introduce TaskOnce

ts/taskbuffer.classes.taskonce.ts

@@ -0,0 +1,24 @@
+import * as plugins from './taskbuffer.plugins'
+
+import { Task,  ITaskFunction} from './taskbuffer.classes.task'
+
+/**
+ * TaskOnce is run exactly once, no matter how often it is triggered
+ */
+export class TaskOnce extends Task {
+  hasTriggered: boolean = false
+  constructor (optionsArg: {
+    name?: string,
+    taskFunction: ITaskFunction
+  }) {
+    super({
+      name: optionsArg.name,
+      taskFunction: async () => {
+        if (!this.hasTriggered) {
+          this.hasTriggered = true
+          await optionsArg.taskFunction()
+        }
+      }
+    })
+  }
+}