shopping-cart.service.ts

import { Observable } from 'rxjs/Observable';
import { ShoppingCart } from './models/shopping-cart';
import { Injectable } from '@angular/core';
import { AngularFireDatabase, FirebaseObjectObservable } from 'angularfire2/database';
import { Product } from './models/product';
import 'rxjs/add/operator/take';
import 'rxjs/add/operator/map';
import { promise } from 'protractor';

@Injectable()
export class ShoppingCartService {

  constructor(private db: AngularFireDatabase) { }
  
  async getCart(): Promise<Observable<ShoppingCart>>{
    let cartId =await this.getOrCreateCartId();
   return this.db.object('/shopping-carts/' + cartId)
   .map(x => new ShoppingCart(x.items));
  }

  async addToCart(product: Product){
    this.updateItem(product, 1);
  }

  async removeFromCart(product: Product){
    this.updateItem(product,-1);
  }

  async clearCart(){
    let cartId = await this.getOrCreateCartId();
    this.db.object('/shopping-carts/' + cartId + '/items').remove();
  }

  private create(){
    return this.db.list('/shopping-carts').push({
      dateCtreted: new Date().getTime()
    });
  }
  
  private getItem(cartId: string, productId: string){
    return this.db.object('/shopping-carts/' + cartId + '/items/' + productId);
  }

  private async getOrCreateCartId(): Promise<string>{
    let cartId=localStorage.getItem('cartId');
    if(cartId) return cartId;
    
    let result = await this.create();
    localStorage.setItem('cartId', result.key);
    return result.key;
   
  }

  private async updateItem(product:Product, change: number){
    let cartId = await this.getOrCreateCartId();
    let item$ = this.getItem(cartId, product.$key);
    item$.take(1).subscribe(item =>{
      let quantity = (item.quantity || 0)+ change ; 
      if(quantity === 0) item$.remove();
      else item$.update({ 
        title: product.title,
        imageUrl: product.imageUrl,
        price: product.price,
        quantity: quantity
      });
  
    });

  }

}