feat(vault): initialize fresh instances with public example notes

internal/vault/examples.go

@@ -0,0 +1,72 @@
+package vault
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"path/filepath"
+)
+
+// SeedExamples populates only a completely unused vault, before the watcher starts.
+// Existing folders, hidden files, icons, or recycled notes count as user data.
+func (v *Vault) SeedExamples(examples fs.FS) (err error) {
+	v.mu.Lock()
+	defer v.mu.Unlock()
+
+	entries, err := os.ReadDir(v.root)
+	if err != nil {
+		return err
+	}
+	for _, entry := range entries {
+		if entry.Name() != metaDir || !entry.IsDir() {
+			return nil
+		}
+	}
+	metadata, err := os.ReadDir(filepath.Join(v.root, metaDir))
+	if err != nil {
+		return err
+	}
+	for _, entry := range metadata {
+		if entry.Name() != "trash" || !entry.IsDir() {
+			return nil
+		}
+	}
+	trash, err := os.ReadDir(v.trash)
+	if err != nil || len(trash) != 0 {
+		return err
+	}
+
+	stage, err := os.MkdirTemp(v.root, tmpPrefix+"examples-")
+	if err != nil {
+		return err
+	}
+	cleanup := true
+	defer func() {
+		if cleanup {
+			err = errors.Join(err, os.RemoveAll(stage))
+		}
+	}()
+	if err = os.CopyFS(stage, examples); err != nil {
+		return err
+	}
+	entries, err = os.ReadDir(stage)
+	if err != nil {
+		return err
+	}
+	var published []string
+	for _, entry := range entries {
+		name := entry.Name()
+		if err = os.Rename(filepath.Join(stage, name), filepath.Join(v.root, name)); err != nil {
+			for _, previous := range published {
+				if rollback := os.Rename(filepath.Join(v.root, previous), filepath.Join(stage, previous)); rollback != nil {
+					// Preserve the staging directory if it contains the only copy of any files.
+					cleanup = false
+					err = errors.Join(err, rollback)
+				}
+			}
+			return err
+		}
+		published = append(published, name)
+	}
+	return nil
+}