initial working version

internal/config/config.go

@@ -0,0 +1,64 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/adrg/xdg"
+	toml "github.com/pelletier/go-toml/v2"
+)
+
+type Config struct {
+	Issuer       string `toml:"issuer"`
+	ClientID     string `toml:"client_id"`
+	ClientSecret string `toml:"client_secret,omitempty"`
+	CacheHost    string `toml:"cache_host"`
+	NetrcPath    string `toml:"netrc_path"`
+}
+
+// Load reads the config from the given path, or from the default XDG location.
+func Load(path string) (*Config, error) {
+	if path == "" {
+		path = filepath.Join(xdg.ConfigHome, "nix-cache-login", "config.toml")
+	}
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("reading config file: %w", err)
+	}
+
+	var cfg Config
+	if err := toml.Unmarshal(data, &cfg); err != nil {
+		return nil, fmt.Errorf("parsing config file: %w", err)
+	}
+
+	cfg.NetrcPath = os.ExpandEnv(cfg.NetrcPath)
+
+	if err := cfg.validate(); err != nil {
+		return nil, err
+	}
+
+	return &cfg, nil
+}
+
+func (c *Config) validate() error {
+	if c.Issuer == "" {
+		return fmt.Errorf("config: issuer is required")
+	}
+	if c.ClientID == "" {
+		return fmt.Errorf("config: client_id is required")
+	}
+	if c.CacheHost == "" {
+		return fmt.Errorf("config: cache_host is required")
+	}
+	if c.NetrcPath == "" {
+		return fmt.Errorf("config: netrc_path is required")
+	}
+	return nil
+}
+
+// RefreshTokenPath returns the path to the stored refresh token.
+func RefreshTokenPath() string {
+	return filepath.Join(xdg.ConfigHome, "nix-cache-login", "refresh-token")
+}