vim-surround toggling quotes

togglesurround.vim

function! Toggle_Surround(char)
  let pos = getcurpos()
  let cur = col(".")
  exe "norm! va".a:char
  let start = col("v")
  let end = col(".")
  exe "norm! \<esc>"
  call cursor(pos[1], pos[2])
  if start <= cur && cur <= end && start != end
    " inside quote :)
    exe "norm ds".a:char
    call cursor(pos[1], pos[2]-len(a:char))
  else
    " not inside a quote
    " hapens when cur <= start or end <= cur_sol or cur == start == end
    exe "norm ysiw".a:char
    call cursor(pos[1], pos[2]+len(a:char))
  endif
endfunction

nmap <silent> "" :call Toggle_Surround('"')<cr>