[xdecor.git] / src / chess.lua

local realchess = {}
screwdriver = screwdriver or {}

local function index_to_xy(idx)
        if not idx then
                return nil
        end

        idx = idx - 1

        local x = idx % 8
        local y = (idx - x) / 8

        return x, y
end

local function xy_to_index(x, y)
        return x + y * 8 + 1
end

local function get_square(a, b)
        return (a * 8) - (8 - b)
end

local chat_prefix = minetest.colorize("#FFFF00", "[Chess] ")
local letters = {'A','B','C','D','E','F','G','H'}

local function board_to_table(inv)
        local t = {}
        for i = 1, 64 do
                t[#t + 1] = inv:get_stack("board", i):get_name()
        end

        return t
end

local piece_values = {
        pawn   = 10,
        knight = 30,
        bishop = 30,
        rook   = 50,
        queen  = 90,
        king   = 900
}

local function get_possible_moves(board, from_idx)
        local piece, color = board[from_idx]:match(":(%w+)_(%w+)")
        if not piece then return end
        local moves = {}
        local from_x, from_y = index_to_xy(from_idx)

        for i = 1, 64 do
                local stack_name = board[i]
                if stack_name:find((color == "black" and "white" or "black")) or
                                stack_name == "" then
                        moves[i] = 0
                end
        end

        for to_idx in pairs(moves) do
                local pieceTo    = board[to_idx]
                local to_x, to_y = index_to_xy(to_idx)

                -- PAWN
                if piece == "pawn" then
                        if color == "white" then
                                local pawnWhiteMove = board[xy_to_index(from_x, from_y - 1)]
                                -- white pawns can go up only
                                if from_y - 1 == to_y then
                                        if from_x == to_x then
                                                if pieceTo ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        elseif from_x - 1 == to_x or from_x + 1 == to_x then
                                                if not pieceTo:find("black") then
                                                        moves[to_idx] = nil
                                                end
                                        else
                                                moves[to_idx] = nil
                                        end
                                elseif from_y - 2 == to_y then
                                        if pieceTo ~= "" or from_y < 6 or pawnWhiteMove ~= "" then
                                                moves[to_idx] = nil
                                        end
                                else
                                        moves[to_idx] = nil
                                end

                                --[[
                                     if x not changed
                                          ensure that destination cell is empty
                                     elseif x changed one unit left or right
                                          ensure the pawn is killing opponent piece
                                     else
                                          move is not legal - abort
                                ]]

                                if from_x == to_x then
                                        if pieceTo ~= "" then
                                                moves[to_idx] = nil
                                        end
                                elseif from_x - 1 == to_x or from_x + 1 == to_x then
                                        if not pieceTo:find("black") then
                                                moves[to_idx] = nil
                                        end
                                else
                                        moves[to_idx] = nil
                                end

                        elseif color == "black" then
                                local pawnBlackMove = board[xy_to_index(from_x, from_y + 1)]
                                -- black pawns can go down only
                                if from_y + 1 == to_y then
                                        if from_x == to_x then
                                                if pieceTo ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        elseif from_x - 1 == to_x or from_x + 1 == to_x then
                                                if not pieceTo:find("white") then
                                                        moves[to_idx] = nil
                                                end
                                        else
                                                moves[to_idx] = nil
                                        end
                                elseif from_y + 2 == to_y then
                                        if pieceTo ~= "" or from_y > 1 or pawnBlackMove ~= "" then
                                                moves[to_idx] = nil
                                        end
                                else
                                        moves[to_idx] = nil
                                end

                                --[[
                                     if x not changed
                                          ensure that destination cell is empty
                                     elseif x changed one unit left or right
                                          ensure the pawn is killing opponent piece
                                     else
                                          move is not legal - abort
                                ]]

                                if from_x == to_x then
                                        if pieceTo ~= "" then
                                                moves[to_idx] = nil
                                        end
                                elseif from_x - 1 == to_x or from_x + 1 == to_x then
                                        if not pieceTo:find("white") then
                                                moves[to_idx] = nil
                                        end
                                else
                                        moves[to_idx] = nil
                                end
                        else
                                moves[to_idx] = nil
                        end

                -- ROOK
                elseif piece == "rook" then
                        if from_x == to_x then
                                -- Moving vertically
                                if from_y < to_y then
                                        -- Moving down
                                        -- Ensure that no piece disturbs the way
                                        for i = from_y + 1, to_y - 1 do
                                                if board[xy_to_index(from_x, i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                else
                                        -- Mocing up
                                        -- Ensure that no piece disturbs the way
                                        for i = to_y + 1, from_y - 1 do
                                                if board[xy_to_index(from_x, i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                end
                        elseif from_y == to_y then
                                -- Mocing horizontally
                                if from_x < to_x then
                                        -- mocing right
                                        -- ensure that no piece disturbs the way
                                        for i = from_x + 1, to_x - 1 do
                                                if board[xy_to_index(i, from_y)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                else
                                        -- Mocing left
                                        -- Ensure that no piece disturbs the way
                                        for i = to_x + 1, from_x - 1 do
                                                if board[xy_to_index(i, from_y)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                end
                        else
                                -- Attempt to move arbitrarily -> abort
                                moves[to_idx] = nil
                        end

                -- KNIGHT
                elseif piece == "knight" then
                        -- Get relative pos
                        local dx = from_x - to_x
                        local dy = from_y - to_y

