common/
├── base.go           # BaseModel: GORM entity with snowflake ID + audit fields
├── env.go            # GetEnv / GetEnvXxx with TTL+LRU cache
├── dbs.go            # InitDatabase: GORM connection factory
├── dbs_mysql.go      # MySQL driver    (build tag: mysql)
├── dbs_pg.go         # PostgreSQL driver (build tag: pg)
├── dbs_sqlite.go     # SQLite fallback  (default build)
├── content_type.go   # File extension -> MIME type map
├── file_type.go      # File category constants (image/audio/media/file)
├── files.go          # File hash, size, save helpers
├── array.go          # Generic Join[T] helper
├── strings.go        # Zero-copy string <-> []byte conversions
├── geo.go            # Haversine distance between two coordinates
├── signals.go        # Signal/event handler registry
└── snowflake.go      # Deprecated snowflake aliases (use common/idgen)

// BaseModel is embedded by all GORM entities.
type BaseModel struct {
    ID        uint           `gorm:"primaryKey"`
    CreatedAt time.Time
    UpdatedAt time.Time
    DeletedAt gorm.DeletedAt `gorm:"index"`
    CreateBy  string
    UpdateBy  string
    Remark    string
}

// InitDatabase creates a GORM DB from driver + DSN (falls back to env vars).
func InitDatabase(logWrite io.Writer, driver, dsn string) (*gorm.DB, error)

// GetEnv reads an env var with TTL+LRU caching.
func GetEnv(key string) string

import "github.com/LingByte/ling-base/common"

// Environment variables (cached)
dbHost := common.GetEnv("DB_HOST")
port := common.GetEnvInt("DB_PORT", 3306)

// GORM database
db, err := common.InitDatabase(nil, "mysql", "user:pass@tcp(127.0.0.1:3306)/db")

// Content type lookup
ct := common.GetContentType(".json") // "application/json"

// Snowflake ID (via idgen)
id := common.NextSnowflakeUint()