feat(theming): add theme discovery with gruvbox assets

internal/theming/theming.go

@@ -0,0 +1,97 @@
+// Package theming applies a selected colorscheme across starship, zellij,
+// yazi, lazygit, and NvChad. Themes are discovered from embedded manifest
+// files under assets/<id>/theme.yaml at package init time.
+package theming
+
+import (
+	"embed"
+	"fmt"
+	"io/fs"
+	"path/filepath"
+	"sort"
+
+	"gopkg.in/yaml.v3"
+)
+
+//go:embed assets
+var assetsFS embed.FS
+
+// Theme describes a colorscheme discovered under assets/<id>/theme.yaml.
+type Theme struct {
+	ID          string
+	DisplayName string
+	NvChadTheme string
+}
+
+type manifest struct {
+	DisplayName string `yaml:"display_name"`
+	NvChad      string `yaml:"nvchad"`
+}
+
+var discovered []Theme
+
+func init() {
+	themes, err := discover()
+	if err != nil {
+		// Package is embed-only; discovery failure is a programmer error,
+		// not runtime input. Panic so tests surface the mistake early.
+		panic(fmt.Errorf("theming: discover themes: %w", err))
+	}
+	discovered = themes
+}
+
+func discover() ([]Theme, error) {
+	entries, err := fs.ReadDir(assetsFS, "assets")
+	if err != nil {
+		return nil, err
+	}
+	var out []Theme
+	for _, e := range entries {
+		if !e.IsDir() {
+			continue
+		}
+		id := e.Name()
+		m, err := readManifest(id)
+		if err != nil {
+			return nil, fmt.Errorf("theme %q: %w", id, err)
+		}
+		out = append(out, Theme{ID: id, DisplayName: m.DisplayName, NvChadTheme: m.NvChad})
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].ID < out[j].ID })
+	return out, nil
+}
+
+func readManifest(id string) (manifest, error) {
+	data, err := assetsFS.ReadFile(filepath.Join("assets", id, "theme.yaml"))
+	if err != nil {
+		return manifest{}, err
+	}
+	var m manifest
+	if err := yaml.Unmarshal(data, &m); err != nil {
+		return manifest{}, err
+	}
+	if m.DisplayName == "" {
+		return manifest{}, fmt.Errorf("empty display_name")
+	}
+	if m.NvChad == "" {
+		return manifest{}, fmt.Errorf("empty nvchad")
+	}
+	return m, nil
+}
+
+// List returns the themes sorted by ID.
+func List() []Theme {
+	out := make([]Theme, len(discovered))
+	copy(out, discovered)
+	return out
+}
+
+// Get returns the theme with the given ID, if present.
+func Get(id string) (Theme, bool) {
+	for _, t := range discovered {
+		if t.ID == id {
+			return t, true
+		}
+	}
+	return Theme{}, false
+}