                        -- Get absolute values
                        if dx < 0 then
                                dx = -dx
                        end

                        if dy < 0 then
                                dy = -dy
                        end

                        -- Sort x and y
                        if dx > dy then
                                dx, dy = dy, dx
                        end

                        -- Ensure that dx == 1 and dy == 2
                        if dx ~= 1 or dy ~= 2 then
                                moves[to_idx] = nil
                        end
                        -- Just ensure that destination cell does not contain friend piece
                        -- ^ It was done already thus everything ok

                -- BISHOP
                elseif piece == "bishop" then
                        -- Get relative pos
                        local dx = from_x - to_x
                        local dy = from_y - to_y

                        -- Get absolute values
                        if dx < 0 then
                                dx = -dx
                        end

                        if dy < 0 then
                                dy = -dy
                        end

                        -- Ensure dx and dy are equal
                        if dx ~= dy then
                                moves[to_idx] = nil
                        end

                        if from_x < to_x then
                                if from_y < to_y then
                                        -- Moving right-down
                                        -- Ensure that no piece disturbs the way
                                        for i = 1, dx - 1 do
                                                if board[xy_to_index(from_x + i, from_y + i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                else
                                        -- Moving right-up
                                        -- Ensure that no piece disturbs the way
                                        for i = 1, dx - 1 do
                                                if board[xy_to_index(from_x + i, from_y - i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                end
                        else
                                if from_y < to_y then
                                        -- Moving left-down
                                        -- Ensure that no piece disturbs the way
                                        for i = 1, dx - 1 do
                                                if board[xy_to_index(from_x - i, from_y + i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                else
                                        -- Moving left-up
                                        -- ensure that no piece disturbs the way
                                        for i = 1, dx - 1 do
                                                if board[xy_to_index(from_x - i, from_y - i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                end
                        end

                -- QUEEN
                elseif piece == "queen" then
                        local dx = from_x - to_x
                        local dy = from_y - to_y

                        -- Get absolute values
                        if dx < 0 then
                                dx = -dx
                        end

                        if dy < 0 then
                                dy = -dy
                        end

                        -- Ensure valid relative move
                        if dx ~= 0 and dy ~= 0 and dx ~= dy then
                                moves[to_idx] = nil
                        end

                        if from_x == to_x then
                                -- Moving vertically
                                if from_y < to_y then
                                        -- Moving down
                                        -- Ensure that no piece disturbs the way
                                        for i = from_y + 1, to_y - 1 do
                                                if board[xy_to_index(from_x, i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                else
                                        -- Mocing up
                                        -- Ensure that no piece disturbs the way
                                        for i = to_y + 1, from_y - 1 do
                                                if board[xy_to_index(from_x, i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                end
                        elseif from_x < to_x then
                                if from_y == to_y then
                                        -- Goes right
                                        -- Ensure that no piece disturbs the way
                                        for i = 1, dx - 1 do
                                                if board[xy_to_index(from_x + i, from_y)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                elseif from_y < to_y then
                                        -- Goes right-down
                                        -- Ensure that no piece disturbs the way
                                        for i = 1, dx - 1 do
                                                if board[xy_to_index(from_x + i, from_y + i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                else
                                        -- Goes right-up
                                        -- Ensure that no piece disturbs the way
                                        for i = 1, dx - 1 do
                                                if board[xy_to_index(from_x + i, from_y - i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                end
                        else
                                if from_y == to_y then
                                        -- Mocing horizontally
                                        if from_x < to_x then
                                                -- mocing right
                                                -- ensure that no piece disturbs the way
                                                for i = from_x + 1, to_x - 1 do
                                                        if board[xy_to_index(i, from_y)] ~= "" then
                                                                moves[to_idx] = nil
                                                        end
                                                end
                                        else
                                                -- Mocing left
                                                -- Ensure that no piece disturbs the way
                                                for i = to_x + 1, from_x - 1 do
                                                        if board[xy_to_index(i, from_y)] ~= "" then
                                                                moves[to_idx] = nil
                                                        end
                                                end
                                        end
                                elseif from_y < to_y then
                                        -- Goes left-down
                                        -- Ensure that no piece disturbs the way
                                        for i = 1, dx - 1 do
                                                if board[xy_to_index(from_x - i, from_y + i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                else
                                        -- Goes left-up
                                        -- Ensure that no piece disturbs the way
                                        for i = 1, dx - 1 do
                                                if board[xy_to_index(from_x - i, from_y - i)] ~= "" then
                                                        moves[to_idx] = nil
                                                end
                                        end
                                end
                        end

                -- KING
                elseif piece == "king" then
                        local dx = from_x - to_x
                        local dy = from_y - to_y

                        if dx < 0 then
                                dx = -dx
                        end

                        if dy < 0 then
                                dy = -dy
                        end

