Upgrading an existing javascript for a puzzle/crossword game

1. The current script enables to click on an empty cell on the crossword and than clicking on a possible letter from possible letters list. 2. On top of the current script, the upgrade should give the user the option to “drag & drop” letters from the list into the crossword. Both options should work simultaneously. 3. The crossword is responsive. The current script is working on a desktop and mobile version. For desktop it uses mouse events, and for mobile it uses touch event. The upgrade should be also work on both options. 4. I need a clear & visible dragging option and not like the “drag & drop” option available with HTML5, where the drag object becomes transparent. So when a letter drag happens, a new letter object should be created and it is the one that should be moved around. The original letter object should stay in it's original place. 5. If dragging was successful, and letter was placed in a valid cell the corresponding function(put_letter) from the previous script will be triggered(i.ie. updating possible letters list). 6. If a user decide to delete a letter from crossword. The upgrade script should be able to drag a valid letter outside the crossword and drop it there. An animation of the letter start from the drop (outside crossword), to it's initial location. Than triggering a delete function (put_letter) from previous script(i.e. updating possible letters list). 7. If a user wants to switch 2 letters that are on the crossword, he can drag one letter on top of the other and release it. This will trigger a switch of position. Animating the movement of the letter to it's new location is required. 8. The new script should allow switching letter that will be dragged from the possible letters list to a valid occupied cell over the crossword. This will (delete) the letter that was on the puzzle( animating its return to it's location on the free letters list, and triggering corresponding function(put_letter) from previous script), and the new dragged letter will take it's place instead, also triggering the function(put_letter) to update possible letters list. 9. On the new script if a user drags a letter from the possible letters list, and changes his mind and drops the letter outside the puzzle, animation will take the letter to it's original place. 10. When dragging a letter over the puzzle cells, valid cells will be marked with a thicker border, to mark it's a possible “drop” zone. When the drag leaves the marked cells and continue(no drop was made), the border returns to normal. 11. It is possible that initial puzzle is not blank and some valid cells already has letters, please take it into account(I'll provide HTML for that). 12. Please keep track after changes and provide full comments as well. Because I will embed your script with mine after work completed. 13. Javascript only. Sorry Jquery people:( 14. You will need to sign an NDA and disclaimer agreement. 15. Appropriate freelancers will receive the HTML and old JS script to work with.