Allow signature requests only on current published version

Requesting a signature only validated that the version was PUBLISHED, so a
signature could be requested on a superseded (older) published version. Reject
versions that are not the document's current published major/minor, and hide
the request button in the console for non-current versions.

Signed-off-by: Sacha Al Himdani <sacha@probo.com>

pkg/probo/document_service.go

@@ -68,6 +68,9 @@ type (
 	ErrDocumentVersionNotPublished struct {
 	}
 
+	ErrDocumentVersionNotCurrent struct {
+	}
+
 	ErrDocumentVersionPendingApproval struct {
 	}
 
@@ -270,6 +273,10 @@ func (e ErrDocumentVersionNotPublished) Error() string {
 	return "document version is not published"
 }
 
+func (e ErrDocumentVersionNotCurrent) Error() string {
+	return "document version is not the current published version"
+}
+
 func (e ErrDocumentVersionPendingApproval) Error() string {
 	return "cannot publish a document version that is pending approval"
 }
@@ -1104,6 +1111,13 @@ func (s *DocumentService) RequestSignature(
 				return &ErrDocumentVersionNotPublished{}
 			}
 
+			if document.CurrentPublishedMajor == nil ||
+				document.CurrentPublishedMinor == nil ||
+				documentVersion.Major != *document.CurrentPublishedMajor ||
+				documentVersion.Minor != *document.CurrentPublishedMinor {
+				return &ErrDocumentVersionNotCurrent{}
+			}
+
 			profile := &coredata.MembershipProfile{}
 			if err := profile.LoadByID(ctx, tx, scope, req.Signatory); err != nil {
 				return fmt.Errorf("cannot load signatory profile: %w", err)