games/snake/store.go

package snake

import (
	"crypto/rand"
	"encoding/hex"
	"sync"
)

type PubSub interface {
	Publish(subject string, data []byte) error
}

type Persister interface {
	SaveSnakeGame(sg *SnakeGame) error
	LoadSnakeGame(id string) (*SnakeGame, error)
	SaveSnakePlayer(gameID string, player *Player) error
	LoadSnakePlayers(gameID string) ([]*Player, error)
	DeleteSnakeGame(id string) error
}

type SnakeStore struct {
	games     map[string]*SnakeGameInstance
	gamesMu   sync.RWMutex
	persister Persister
	pubsub    PubSub
}

func NewSnakeStore() *SnakeStore {
	return &SnakeStore{
		games: make(map[string]*SnakeGameInstance),
	}
}

func (ss *SnakeStore) SetPersister(p Persister) {
	ss.persister = p
}

func (ss *SnakeStore) SetPubSub(ps PubSub) {
	ss.pubsub = ps
}

func (ss *SnakeStore) makeNotify(gameID string) func() {
	return func() {
		if ss.pubsub != nil {
			ss.pubsub.Publish("snake."+gameID, nil)
		}
	}
}

func (ss *SnakeStore) Create(width, height int, mode GameMode) *SnakeGameInstance {
	id := generateID(4)
	sg := &SnakeGame{
		ID: id,
		State: &GameState{
			Width:  width,
			Height: height,
		},
		Players: make([]*Player, 8),
		Status:  StatusWaitingForPlayers,
		Mode:    mode,
	}
	si := &SnakeGameInstance{
		game:      sg,
		notify:    ss.makeNotify(id),
		persister: ss.persister,
		store:     ss,
	}

	ss.gamesMu.Lock()
	ss.games[id] = si
	ss.gamesMu.Unlock()

	if ss.persister != nil {
		ss.persister.SaveSnakeGame(sg)
	}

	return si
}

func (ss *SnakeStore) Get(id string) (*SnakeGameInstance, bool) {
	ss.gamesMu.RLock()
	si, ok := ss.games[id]
	ss.gamesMu.RUnlock()

	if ok {
		return si, true
	}

	if ss.persister == nil {
		return nil, false
	}

	sg, err := ss.persister.LoadSnakeGame(id)
	if err != nil || sg == nil {
		return nil, false
	}

	players, _ := ss.persister.LoadSnakePlayers(id)
	if sg.Players == nil {
		sg.Players = make([]*Player, 8)
	}
	for _, p := range players {
		if p.Slot >= 0 && p.Slot < 8 {
			sg.Players[p.Slot] = p
		}
	}

	si = &SnakeGameInstance{
		game:      sg,
		notify:    ss.makeNotify(id),
		persister: ss.persister,
		store:     ss,
	}

	ss.gamesMu.Lock()
	ss.games[id] = si
	ss.gamesMu.Unlock()

	return si, true
}

func (ss *SnakeStore) Delete(id string) error {
	ss.gamesMu.Lock()
	si, ok := ss.games[id]
	delete(ss.games, id)
	ss.gamesMu.Unlock()

	if ok && si != nil {
		si.Stop()
	}

	if ss.persister != nil {
		return ss.persister.DeleteSnakeGame(id)
	}
	return nil
}

// ActiveGames returns metadata of multiplayer games that can be joined.
// Single player games are excluded. Copies game data to avoid holding nested locks.
func (ss *SnakeStore) ActiveGames() []*SnakeGame {
	ss.gamesMu.RLock()
	instances := make([]*SnakeGameInstance, 0, len(ss.games))
	for _, si := range ss.games {
		instances = append(instances, si)
	}
	ss.gamesMu.RUnlock()

	var games []*SnakeGame
	for _, si := range instances {
		si.gameMu.RLock()
		g := si.game
		if g.Mode == ModeMultiplayer && (g.Status == StatusWaitingForPlayers || g.Status == StatusCountdown) {
			games = append(games, g)
		}
		si.gameMu.RUnlock()
	}
	return games
}

type SnakeGameInstance struct {
	game       *SnakeGame
	gameMu     sync.RWMutex
	pendingDir [8]*Direction
	notify     func()
	persister  Persister
	store      *SnakeStore
	stopCh     chan struct{}
	loopOnce   sync.Once
}

func (si *SnakeGameInstance) ID() string {
	si.gameMu.RLock()
	defer si.gameMu.RUnlock()
	return si.game.ID
}

