From 77475cf4586c488ce4c538853a65d3511ac29d9f Mon Sep 17 00:00:00 2001
From: Dan Barber <github@danbarber.me>
Date: Wed, 18 Jan 2017 18:20:10 +0000
Subject: [PATCH] Add moves model and tests for pawns

---
 test/models/moves_test.exs | 39 ++++++++++++++++++++++++++++++++++++++
 web/models/moves.ex        | 21 ++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 test/models/moves_test.exs
 create mode 100644 web/models/moves.ex

diff --git a/test/models/moves_test.exs b/test/models/moves_test.exs
new file mode 100644
index 0000000..33457dc
--- /dev/null
+++ b/test/models/moves_test.exs
@@ -0,0 +1,39 @@
+defmodule Chess.MovesTest do
+  use Chess.ModelCase
+
+  alias Chess.Moves
+
+  test "white pawn can move forward one or two spaces" do
+    moves = Moves.available(board(), {4, 1})
+
+    expected_moves = [{4, 2}, {4, 3}]
+    assert moves == expected_moves
+  end
+
+  test "black pawn can move forward one or two spaces" do
+    moves = Moves.available(board(), {4, 6})
+
+    expected_moves = [{4, 5}, {4, 4}]
+    assert moves == expected_moves
+  end
+
+  test "white pawn not on starting square can move forward one space" do
+    board = %{ "4,2" => %{type: :pawn, colour: :white} }
+    moves = Moves.available(board, {4, 2})
+
+    expected_moves = [{4, 3}]
+    assert moves == expected_moves
+  end
+
+  test "black pawn not on starting square can move forward one space" do
+    board = %{ "4,5" => %{type: :pawn, colour: :black} }
+    moves = Moves.available(board, {4, 5})
+
+    expected_moves = [{4, 4}]
+    assert moves == expected_moves
+  end
+
+  def board do
+    Chess.Board.default
+  end
+end
diff --git a/web/models/moves.ex b/web/models/moves.ex
new file mode 100644
index 0000000..c66fc3f
--- /dev/null
+++ b/web/models/moves.ex
@@ -0,0 +1,21 @@
+defmodule Chess.Moves do
+  def available(board, square) do
+    {file, rank} = square
+    piece = board["#{file},#{rank}"]
+
+    case piece do
+      %{type: :pawn, colour: :white} ->
+        case rank do
+          1 -> [{file, rank + 1}, {file, rank + 2}]
+          _ -> [{file, rank + 1}]
+        end
+      %{type: :pawn, colour: :black} ->
+        case rank do
+          6 -> [{file, rank - 1}, {file, rank - 2}]
+          _ -> [{file, rank - 1}]
+        end
+      %{type: :rook} ->
+        []
+    end
+  end
+end