refactor: modularize chat backend, update docs for .m4s segments

backend/chat/src/db/db.go

@@ -0,0 +1,82 @@
+package db
+
+import (
+	"context"
+	"log"
+	"strings"
+	"time"
+
+	"gorm.io/driver/postgres"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+)
+
+// DBClient wraps gorm.DB for testability.
+type DBClient struct {
+	*gorm.DB
+}
+
+// InitDB initializes configured SQL storage for chat, moderation, and admin metadata (ADR-006).
+// Returns the client and the driver name.
+func InitDB(databaseURL string) (*DBClient, string, error) {
+	var (
+		gormDB *gorm.DB
+		err    error
+		driver = "sqlite"
+	)
+
+	switch {
+	case databaseURL == "":
+		gormDB, err = gorm.Open(sqlite.Open("chat.db"), &gorm.Config{})
+	case strings.HasPrefix(databaseURL, "sqlite://"):
+		sqlitePath := strings.TrimPrefix(databaseURL, "sqlite://")
+		if sqlitePath == "" {
+			sqlitePath = "chat.db"
+		}
+		gormDB, err = gorm.Open(sqlite.Open(sqlitePath), &gorm.Config{})
+	case strings.HasPrefix(databaseURL, "postgres://") || strings.HasPrefix(databaseURL, "postgresql://"):
+		driver = "postgres"
+		gormDB, err = gorm.Open(postgres.Open(databaseURL), &gorm.Config{})
+	default:
+		log.Fatalf("Unsupported DATABASE_URL scheme: %s", databaseURL)
+	}
+
+	if err != nil {
+		return nil, driver, err
+	}
+
+	gormDB.AutoMigrate(&Message{}, &ModerationLog{}, &Media{}, &ScheduleOverride{})
+	log.Printf("%s database initialized (chat history, moderation log, media metadata)", strings.Title(driver))
+
+	return &DBClient{DB: gormDB}, driver, nil
+}
+
+// RedisClient wraps the Redis client for testability.
+// Interface defined for mocking in tests.
+type RedisClient interface {
+	Ping(ctx context.Context) error
+	Set(ctx context.Context, key string, value interface{}, expiration time.Duration) error
+	Get(ctx context.Context, key string) (string, error)
+	Del(ctx context.Context, keys ...string) error
+	Incr(ctx context.Context, key string) (int64, error)
+	Decr(ctx context.Context, key string) (int64, error)
+	Expire(ctx context.Context, key string, expiration time.Duration) error
+	Exists(ctx context.Context, keys ...string) (int64, error)
+	Publish(ctx context.Context, channel string, message interface{}) error
+	PSubscribe(ctx context.Context, channels ...string) PubSub
+	Scan(ctx context.Context, cursor uint64, match string, count int64) ([]string, uint64, error)
+	Info(ctx context.Context, sections ...string) (string, error)
+	Close() error
+}
+
+// PubSub wraps Redis pub/sub subscription.
+type PubSub interface {
+	ReceiveMessage(ctx context.Context) (*PubSubMessage, error)
+	Close() error
+}
+
+// PubSubMessage represents a received pub/sub message.
+type PubSubMessage struct {
+	Channel string
+	Payload string
+}