Shopping cart in EmberJS: trying to add product model to cart model

A complete newbie to Emberjs here and a sort of newbie to web development. I'm trying to build a very simple e-tailer website in order to get familiar with Ember. The process where I'm getting stuck is getting my product model to get added to cart.

The details of the project: emberjs: 1.13.2 ember-data: 1.13.4 ember-cli: 0.2.7

The backend is being mocked by ember-cli-mirage

The code is as follows:

models/product.js

import DS from 'ember-data';

export default DS.Model.extend({
  name: DS.attr('string'),
  description: DS.attr('string'),
  category: DS.attr('string'),
  price: DS.attr('number'),
  quantityInStock: DS.attr('number'),
  imageUrl: DS.attr('string')
});

models/item.js

import DS from 'ember-data';

export default DS.Model.extend({
  product: DS.belongsTo('product'),
  cart: DS.belongsTo('cart'),
  quantity: DS.attr('number'),
  subTotal: function() {
    return this.get('product').get('price') * this.get('quantity');
  }.property('product', 'quantity')
});

models/cart.js

import DS from 'ember-data';

export default DS.Model.extend({
  items: DS.hasMany('item')
});

controllers/products.js

import Ember from 'ember';

export default Ember.Controller.extend({
  needs: ['cart'],
  cart: Ember.computed.alias('controllers.cart'),
  actions: {
    addToCart: function(product) {
      this.get('cart').add(product);
    }
  }
});

controllers/cart.js

import Ember from 'ember';

export default Ember.Controller.extend({
  add: function(product) {

  }
});

What I can't figure out is how to get the cart controller to handle the action. I think the code is supposed to do this:

1. find the cart model from the data store
2. check to see if the item being added to the cart is already in the cart
3. if it is: increment its property by 1
4. if it is not: create a new item, make it belong to the cart, give it the product, give it a quantity of 1. Then, save it.
5. Finally, add this item to the cart. Save the cart to the backend.

Some notes, thoughts & other problems

Note #1: I only have routes to handle product and cart on the backend (I don't see why I would handle item since it would be in the cart hash).

But, saving an item makes a call to the back-end. I'm guessing I should save the item in localstorage? Not sure how to go about doing that in the latest version of ember-data.

Note #2: I don't use any dynamic urls. all the products load on a single page. There are only two routes: products and cart.

Note #3: the item model is a line item.

Note #4: I'm not even sure if this is the best way to handle it. Should I just load multiple models on the product route. Would that simplify it?

I'm not sure if I should include any other code but the github is here:

ember-responsive-retailer

Thanks a lot!