Function to complement the maparg() function in Vim. Given the 'rhs' of a mapping, this function returns the 'lhs'

MapKey.vim

function! MapKey( rhs, mode )
  " Description: Get LHS of a mapping. Inverse of maparg().
  " Note that hasmapto() returns a binary result while MapKey() returns the value of the LHS.
  " Pass in a key sequence and the first letter of a vim mode.
  " Returns key mapping mapped to it in that mode, else '' if none.
  " Eg:
  "   :nnoremap <Tab> :bn<CR>
  "   :call Mapkey(':bn<CR>', 'n')
  " returns <Tab>
  " TODO:
  " * Modify the function to be capable of returning multiple values.
  "   Eg. if multiple lhs mappings perform the same action then calling MapKey() should return all of them
  execute 'redir => l:mappings | silent! ' . a:mode . 'map | redir END'

  " Convert all text between angle-brackets to lowercase
  " Required to recognize all case-variants of <c-A> and <C-a> as the same thing
  " Note that Alt mappings are case-sensitive. However, this is not an issue as <A-x> is " replaced with its approriate
  " keycode for eg. <A-a> becomes á
  let l:rhs = substitute(a:rhs, '<[^>]\+>', "\\L\\0", 'g')

  for l:map in split(l:mappings, '\n')
    " Get rhs for each mapping
    let l:lhs = split(l:map, '\s\+')[1]
    let l:lhs_map = maparg(l:lhs, a:mode)

    if substitute(l:lhs_map, '<[^>]\+>', "\\L\\0", 'g') ==# l:rhs
      return l:lhs
    endif
  endfor
  return ''
endfunction