From 8c9d52a0a43618a9a21ca3690d7a27c043d014ea Mon Sep 17 00:00:00 2001
From: Dan Barber <github@danbarber.me>
Date: Mon, 12 Mar 2018 15:39:16 -0400
Subject: [PATCH] King moves

---
 lib/chess/moves.ex             |  3 ++-
 lib/chess/moves/king.ex        | 15 +++++++++++++++
 test/chess/moves/king_test.exs | 29 +++++++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 1 deletion(-)
 create mode 100644 lib/chess/moves/king.ex
 create mode 100644 test/chess/moves/king_test.exs

diff --git a/lib/chess/moves.ex b/lib/chess/moves.ex
index b863d9e..da153ae 100644
--- a/lib/chess/moves.ex
+++ b/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
diff --git a/lib/chess/moves/king.ex b/lib/chess/moves/king.ex
new file mode 100644
index 0000000..a556235
--- /dev/null
+++ b/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
diff --git a/test/chess/moves/king_test.exs b/test/chess/moves/king_test.exs
new file mode 100644
index 0000000..5cc8b2b
--- /dev/null
+++ b/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