1 files changed, 99 insertions, 0 deletions
diff --git a/internal/fsutil/path.go b/internal/fsutil/path.go
new file mode 100644
index 0000000..c872a5b
--- /dev/null
+++ b/internal/fsutil/path.go
@@ -0,0 +1,99 @@
+package fsutil
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"os/user"
+	"path/filepath"
+	"strings"
+)
+
+// ResolveRootPath expands and validates the supplied root path. When the
+// caller did not specify a value, defaultValue is used and created on demand.
+func ResolveRootPath(input, defaultValue string) (string, error) {
+	value, isDefault := normalizeRootInput(input, defaultValue)
+	expanded, err := expandPath(value)
+	if err != nil {
+		return "", fmt.Errorf("cannot expand root path %q: %w", value, err)
+	}
+	abs, err := filepath.Abs(expanded)
+	if err != nil {
+		return "", fmt.Errorf("cannot resolve root path %q: %w", expanded, err)
+	}
+	info, err := ensureRootExists(abs, isDefault)
+	if err != nil {
+		return "", err
+	}
+	if !info.IsDir() && !info.Mode().IsRegular() {
+		return "", fmt.Errorf("root path %q is not a file or directory", abs)
+	}
+	return abs, nil
+}
+
+func normalizeRootInput(input, defaultValue string) (value string, isDefault bool) {
+	trimmed := strings.TrimSpace(input)
+	if trimmed == "" {
+		return defaultValue, true
+	}
+	return trimmed, false
+}
+
+func ensureRootExists(path string, allowCreate bool) (fs.FileInfo, error) {
+	info, err := os.Stat(path)
+	if err == nil {
+		return info, nil
+	}
+	if !errors.Is(err, fs.ErrNotExist) {
+		return nil, fmt.Errorf("cannot access root path %q: %w", path, err)
+	}
+	if !allowCreate {
+		return nil, fmt.Errorf("root path does not exist: %s", path)
+	}
+	if mkErr := os.MkdirAll(path, 0o755); mkErr != nil {
+		return nil, fmt.Errorf("cannot create default directory %q: %w", path, mkErr)
+	}
+	info, err = os.Stat(path)
+	if err != nil {
+		return nil, fmt.Errorf("cannot stat default directory %q: %w", path, err)
+	}
+	return info, nil
+}
+
+func expandPath(p string) (string, error) {
+	if p == "" || p[0] != '~' {
+		return p, nil
+	}
+	if len(p) == 1 {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return "", err
+		}
+		return home, nil
+	}
+	if p[1] == '/' {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return "", err
+		}
+		return filepath.Join(home, p[2:]), nil
+	}
+	username, rest := splitUserPath(p)
+	usr, err := user.Lookup(username)
+	if err != nil {
+		return "", err
+	}
+	if rest == "" {
+		return usr.HomeDir, nil
+	}
+	return filepath.Join(usr.HomeDir, rest), nil
+}
+
+func splitUserPath(p string) (string, string) {
+	sep := strings.IndexRune(p, '/')
+	if sep == -1 {
+		return p[1:], ""
+	}
+	return p[1:sep], p[sep:]
+}