Allow sorting widget_cards on homepage

Note that we keep :created_at order as complement to new :order field.

We do this so that current installations will not notice any change in the
sorting of their cards when upgrading, as the default "order" field will always
be 1, so it will continue to sort by the "created_at".

app/models/widget/card.rb

@@ -12,12 +12,14 @@ class Widget::Card < ApplicationRecord
   validates :link_url, presence: true, if: -> { !header? || link_text.present? }
   validates :order, numericality: { greater_than_or_equal_to: 1 }
 
+  scope :sort_by_order, -> { order(:order, :created_at) }
+
   def self.header
     where(header: true)
   end
 
   def self.body
-    where(header: false, cardable_id: nil).order(:created_at)
+    where(header: false, cardable_id: nil).sort_by_order
   end
 
   def header_or_sdg_header?

spec/models/widget/card_spec.rb

@@ -86,5 +86,14 @@ describe Widget::Card do
       expect(Widget::Card.body).not_to include(header)
       expect(Widget::Card.body).not_to include(page_card)
     end
+
+    it "returns cards sorted by defined order, then by 'created_at' when order is equal" do
+      card1 = create(:widget_card, order: 1)
+      card2 = create(:widget_card, order: 3)
+      card3 = create(:widget_card, order: 2)
+      card4 = create(:widget_card, order: 3)
+
+      expect(Widget::Card.body).to eq [card1, card3, card2, card4]
+    end
   end
 end

spec/system/home_spec.rb

@@ -143,6 +143,21 @@ describe "Home" do
     expect(page).not_to have_css(".title", text: "Featured")
   end
 
+  scenario "cards are first sorted by 'order' field, then by 'created_at' when order is equal" do
+    create(:widget_card, title: "Card one", order: 1)
+    create(:widget_card, title: "Card two", order: 3)
+    create(:widget_card, title: "Card three", order: 2)
+    create(:widget_card, title: "Card four", order: 3)
+
+    visit root_path
+
+    within(".cards-container") do
+      expect("CARD ONE").to appear_before("CARD THREE")
+      expect("CARD THREE").to appear_before("CARD TWO")
+      expect("CARD TWO").to appear_before("CARD FOUR")
+    end
+  end
+
   describe "Header Card" do
     scenario "if there is header card with link, the link content is rendered" do
       create(:widget_card, :header, link_text: "Link text", link_url: "consul.dev")