Checks whether a player is checkmated

lib/chess/game.ex

@@ -1,21 +0,0 @@
-defmodule Chess.Game do
-  @moduledoc false
-
-  alias Chess.Board
-  alias Chess.Moves.Piece
-
-  def player_checkmated?(board, colour) do
-    board
-    |> Board.search(%{"colour" => colour})
-  end
-
-  def king_in_check?(board, colour) do
-    king =
-      board
-      |> Board.search(%{"type" => "king", "colour" => colour})
-      |> List.first
-
-    board
-    |> Piece.attacked?(king)
-  end
-end

lib/chess/game_state.ex

@@ -0,0 +1,40 @@
+defmodule Chess.GameState do
+  @moduledoc false
+
+  alias Chess.Board
+  alias Chess.Moves
+  alias Chess.Moves.Piece
+
+  def player_checkmated?(board, colour) do
+    board
+    |> Board.search(%{"colour" => colour})
+    |> Enum.all?(fn({file, rank}) ->
+      board
+      |> cannot_escape_check?({file, rank})
+    end)
+  end
+
+  def cannot_escape_check?(board, {file, rank}) do
+    piece =
+      board
+      |> Board.piece({file, rank})
+
+    board
+    |> Moves.available({file, rank})
+    |> Enum.all?(fn({to_file, to_rank}) ->
+      board
+      |> Board.move_piece(%{"from" => [file, rank], "to" => [to_file, to_rank]})
+      |> king_in_check?(piece["colour"])
+    end)
+  end
+
+  def king_in_check?(board, colour) do
+    king =
+      board
+      |> Board.search(%{"type" => "king", "colour" => colour})
+      |> List.first
+
+    board
+    |> Piece.attacked?(king)
+  end
+end

lib/chess/store/game.ex

@@ -10,6 +10,7 @@ defmodule Chess.Store.Game do
 
   alias Chess.Board
   alias Chess.Store.Game
+  alias Chess.GameState
 
   schema "games" do
     field :board, :map, default: Board.default()
@@ -49,7 +50,7 @@ defmodule Chess.Store.Game do
   end
 
   def validate_king_in_check(changeset, %Game{turn: turn}, %{board: board}) do
-    if Board.king_in_check?(board, turn) do
+    if GameState.king_in_check?(board, turn) do
       changeset
       |> add_error(
         :board,

test/chess/game_state_test.exs

@@ -0,0 +1,94 @@
+defmodule Chess.GameStateTest do
+  @moduledoc false
+
+  use Chess.DataCase
+
+  alias Chess.GameState
+
+  test "king is in check" do
+    board = %{
+      "4,0" => %{"type" => "king", "colour" => "white"},
+      "4,7" => %{"type" => "queen", "colour" => "black"},
+    }
+
+    assert GameState.king_in_check?(board, "white")
+  end
+
+  test "king is not in check" do
+    board = %{
+      "5,0" => %{"type" => "king", "colour" => "white"},
+      "4,7" => %{"type" => "queen", "colour" => "black"},
+    }
+
+    refute GameState.king_in_check?(board, "white")
+  end
+
+  test "king is in check by a knight" do
+    board = %{
+      "4,0" => %{"type" => "king", "colour" => "white"},
+      "3,2" => %{"type" => "knight", "colour" => "black"},
+    }
+
+    assert GameState.king_in_check?(board, "white")
+  end
+
+  test "king is in check by a pawn" do
+    board = %{
+      "4,0" => %{"type" => "king", "colour" => "white"},
+      "3,1" => %{"type" => "pawn", "colour" => "black"},
+    }
+
+    assert GameState.king_in_check?(board, "white")
+  end
+
+  test "king is in checkmate by queen and rook" do
+    board = %{
+      "0,0" => %{"type" => "king", "colour" => "white"},
+      "0,4" => %{"type" => "queen", "colour" => "black"},
+      "1,4" => %{"type" => "rook", "colour" => "black"},
+    }
+
+    assert GameState.player_checkmated?(board, "white")
+  end
+
+  test "king is not in checkmate by a queen" do
+    board = %{
+      "0,0" => %{"type" => "king", "colour" => "white"},
+      "0,4" => %{"type" => "queen", "colour" => "black"},
+    }
+
+    refute GameState.player_checkmated?(board, "white")
+  end
+
+  test "king is checkmate by a queen and a  knight" do
+    board = %{
+      "0,0" => %{"type" => "king", "colour" => "white"},
+      "1,1" => %{"type" => "queen", "colour" => "black"},
+      "2,3" => %{"type" => "knight", "colour" => "black"},
+    }
+
+    assert GameState.player_checkmated?(board, "white")
+  end
+
+  test "knight can block checkmate by queen and rook" do
+    board = %{
+      "0,0" => %{"type" => "king", "colour" => "white"},
+      "2,0" => %{"type" => "knight", "colour" => "white"},
+      "0,5" => %{"type" => "queen", "colour" => "black"},
+      "1,5" => %{"type" => "rook", "colour" => "black"},
+    }
+
+    refute GameState.player_checkmated?(board, "white")
+  end
+
+  test "bishop can take checking queen" do
+    board = %{
+      "0,0" => %{"type" => "king", "colour" => "white"},
+      "2,3" => %{"type" => "bishop", "colour" => "white"},
+      "0,5" => %{"type" => "queen", "colour" => "black"},
+      "1,5" => %{"type" => "rook", "colour" => "black"},
+    }
+
+    refute GameState.player_checkmated?(board, "white")
+  end
+end

test/chess/game_test.ex

@@ -1,43 +0,0 @@
-defmodule Chess.GameTest do
-  @moduledoc false
-
-  use Chess.DataCase
-
-  alias Chess.Game
-
-  test "recognise when the king is in check" do
-    board = %{
-      "4,0" => %{"type" => "king", "colour" => "white"},
-      "4,7" => %{"type" => "queen", "colour" => "black"},
-    }
-
-    assert Game.king_in_check?(board, "white")
-  end
-
-  test "recognise when the king is not in check" do
-    board = %{
-      "5,0" => %{"type" => "king", "colour" => "white"},
-      "4,7" => %{"type" => "queen", "colour" => "black"},
-    }
-
-    refute Game.king_in_check?(board, "white")
-  end
-
-  test "recognize when the king is in check by a knight" do
-    board = %{
-      "4,0" => %{"type" => "king", "colour" => "white"},
-      "3,2" => %{"type" => "knight", "colour" => "black"},
-    }
-
-    assert Game.king_in_check?(board, "white")
-  end
-
-  test "recognize when the king is in check by a pawn" do
-    board = %{
-      "4,0" => %{"type" => "king", "colour" => "white"},
-      "3,1" => %{"type" => "pawn", "colour" => "black"},
-    }
-
-    assert Game.king_in_check?(board, "white")
-  end
-end