Refactor chess code to access node meta less often

src/chess.lua

@@ -327,11 +327,10 @@ local function en_passant_to_string(double_step)
 	return s_en_passant
 end
 
-local function can_castle(meta, board, from_list, from_idx, to_idx)
+local function can_castle(board, from_idx, to_idx, castlingRights)
 	local from_x, from_y = index_to_xy(from_idx)
 	local to_x, to_y = index_to_xy(to_idx)
-	local inv = meta:get_inventory()
+	local kingPiece = board[from_idx]
-	local kingPiece = inv:get_stack(from_list, from_idx):get_name()
 	local kingColor
 	if kingPiece:find("black") then
 		kingColor = "black"
@@ -340,21 +339,21 @@ local function can_castle(meta, board, from_list, from_idx, to_idx)
 	end
 	local possible_castles = {
 		-- white queenside
-		{ y = 7, to_x = 2, rook_idx = 57, rook_goal = 60, acheck_dir = -1, color = "white", meta = "castlingWhiteL", rook_id = 1 },
+		{ y = 7, to_x = 2, rook_idx = 57, rook_goal = 60, acheck_dir = -1, color = "white", rightName = "castlingWhiteL", rook_id = 1 },
 		-- white kingside
-		{ y = 7, to_x = 6, rook_idx = 64, rook_goal = 62, acheck_dir = 1, color = "white", meta = "castlingWhiteR", rook_id = 2 },
+		{ y = 7, to_x = 6, rook_idx = 64, rook_goal = 62, acheck_dir = 1, color = "white", rightName = "castlingWhiteR", rook_id = 2 },
 		-- black queenside
-		{ y = 0, to_x = 2, rook_idx = 1, rook_goal = 4, acheck_dir = -1, color = "black", meta = "castlingBlackL", rook_id = 1 },
+		{ y = 0, to_x = 2, rook_idx = 1, rook_goal = 4, acheck_dir = -1, color = "black", rightName = "castlingBlackL", rook_id = 1 },
 		-- black kingside
-		{ y = 0, to_x = 6, rook_idx = 8, rook_goal = 6, acheck_dir = 1, color = "black", meta = "castlingBlackR", rook_id = 2 },
+		{ y = 0, to_x = 6, rook_idx = 8, rook_goal = 6, acheck_dir = 1, color = "black", rightName = "castlingBlackR", rook_id = 2 },
 	}
 
 	for p=1, #possible_castles do
 		local pc = possible_castles[p]
 		if pc.color == kingColor and pc.to_x == to_x and to_y == pc.y and from_y == pc.y then
-			local castlingMeta = meta:get_int(pc.meta)
+			local castlingRightVal = castlingRights[pc.rightName]
-			local rookPiece = inv:get_stack(from_list, pc.rook_idx):get_name()
+			local rookPiece = board[pc.rook_idx]
-			if castlingMeta == 1 and rookPiece == "realchess:rook_"..kingColor.."_"..pc.rook_id then
+			if castlingRightVal == 1 and rookPiece == "realchess:rook_"..kingColor.."_"..pc.rook_id then
 				-- Check if all squares between king and rook are empty
 				local empty_start, empty_end
 				if pc.acheck_dir == -1 then
@@ -367,7 +366,7 @@ local function can_castle(meta, board, from_list, from_idx, to_idx)
 					empty_end = pc.rook_idx - 1
 				end
 				for i = empty_start, empty_end do
-					if inv:get_stack(from_list, i):get_name() ~= "" then
+					if board[i] ~= "" then
 						return false
 					end
 				end
@@ -389,15 +388,15 @@ end
 -- Checks if a square to check if there is a piece that can be captured en passant. Returns true if this
 -- is the case, false otherwise.
 -- Parameters:
--- * meta: chessboard node metadata
+-- * board: chessboard table
 -- * victim_color: color of the opponent to capture a piece from. "white" or "black". (so in White's turn, pass "black" here)
 -- * victim_index: board index of the square where you expect the victim to be
-local function can_capture_en_passant(meta, victim_color, victim_index)
+-- * prevDoublePawnStepTo: if a pawn did a double-step in the previous halfmove, this is the board index of the destination.
-	local inv = meta:get_inventory()
+--   if no pawn made a double-step in the previous halfmove, this is nil or 0.
-	local victimPiece = inv:get_stack("board", victim_index)
+local function can_capture_en_passant(board, victim_color, victim_index, prevDoublePawnStepTo)
-	local double_step_index = meta:get_int("prevDoublePawnStepTo")
+	local victimPiece = board[victim_index]
-	local victim_name = victimPiece:get_name()
+	local double_step_index = prevDoublePawnStepTo or 0
-	if double_step_index ~= 0 and double_step_index == victim_index and victim_name:find(victim_color) and victim_name:sub(11,14) == "pawn" then
+	if double_step_index ~= 0 and double_step_index == victim_index and victimPiece:find(victim_color) and victimPiece:sub(11,14) == "pawn" then
 		return true
 	end
 	return false
@@ -413,7 +412,7 @@ end
 --    Any key with a numeric value is a possible destination.
 --    The numeric value is a move rating for the bot and is 0 by default.
 -- Example: { [4] = 0, [9] = 0 } -- can move to squares 4 and 9
-local function get_theoretical_moves_from(meta, board, from_idx)
+local function get_theoretical_moves_from(board, from_idx, prevDoublePawnStepTo, castlingRights)
 	local piece, color = board[from_idx]:match(":(%w+)_(%w+)")
 	if not piece then
 		return {}
@@ -450,7 +449,7 @@ local function get_theoretical_moves_from(meta, board, from_idx)
 							can_capture = true
 						else
 							-- en passant
-							if can_capture_en_passant(meta, "black", xy_to_index(to_x, from_y)) then
+							if can_capture_en_passant(board, "black", xy_to_index(to_x, from_y), prevDoublePawnStepTo) then
 								can_capture = true
 								en_passant = true
 							end
@@ -505,7 +504,7 @@ local function get_theoretical_moves_from(meta, board, from_idx)
 							can_capture = true
 						else
 							-- en passant
-							if can_capture_en_passant(meta, "white", xy_to_index(to_x, from_y)) then
+							if can_capture_en_passant(board, "white", xy_to_index(to_x, from_y), prevDoublePawnStepTo) then
 								can_capture = true
 								en_passant = true
 							end
@@ -783,11 +782,10 @@ local function get_theoretical_moves_from(meta, board, from_idx)
 
