ostree: ostree parameter validation and resolve function

Validates the ostree parameters and resolves the parent ID.

internal/ostree/ostree.go

@@ -9,6 +9,8 @@ import (
 	"path"
 	"regexp"
 	"strings"
+
+	"github.com/osbuild/osbuild-composer/internal/distro"
 )
 
 var ostreeRefRE = regexp.MustCompile(`^(?:[\w\d][-._\w\d]*\/)*[\w\d][-._\w\d]*$`)
@@ -51,3 +53,32 @@ func ResolveRef(location, ref string) (string, error) {
 	}
 	return parent, nil
 }
+
+func ResolveParams(params OSTreeRequest, imageType distro.ImageType) (OSTreeRequest, error) {
+	resolved := OSTreeRequest{}
+	resolved.Ref = params.Ref
+	// if ref is not provided, use distro default
+	if resolved.Ref == "" {
+		resolved.Ref = imageType.OSTreeRef()
+	} else if !VerifyRef(params.Ref) { // only verify if specified in params
+		return resolved, fmt.Errorf("Invalid ostree ref")
+	}
+
+	resolved.URL = params.URL
+	// Fetch parent ostree commit from ref + url if commit is not
+	// provided. The parameter name "parent" is perhaps slightly misleading
+	// as it represent whatever commit sha the image type requires, not
+	// strictly speaking just the parent commit.
+	if resolved.Ref != "" && resolved.URL != "" {
+		if params.Parent != "" {
+			return resolved, fmt.Errorf("Supply at most one of Parent and URL")
+		}
+
+		parent, err := ResolveRef(resolved.URL, resolved.Ref)
+		if err != nil {
+			return resolved, err
+		}
+		resolved.Parent = parent
+	}
+	return resolved, nil
+}