                        if dx > 1 or dy > 1 then
                                moves[to_idx] = nil
                        end
                end
        end

        if not next(moves) then return end

        for i in pairs(moves) do
                local stack_name = board[tonumber(i)]
                if stack_name ~= "" then
                        for p, value in pairs(piece_values) do
                                if stack_name:find(p) then
                                        moves[i] = value
                                end
                        end
                end
        end

        return moves
end

local function best_move(moves)
        local value, choices = 0, {}

        for from, _ in pairs(moves) do
        for to, val in pairs(_) do
                if val > value then
                        value = val
                        choices = {{
                                from = from,
                                to = to
                        }}
                elseif val == value then
                        choices[#choices + 1] = {
                                from = from,
                                to = to
                        }
                end
        end
        end

        local random = math.random(1, #choices)
        local choice_from, choice_to = choices[random].from, choices[random].to

        return tonumber(choice_from), choice_to
end

local rowDirs = {-1, -1, -1, 0, 0, 1, 1, 1}
local colDirs = {-1, 0, 1, -1, 1, -1, 0, 1}

local rowDirsKnight = { 2,  1, 2, 1, -2, -1, -2, -1}
local colDirsKnight = {-1, -2, 1, 2,  1,  2, -1, -2}

local bishopThreats = {true,  false, true,  false, false, true,  false, true}
local rookThreats   = {false, true,  false, true,  true,  false, true,  false}
local queenThreats  = {true,  true,  true,  true,  true,  true,  true,  true}
local kingThreats   = {true,  true,  true,  true,  true,  true,  true,  true}

local function attacked(color, idx, board)
        local threatDetected = false
        local kill           = color == "white"
        local pawnThreats    = {kill, false, kill, false, false, not kill, false, not kill}

        for dir = 1, 8 do
                if not threatDetected then
                        local col, row = index_to_xy(idx)
                        col, row = col + 1, row + 1

                        for step = 1, 8 do
                                row = row + rowDirs[dir]
                                col = col + colDirs[dir]

                                if row >= 1 and row <= 8 and col >= 1 and col <= 8 then
                                        local square            = get_square(row, col)
                                        local square_name       = board[square]
                                        local piece, pieceColor = square_name:match(":(%w+)_(%w+)")

                                        if piece then
                                                if pieceColor ~= color then
                                                        if piece == "bishop" and bishopThreats[dir] then
                                                                threatDetected = true
                                                        elseif piece == "rook" and rookThreats[dir] then
                                                                threatDetected = true
                                                        elseif piece == "queen" and queenThreats[dir] then
                                                                threatDetected = true
                                                        else
                                                                if step == 1 then
                                                                        if piece == "pawn" and pawnThreats[dir] then
                                                                                threatDetected = true
                                                                        end
                                                                        if piece == "king" and kingThreats[dir] then
                                                                                threatDetected = true
                                                                        end
                                                                end
                                                        end
                                                end
                                                break
                                        end
                                end
                        end

                        local colK, rowK = index_to_xy(idx)
                        colK, rowK = colK + 1, rowK + 1
                        rowK = rowK + rowDirsKnight[dir]
                        colK = colK + colDirsKnight[dir]

                        if rowK >= 1 and rowK <= 8 and colK >= 1 and colK <= 8 then
                                local square            = get_square(rowK, colK)
                                local square_name       = board[square]
                                local piece, pieceColor = square_name:match(":(%w+)_(%w+)")

                                if piece and pieceColor ~= color and piece == "knight" then
                                        threatDetected = true
                                end
                        end
                end
        end

        return threatDetected
end

local function locate_kings(board)
        local Bidx, Widx
        for i = 1, 64 do
                local piece, color = board[i]:match(":(%w+)_(%w+)")
                if piece == "king" then
                        if color == "black" then
                                Bidx = i
                        else
                                Widx = i
                        end
                end
        end

        return Bidx, Widx
end

local pieces = {
        "realchess:rook_black_1",
        "realchess:knight_black_1",
        "realchess:bishop_black_1",
        "realchess:queen_black",
        "realchess:king_black",
        "realchess:bishop_black_2",
        "realchess:knight_black_2",
        "realchess:rook_black_2",
        "realchess:pawn_black_1",
        "realchess:pawn_black_2",
        "realchess:pawn_black_3",
        "realchess:pawn_black_4",
        "realchess:pawn_black_5",
        "realchess:pawn_black_6",
        "realchess:pawn_black_7",
        "realchess:pawn_black_8",
        '','','','','','','','','','','','','','','','',
        '','','','','','','','','','','','','','','','',
        "realchess:pawn_white_1",
        "realchess:pawn_white_2",
        "realchess:pawn_white_3",
        "realchess:pawn_white_4",
        "realchess:pawn_white_5",
        "realchess:pawn_white_6",
        "realchess:pawn_white_7",
        "realchess:pawn_white_8",
        "realchess:rook_white_1",
        "realchess:knight_white_1",
        "realchess:bishop_white_1",
        "realchess:queen_white",
        "realchess:king_white",
        "realchess:bishop_white_2",
        "realchess:knight_white_2",
        "realchess:rook_white_2"
}

local pieces_str, x = "", 0
for i = 1, #pieces do
        local p = pieces[i]:match(":(%w+_%w+)")
        if pieces[i]:find(":(%w+)_(%w+)") and not pieces_str:find(p) then
                pieces_str = pieces_str .. x .. "=" .. p .. ".png,"
                x = x + 1
        end
end
pieces_str = pieces_str .. "69=mailbox_blank16.png"

local fs_init = [[
        size[4,1.2;]
        no_prepend[]
        label[0,0;Select a mode:]
        button[0,0.5;2,1;single;Singleplayer]
        button[2,0.5;2,1;multi;Multiplayer]
]]

