refactor: extract GameService for Connect 4 NATS/chat handling

Move NATS subscription and chat room management into a dedicated
GameService, following the portigo service pattern. Handlers now
receive the service and call its methods instead of managing
NATS connections directly.

features/c4game/services/game_service.go

@@ -0,0 +1,70 @@
+// Package services provides the game service layer for Connect 4,
+// handling NATS subscriptions and chat room management.
+package services
+
+import (
+	"fmt"
+
+	"github.com/nats-io/nats.go"
+
+	"github.com/ryanhamamura/games/chat"
+	chatcomponents "github.com/ryanhamamura/games/chat/components"
+	"github.com/ryanhamamura/games/connect4"
+	"github.com/ryanhamamura/games/db/repository"
+)
+
+// c4ChatColors maps player slot (0-indexed) to CSS background colors.
+var c4ChatColors = map[int]string{
+	0: "#4a2a3a", // Red player
+	1: "#2a4545", // Yellow player
+}
+
+func c4ChatColor(slot int) string {
+	if c, ok := c4ChatColors[slot]; ok {
+		return c
+	}
+	return "#666"
+}
+
+// GameService manages NATS subscriptions and chat for Connect 4 games.
+type GameService struct {
+	nc      *nats.Conn
+	queries *repository.Queries
+}
+
+// NewGameService creates a new game service.
+func NewGameService(nc *nats.Conn, queries *repository.Queries) *GameService {
+	return &GameService{
+		nc:      nc,
+		queries: queries,
+	}
+}
+
+// SubscribeGameUpdates returns a NATS subscription and channel for game state updates.
+func (s *GameService) SubscribeGameUpdates(gameID string) (*nats.Subscription, <-chan *nats.Msg, error) {
+	ch := make(chan *nats.Msg, 64)
+	sub, err := s.nc.ChanSubscribe(connect4.GameSubject(gameID), ch)
+	if err != nil {
+		return nil, nil, fmt.Errorf("subscribing to game updates: %w", err)
+	}
+	return sub, ch, nil
+}
+
+// ChatConfig returns the chat configuration for a game.
+func (s *GameService) ChatConfig(gameID string) chatcomponents.Config {
+	return chatcomponents.Config{
+		CSSPrefix: "c4",
+		PostURL:   fmt.Sprintf("/games/%s/chat", gameID),
+		Color:     c4ChatColor,
+	}
+}
+
+// ChatRoom returns a persistent chat room for a game.
+func (s *GameService) ChatRoom(gameID string) *chat.Room {
+	return chat.NewPersistentRoom(s.nc, connect4.ChatSubject(gameID), s.queries, gameID)
+}
+
+// PublishGameUpdate sends a notification that the game state has changed.
+func (s *GameService) PublishGameUpdate(gameID string) error {
+	return s.nc.Publish(connect4.GameSubject(gameID), nil)
+}