Update lf.vim to work with Neovim and in GUI and use fallbacks

etc/lf.vim

@@ -13,22 +13,68 @@
 "     nnoremap <leader>l :LF<cr>
 "
 
-function! LF()
-    let temp = tempname()
-    exec 'silent !lf -selection-path=' . shellescape(temp)
-    if !filereadable(temp)
-        redraw!
-        return
+let s:temp = tempname()
+if executable('lf')
+  command! -nargs=? -bar -complete=dir FilePicker call FilePicker('lf', '-selection-path', s:temp, <q-args>)
+elseif executable('ranger')
+  " The option --choosefiles was added in ranger 1.5.1.
+  " Use --choosefile with ranger 1.4.2 through 1.5.0 instead.
+  command! -nargs=? -bar -complete=dir FilePicker call FilePicker('ranger', '--choosefiles='..s:temp, '--selectfile', <q-args>)
+elseif executable('nnn')
+  command! -nargs=? -bar -complete=dir FilePicker call FilePicker('nnn', '-p', s:temp, <q-args>)
+endif
+
+if exists(':FilePicker') == 2
+  function! FilePicker(...)
+    let path = a:000[-1]
+    let cmd = a:000[:-2] + (empty(path) ?
+          \ [filereadable(expand('%')) ? shellescape(expand('%'),1) : '.'] : [path])
+    if has('nvim')
+      enew
+      call termopen(cmd, { 'on_exit': function('s:open') })
+    else
+      if has('gui_running')
+        if has('terminal')
+          call term_start(cmd, {'exit_cb': function('s:term_close'), 'curwin': 1})
+        else
+          echomsg 'GUI is running but terminal is not supported.'
+        endif
+      else
+        exec 'silent !'..join(cmd) | call s:open()
+      endif
+    endif
+  endfunction
+
+  if has('gui_running') && has('terminal')
+    function! s:term_close(job_id, event)
+      if a:event == 'exit'
+        bwipeout!
+        call s:open()
+      endif
+    endfunction
+  endif
+
+  function! s:open(...)
+    if !filereadable(s:temp)
+      " if &buftype ==# 'terminal'
+      "   bwipeout!
+      " endif
+      redraw!
+      " Nothing to read.
+      return
     endif
-    let names = readfile(temp)
+    let names = readfile(s:temp)
     if empty(names)
-        redraw!
-        return
+      redraw!
+      " Nothing to open.
+      return
     endif
-    exec 'edit ' . fnameescape(names[0])
+    " Edit the first item.
+    exec 'edit' fnameescape(names[0])
+    " Add any remaning items to the arg list/buffer list.
     for name in names[1:]
-        exec 'argadd ' . fnameescape(name)
+      exec 'argadd' fnameescape(name)
     endfor
     redraw!
-endfunction
-command! -bar LF call LF()
+  endfunction
+endif