feat(config): config at XDG dir

cmd/config.go

@@ -0,0 +1,67 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/BurntSushi/toml"
+	gap "github.com/muesli/go-app-paths"
+)
+
+type Config struct {
+	DefaultDB string `toml:"default_db"`
+}
+
+var (
+	config    Config
+	configErr error
+)
+
+func init() {
+	config, configErr = loadConfig()
+}
+
+func defaultConfig() Config {
+	return Config{
+		DefaultDB: "default",
+	}
+}
+
+func loadConfig() (Config, error) {
+	cfg := defaultConfig()
+
+	path, err := configPath()
+	if err != nil {
+		return cfg, err
+	}
+
+	if _, err := os.Stat(path); err != nil {
+		if os.IsNotExist(err) {
+			return cfg, nil
+		}
+		return cfg, err
+	}
+
+	if _, err := toml.DecodeFile(path, &cfg); err != nil {
+		return cfg, fmt.Errorf("parse %s: %w", path, err)
+	}
+
+	if cfg.DefaultDB == "" {
+		cfg.DefaultDB = defaultConfig().DefaultDB
+	}
+
+	return cfg, nil
+}
+
+func configPath() (string, error) {
+	if override := os.Getenv("PDA_CONFIG"); override != "" {
+		return override, nil
+	}
+	scope := gap.NewVendorScope(gap.User, "pda", "config")
+	dir, err := scope.ConfigPath("")
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(dir, "config.toml"), nil
+}