Merge pull request #736 from CommitChange/add-event-stack

Add EventStack from #456

javascripts/src/lib/EventStack.spec.ts

@@ -0,0 +1,41 @@
+// License: LGPL-3.0-or-later
+import EventStack from './EventStack';
+
+describe('EventStack', () => {
+ const firstEvent = {type:"first"}
+ describe('.top', () => {
+ it('returns undefined if no events have been added', () => {
+ const stack = new EventStack();
+ expect(stack.top).toBeUndefined();
+ })
+
+ it('returns the top event after an event is pushed', () => {
+ const stack = new EventStack();
+ stack.push(firstEvent)
+ expect(stack.top).toEqual(firstEvent);
+ })
+ })
+
+ describe('.push', () => {
+ it("returns event when an event is added", () => {
+ const stack = new EventStack();
+ expect(stack.push(firstEvent)).toEqual(firstEvent)
+
+ });
+
+ it ("returns undefined when the event isn't added because it's already the top", () => {
+ const stack = new EventStack();
+ stack.push(firstEvent)
+ expect(stack.push(firstEvent)).toBeUndefined();
+ })
+
+ it("returns and adds event when it doesn't match another object based on deep comparison", () => {
+ const stack = new EventStack();
+ stack.push(firstEvent)
+
+ const secondEvent = {type:"first", but:"different"}
+ expect(stack.push(secondEvent)).toEqual(secondEvent);
+ })
+ })
+
+})

javascripts/src/lib/EventStack.ts

@@ -0,0 +1,34 @@
+// License: LGPL-3.0-or-later
+import last from 'lodash/last';
+import isEqual from 'lodash/isEqual'
+
+
+interface EventObjectBase {
+ type: string
+}
+
+/**
+ * A simple class for recording the list of events that occurred for a system
+ */
+export default class EventStack<TEventObjects extends EventObjectBase> {
+
+ private events:Array<TEventObjects> = []
+
+ push(event: TEventObjects): TEventObjects | undefined {
+ if (!this.top) {
+ this.events.push(event)
+ return event;
+ }
+ else if (!isEqual(this.top, event)) {
+ this.events.push(event);
+ return event;
+ }
+ return undefined;
+ }
+
+ get top(): TEventObjects | undefined {
+ return last(this.events);
+ }
+
+
+}