refactor: use position candidates to remove illegal moves from

lib/move/base.rb

@@ -12,7 +12,10 @@ def initialize(board, position)
     end
 
     def legal_target_positions
-
+      positions = position_candidates
+      positions -= target_positions_that_are_occupied_by_friend(positions)
+      positions -= target_positions_that_create_check_for_own_king(positions)
+      positions
     end
 
     private
@@ -42,12 +45,6 @@ def occupied_by_enemy?(target_position)
       other_piece && other_piece.color != piece.color
     end
 
-    def without_illegal_target_positions(positions)
-      positions -= target_positions_that_are_occupied_by_friend(positions)
-      positions -= target_positions_that_create_check_for_own_king(positions)
-      positions
-    end
-
     def target_positions_that_are_occupied_by_friend(positions)
       positions.select { |target_position| occupied_by_friend?(target_position) }
     end

lib/move/diagonal.rb

@@ -3,7 +3,7 @@
 module Move
   # unlimited horizontal movement for a piece
   class Diagonal < Base
-    def legal_target_positions
+    def position_candidates
       [
         position.positions_up_left,
         position.positions_up_right,

lib/move/horizontal.rb

@@ -3,10 +3,9 @@
 module Move
   # unlimited horizontal movement for a piece
   class Horizontal < Base
-    def legal_target_positions
-      without_illegal_target_positions(
+    def position_candidates
       legal_target_positions_in_line(position.positions_to_the_left) +
-        legal_target_positions_in_line(position.positions_to_the_right))
+        legal_target_positions_in_line(position.positions_to_the_right)
     end
   end
 end

lib/move/knight.rb

@@ -3,11 +3,10 @@
 module Move
   # knight moves in ls
   class Knight < Base
-    def legal_target_positions
-      positions = directions.map do |direction|
+    def position_candidates
+      directions.map do |direction|
         position.go(*direction)
-      end
-      without_illegal_target_positions(positions.compact)
+      end.compact
     end
 
     private

lib/move/one_down.rb

@@ -3,8 +3,8 @@
 module Move
   # king moves
   class OneDown < Base
-    def legal_target_positions
-      without_illegal_target_positions([position.down])
+    def position_candidates
+      [position.down]
     end
   end
 end

lib/move/one_into_any_direction.rb

@@ -3,11 +3,11 @@
 module Move
   # king moves
   class OneIntoAnyDirection < Base
-    def legal_target_positions
+    def position_candidates
       positions = directions.map do |direction|
         position.go(*direction)
       end
-      without_illegal_target_positions(positions.compact)
+      positions.compact
     end
 
     private

lib/move/one_up.rb

@@ -3,8 +3,8 @@
 module Move
   # king moves
   class OneUp < Base
-    def legal_target_positions
-      without_illegal_target_positions([position.down])
+    def position_candidates
+      [position.down]
     end
   end
 end

lib/move/two_down.rb

@@ -3,7 +3,7 @@
 module Move
   # move down two squares if not occupied
   class TwoDown < Base
-    def legal_target_positions
+    def position_candidates
       if no_piece_in_the_way? && target_piece_not_occupied?
         [position.down.down]
       else

lib/move/two_up.rb

@@ -3,7 +3,7 @@
 module Move
   # move down two squares if not occupied
   class TwoUp < Base
-    def legal_target_positions
+    def position_candidates
       if no_piece_in_the_way? && target_piece_not_occupied?
         [position.up.up]
       else

lib/move/vertical.rb

@@ -3,11 +3,9 @@
 module Move
   # unlimited vertical movement for a piece
   class Vertical < Base
-    def legal_target_positions
-      without_illegal_target_positions(
-
-        legal_target_positions_in_line(position.positions_upwards) +
-          legal_target_positions_in_line(position.positions_downwards))
-      end
+    def position_candidates
+      legal_target_positions_in_line(position.positions_upwards) +
+        legal_target_positions_in_line(position.positions_downwards)
+    end
   end
 end