card_shark

defmodule CardShark.Compare do
  @moduledoc "Module for comparing various cards and determining a 'winner'"

  alias CardShark.Card

  @doc """
  Return the high card from the given set, along with it's index.

  Accepts an optional trump suit atom

  The list of cards given should be in the order played, and it is assumed
  that the first card played determines the suit other cards need to be to be
  the high card (or be a trump card)

  ## Examples
      iex> cards = [%Card{face: "3", suit: :spades, value: 3}]
      iex> Compare.high_card(cards)
      {%Card{face: "3", suit: :spades, value: 3}, 0}

      iex> cards = [
      ...>   %Card{face: "3", suit: :spades, value: 3},
      ...>   %Card{face: "6", suit: :diamonds, value: 6}
      ...> ]
      iex> Compare.high_card(cards)
      {%Card{face: "3", suit: :spades, value: 3}, 0}

      iex> cards = [
      ...>   %Card{face: "3", suit: :clubs, value: 3},
      ...>   %Card{face: "8", suit: :clubs, value: 8}
      ...> ]
      iex> Compare.high_card(cards)
      {%Card{face: "8", suit: :clubs, value: 8}, 1}

      iex> cards = [
      ...>   %Card{face: "3", suit: :clubs, value: 3},
      ...>   %Card{face: "ace", suit: :spades, value: 14},
      ...>   %Card{face: "king", suit: :clubs, value: 13}
      ...> ]
      iex> Compare.high_card(cards)
      {%Card{face: "king", suit: :clubs, value: 13}, 2}

      iex> cards = [
      ...>   %Card{face: "3", suit: :clubs, value: 3},
      ...>   %Card{face: "2", suit: :spades, value: 2},
      ...>   %Card{face: "king", suit: :clubs, value: 13}
      ...> ]
      iex> Compare.high_card(cards, :spades)
      {%Card{face: "2", suit: :spades, value: 2}, 1}

      iex> cards = [
      ...>   %Card{face: "2", suit: :spades, value: 2},
      ...>   %Card{face: "3", suit: :clubs, value: 3},
      ...>   %Card{face: "king", suit: :clubs, value: 13}
      ...> ]
      iex> Compare.high_card(cards, :spades)
      {%Card{face: "2", suit: :spades, value: 2}, 0}

      iex> cards = [
      ...>   %Card{face: "2", suit: :spades, value: 2},
      ...>   %Card{face: "3", suit: :clubs, value: 3},
      ...>   %Card{face: "king", suit: :spades, value: 13}
      ...> ]
      iex> Compare.high_card(cards, :diamonds)
      {%Card{face: "king", suit: :spades, value: 13}, 2}
  """
  @spec high_card([%Card{}], atom | nil) :: {}
  def high_card(cards, trump \\ nil) when is_list(cards) and is_atom(trump) do
    [first | rest] = Enum.with_index(cards)

    compare(first, rest, trump)
  end

  @spec compare({%Card{}, integer}, [%Card{}], atom) :: {%Card{}, integer}
  defp compare({_card, _index} = high, [], _trump), do: high

  # when a trump card is encountered and it isn't the suit of the high card
  defp compare({%Card{suit: h_suit}, _}, [{%Card{suit: trump}, _} = card | rest], trump)
       when h_suit != trump do
    compare(card, rest, trump)
  end

  # when the card suits match then values are compared
  defp compare(
         {%Card{suit: suit, value: h_value}, _},
         [{%Card{suit: suit, value: value}, _} = card | rest],
         trump
       )
       when value > h_value do
    compare(card, rest, trump)
  end

  defp compare({%Card{}, _} = high, [{%Card{}, _} | rest], trump) do
    compare(high, rest, trump)
  end
end