 		-- KING
 		elseif piece == "king" then
-			local inv = meta:get_inventory()
 			-- King can't move to any attacked square
 			-- king_board simulates the board with the king moved already.
 			-- Required for the attacked() check to work
-			local king_board = realchess.board_to_table(inv)
+			local king_board = table.copy(board)
 			king_board[to_idx] = king_board[from_idx]
 			king_board[from_idx] = ""
 			if realchess.attacked(color, to_idx, king_board) then
@@ -805,7 +803,7 @@ local function get_theoretical_moves_from(meta, board, from_idx)
 				end
 
 				if dx > 1 or dy > 1 then
-					local cc = can_castle(meta, board, "board", from_idx, to_idx)
+					local cc = can_castle(board, from_idx, to_idx, castlingRights)
 					if not cc then
 						moves[to_idx] = nil
 					end
@@ -847,10 +845,10 @@ end
 --   origin_index is the board index for the square to start the piece from (as string)
 --   and this is the key for a list of destination indixes.
 --   r1, r2, r3 ... are numeric values (normally 0) to "rate" this square for the bot.
-function realchess.get_theoretical_moves_for(meta, board, player)
+function realchess.get_theoretical_moves_for(board, player, prevDoublePawnStepTo, castlingRights)
 	local moves = {}
 	for i = 1, 64 do
-		local possibleMoves = get_theoretical_moves_from(meta, board, i)
+		local possibleMoves = get_theoretical_moves_from(board, i, prevDoublePawnStepTo, castlingRights)
 		if next(possibleMoves) then
 			local stack_name = board[i]
 			if stack_name:find(player) then
@@ -1899,13 +1897,20 @@ local function update_game_result(meta, lastMove)
 
 	local playerWhite = meta:get_string("playerWhite")
 	local playerBlack = meta:get_string("playerBlack")
+	local prevDoublePawnStepTo = meta:get_int("prevDoublePawnStepTo")
+	local castlingRights = {
+		castlingWhiteR = meta:get_int("castlingWhiteR"),
+		castlingWhiteL = meta:get_int("castlingWhiteL"),
+		castlingBlackR = meta:get_int("castlingBlackR"),
+		castlingBlackL = meta:get_int("castlingBlackL"),
+	}
 
