refactor: use new struct in backend

backend/config/config.go

@@ -0,0 +1,151 @@
+package config
+
+import (
+	"fmt"
+
+	"github.com/BurntSushi/toml"
+)
+
+// DatabaseDriver represents the database driver specified in the config file,
+// mirroring the legacy DatabaseDriver(StrEnum). It is a numeric enum simulated
+// with const + iota; its string form is produced by databaseDriverFromString.
+type DatabaseDriver int
+
+const (
+	// DatabaseDriverSqlite means the SQLite database is used.
+	DatabaseDriverSqlite DatabaseDriver = iota
+	// DatabaseDriverMysql means the MySQL database is used.
+	DatabaseDriverMysql
+)
+
+// databaseDriverFromString converts a driver string from the config file into a
+// DatabaseDriver. An unrecognized string returns an error.
+func databaseDriverFromString(s string) (DatabaseDriver, error) {
+	switch s {
+	case "sqlite":
+		return DatabaseDriverSqlite, nil
+	case "mysql":
+		return DatabaseDriverMysql, nil
+	default:
+		return 0, fmt.Errorf("invalid database driver: %q", s)
+	}
+}
+
+// SqliteDatabaseConfig is the connection config for SQLite, mirroring the
+// legacy SqliteDatabaseConfig.
+type SqliteDatabaseConfig struct {
+	// Path is the database file path.
+	Path string `toml:"path"`
+}
+
+// MysqlDatabaseConfig is the connection config for MySQL, mirroring the legacy
+// MysqlDatabaseConfig.
+type MysqlDatabaseConfig struct {
+	// Host is the database host.
+	Host string `toml:"host"`
+	// Port is the database port.
+	Port int `toml:"port"`
+	// User is the database user.
+	User string `toml:"user"`
+	// Password is the database password.
+	Password string `toml:"password"`
+	// Database is the database name.
+	Database string `toml:"database"`
+}
+
+// DatabaseConfig describes the database driver and its concrete config, mirroring
+// the legacy DatabaseConfig. Driver is the discriminator deciding whether Sqlite
+// or Mysql is populated.
+type DatabaseConfig struct {
+	// Driver is the selected database driver.
+	Driver DatabaseDriver
+	// Sqlite is non-nil when Driver is DatabaseDriverSqlite.
+	Sqlite *SqliteDatabaseConfig
+	// Mysql is non-nil when Driver is DatabaseDriverMysql.
+	Mysql *MysqlDatabaseConfig
+}
+
+// WebConfig is the web server config, mirroring the legacy WebConfig.
+type WebConfig struct {
+	// Port is the web server listening port.
+	Port int `toml:"port"`
+}
+
+// OthersConfig holds miscellaneous options, mirroring the legacy OthersConfig.
+type OthersConfig struct {
+	// Debug indicates whether debug mode is enabled.
+	Debug bool `toml:"debug"`
+	// AutoTokenCleanDuration is the interval (in seconds) for auto-cleaning
+	// outdated tokens.
+	AutoTokenCleanDuration int `toml:"auto-token-clean-duration"`
+}
+
+// Config is the full configuration parsed from the config file, mirroring the
+// legacy Config.
+type Config struct {
+	// Database is the database-related config.
+	Database DatabaseConfig
+	// Web is the web-server-related config.
+	Web WebConfig
+	// Others is the miscellaneous config.
+	Others OthersConfig
+}
+
+// rawDatabaseConfig is an internal struct used only for TOML decoding. Its
+// Config field is stored as a toml.Primitive so it can be dispatched and decoded
+// in two phases based on Driver.
+type rawDatabaseConfig struct {
+	Driver string         `toml:"driver"`
+	Config toml.Primitive `toml:"config"`
+}
+
+// rawConfig is an internal struct used only for TOML decoding, in tandem with
+// the two-phase decode.
+type rawConfig struct {
+	Database rawDatabaseConfig `toml:"database"`
+	Web      WebConfig         `toml:"web"`
+	Others   OthersConfig      `toml:"others"`
+}
+
+// Load reads and parses the TOML config file at the given path, returning the
+// parsed config or an error. It merges the legacy setup_config and get_config:
+// the first phase uses toml.DecodeFile to defer database.config, and the second
+// phase dispatches PrimitiveDecode into SqliteDatabaseConfig or
+// MysqlDatabaseConfig based on the driver.
+func Load(path string) (*Config, error) {
+	var raw rawConfig
+	meta, err := toml.DecodeFile(path, &raw)
+	if err != nil {
+		return nil, err
+	}
+
+	driver, err := databaseDriverFromString(raw.Database.Driver)
+	if err != nil {
+		return nil, err
+	}
+
+	cfg := &Config{
+		Web:    raw.Web,
+		Others: raw.Others,
+		Database: DatabaseConfig{
+			Driver: driver,
+		},
+	}
+
+	switch driver {
+	case DatabaseDriverSqlite:
+		var s SqliteDatabaseConfig
+		if err := meta.PrimitiveDecode(raw.Database.Config, &s); err != nil {
+			return nil, err
+		}
+		cfg.Database.Sqlite = &s
+	case DatabaseDriverMysql:
+		var m MysqlDatabaseConfig
+		if err := meta.PrimitiveDecode(raw.Database.Config, &m); err != nil {
+			return nil, err
+		}
+		cfg.Database.Mysql = &m
+	}
+
+	return cfg, nil
+}