private Block Turn(Block block, int rotation)
{
if (block.Shape == Shape.O)
{
return(null);
}
var source = Offset(block);
var target = Offset(block, rotation);
var col = target.Column - source.Column;
var flr = target.Floor - source.Floor;
col += block.Column;
flr += block.Offset;
return(rows.Block(block.Shape, block.Rotation.Rotate(rotation), col, flr));
}