Add Rook moves

lib/chess/moves.ex

@@ -2,6 +2,7 @@ defmodule Chess.Moves do
   @moduledoc false
 
   alias Chess.Moves.Pawn
+  alias Chess.Moves.Rook
 
   def available(board, {file, rank}) do
     piece = board["#{file},#{rank}"]
@@ -9,6 +10,8 @@ defmodule Chess.Moves do
     case piece do
       %{"type" => "pawn"} ->
         Pawn.moves(board, {file, rank})
+      %{"type" => "rook"} ->
+        Rook.moves(board, {file, rank})
     end
   end
 end

lib/chess/moves/rook.ex

@@ -0,0 +1,30 @@
+defmodule Chess.Moves.Rook do
+  @moduledoc false
+
+  def moves(board, {file, rank}) do
+    moves_north(board, {file, rank}) ++
+      moves_south(board, {file, rank}) ++
+      moves_east(board, {file, rank}) ++
+      moves_west(board, {file, rank})
+  end
+
+  defp moves_north(_board, {_file, 7}), do: []
+  defp moves_north(board, {file, rank}) do
+    [{file, rank + 1} | moves_north(board, {file, rank + 1})]
+  end
+
+  defp moves_south(_board, {_file, 0}), do: []
+  defp moves_south(board, {file, rank}) do
+    [{file, rank - 1} | moves_south(board, {file, rank - 1})]
+  end
+
+  defp moves_east(_board, {7, _rank}), do: []
+  defp moves_east(board, {file, rank}) do
+    [{file + 1, rank} | moves_east(board, {file + 1, rank})]
+  end
+
+  defp moves_west(_board, {0, _rank}), do: []
+  defp moves_west(board, {file, rank}) do
+    [{file - 1, rank} | moves_west(board, {file - 1, rank})]
+  end
+end

test/chess/moves/rook_test.exs

@@ -0,0 +1,31 @@
+defmodule Chess.Moves.RookTest do
+  use Chess.DataCase
+
+  alias Chess.Moves.Rook
+
+  test "rooks can move horizontally or vertically" do
+    board = %{"4,5" => %{"type" => "rook", "colour" => "white"}}
+    moves = Rook.moves(board, {4, 5})
+
+    expected_moves = Enum.sort([
+      {4, 0}, {4, 1}, {4, 2}, {4, 3}, {4, 4}, {4, 6}, {4, 7},
+      {0, 5}, {1, 5}, {2, 5}, {3, 5}, {5, 5}, {6, 5}, {7, 5}, 
+    ])
+    assert Enum.sort(moves) == expected_moves
+  end
+
+  test "rook cannot move further than the edge" do
+    board = %{"0,0" => %{type: :rook, colour: :white}}
+    moves = Rook.moves(board, {0, 0})
+
+    expected_moves = Enum.sort([
+      {0, 1}, {0, 2}, {0, 3}, {0, 4}, {0, 5}, {0, 6}, {0, 7},
+      {1, 0}, {2, 0}, {3, 0}, {4, 0}, {5, 0}, {6, 0}, {7, 0}, 
+    ])
+    assert Enum.sort(moves) == expected_moves
+  end
+
+  def board do
+    Chess.Board.default
+  end
+end