// GetGame returns a snapshot of the game state safe for concurrent read.
func (si *SnakeGameInstance) GetGame() *SnakeGame {
	si.gameMu.RLock()
	defer si.gameMu.RUnlock()
	return si.game.snapshot()
}

func (si *SnakeGameInstance) GetPlayerSlot(pid PlayerID) int {
	si.gameMu.RLock()
	defer si.gameMu.RUnlock()
	for i, p := range si.game.Players {
		if p != nil && p.ID == pid {
			return i
		}
	}
	return -1
}

func (si *SnakeGameInstance) Join(player *Player) bool {
	si.gameMu.Lock()
	defer si.gameMu.Unlock()

	if si.game.Status == StatusInProgress || si.game.Status == StatusFinished {
		return false
	}

	slot := -1
	for i, p := range si.game.Players {
		if p == nil {
			slot = i
			break
		}
	}
	if slot == -1 {
		return false
	}

	player.Slot = slot
	si.game.Players[slot] = player

	if si.persister != nil {
		si.persister.SaveSnakePlayer(si.game.ID, player)
		si.persister.SaveSnakeGame(si.game)
	}

	si.notify()

	// Single player starts countdown immediately when 1 player joins
	if si.game.Mode == ModeSinglePlayer && si.game.PlayerCount() >= 1 {
		si.startOrResetCountdownLocked()
	} else if si.game.Mode == ModeMultiplayer && si.game.PlayerCount() >= 2 {
		si.startOrResetCountdownLocked()
	}

	return true
}

// SetDirection buffers a direction change for the given slot.
// The write happens under the game lock to avoid a data race with the game loop.
func (si *SnakeGameInstance) SetDirection(slot int, dir Direction) {
	if slot < 0 || slot >= 8 {
		return
	}
	si.gameMu.Lock()
	defer si.gameMu.Unlock()

	if si.game.State != nil && slot < len(si.game.State.Snakes) {
		s := si.game.State.Snakes[slot]
		if s != nil && s.Alive && !ValidateDirection(s.Dir, dir) {
			return
		}
	}
	si.pendingDir[slot] = &dir
}

func (si *SnakeGameInstance) Stop() {
	if si.stopCh != nil {
		select {
		case <-si.stopCh:
		default:
			close(si.stopCh)
		}
	}
}

func (si *SnakeGameInstance) CreateRematch() *SnakeGameInstance {
	si.gameMu.Lock()

	if !si.game.IsFinished() || si.game.RematchGameID != nil {
		si.gameMu.Unlock()
		return nil
	}

	// Capture state needed, then release lock before calling store.Create
	// (which acquires gamesMu) to avoid lock ordering deadlock.
	width := si.game.State.Width
	height := si.game.State.Height
	mode := si.game.Mode
	si.gameMu.Unlock()

	newSI := si.store.Create(width, height, mode)
	newID := newSI.ID()

	si.gameMu.Lock()
	// Re-check after reacquiring lock
	if si.game.RematchGameID != nil {
		si.gameMu.Unlock()
		return newSI
	}
	si.game.RematchGameID = &newID

	if si.persister != nil {
		si.persister.SaveSnakeGame(si.game)
	}
	si.gameMu.Unlock()

	si.notify()
	return newSI
}

func generateID(size int) string {
	b := make([]byte, size)
	rand.Read(b)
	return hex.EncodeToString(b)
}