local fs = [[
        size[14.7,10;]
        no_prepend[]
        bgcolor[#080808BB;true]
        background[0,0;14.7,10;chess_bg.png]
        list[context;board;0.3,1;8,8;]
        listcolors[#00000000;#00000000;#00000000;#30434C;#FFF]
        tableoptions[background=#00000000;highlight=#00000000;border=false]
        button[10.5,8.5;2,2;new;New game]
]] ..  "tablecolumns[image," .. pieces_str ..
                ";text;color;text;color;text;image," .. pieces_str .. "]"

local function update_formspec(meta)
        local black_king_attacked = meta:get_string("blackAttacked") == "true"
        local white_king_attacked = meta:get_string("whiteAttacked") == "true"

        local playerWhite = meta:get_string("playerWhite")
        local playerBlack = meta:get_string("playerBlack")

        local moves     = meta:get_string("moves")
        local eaten_img = meta:get_string("eaten_img")
        local lastMove  = meta:get_string("lastMove")
        local turnBlack = minetest.colorize("#000001", (lastMove == "white" and playerBlack ~= "") and
                          playerBlack .. "..." or playerBlack)
        local turnWhite = minetest.colorize("#000001", (lastMove == "black" and playerWhite ~= "") and
                          playerWhite .. "..." or playerWhite)
        local check_s   = minetest.colorize("#FF0000", "\\[check\\]")

        local formspec = fs ..
                "label[1.9,0.3;"  .. turnBlack .. (black_king_attacked and " " .. check_s or "") .. "]" ..
                "label[1.9,9.15;" .. turnWhite .. (white_king_attacked and " " .. check_s or "") .. "]" ..
                "table[8.9,1.05;5.07,3.75;moves;" .. moves:sub(1,-2) .. ";1]" ..
                eaten_img

        meta:set_string("formspec", formspec)
end

local function get_moves_list(meta, pieceFrom, pieceTo, pieceTo_s, from_idx, to_idx)
        local from_x, from_y  = index_to_xy(from_idx)
        local to_x, to_y      = index_to_xy(to_idx)
        local moves           = meta:get_string("moves")
        local pieceFrom_s     = pieceFrom:match(":(%w+_%w+)")
        local pieceFrom_si_id = pieces_str:match("(%d+)=" .. pieceFrom_s)
        local pieceTo_si_id   = pieceTo_s ~= "" and pieces_str:match("(%d+)=" .. pieceTo_s) or ""

        local coordFrom = letters[from_x + 1] .. math.abs(from_y - 8)
        local coordTo   = letters[to_x   + 1] .. math.abs(to_y   - 8)

        local new_moves = pieceFrom_si_id .. "," ..
                coordFrom .. "," ..
                        (pieceTo ~= "" and "#33FF33" or "#FFFFFF") .. ", > ,#FFFFFF," ..
                coordTo .. "," ..
                (pieceTo ~= "" and pieceTo_si_id or "69") .. "," ..
                moves

        meta:set_string("moves", new_moves)
end

local function get_eaten_list(meta, pieceTo, pieceTo_s)
        local eaten = meta:get_string("eaten")
        if pieceTo ~= "" then
                eaten = eaten .. pieceTo_s .. ","
        end

        meta:set_string("eaten", eaten)

        local eaten_t   = string.split(eaten, ",")
        local eaten_img = ""

        local a, b = 0, 0
        for i = 1, #eaten_t do
                local is_white = eaten_t[i]:sub(-5,-1) == "white"
                local X = (is_white and a or b) % 4
                local Y = ((is_white and a or b) % 16 - X) / 4

                if is_white then
                        a = a + 1
                else
                        b = b + 1
                end

                eaten_img = eaten_img ..
                        "image[" .. ((X + (is_white and 11.67 or 8.8)) - (X * 0.45)) .. "," ..
                                    ((Y + 5.56) - (Y * 0.2)) .. ";1,1;" .. eaten_t[i] .. ".png]"
        end

        meta:set_string("eaten_img", eaten_img)
end

function realchess.init(pos)
        local meta = minetest.get_meta(pos)
        local inv  = meta:get_inventory()

        meta:set_string("formspec", fs_init)
        meta:set_string("infotext", "Chess Board")
        meta:set_string("playerBlack", "")
        meta:set_string("playerWhite", "")
        meta:set_string("lastMove",    "")
        meta:set_string("blackAttacked", "")
        meta:set_string("whiteAttacked", "")

        meta:set_int("lastMoveTime",   0)
        meta:set_int("castlingBlackL", 1)
        meta:set_int("castlingBlackR", 1)
        meta:set_int("castlingWhiteL", 1)
        meta:set_int("castlingWhiteR", 1)

        meta:set_string("moves", "")
        meta:set_string("eaten", "")
        meta:set_string("mode", "")

        inv:set_list("board", pieces)
        inv:set_size("board", 64)
end

function realchess.move(pos, from_list, from_index, to_list, to_index, _, player)
        if from_list ~= "board" and to_list ~= "board" then
                return 0
        end

        local meta        = minetest.get_meta(pos)
        local playerName  = player:get_player_name()
        local inv         = meta:get_inventory()
        local pieceFrom   = inv:get_stack(from_list, from_index):get_name()
        local pieceTo     = inv:get_stack(to_list, to_index):get_name()
        local lastMove    = meta:get_string("lastMove")
        local playerWhite = meta:get_string("playerWhite")
        local playerBlack = meta:get_string("playerBlack")
        local thisMove    -- Will replace lastMove when move is legal

