Write small Software

My idea is a small JavaScript program which I will attach to my WordPress blog post. The specifications are as follows: There should be a 12x12 grid onto which the user should be able to drag L-shaped tetrominoes (like this: [login to view URL]). The user should be able to rotate (and flip) the L before dragging it to the grid, and if not too complicated, the next L would be a different color so it would be distinguishable on the grid (using 4-5 colours in total should be fine). There should also be a textbox that keeps track of how many Ls are currently on the screen and an undo-button (not included in the sketch which I attached) so that the user can go back.