King moves

lib/chess/moves.ex

@@ -6,6 +6,7 @@ defmodule Chess.Moves do
   alias Chess.Moves.Knight
   alias Chess.Moves.Rook
   alias Chess.Moves.Queen
+  alias Chess.Moves.King
 
   def available(board, {file, rank}) do
     piece = board["#{file},#{rank}"]
@@ -20,7 +21,7 @@ defmodule Chess.Moves do
       %{"type" => "knight"} ->
         Knight.moves(board, {file, rank})
       %{"type" => "king"} ->
-        []
+        King.moves(board, {file, rank})
       %{"type" => "queen"} ->
         Queen.moves(board, {file, rank})
     end

lib/chess/moves/king.ex

@@ -0,0 +1,15 @@
+defmodule Chess.Moves.King do
+  @moduledoc false
+
+  def moves(_board, {file, rank}) do
+    patterns
+    |> Enum.map(fn ({fv, rv}) -> {file + fv, rank + rv} end)
+    |> Enum.reject(fn ({file, rank}) ->
+      file < 0 || rank < 0 || file > 7 || rank > 7
+    end)
+  end
+
+  defp patterns do
+    [{1, 1}, {1, 0}, {1, -1}, {0, -1}, {-1, -1}, {-1, 0}, {-1, 1}, {0, 1}]
+  end
+end

test/chess/moves/king_test.exs

@@ -0,0 +1,29 @@
+defmodule Chess.Moves.KingTest do
+  use Chess.DataCase
+
+  alias Chess.Moves
+
+  test "kings can move one square in any direction" do
+    board = %{"4,5" => %{"type" => "king", "colour" => "white"}}
+    moves = Moves.available(board, {4, 5})
+
+    expected_moves = Enum.sort([
+      {3, 4}, {4, 4}, {5, 4}, {5, 5}, {5, 6}, {4, 6}, {3, 6}, {3, 5},
+    ])
+    assert Enum.sort(moves) == expected_moves
+  end
+
+  test "knights cannot move beyond the edges of the board" do
+    board = %{"0,0" => %{"type" => "knight", "colour" => "white"}}
+    moves = Moves.available(board, {0, 0})
+
+    expected_moves = Enum.sort([
+      {1, 2}, {2, 1}
+    ])
+    assert Enum.sort(moves) == expected_moves
+  end
+
+  def board do
+    Chess.Board.default
+  end
+end