        if pieceFrom:find("white") then
                if playerWhite ~= "" and playerWhite ~= playerName then
                        minetest.chat_send_player(playerName, chat_prefix .. "Someone else plays white pieces!")
                        return 0
                end

                if lastMove ~= "" and lastMove ~= "black" then
                        return 0
                end

                if pieceTo:find("white") then
                        -- Don't replace pieces of same color
                        return 0
                end

                playerWhite = playerName
                thisMove = "white"

        elseif pieceFrom:find("black") then
                if playerBlack ~= "" and playerBlack ~= playerName then
                        minetest.chat_send_player(playerName, chat_prefix .. "Someone else plays black pieces!")
                        return 0
                end

                if lastMove ~= "" and lastMove ~= "white" then
                        return 0
                end

                if pieceTo:find("black") then
                        -- Don't replace pieces of same color
                        return 0
                end

                playerBlack = playerName
                thisMove = "black"
        end

        -- MOVE LOGIC

        local from_x, from_y = index_to_xy(from_index)
        local to_x, to_y     = index_to_xy(to_index)

        -- PAWN
        if pieceFrom:sub(11,14) == "pawn" then
                if thisMove == "white" then
                        local pawnWhiteMove = inv:get_stack(from_list, xy_to_index(from_x, from_y - 1)):get_name()
                        -- white pawns can go up only
                        if from_y - 1 == to_y then
                                if from_x == to_x then
                                        if pieceTo ~= "" then
                                                return 0
                                        elseif to_index >= 1 and to_index <= 8 then
                                                inv:set_stack(from_list, from_index, "realchess:queen_white")
                                        end
                                elseif from_x - 1 == to_x or from_x + 1 == to_x then
                                        if not pieceTo:find("black") then
                                                return 0
                                        elseif to_index >= 1 and to_index <= 8 then
                                                inv:set_stack(from_list, from_index, "realchess:queen_white")
                                        end
                                else
                                        return 0
                                end
                        elseif from_y - 2 == to_y then
                                if pieceTo ~= "" or from_y < 6 or pawnWhiteMove ~= "" then
                                        return 0
                                end
                        else
                                return 0
                        end

                        --[[
                             if x not changed
                                  ensure that destination cell is empty
                             elseif x changed one unit left or right
                                  ensure the pawn is killing opponent piece
                             else
                                  move is not legal - abort
                        ]]

                        if from_x == to_x then
                                if pieceTo ~= "" then
                                        return 0
                                end
                        elseif from_x - 1 == to_x or from_x + 1 == to_x then
                                if not pieceTo:find("black") then
                                        return 0
                                end
                        else
                                return 0
                        end

                elseif thisMove == "black" then
                        local pawnBlackMove = inv:get_stack(from_list, xy_to_index(from_x, from_y + 1)):get_name()
                        -- black pawns can go down only
                        if from_y + 1 == to_y then
                                if from_x == to_x then
                                        if pieceTo ~= "" then
                                                return 0
                                        elseif to_index >= 57 and to_index <= 64 then
                                                inv:set_stack(from_list, from_index, "realchess:queen_black")
                                        end
                                elseif from_x - 1 == to_x or from_x + 1 == to_x then
                                        if not pieceTo:find("white") then
                                                return 0
                                        elseif to_index >= 57 and to_index <= 64 then
                                                inv:set_stack(from_list, from_index, "realchess:queen_black")
                                        end
                                else
                                        return 0
                                end
                        elseif from_y + 2 == to_y then
                                if pieceTo ~= "" or from_y > 1 or pawnBlackMove ~= "" then
                                        return 0
                                end
                        else
                                return 0
                        end

                        --[[
                             if x not changed
                                  ensure that destination cell is empty
                             elseif x changed one unit left or right
                                  ensure the pawn is killing opponent piece
                             else
                                  move is not legal - abort
                        ]]

                        if from_x == to_x then
                                if pieceTo ~= "" then
                                        return 0
                                end
                        elseif from_x - 1 == to_x or from_x + 1 == to_x then
                                if not pieceTo:find("white") then
                                        return 0
                                end
                        else
                                return 0
                        end
                else
                        return 0
                end

        -- ROOK
        elseif pieceFrom:sub(11,14) == "rook" then
                if from_x == to_x then
                        -- Moving vertically
                        if from_y < to_y then
                                -- Moving down
                                -- Ensure that no piece disturbs the way
                                for i = from_y + 1, to_y - 1 do
                                        if inv:get_stack(from_list, xy_to_index(from_x, i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        else
                                -- Mocing up
                                -- Ensure that no piece disturbs the way
                                for i = to_y + 1, from_y - 1 do
                                        if inv:get_stack(from_list, xy_to_index(from_x, i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        end
                elseif from_y == to_y then
                        -- Mocing horizontally
                        if from_x < to_x then
                                -- mocing right
                                -- ensure that no piece disturbs the way
                                for i = from_x + 1, to_x - 1 do
                                        if inv:get_stack(from_list, xy_to_index(i, from_y)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        else
                                -- Mocing left
                                -- Ensure that no piece disturbs the way
                                for i = to_x + 1, from_x - 1 do
                                        if inv:get_stack(from_list, xy_to_index(i, from_y)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        end
                else
                        -- Attempt to move arbitrarily -> abort
                        return 0
                end

                if thisMove == "white" or thisMove == "black" then
                        if pieceFrom:sub(-1) == "1" then
                                meta:set_int("castlingWhiteL", 0)
                        elseif pieceFrom:sub(-1) == "2" then
                                meta:set_int("castlingWhiteR", 0)
                        end
                end

