getCategories() // Wraps ajax call and returns payload with array of categories
      .switchMap(categories => Observable.from(categories))
      .mergeMap(category =>
        getSubCategories(category) // Wraps ajax call and returns payload with array of sub categories
          .catch(err => {
            console.error('Error when fetching sub categories for category:', category);
            console.error(err);
            return Observable.empty();
          })
      )
      .mergeMap(subCategories => Observable.from(subCategories))
      .mergeMap(subCategory =>
        getProducts(subCategory) // Wraps ajax call and returns payload with array of products
        .catch(err => {
          console.error('Error when fetching products for sub category:', subCategory);
          console.error(err);
          return Observable.empty();
        })
      )
      .mergeMap(products => Observable.from(products))
      .mergeMap(product =>
        getProductDetails(product) // Wraps ajax call and returns payload with product details
        .catch(err => {
          console.error('Error when fetching product details for product:', product);
          console.error(err);
          return Observable.empty();
        })
      )
      .mergeMap(productDetails => saveToDb(productDetails))
      .catch(err => {
        console.error(err);
      })
      .subscribe();