From aa7f685521e0a2ed7f3088e163e1478ee5979584 Mon Sep 17 00:00:00 2001
From: Dan Barber <github@danbarber.me>
Date: Sun, 18 Mar 2018 19:48:26 -0400
Subject: [PATCH] Check for attacks from pawns

---
 lib/chess/board.ex              | 15 +++++++++++++++
 lib/chess/moves/piece.ex        | 27 ++++++++++++++++++++++-----
 test/chess/moves/piece_test.exs | 27 +++++++++++++++++++++++++++
 3 files changed, 64 insertions(+), 5 deletions(-)

diff --git a/lib/chess/board.ex b/lib/chess/board.ex
index 553d2de..1157ac2 100644
--- a/lib/chess/board.ex
+++ b/lib/chess/board.ex
@@ -9,6 +9,14 @@ defmodule Chess.Board do
     end)
   end
 
+  def search(board, %{"type" => type, "colour" => colour}) do
+    board
+    |> Enum.filter(fn({_index, piece}) ->
+      match?(%{"type" => ^type, "colour" => ^colour}, piece)
+    end)
+    |> Enum.map(fn({index, _piece}) -> index_to_tuple(index) end)
+  end
+
   def piece(board, {file, rank}) do
     board["#{file},#{rank}"]
   end
@@ -61,4 +69,11 @@ defmodule Chess.Board do
       "7,0" => %{"type" => "rook",   "colour" => "white"}
     }
   end
+
+  defp index_to_tuple(index) do
+    index
+    |> String.split(",")
+    |> Enum.map(&(String.to_integer(&1)))
+    |> List.to_tuple
+  end
 end
diff --git a/lib/chess/moves/piece.ex b/lib/chess/moves/piece.ex
index 635b1e1..fb8cc30 100644
--- a/lib/chess/moves/piece.ex
+++ b/lib/chess/moves/piece.ex
@@ -4,14 +4,13 @@ defmodule Chess.Moves.Piece do
   alias Chess.Board
   alias Chess.Moves.Generator
   alias Chess.Moves.Pieces.Knight
-
-  def find(board, piece) do
-  end
+  alias Chess.Moves.Pieces.Pawn
 
   def attacked?(board, {file, rank}) do
     attacked_by_rook_or_queen?(board, {file, rank}) ||
       attacked_by_bishop_or_queen?(board, {file, rank}) ||
-      attacked_by_knight?(board, {file, rank})
+      attacked_by_knight?(board, {file, rank}) ||
+      attacked_by_pawn?(board, {file, rank})
   end
 
   defp attacked_by_rook_or_queen?(board, {file, rank}) do
@@ -32,6 +31,24 @@ defmodule Chess.Moves.Piece do
     _attacked?(board, {file, rank}, Knight.pattern, "knight")
   end
 
+  defp attacked_by_pawn?(board, {file, rank}) do
+    colour =
+      board
+      |> Board.piece({file, rank})
+      |> Map.get("colour")
+
+    board
+    |> _attacked_by_pawn?({file, rank}, Pawn.pattern(colour))
+  end
+
+  defp _attacked_by_pawn?(board, {file, rank}, pattern) do
+    moves =
+      board
+      |> Generator.moves({file, rank}, pattern)
+
+    Enum.any?(moves, &(match_piece(board, &1, "pawn")))
+  end
+
   defp _attacked?(board, {file, rank}, {fv, rv}, pieces) do
     {file, rank} =
       board
@@ -40,7 +57,7 @@ defmodule Chess.Moves.Piece do
 
     piece = board["#{file},#{rank}"]
 
-    Enum.any?(pieces, &(match?(%{"type" => &1}, piece)))
+    Enum.any?(pieces, &(match?(%{"type" => ^&1}, piece)))
   end
 
   defp _attacked?(board, {file, rank}, pattern, piece_type) do
diff --git a/test/chess/moves/piece_test.exs b/test/chess/moves/piece_test.exs
index c861f31..8b20e4d 100644
--- a/test/chess/moves/piece_test.exs
+++ b/test/chess/moves/piece_test.exs
@@ -12,6 +12,15 @@ defmodule Chess.Moves.PieceTest do
     refute Piece.attacked?(board, {4, 5})
   end
 
+  test "piece is not being attacked by piece of its own colour" do
+    board = %{
+      "4,5" => %{"type" => "king", "colour" => "white"},
+      "2,5" => %{"type" => "rook", "colour" => "white"},
+    }
+
+    refute Piece.attacked?(board, {4, 5})
+  end
+
   test "piece can be attacked by a rook" do
     board = %{
       "4,5" => %{"type" => "king", "colour" => "white"},
@@ -56,4 +65,22 @@ defmodule Chess.Moves.PieceTest do
 
     assert Piece.attacked?(board, {4, 5})
   end
+
+  test "piece can be attacked by a pawn" do
+    board = %{
+      "4,5" => %{"type" => "king", "colour" => "white"},
+      "5,6" => %{"type" => "pawn", "colour" => "black"},
+    }
+
+    assert Piece.attacked?(board, {4, 5})
+  end
+
+  test "piece is not attacked by a pawn directly in front" do
+    board = %{
+      "4,5" => %{"type" => "king", "colour" => "white"},
+      "4,6" => %{"type" => "pawn", "colour" => "black"},
+    }
+
+    refute Piece.attacked?(board, {4, 5})
+  end
 end