        -- KNIGHT
        elseif pieceFrom:sub(11,16) == "knight" then
                -- Get relative pos
                local dx = from_x - to_x
                local dy = from_y - to_y

                -- Get absolute values
                if dx < 0 then dx = -dx end
                if dy < 0 then dy = -dy end

                -- Sort x and y
                if dx > dy then dx, dy = dy, dx end

                -- Ensure that dx == 1 and dy == 2
                if dx ~= 1 or dy ~= 2 then
                        return 0
                end
                -- Just ensure that destination cell does not contain friend piece
                -- ^ It was done already thus everything ok

        -- BISHOP
        elseif pieceFrom:sub(11,16) == "bishop" then
                -- Get relative pos
                local dx = from_x - to_x
                local dy = from_y - to_y

                -- Get absolute values
                if dx < 0 then dx = -dx end
                if dy < 0 then dy = -dy end

                -- Ensure dx and dy are equal
                if dx ~= dy then return 0 end

                if from_x < to_x then
                        if from_y < to_y then
                                -- Moving right-down
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x + i, from_y + i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        else
                                -- Moving right-up
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x + i, from_y - i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        end
                else
                        if from_y < to_y then
                                -- Moving left-down
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x - i, from_y + i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        else
                                -- Moving left-up
                                -- ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x - i, from_y - i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        end
                end

        -- QUEEN
        elseif pieceFrom:sub(11,15) == "queen" then
                local dx = from_x - to_x
                local dy = from_y - to_y

                -- Get absolute values
                if dx < 0 then dx = -dx end
                if dy < 0 then dy = -dy end

                -- Ensure valid relative move
                if dx ~= 0 and dy ~= 0 and dx ~= dy then
                        return 0
                end

                if from_x == to_x then
                        if from_y < to_y then
                                -- Goes down
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x, from_y + i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        else
                                -- Goes up
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x, from_y - i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        end
                elseif from_x < to_x then
                        if from_y == to_y then
                                -- Goes right
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x + i, from_y)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        elseif from_y < to_y then
                                -- Goes right-down
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x + i, from_y + i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        else
                                -- Goes right-up
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x + i, from_y - i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        end
                else
                        if from_y == to_y then
                                -- Goes left
                                -- Ensure that no piece disturbs the way and destination cell does
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x - i, from_y)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        elseif from_y < to_y then
                                -- Goes left-down
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x - i, from_y + i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        else
                                -- Goes left-up
                                -- Ensure that no piece disturbs the way
                                for i = 1, dx - 1 do
                                        if inv:get_stack(
                                                from_list, xy_to_index(from_x - i, from_y - i)):get_name() ~= "" then
                                                return 0
                                        end
                                end
                        end
                end

        -- KING
        elseif pieceFrom:sub(11,14) == "king" then
                local dx = from_x - to_x
                local dy = from_y - to_y
                local check = true

                if thisMove == "white" then
                        if from_y == 7 and to_y == 7 then
                                if to_x == 1 then
                                        local castlingWhiteL = meta:get_int("castlingWhiteL")
                                        local idx57 = inv:get_stack(from_list, 57):get_name()

                                        if castlingWhiteL == 1 and idx57 == "realchess:rook_white_1" then
                                                for i = 58, from_index - 1 do
                                                        if inv:get_stack(from_list, i):get_name() ~= "" then
                                                                return 0
                                                        end
                                                end

                                                inv:set_stack(from_list, 57, "")
                                                inv:set_stack(from_list, 59, "realchess:rook_white_1")
                                                check = false
                                        end
                                elseif to_x == 6 then
                                        local castlingWhiteR = meta:get_int("castlingWhiteR")
                                        local idx64 = inv:get_stack(from_list, 64):get_name()

                                        if castlingWhiteR == 1 and idx64 == "realchess:rook_white_2" then
                                                for i = from_index + 1, 63 do
                                                        if inv:get_stack(from_list, i):get_name() ~= "" then
                                                                return 0
                                                        end
                                                end

                                                inv:set_stack(from_list, 62, "realchess:rook_white_2")
                                                inv:set_stack(from_list, 64, "")
                                                check = false
                                        end
                                end
                        end
                elseif thisMove == "black" then
                        if from_y == 0 and to_y == 0 then
                                if to_x == 1 then
                                        local castlingBlackL = meta:get_int("castlingBlackL")
                                        local idx1 = inv:get_stack(from_list, 1):get_name()

                                        if castlingBlackL == 1 and idx1 == "realchess:rook_black_1" then
                                                for i = 2, from_index - 1 do
                                                        if inv:get_stack(from_list, i):get_name() ~= "" then
                                                                return 0
                                                        end
                                                end

                                                inv:set_stack(from_list, 1, "")
                                                inv:set_stack(from_list, 3, "realchess:rook_black_1")
                                                check = false
                                        end
                                elseif to_x == 6 then
                                        local castlingBlackR = meta:get_int("castlingBlackR")
                                        local idx8 = inv:get_stack(from_list, 8):get_name()

                                        if castlingBlackR == 1 and idx8 == "realchess:rook_black_2" then
                                                for i = from_index + 1, 7 do
                                                        if inv:get_stack(from_list, i):get_name() ~= "" then
                                                                return 0
                                                        end
                                                end

