translate commands on error

lib/enums/GraphStreamCommand.ts

@@ -1,11 +1,28 @@
 /* eslint-disable line-comment-position */
 /* eslint-disable no-inline-comments */
-export type GraphStreamCommand =
-  'cn'| // create node
-  'en'| // end node
-  'cug'| // create unordered graph
-  'cdg'| // create directional graph
-  'csg'| // create subgraph
-  'eg'| // end graph
-  'at'| // add attributes
-  'ce' // create edge
+type GraphStreamCommand =
+  'cn'|
+  'en'|
+  'cug'|
+  'cdg'|
+  'csg'|
+  'eg'|
+  'at'|
+  'ce'
+
+function translate_command (cmd: GraphStreamCommand|''): string {
+  const translations = {
+    cn:  'create node',
+    en:  'end node',
+    cug: 'create unordered graph',
+    cdg: 'create directional graph',
+    csg: 'create subgraph',
+    eg:  'end graph',
+    at:  'attributes',
+    ce:  'create edge',
+    '':  'start'
+  };
+  return translations[cmd];
+}
+
+export { GraphStreamCommand, translate_command };