		return
	}

	s.userData = savedUsers
	log.Printf("Loaded data for %d users", len(savedUsers))
}

func (s *Server) saveUserData() {
	s.mutex.RLock()
	// Deep copy userData to avoid holding lock during file I/O
	savedUsers := make(map[string]*UserData)
	for username, data := range s.userData {
		savedUsers[username] = &UserData{
			Username: data.Username,
			Color:    data.Color,
			Position: data.Position,
		}
	}
	s.mutex.RUnlock()

	data, err := json.MarshalIndent(savedUsers, "", "  ")
	if err != nil {
		log.Printf("Failed to marshal user data: %v", err)
		return
	}
	
	if err := os.WriteFile("players.json", data, 0644); err != nil {
		log.Printf("Failed to save user data: %v", err)
	}
}