diff --git a/autoload/fern/action.vim b/autoload/fern/action.vim
new file mode 100644
index 00000000..b3cea2d4
--- /dev/null
+++ b/autoload/fern/action.vim
@@ -0,0 +1,13 @@
+let s:Action = vital#fern#import('App.Action')
+
+function! fern#action#_init() abort
+  call s:Action.init()
+endfunction
+
+function! fern#action#call(...) abort
+  call call(s:Action.call, a:000, s:Action)
+endfunction
+
+function! fern#action#list(...) abort
+  return call(s:Action.list, a:000, s:Action)
+endfunction
diff --git a/autoload/fern/internal/action.vim b/autoload/fern/internal/action.vim
deleted file mode 100644
index cc16c1c2..00000000
--- a/autoload/fern/internal/action.vim
+++ /dev/null
@@ -1,188 +0,0 @@
-function! fern#internal#action#init() abort
-  nnoremap <buffer><silent> <Plug>(fern-action-choice) :<C-u>call <SID>map_choice()<CR>
-  nnoremap <buffer><silent> <Plug>(fern-action-repeat) :<C-u>call <SID>map_repeat()<CR>
-  nnoremap <buffer><silent> <Plug>(fern-action-help) :<C-u>call <SID>map_help(0)<CR>
-  nnoremap <buffer><silent> <Plug>(fern-action-help:all) :<C-u>call <SID>map_help(1)<CR>
-
-  " NOTE:
-  " Action is core feature of fern so do NOT refer g:fern#disable_default_mappings
-  if !hasmapto('<Plug>(fern-action-choice)', 'n')
-    nmap <buffer> a <Plug>(fern-action-choice)
-  endif
-  if !hasmapto('<Plug>(fern-action-repeat)', 'n')
-    nmap <buffer> . <Plug>(fern-action-repeat)
-  endif
-  if !hasmapto('<Plug>(fern-action-help)', 'n')
-    nmap <buffer> ? <Plug>(fern-action-help)
-  endif
-
-  let prefix = 'fern-action-'
-  let b:fern_action = {
-        \ 'actions': s:build_actions(prefix),
-        \ 'previous': '',
-        \}
-endfunction
-
-function! fern#internal#action#call(name, ...) abort
-  let options = extend({
-        \ 'capture': 0,
-        \ 'verbose': 0,
-        \}, a:0 ? a:1 : {},
-        \)
-  if !exists('b:fern_action')
-    throw 'the buffer has not been initialized for actions'
-  endif
-  if index(b:fern_action.actions, a:name) is# -1
-    throw printf('no action %s found in the buffer', a:name)
-  endif
-  let b:fern_action.previous = a:name
-  let Fn = funcref('s:call', [a:name])
-  if options.verbose
-    let Fn = funcref('s:verbose', [Fn])
-  endif
-  if options.capture
-    let Fn = funcref('s:capture', [Fn])
-  endif
-  call Fn()
-endfunction
-
-function! s:map_choice() abort
-  if !exists('b:fern_action')
-    throw 'the buffer has not been initialized for actions'
-  endif
-  call inputsave()
-  try
-    let fn = get(function('s:complete_choice'), 'name')
-    let expr = input('action: ', '', printf('customlist,%s', fn))
-  finally
-    call inputrestore()
-  endtry
-  let r = s:parse_expr(expr)
-  let ns = copy(b:fern_action.actions)
-  let r.name = get(filter(ns, { -> v:val =~# '^' . r.name }), 0)
-  if empty(r.name)
-    return
-  endif
-  call fern#internal#action#call(r.name, {
-       \ 'capture': r.capture,
-       \ 'verbose': r.verbose,
-       \})
-endfunction
-
-function! s:map_repeat() abort
-  if !exists('b:fern_action')
-    throw 'the buffer has not been initialized for actions'
-  endif
-  if empty(b:fern_action.previous)
-    return
-  endif
-  call fern#internal#action#call(b:fern_action.previous)
-endfunction
-
-function! s:map_help(all) abort
-  let Sort = { a, b -> s:compare(a[1], b[1]) }
-  let rs = split(execute('nmap'), '\n')
-  call map(rs, { _, v -> v[3:] })
-  call map(rs, { _, v -> matchlist(v, '^\([^ ]\+\)\s*\*\?@\?\(.*\)$')[1:2] })
-
-  " To action mapping
-  let rs1 = map(copy(rs), { _, v -> v + [matchstr(v[1], '^<Plug>(fern-action-\zs.*\ze)$')] })
-  call filter(rs1, { _, v -> !empty(v[2]) })
-  call filter(rs1, { _, v -> v[0] !~# '^<Plug>' || v[0] =~# '^<Plug>(fern-action-' })
-  call map(rs1, { _, v -> [v[0], v[2], v[1]] })
-
-  " From action mapping
-  let rs2 = map(copy(rs), { _, v -> v + [matchstr(v[0], '^<Plug>(fern-action-\zs.*\ze)$')] })
-  call filter(rs2, { _, v -> !empty(v[2]) })
-  call map(rs2, { _, v -> ['', v[2], v[0]] })
-
-  let rs = uniq(sort(rs1 + rs2, Sort), Sort)
-  if !a:all
-    call filter(rs, { -> v:val[1] !~# ':' || !empty(v:val[0]) })
-  endif
-  let len0 = max(map(copy(rs), { -> len(v:val[0]) }))
-  let len1 = max(map(copy(rs), { -> len(v:val[1]) }))
-  let len2 = max(map(copy(rs), { -> len(v:val[2]) }))
-  call map(rs, { _, v -> [
-       \   printf(printf('%%-%dS', len0), v[0]),
-       \   printf(printf('%%-%dS', len1), v[1]),
-       \   printf(printf('%%-%dS', len2), v[2]),
-       \ ]
-       \})
-
-  call map(rs, { -> join(v:val, '  ') })
-  if !a:all
-    echohl Title
-    echo "NOTE: Some actions are concealed. Use 'help:all' action to see all actions."