 	update_formspec(meta)
 	local blackCanMove = false
 	local whiteCanMove = false
 
-	local blackMoves = realchess.get_theoretical_moves_for(meta, board_t, "black")
+	local blackMoves = realchess.get_theoretical_moves_for(board_t, "black", prevDoublePawnStepTo, castlingRights)
-	local whiteMoves = realchess.get_theoretical_moves_for(meta, board_t, "white")
+	local whiteMoves = realchess.get_theoretical_moves_for(board_t, "white", prevDoublePawnStepTo, castlingRights)
 	if next(blackMoves) then
 		blackCanMove = true
 	end
@@ -2230,6 +2235,7 @@ function realchess.move(meta, from_list, from_index, to_list, to_index, playerNa
 	local lastMove    = meta:get_string("lastMove")
 	local playerWhite = meta:get_string("playerWhite")
 	local playerBlack = meta:get_string("playerBlack")
+	local prevDoublePawnStepTo = meta:get_int("prevDoublePawnStepTo")
 	local kingMoved   = false
 	local thisMove    -- Will replace lastMove when move is legal
 
@@ -2346,7 +2352,8 @@ function realchess.move(meta, from_list, from_index, to_list, to_index, playerNa
 					can_capture = true
 				else
 					-- en passant
-					if can_capture_en_passant(meta, "black", xy_to_index(to_x, from_y)) then
+					local board = realchess.board_to_table(inv)
+					if can_capture_en_passant(board, "black", xy_to_index(to_x, from_y), prevDoublePawnStepTo) then
 						can_capture = true
 						en_passant_target = xy_to_index(to_x, from_y)
 					end
@@ -2414,7 +2421,8 @@ function realchess.move(meta, from_list, from_index, to_list, to_index, playerNa
 					can_capture = true
 				else
 					-- en passant
-					if can_capture_en_passant(meta, "white", xy_to_index(to_x, from_y)) then
+					local board = realchess.board_to_table(inv)
+					if can_capture_en_passant(board, "white", xy_to_index(to_x, from_y), prevDoublePawnStepTo) then
 						can_capture = true
 						en_passant_target = xy_to_index(to_x, from_y)
 					end
@@ -2666,9 +2674,15 @@ function realchess.move(meta, from_list, from_index, to_list, to_index, playerNa
 		local check = true
 		local inv = meta:get_inventory()
 		local board = realchess.board_to_table(inv)
+		local castlingRights = {
+			castlingWhiteR = meta:get_int("castlingWhiteR"),
+			castlingWhiteL = meta:get_int("castlingWhiteL"),
+			castlingBlackR = meta:get_int("castlingBlackR"),
+			castlingBlackL = meta:get_int("castlingBlackL"),
+		}
 
 		-- Castling
-		local cc, rook_start, rook_goal, rook_name = can_castle(meta, board, from_list, from_index, to_index)
+		local cc, rook_start, rook_goal, rook_name = can_castle(board, from_index, to_index, castlingRights)
 		if cc then
 			inv:set_stack(from_list, rook_goal, rook_name)
 			inv:set_stack(from_list, rook_start, "")

src/chessbot.lua

@@ -3,7 +3,7 @@ local chessbot = {}
 local realchess = xdecor.chess
 
 -- Delay in seconds for a bot moving a piece (excluding choosing a promotion)
-local BOT_DELAY_MOVE = 1.0
+local BOT_DELAY_MOVE = 0.2
 -- Delay in seconds for a bot promoting a piece
 local BOT_DELAY_PROMOTE = 1.0
 
@@ -36,15 +36,58 @@ local function best_move(moves)
 	return tonumber(choice_from), choice_to
 end
 
