chore(simulator): refactor ParallelGatewayBehavior

lib/simulator/behaviors/ParallelGatewayBehavior.js

@@ -15,10 +15,39 @@ export default function ParallelGatewayBehavior(
 
 ParallelGatewayBehavior.prototype.enter = function(context) {
 
+  const {
+    scope
+  } = context;
+
+  const joiningScopes = this._findJoiningScopes(context);
+
+  if (joiningScopes.length) {
+
+    for (const childScope of joiningScopes) {
+
+      if (childScope !== scope) {
+
+        // complete joining child scope
+        this._simulator.destroyScope(childScope.complete(), scope);
+      }
+    }
+
+    this._simulator.exit(context);
+  }
+};
+
+/**
+ * Find scopes that will be joined by this transition.
+ *
+ * @param {Object} enterContext
+ * @return {Scope[]} scopes joined by this transition
+ */
+ParallelGatewayBehavior.prototype._findJoiningScopes = function(enterContext) {
+
   const {
     scope,
     element
-  } = context;
+  } = enterContext;
 
   const sequenceFlows = filterSequenceFlows(element.incoming);
 
@@ -31,25 +60,17 @@ ParallelGatewayBehavior.prototype.enter = function(context) {
     element: element
   });
 
-  const finishedScopes = sequenceFlows
+  const matchingScopes = sequenceFlows
     .map(
       flow => elementScopes
         .find(scope => scope.initiator.element === flow)
     )
     .filter(scope => scope);
 
-  if (finishedScopes.length === sequenceFlows.length) {
-
-    for (const childScope of finishedScopes) {
-
-      if (childScope !== scope) {
-
-        // complete joining child scope
-        this._simulator.destroyScope(childScope.complete(), scope);
-      }
-    }
-
-    this._simulator.exit(context);
+  if (matchingScopes.length === sequenceFlows.length) {
+    return matchingScopes;
+  } else {
+    return [];
   }
 };