Debounce auto save for rapid config changes

package/spec/editor/models/mixins/configurationContainer-spec.js

@@ -102,6 +102,91 @@ describe('configurationContainer', () => {
     expect(model.save).toHaveBeenCalled();
   });
 
+  it('debounces auto save for rapid changes', () => {
+    jest.useFakeTimers();
+    const Model = Backbone.Model.extend({
+      mixins: [configurationContainer({autoSave: true})],
+    });
+    const model = new Model({id: 5, configuration: {some: 'value'}});
+    model.save = jest.fn();
+
+    model.configuration.set('some', 'a');
+    model.configuration.set('some', 'b');
+    model.configuration.set('some', 'c');
+
+    expect(model.save).toHaveBeenCalledTimes(1);
+
+    jest.runAllTimers();
+
+    expect(model.save).toHaveBeenCalledTimes(2);
+    jest.useRealTimers();
+  });
+
+  it('resets trailing save delay on each new change', () => {
+    jest.useFakeTimers();
+    const Model = Backbone.Model.extend({
+      mixins: [configurationContainer({autoSave: true})],
+    });
+    const model = new Model({id: 5, configuration: {some: 'value'}});
+    model.save = jest.fn();
+
+    model.configuration.set('some', 'a');
+    expect(model.save).toHaveBeenCalledTimes(1);
+
+    jest.advanceTimersByTime(300);
+    model.configuration.set('some', 'b');
+
+    jest.advanceTimersByTime(300);
+    expect(model.save).toHaveBeenCalledTimes(1);
+
+    jest.advanceTimersByTime(200);
+    expect(model.save).toHaveBeenCalledTimes(2);
+    jest.useRealTimers();
+  });
+
+  it('does not fire trailing save for single change', () => {
+    jest.useFakeTimers();
+    const Model = Backbone.Model.extend({
+      mixins: [configurationContainer({autoSave: true})],
+    });
+    const model = new Model({id: 5, configuration: {some: 'value'}});
+    model.save = jest.fn();
+
+    model.configuration.set('some', 'other value');
+
+    expect(model.save).toHaveBeenCalledTimes(1);
+
+    jest.runAllTimers();
+
+    expect(model.save).toHaveBeenCalledTimes(1);
+    jest.useRealTimers();
+  });
+
+  it('does not fire trailing save for destroyed model', () => {
+    jest.useFakeTimers();
+    const Model = Backbone.Model.extend({
+      mixins: [
+        configurationContainer({autoSave: true}),
+        delayedDestroying
+      ],
+    });
+    const model = new Model({id: 5, configuration: {some: 'value'}}, {urlRoot: '/models'});
+    model.save = jest.fn();
+
+    model.configuration.set('some', 'a');
+    model.configuration.set('some', 'b');
+
+    expect(model.save).toHaveBeenCalledTimes(1);
+
+    model.destroyWithDelay();
+    testContext.requests[0].respond(204, { 'Content-Type': 'application/json' }, '');
+
+    jest.runAllTimers();
+
+    expect(model.save).toHaveBeenCalledTimes(1);
+    jest.useRealTimers();
+  });
+
   it('does not auto save new model', () => {
     const Model = Backbone.Model.extend({
       mixins: [configurationContainer({autoSave: true})],

package/src/editor/models/mixins/configurationContainer.js

@@ -44,14 +44,21 @@ export function configurationContainer({configurationModel, autoSave, includeAtt
       this.configuration = new configurationModel(this.get('configuration'));
       this.configuration.parent = this;
 
-      this.listenTo(this.configuration, 'change', function(model, options) {
-        if (!this.isNew() &&
-            (!this.isDestroying || !this.isDestroying()) &&
-            (!this.isDestroyed || !this.isDestroyed()) &&
-            autoSave &&
-            options.autoSave !== false) {
+      const canSave = () =>
+        !this.isNew() &&
+        (!this.isDestroying || !this.isDestroying()) &&
+        (!this.isDestroyed || !this.isDestroyed());
+
+      const debouncedSave = leadingTrailingDebounce(() => {
+        if (canSave()) {
           this.save();
         }
+      }, 500);
+
+      this.listenTo(this.configuration, 'change', function(model, options) {
+        if (canSave() && autoSave && options.autoSave !== false) {
+          debouncedSave();
+        }
 
         this.trigger('change:configuration', this, undefined, options);
 
@@ -81,3 +88,29 @@ export function configurationContainer({configurationModel, autoSave, includeAtt
     }
   };
 }
+
+function leadingTrailingDebounce(fn, delay) {
+  let timer = null;
+  let pendingTrailing = false;
+
+  function debounced() {
+    if (timer === null) {
+      fn();
+    }
+    else {
+      pendingTrailing = true;
+      clearTimeout(timer);
+    }
+
+    timer = setTimeout(() => {
+      timer = null;
+
+      if (pendingTrailing) {
+        pendingTrailing = false;
+        fn();
+      }
+    }, delay);
+  }
+
+  return debounced;
+}