feat(config): load embedded defaults and merge optional overlay

go.mod

@@ -7,4 +7,5 @@ require github.com/spf13/cobra v1.10.2
 require (
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/spf13/pflag v1.0.9 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -8,3 +8,5 @@ github.com/spf13/pflag v1.0.9 h1:9exaQaMOCwffKiiiYk6/BndUBv+iRViNW+4lEMi0PvY=
 github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

internal/config/config.go

@@ -0,0 +1,82 @@
+// Package config loads embedded defaults and optionally merges a user
+// overlay from ~/.config/archduino/overlay.yaml.
+package config
+
+import (
+	_ "embed"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"gopkg.in/yaml.v3"
+)
+
+//go:embed defaults.yaml
+var defaultsYAML []byte
+
+// Config is the fully-resolved runtime configuration.
+type Config struct {
+	Version         int               `yaml:"version"`
+	ExtraPackages   []string          `yaml:"extra_packages"`
+	DisabledModules []string          `yaml:"disabled_modules"`
+	ThemeOverrides  map[string]string `yaml:"theme_overrides"`
+}
+
+const currentVersion = 1
+
+// Load returns defaults merged with the overlay at overlayPath (if present).
+// If overlayPath is "", the default location (~/.config/archduino/overlay.yaml)
+// is used. A missing overlay is not an error.
+func Load(overlayPath string) (Config, error) {
+	var cfg Config
+	if err := yaml.Unmarshal(defaultsYAML, &cfg); err != nil {
+		return Config{}, fmt.Errorf("parse embedded defaults: %w", err)
+	}
+
+	if overlayPath == "" {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return cfg, nil
+		}
+		overlayPath = filepath.Join(home, ".config", "archduino", "overlay.yaml")
+	}
+
+	data, err := os.ReadFile(overlayPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return cfg, nil
+		}
+		return Config{}, fmt.Errorf("read overlay %s: %w", overlayPath, err)
+	}
+
+	var overlay Config
+	if err := yaml.Unmarshal(data, &overlay); err != nil {
+		return Config{}, fmt.Errorf("parse overlay %s: %w", overlayPath, err)
+	}
+	if overlay.Version != 0 && overlay.Version != currentVersion {
+		return Config{}, fmt.Errorf("overlay %s: unsupported version %d (want %d)", overlayPath, overlay.Version, currentVersion)
+	}
+
+	return merge(cfg, overlay), nil
+}
+
+func merge(base, over Config) Config {
+	out := base
+	if len(over.ExtraPackages) > 0 {
+		out.ExtraPackages = append(append([]string{}, base.ExtraPackages...), over.ExtraPackages...)
+	}
+	if len(over.DisabledModules) > 0 {
+		out.DisabledModules = append(append([]string{}, base.DisabledModules...), over.DisabledModules...)
+	}
+	if len(over.ThemeOverrides) > 0 {
+		merged := make(map[string]string, len(base.ThemeOverrides)+len(over.ThemeOverrides))
+		for k, v := range base.ThemeOverrides {
+			merged[k] = v
+		}
+		for k, v := range over.ThemeOverrides {
+			merged[k] = v
+		}
+		out.ThemeOverrides = merged
+	}
+	return out
+}

internal/config/config_test.go

@@ -0,0 +1,60 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadDefaultsWhenNoOverlay(t *testing.T) {
+	dir := t.TempDir()
+	cfg, err := Load(filepath.Join(dir, "missing.yaml"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cfg.Version != 1 {
+		t.Errorf("version = %d", cfg.Version)
+	}
+	if len(cfg.ExtraPackages) != 0 {
+		t.Errorf("extra_packages = %v", cfg.ExtraPackages)
+	}
+}
+
+func TestLoadMergesOverlay(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "overlay.yaml")
+	content := []byte(`
+version: 1
+extra_packages: [htop, ncdu]
+disabled_modules: [renode]
+theme_overrides:
+  starship: /tmp/mine.toml
+`)
+	if err := os.WriteFile(path, content, 0o644); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := Load(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := cfg.ExtraPackages; len(got) != 2 || got[0] != "htop" || got[1] != "ncdu" {
+		t.Errorf("extra_packages = %v", got)
+	}
+	if len(cfg.DisabledModules) != 1 || cfg.DisabledModules[0] != "renode" {
+		t.Errorf("disabled_modules = %v", cfg.DisabledModules)
+	}
+	if cfg.ThemeOverrides["starship"] != "/tmp/mine.toml" {
+		t.Errorf("theme_overrides = %v", cfg.ThemeOverrides)
+	}
+}
+
+func TestLoadRejectsUnknownVersion(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "overlay.yaml")
+	if err := os.WriteFile(path, []byte("version: 99\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := Load(path); err == nil {
+		t.Fatal("expected version error")
+	}
+}

internal/config/defaults.yaml

@@ -0,0 +1,4 @@
+version: 1
+extra_packages: []
+disabled_modules: []
+theme_overrides: {}