Automatically enable ibus IME when entering insert mode

gistfile1.vim

" Barry Arthur, March 2015
" Auto-toggle IME when in insert mode
" leaving it "off" in normal mode.
"
" Set your ibus_normal and ibus_insert mode engines in your ~/.vimrc
" In insert mode, use the <LShift> key to toggle between compose and
" passthrough modes. Set your IBus preferences as to which mode you
" start in.

if !exists('ibus_normal')
  let ibus_normal = 'xkb:us::eng'
endif

if !exists('ibus_insert')
  let ibus_insert = 'pinyin'
endif

augroup IBus
  au InsertEnter * :call system('ibus engine ' . g:ibus_insert)
  au InsertLeave * :call system('ibus engine ' . g:ibus_normal)
augroup END

function! IBusEngine()
  return split(system('ibus engine'), "\n")[0]
endfunction

let &statusline = '%f%m%r%h%w [%n:%{&ff}/%Y] %{IBusEngine()}%=[0x%04.4B][%03v][%p%% line %l of %L]'