translate commands on error

lib/classes/GraphStream.ts

@@ -2,7 +2,10 @@
 /* eslint-disable no-inline-comments */
 import { Transform } from 'stream';
 import { GraphStreamJSON } from '../interfaces/GraphStreamJSON';
-import { GraphStreamCommand } from '../enums/GraphStreamCommand';
+import {
+  GraphStreamCommand,
+  translate_command
+} from '../enums/GraphStreamCommand';
 import { validate_name } from '../Helper';
 
 interface Stringable {
@@ -12,7 +15,7 @@ interface Stringable {
 
 export class GraphStream extends Transform {
   private _path: string[] = [];
-  private _state = '';
+  private _state: GraphStreamCommand | '' = '';
   private _directional = false;
 
   public get path (): string {
@@ -24,7 +27,7 @@ export class GraphStream extends Transform {
   }
 
   private expect_state (instr: GraphStreamCommand): void {
-    const states = [];
+    const states: (GraphStreamCommand|'')[] = [];
     if ([
       'cug',
       'cdg'
@@ -50,9 +53,11 @@ export class GraphStream extends Transform {
         break;
     }
     if (!states.includes (this._state)) {
-      throw new Error (`invalid state to execute command ${instr}
-  expected: ${states.join (', ')}
-  actual: ${this._state}`);
+      throw new Error (`invalid state to execute command ${
+        translate_command (instr)}
+  expected: ${states.map ((s) => translate_command (s))
+    .join (', ')}
+  actual: ${translate_command (this._state)}`);
     }
   }