-function chessbot.move(inv, meta)
+function chessbot.choose_move(board_t, meta_t)
-	local board_t = realchess.board_to_table(inv)
+	local lastMove = meta_t["lastMove"]
-	local lastMove = meta:get_string("lastMove")
+	local gameResult = meta_t["gameResult"]
-	local gameResult = meta:get_string("gameResult")
+	local botColor = meta_t["botColor"]
-	local botColor = meta:get_string("botColor")
+	local prevDoublePawnStepTo = meta_t["prevDoublePawnStepTo"]
+	local castlingRights = {
+		castlingWhiteR = meta_t["castlingWhiteR"],
+		castlingWhiteL = meta_t["castlingWhiteL"],
+		castlingBlackR = meta_t["castlingBlackR"],
+		castlingBlackL = meta_t["castlingBlackL"],
+	}
+
 	if botColor == "" then
 		return
 	end
 	local currentBotColor, opponentColor
+	if botColor == "black" then
+		currentBotColor = "black"
+		opponentColor = "white"
+	elseif botColor == "white" then
+		currentBotColor = "white"
+		opponentColor = "black"
+	elseif botColor == "both" then
+		opponentColor = lastMove
+		if lastMove == "black" or lastMove == "" then
+			currentBotColor = "white"
+		else
+			currentBotColor = "black"
+		end
+	end
+	if (lastMove == opponentColor or ((botColor == "white" or botColor == "both") and lastMove == "")) and gameResult == "" then
+
+		local moves = realchess.get_theoretical_moves_for(board_t, currentBotColor, prevDoublePawnStepTo, castlingRights)
+		local safe_moves, safe_moves_count = realchess.get_king_safe_moves(moves, board_t, currentBotColor)
+		if safe_moves_count == 0 then
+			-- No safe move: stalemate or checkmate
+		end
+		local choice_from, choice_to = best_move(safe_moves)
+		if choice_from == nil then
+			-- No best move: stalemate or checkmate
+			return
+		end
+
+		return choice_from, choice_to
+
+	end
+end
+
+chessbot.perform_move = function(choice_from, choice_to, meta)
+	local lastMove = meta:get_string("lastMove")
+	local botColor = meta:get_string("botColor")
+	local currentBotColor, opponentColor
 	local botName
 	if botColor == "black" then
 		currentBotColor = "black"
@@ -60,28 +103,19 @@ function chessbot.move(inv, meta)
 			currentBotColor = "black"
 		end
 	end
+
+	-- Bot resigns if no move chosen
+	if not choice_from or not choice_to then
+		realchess.resign(meta, currentBotColor)
+		return
+	end
+
 	if currentBotColor == "white" then
 		botName = meta:get_string("playerWhite")
 	else
 		botName = meta:get_string("playerBlack")
 	end
-	if (lastMove == opponentColor or ((botColor == "white" or botColor == "both") and lastMove == "")) and gameResult == "" then
 
-		local moves = realchess.get_theoretical_moves_for(meta, board_t, currentBotColor)
-		local safe_moves, safe_moves_count = realchess.get_king_safe_moves(moves, board_t, currentBotColor)
-		if safe_moves_count == 0 then
-			-- No safe move: stalemate or checkmate
-		end
-		local choice_from, choice_to = best_move(safe_moves)
-		if choice_from == nil then
-			-- No best move: stalemate or checkmate
-			return
-		end
-
-		local pieceFrom = inv:get_stack("board", choice_from):get_name()
-		local pieceTo   = inv:get_stack("board", choice_to):get_name()
-
-		minetest.after(BOT_DELAY_MOVE, function()
 	local gameResult = meta:get_string("gameResult")
 	if gameResult ~= "" then
 		return
@@ -111,11 +145,14 @@ function chessbot.move(inv, meta)
 			realchess.resign(meta, currentBotColor)
 		end
 	end
-		end)
-	end
 end
 
-function chessbot.promote(inv, meta, pawnIndex)
+function chessbot.choose_promote(board_t, pawnIndex)
+	-- Bot always promotes to queen
+	return "queen"
+end
+
+function chessbot.perform_promote(meta, promoteTo)
 	minetest.after(BOT_DELAY_PROMOTE, function()
 		local lastMove = meta:get_string("lastMove")
 		local color
@@ -124,9 +161,35 @@ function chessbot.promote(inv, meta, pawnIndex)
 		else
 			color = "black"
 		end
-		-- Always promote to queen
+		realchess.promote_pawn(meta, color, promoteTo)
-		realchess.promote_pawn(meta, color, "queen")
 	end)
 end
 
+function chessbot.move(inv, meta)
+	local board_t = realchess.board_to_table(inv)
+	local meta_t = {
+		lastMove = meta:get_string("lastMove"),
+		gameResult = meta:get_string("gameResult"),
+		botColor = meta:get_string("botColor"),
+		prevDoublePawnStepTo = meta:get_int("prevDoublePawnStepTo"),
+		castlingWhiteL = meta:get_int("castlingWhiteL"),
+		castlingWhiteR = meta:get_int("castlingWhiteR"),
+		castlingBlackL = meta:get_int("castlingBlackL"),
+		castlingBlackR = meta:get_int("castlingBlackR"),
+	}
+	local choice_from, choice_to = chessbot.choose_move(board_t, meta_t)
+	minetest.after(BOT_DELAY_MOVE, function()
+		chessbot.perform_move(choice_from, choice_to, meta)
+	end)
+end
+
+function chessbot.promote(inv, meta, pawnIndex)
+	local board_t = realchess.board_to_table(inv)
+	local promoteTo = chessbot.choose_promote(board_t, pawnIndex)
+	if not promoteTo then
+		promoteTo = "queen"
+	end
+	chessbot.perform_promote(meta, promoteTo)
+end
+
 return chessbot