Knights are obstructed

lib/chess/moves/generator.ex

@@ -1,6 +1,7 @@
 defmodule Chess.Moves.Generator do
   @moduledoc false
 
+  # Move generation for pieces that move in straight lines
   def moves(_colour, _board, {0, _rank}, {-1, _}), do: []
   def moves(_colour, _board, {_file, 0}, {_, -1}), do: []
   def moves(_colour, _board, {7, _rank}, {1, _}), do: []
@@ -10,21 +11,40 @@ defmodule Chess.Moves.Generator do
     cond do
       can_take_piece?(colour, board, next_square) ->
         [next_square]
-      obstruction?(board, next_square) ->
+      obstruction?(colour, board, next_square) ->
         []
       true ->
         [next_square | moves(colour, board, next_square, {fv, rv})]
     end
   end
 
+  # Move generation for pieces that follow a pattern
+  def moves(_colour, _board, {_file, _rank}, []), do: []
+  def moves(colour, board, {file, rank}, [{fv, rv} | moves]) do
+    move_square = {file + fv, rank + rv}
+    cond do
+      outside_board?(move_square) ||
+        obstruction?(colour, board, move_square) ->
+        moves(colour, board, {file, rank}, moves)
+      can_take_piece?(colour, board, move_square) ->
+        [move_square | moves(colour, board, {file, rank}, moves)]
+      true ->
+        [move_square | moves(colour, board, {file, rank}, moves)]
+    end
+  end
+
+  defp outside_board?({file, rank}) do
+    file < 0 || file > 7 ||
+      rank < 0 || rank > 7
+  end
+
   defp can_take_piece?(colour, board, {file, rank}) do
     piece = board["#{file},#{rank}"]
-
     piece && piece["colour"] != colour
   end
 
-  defp obstruction?(board, {file, rank}) do
-    board
-    |> Map.has_key?("#{file},#{rank}")
+  defp obstruction?(colour, board, {file, rank}) do
+    piece = board["#{file},#{rank}"]
+    piece && piece["colour"] == colour
   end
 end

lib/chess/moves/knight.ex

@@ -1,12 +1,12 @@
 defmodule Chess.Moves.Knight 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)
+  alias Chess.Moves.Generator
+
+  def moves(board, {file, rank}) do
+    board["#{file},#{rank}"]
+    |> Map.get("colour")
+    |> Generator.moves(board, {file, rank}, patterns())
   end
 
   defp patterns do

test/chess/moves/knight_test.exs

@@ -23,6 +23,19 @@ defmodule Chess.Moves.KnightTest do
     assert Enum.sort(moves) == expected_moves
   end
 
+  test "knights are blocked by other pieces of the same colour" do
+    board = %{
+      "0,0" => %{"type" => "knight", "colour" => "white"},
+      "1,2" => %{"type" => "king", "colour" => "white"},
+    }
+    moves = Moves.available(board, {0, 0})
+
+    expected_moves = Enum.sort([
+      {2, 1},
+    ])
+    assert Enum.sort(moves) == expected_moves
+  end
+
   def board do
     Chess.Board.default
   end