Add promotion and promotion checks for pawns

spec/lx_chess/game/make_move_spec.cr

@@ -0,0 +1,32 @@
+require "../../spec_helper"
+require "../../../src/lx_chess/board"
+require "../../../src/lx_chess/piece"
+require "../../../src/lx_chess/move_set"
+require "../../../src/lx_chess/game"
+
+include LxChess
+
+describe Game do
+  describe "#make_move" do
+    context "when a move will promote" do
+      it "raises an exception when promotion is not specified" do
+        game = Game.new
+        game.board["e7"] = Piece.from_fen('P')
+        expect_raises(Game::IllegalMove) do
+          game.make_move("e7", "e8")
+        end
+      end
+
+      it "raises an exception when promotion is not specified" do
+        game = Game.new
+        game.board["e7"] = Piece.from_fen('P')
+        game.make_move("e7", "e8", 'Q')
+        piece = game.board["e8"]
+        from = game.board["e7"]
+        from.should be_nil
+        raise "e8 is empty" unless piece
+        piece.fen_symbol.should eq('Q')
+      end
+    end
+  end
+end

src/lx_chess/game.cr

@@ -126,7 +126,7 @@ module LxChess
     end
 
     # TODO: checkmate
-    def move_to_san(from : Int, to : Int, promotion : String? = nil, turn = @turn)
+    def move_to_san(from : Int, to : Int, promotion : Char? = nil, turn = @turn)
       raise "No piece at #{@board.cord(from)}" unless piece = @board[from]
       en_passant = piece.pawn? && to == @en_passant_target
 
@@ -355,6 +355,7 @@ module LxChess
       if piece.pawn?
         distance = from - to
         if distance.abs == @board.width * 2
+          # Double pawn push, set en passant target
           @en_passant_target = distance > 0 ? to + @board.width : to - @board.width
         else
           if to == @en_passant_target
@@ -368,6 +369,22 @@ module LxChess
         @en_passant_target = nil
       end
 
+      # Promotion
+      if piece.pawn?
+        rank = @board.rank(to)
+        if rank == 0 || rank == @board.height - 1
+          if promotion
+            raise IllegalMove.new("Cannot promote to #{promotion}") unless "RNBQ".chars.includes?(promotion.upcase)
+            promotion = piece.white? ? promotion.upcase : promotion.downcase
+            @board[from] = Piece.from_fen(promotion)
+          else
+            raise IllegalMove.new("Pawns must promote on the last rank")
+          end
+        elsif promotion
+          raise IllegalMove.new("Cannot promote on #{@board.cord(to)}")
+        end
+      end
+
       @board.move(from, to)
       next_turn!
       @pgn.history << san
@@ -408,6 +425,7 @@ module LxChess
 
     # Get the next turn index
     def next_turn
+      return 0.to_i8 if @players.size == 0
       (@turn + 1) % @players.size
     end
   end

src/lx_chess/piece.cr

@@ -12,6 +12,7 @@ module LxChess
     KNIGHT = 5
 
     def self.from_fen(fen : Char)
+      raise "#{fen} is not a valid FEN symbol" unless FEN_SYMBOLS.chars.includes?(fen)
       id = FEN_SYMBOLS.index(fen).as(Int32).to_i8
       Piece.new(id)
     end

src/lx_chess/term_game.cr

@@ -71,7 +71,7 @@ module LxChess
                     end
             if from && to
               @gb.clear
-              san = @game.make_move(from, to)
+              san = @game.make_move(from, to, promo)
               @gb.highlight([@game.board.index(from), @game.board.index(to)])
               @log.unshift "#{san.to_s}: #{from} => #{to}"
             end
@@ -84,7 +84,7 @@ module LxChess
           from, to = @game.parse_san(notation)
           if from && to
             @gb.clear
-            san = @game.make_move(from, to)
+            san = @game.make_move(from, to, notation.promotion)
             @gb.highlight([from.to_i16, to.to_i16])
             @log.unshift "#{san.to_s}: #{@game.board.cord(from)} => #{@game.board.cord(to)}"
           end