$( document ).ready(function() {			
      let board = Array(8).fill().map(() => Array(8).fill().map(() => Array(8).fill(false)));
			let boards = Array;
			let max_placed_queens = 0;
      let placed_queens = 0;

      function pieceTheme (piece) {
        return 'https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/Chess_qdt45.svg/26px-Chess_qdt45.svg.png';
      }

      var config = {
        showErrors: true,
        pieceTheme: pieceTheme
      };

			for (let i = 0; i < 8; i++) {
				boards[i] = Chessboard('board' + i, config);
        update_board(boards[i], i);
			}

			setTimeout(function() { place_queen(0,0) }, 500);

			function place_queen(h, col) {

				// Found a solution
				if ((h * 8 + col) > 63)
					return true;

				// Next level
				if (col > 7) {
					h++;
					col -= 8;
				};

				// Place a queen
				for (let i = 0; i <= 8; i++) {
          if (i == 8 && (h * 8 + col + 1) < 64) {
            if ( place_queen(h,col+1) )
              return true;
          }
          
					if (i != 8 && valid_placement(h, i, col)) {
						board[h][i][col] = true;
            placed_queens++;
            
            console.log('Trying:', h, i, col, placed_queens);

						// Update the board with the best solution
						if ( max_placed_queens < placed_queens ) {
              console.log(placed_queens + ' Placed');

              for (let j = 0; j < 8; j++) {
                update_board(boards[j], j);
              }
              
              if (placed_queens > 33) {
                return true;
              }
              
							max_placed_queens = placed_queens;
						}

						// Place another queen
						if (place_queen(h,col+1))
							return true;
            
            placed_queens--;

						board[h][i][col] = false;
					}
				}

				// This branch has failed
				return false;
			}

			function valid_placement(height, row, col) {
				let i,j,k,o,a,b;

				for (i = 0; i < 8; i++) {
					if (board[height][row][i])
						return false;
 					if (board[height][i][col])
						return false;         
				}

        //o = (row > col) ? row : col;
        o = 8 - col - 1;
				for (i = row + o, j = col + o; i >=0 && j >= 0; i--, j--) {
          if (i >= 0 && j >= 0 && i < 8 && j < 8 && board[height][i][j]) 
						return false;
				}

				for (i = row - o,  j = col + o; i < 8 && j >= 0; i++, j--) {
          if (i >= 0 && j >= 0 && i < 8 && j < 8 && board[height][i][j])
					  return false;
				}

				for (k =  7; k >= 0; k--) {
					let range = height - k;
          if (range < 0)
            range = -range;
					let ranges = [-range, 0, range];

					for ( i = 0; i < 3; i++ ) {
						for ( j = 0; j < 3; j++ ) {
							a = row + ranges[i];
							b = col + ranges[j];

							// Out of bound;
							if (a >= 0 && b >= 0 && a < 8 && b < 8) {
								if (board[k][a][b])
									return false;
							}
						}
					}
				}

				return true;
			}

			function update_board(display_board, z) {
				let positions = {};

				for (let i = 0; i < 8; i++) {
					for (let j = 0; j < 8; j++) {
						if (board[z][i][j] == true) {
							let letter = (j + 10).toString(36);
							let number = i + 1;
							positions[letter + number] = 'bQ';
						}
					}
				}

        display_board.position(positions, false);
			}
});