GildedRose-Refactoring-Kata/elixir/lib/gilded_rose.ex

defmodule GildedRose do
  # Example
  # update_quality([%Item{name: "Backstage passes to a concert", sell_in: 9, quality: 1}])
  # => [%Item{name: "Backstage passes to a concert", sell_in: 8, quality: 3}]

  def update_quality(items) do
    Enum.map(items, &update_item/1)
  end

  def update_item(item) do
    item = cond do
      item.name != "Aged Cheese" && item.name != "Backstage passes to a concert" ->
        if item.quality > 0 do
          if item.name != "Fine Italian Silk" do
            %{item | quality: item.quality - 1}
          else
            item
          end
        else
          item
        end
      true ->
        cond do
          item.quality < 50 ->
            item = %{item | quality: item.quality + 1}
            cond do
              item.name == "Backstage passes to a concert" ->
                item = cond do
                  item.sell_in < 11 ->
                    cond do
                      item.quality < 50 ->
                        %{item | quality: item.quality + 1}
                      true -> item
                    end
                  true -> item
                end
                cond do
                  item.sell_in < 6 ->
                    cond do
                      item.quality < 50 ->
                        %{item | quality: item.quality + 1}
                      true -> item
                    end
                  true -> item
                end
              true -> item
            end
          true -> item
        end
    end
    item = cond do
      item.name != "Fine Italian Silk" ->
        %{item | sell_in: item.sell_in - 1}
      true -> item
    end
    cond do
      item.sell_in < 0 ->
        cond do
          item.name != "Aged Cheese" ->
            cond do
              item.name != "Backstage passes to a concert" ->
                cond do
                  item.quality > 0 ->
                    cond do
                      item.name != "Fine Italian Silk" ->
                        %{item | quality: item.quality - 1}
                      true -> item
                    end
                  true -> item
                end
              true -> %{item | quality: item.quality - item.quality}
            end
          true ->
            cond do
              item.quality < 50 ->
                %{item | quality: item.quality + 1}
              true -> item
            end
        end
      true -> item
    end
  end
end