                                                inv:set_stack(from_list, 6, "realchess:rook_black_2")
                                                inv:set_stack(from_list, 8, "")
                                                check = false
                                        end
                                end
                        end
                end

                if check then
                        if dx < 0 then
                                dx = -dx
                        end

                        if dy < 0 then
                                dy = -dy
                        end

                        if dx > 1 or dy > 1 then
                                return 0
                        end
                end

                if thisMove == "white" then
                        meta:set_int("castlingWhiteL", 0)
                        meta:set_int("castlingWhiteR", 0)

                elseif thisMove == "black" then
                        meta:set_int("castlingBlackL", 0)
                        meta:set_int("castlingBlackR", 0)
                end
        end

        local board       = board_to_table(inv)
        board[to_index]   = board[from_index]
        board[from_index] = ""

        local black_king_idx, white_king_idx = locate_kings(board)
        if not black_king_idx or not white_king_idx then
                return 0
        end
        local blackAttacked = attacked("black", black_king_idx, board)
        local whiteAttacked = attacked("white", white_king_idx, board)

        if blackAttacked then
                if thisMove == "black" then
                        --[(*)[ and meta:get_string("blackAttacked") == "true" ]] then
                        return 0
                else
                        meta:set_string("blackAttacked", "true")
                end
        else
                meta:set_string("blackAttacked", "")
        end

        if whiteAttacked then
                if thisMove == "white" then
                        --[(*)[ and meta:get_string("whiteAttacked") == "true" ]] then
                        return 0
                else
                        meta:set_string("whiteAttacked", "true")
                end
        else
                meta:set_string("whiteAttacked", "")
        end

        --(*) Allow a piece to move and put its king in check. Maybe not in the chess rules though?

        lastMove = thisMove
        meta:set_string("lastMove", lastMove)
        meta:set_int("lastMoveTime", minetest.get_gametime())

        if meta:get_string("playerWhite") == "" then
                meta:set_string("playerWhite", playerWhite)
        elseif meta:get_string("playerBlack") == "" then
                meta:set_string("playerBlack", playerBlack)
        end

        local pieceTo_s = pieceTo ~= "" and pieceTo:match(":(%w+_%w+)") or ""
        get_moves_list(meta, pieceFrom, pieceTo, pieceTo_s, from_index, to_index)
        get_eaten_list(meta, pieceTo, pieceTo_s)

        return 1
end

local function ai_move(inv, meta)
        local board_t = board_to_table(inv)
        local lastMove = meta:get_string("lastMove")

        if lastMove == "white" then
                update_formspec(meta)
                local moves = {}

                for i = 1, 64 do
                        local possibleMoves = get_possible_moves(board_t, i)
                        local stack_name    = inv:get_stack("board", i):get_name()

                        if stack_name:find("black") then
                                moves[tostring(i)] = possibleMoves
                        end
                end

                local choice_from, choice_to = best_move(moves)

                local pieceFrom = inv:get_stack("board", choice_from):get_name()
                local pieceTo   = inv:get_stack("board", choice_to):get_name()
                local pieceTo_s = pieceTo ~= "" and pieceTo:match(":(%w+_%w+)") or ""

                local board          = board_to_table(inv)
                local black_king_idx = locate_kings(board)
                local blackAttacked  = attacked("black", black_king_idx, board)
                local kingSafe       = true
                local bestMoveSaveFrom, bestMoveSaveTo

                if blackAttacked then
                        kingSafe = false
                        meta:set_string("blackAttacked", "true")
                        local save_moves = {}

                        for from_idx, _ in pairs(moves) do
                        for to_idx, value in pairs(_) do
                                from_idx = tonumber(from_idx)
                                local from_idx_bak, to_idx_bak = board[from_idx], board[to_idx]
                                board[to_idx]   = board[from_idx]
                                board[from_idx] = ""
                                black_king_idx  = locate_kings(board)

                                if black_king_idx then
                                        blackAttacked = attacked("black", black_king_idx, board)
                                        if not blackAttacked then
                                                save_moves[from_idx] = save_moves[from_idx] or {}
                                                save_moves[from_idx][to_idx] = value
                                        end
                                end

                                board[from_idx], board[to_idx] = from_idx_bak, to_idx_bak
                        end
                        end

                        if next(save_moves) then
                                bestMoveSaveFrom, bestMoveSaveTo = best_move(save_moves)
                        end
                end

                minetest.after(1.0, function()
                        local lastMoveTime = meta:get_int("lastMoveTime")
                        if lastMoveTime > 0 then
                                if not kingSafe then
                                        if bestMoveSaveTo then
                                                inv:set_stack("board", bestMoveSaveTo, board[bestMoveSaveFrom])
                                                inv:set_stack("board", bestMoveSaveFrom, "")
                                                meta:set_string("blackAttacked", "")
                                        else
                                                return
                                        end
                                else
                                        if pieceFrom:find("pawn") and choice_to >= 57 and choice_to <= 64 then
                                                inv:set_stack("board", choice_to, "realchess:queen_black")
                                        else
                                                inv:set_stack("board", choice_to, pieceFrom)
                                        end

                                        inv:set_stack("board", choice_from, "")
                                end

                                board = board_to_table(inv)
                                local _, white_king_idx = locate_kings(board)
                                local whiteAttacked = attacked("white", white_king_idx, board)

