Fancy split navigation with vim and tmux

1-description.md

• In vim I have split navigation mapped to ctrl+h/j/k/l.
• In tmux I navigate splits with prefix + ctrl+h/j/k/l.
• Ideally I would be able to navigate between vim and tmux splits transparently using only ctrl+h/j/k/l.
• I haven't figured that out yet, but I have figured out how to jump out of vim into the next tmux split if I am at the boundary of vim and tmux, without having to prefix jump, which is pretty ace. ie:

    *=cursor position
    
    -----------            -----------            -----------                  -----------
    | vim  *  |            | vim     |            | vim     |                  | vim     |
    -----------            -----------            -----------                  -----------
    | vim     |  <c-j> ->  | vim  *  |  <c-j> ->  | vim     |  prefix<c-k> ->  | vim   * | 
    ===========            ===========            ===========                  ===========
    | term    |            | term    |            | term  * |                  | term    |
    -----------            -----------            -----------                  -----------

Help needed:

• I have no idea how to go from a terminal into vim without using the prefix though. I know I can bind keys without the prefix using -n but that breaks the above behaviour.
• What I think I need is to for <ctrl-j> in tmux bound to a function which checks if the current pane is running vim, if so it send-keys ctrl-j to vim, otherwise it jumps the pane like normal.
• But I have no idea how to do that, do you?

2.vimrc.vim

func! MoveWithTmux(keypressed,direction)
  let k = a:keypressed
  let d = a:direction

  " I don't exactly know how this works, but it does
  " Something like silently move to the next split, and see if we are still in the same split
  let oldw = winnr()
  silent! exe "normal! \<c-w>" . k
  let neww = winnr()
  silent! exe oldw.'wincmd w'
  
  " If we are in the same split, we must be at a boundary so tell tmux to switch split
  if oldw == neww
    exec '!tmux select-pane ' . d
  else
    exe "normal! \<c-w>" . k
  end

endfunction

nnoremap <c-j> :call MoveWithTmux('j', '-D')<cr><cr>
nnoremap <c-k> :call MoveWithTmux('k', '-U')<cr><cr>
nnoremap <c-h> :call MoveWithTmux('h', '-L')<cr><cr>
nnoremap <c-l> :call MoveWithTmux('j', '-R')<cr><cr>

Ok, based on your idea I have written a few scripts that do what you want, check it out.

I just came across this: https://github.com/christoomey/vim-tmux-navigator