                                if whiteAttacked then
                                        meta:set_string("whiteAttacked", "true")
                                end

                                if meta:get_string("playerBlack") == "" then
                                        meta:set_string("playerBlack", "Dumb AI")
                                end

                                meta:set_string("lastMove", "black")
                                meta:set_int("lastMoveTime", minetest.get_gametime())

                                get_moves_list(meta, pieceFrom, pieceTo, pieceTo_s, choice_from, choice_to)
                                get_eaten_list(meta, pieceTo, pieceTo_s)

                                update_formspec(meta)
                        end
                end)
        else
                update_formspec(meta)
        end
end

function realchess.on_move(pos, from_list, from_index)
        local meta = minetest.get_meta(pos)
        local inv  = meta:get_inventory()
        inv:set_stack(from_list, from_index, "")

        if meta:get_string("mode") == "single" then
                ai_move(inv, meta)
        end

        return false
end

local function timeout_format(timeout_limit)
        local time_remaining = timeout_limit - minetest.get_gametime()
        local minutes        = math.floor(time_remaining / 60)
        local seconds        = time_remaining % 60

        if minutes == 0 then
                return seconds .. " sec."
        end

        return minutes .. " min. " .. seconds .. " sec."
end

function realchess.fields(pos, _, fields, sender)
        local playerName    = sender:get_player_name()
        local meta          = minetest.get_meta(pos)
        local timeout_limit = meta:get_int("lastMoveTime") + 300
        local playerWhite   = meta:get_string("playerWhite")
        local playerBlack   = meta:get_string("playerBlack")
        local lastMoveTime  = meta:get_int("lastMoveTime")
        if fields.quit then return end

        if fields.single or fields.multi then
                meta:set_string("mode", (fields.single and "single" or "multi"))
                update_formspec(meta)
                return
        end

        -- Timeout is 5 min. by default for resetting the game (non-players only)
        if fields.new then
                if (playerWhite == playerName or playerBlack == playerName) then
                        realchess.init(pos)

                elseif lastMoveTime > 0 then
                        if minetest.get_gametime() >= timeout_limit and
                                        (playerWhite ~= playerName or playerBlack ~= playerName) then
                                realchess.init(pos)
                        else
                                minetest.chat_send_player(playerName, chat_prefix ..
                                        "You can't reset the chessboard, a game has been started. " ..
                                        "If you aren't a current player, try again in " ..
                                        timeout_format(timeout_limit))
                        end
                end
        end
end

function realchess.dig(pos, player)
        if not player then
                return false
        end

        local meta          = minetest.get_meta(pos)
        local playerName    = player:get_player_name()
        local timeout_limit = meta:get_int("lastMoveTime") + 300
        local lastMoveTime  = meta:get_int("lastMoveTime")

        -- Timeout is 5 min. by default for digging the chessboard (non-players only)
        return (lastMoveTime == 0 and minetest.get_gametime() > timeout_limit) or
                minetest.chat_send_player(playerName, chat_prefix ..
                                "You can't dig the chessboard, a game has been started. " ..
                                "Reset it first if you're a current player, or dig it again in " ..
                                timeout_format(timeout_limit))
end

minetest.register_node(":realchess:chessboard", {
        description = "Chess Board",
        drawtype = "nodebox",
        paramtype = "light",
        paramtype2 = "facedir",
        inventory_image = "chessboard_top.png",
        wield_image = "chessboard_top.png",
        tiles = {"chessboard_top.png", "chessboard_top.png", "chessboard_sides.png"},
        groups = {choppy=3, oddly_breakable_by_hand=2, flammable=3},
        sounds = default.node_sound_wood_defaults(),
        node_box = {type = "fixed", fixed = {-.375, -.5, -.375, .375, -.4375, .375}},
        sunlight_propagates = true,
        on_rotate = screwdriver.rotate_simple,
        can_dig = realchess.dig,
        on_construct = realchess.init,
        on_receive_fields = realchess.fields,
        allow_metadata_inventory_move = realchess.move,
        on_metadata_inventory_move = realchess.on_move,
        allow_metadata_inventory_take = function() return 0 end
})

local function register_piece(name, count)
        for _, color in pairs({"black", "white"}) do
        if not count then
                minetest.register_craftitem(":realchess:" .. name .. "_" .. color, {
                        description = color:gsub("^%l", string.upper) .. " " .. name:gsub("^%l", string.upper),
                        inventory_image = name .. "_" .. color .. ".png",
                        stack_max = 1,
                        groups = {not_in_creative_inventory=1}
                })
        else
                for i = 1, count do
                        minetest.register_craftitem(":realchess:" .. name .. "_" .. color .. "_" .. i, {
                                description = color:gsub("^%l", string.upper) .. " " .. name:gsub("^%l", string.upper),
                                inventory_image = name .. "_" .. color .. ".png",
                                stack_max = 1,
                                groups = {not_in_creative_inventory=1}
                        })
                end
        end
        end
end

register_piece("pawn", 8)
register_piece("rook", 2)
register_piece("knight", 2)
register_piece("bishop", 2)
register_piece("queen")
register_piece("king")

-- Recipes

minetest.register_craft({
        output = "realchess:chessboard",
        recipe = {
                {"dye:black", "dye:white", "dye:black"},
                {"stairs:slab_wood", "stairs:slab_wood", "stairs:slab_wood"}
        }
})