-    echohl None
-  endif
-  echo join(rs, "\n")
-endfunction
-
-function! s:parse_expr(expr) abort
-  if empty(a:expr)
-    return {'name' : '', 'capture': 0, 'verbose': 0}
-  endif
-  let terms = split(a:expr)
-  let name = remove(terms, -1)
-  let Has = { ns, n -> len(filter(copy(ns), { -> v:val ==# n })) }
-  return {
-        \ 'name': name,
-        \ 'capture': Has(terms, 'capture'),
-        \ 'verbose': Has(terms, 'verbose'),
-        \}
-endfunction
-
-function! s:build_actions(prefix) abort
-  let n = len(a:prefix)
-  let ms = split(execute(printf('nmap <Plug>(%s', a:prefix)), '\n')
-  call map(ms, { _, v -> split(v)[1] })
-  call map(ms, { _, v -> matchstr(v, '^<Plug>(\zs.*\ze)$') })
-  call filter(ms, { _, v -> !empty(v) })
-  call map(ms, { _, expr -> expr[n :] })
-  return sort(ms)
-endfunction
-
-function! s:complete_choice(arglead, cmdline, cursorpos) abort
-  if !exists('b:fern_action')
-    return []
-  endif
-  let names = copy(b:fern_action.actions)
-  let names += ['capture', 'verbose']
-  if empty(a:arglead)
-    call filter(names, { -> v:val !~# ':' })
-  endif
-  return filter(names, { -> v:val =~# '^' . a:arglead })
-endfunction
-
-function! s:compare(i1, i2) abort
-  return a:i1 == a:i2 ? 0 : a:i1 > a:i2 ? 1 : -1
-endfunction
-
-function! s:call(name) abort
-  execute printf("normal \<Plug>(fern-action-%s)", a:name)
-endfunction
-
-function! s:capture(fn) abort
-  let output = execute('call a:fn()')
-  let rs = split(output, '\r\?\n')
-  execute printf('botright %dnew', len(rs))
-  call setline(1, rs)
-  setlocal buftype=nofile bufhidden=wipe
-  setlocal noswapfile nobuflisted
-  setlocal nomodifiable nomodified
-  setlocal nolist signcolumn=no
-  setlocal nonumber norelativenumber
-  setlocal cursorline
-  nnoremap <buffer><silent> q :<C-u>q<CR>
-endfunction
-
-function! s:verbose(fn) abort
-  let verbose_saved = &verbose
-  try
-    set verbose
-    call a:fn()
-  finally
-    let &verbose = verbose_saved
-  endtry
-endfunction
diff --git a/autoload/fern/internal/locator.vim b/autoload/fern/internal/locator.vim
index c1b2373d..18900be2 100644
--- a/autoload/fern/internal/locator.vim
+++ b/autoload/fern/internal/locator.vim
@@ -1,52 +1,25 @@
-let s:conditions = [
-      \ { wi -> !wi.loclist },
-      \ { wi -> !wi.quickfix },
-      \ { wi -> !getwinvar(wi.winid, '&winfixwidth', 0) },
-      \ { wi -> !getwinvar(wi.winid, '&winfixheight', 0) },
-      \ { wi -> !getbufvar(wi.bufnr, '&previewwindow', 0) },
-      \]
-function! fern#internal#locator#score(winnr) abort
+let s:WindowLocator = vital#fern#import('App.WindowLocator')
 
-  let winid = win_getid(a:winnr)
-  let wininfo = getwininfo(winid)
-  if empty(wininfo)
-    return 0
-  endif
-  let wi = wininfo[0]
-  let score = 1
-  for Condition in s:conditions
-    let score += Condition(wi)
-  endfor
-  return score
+function! fern#internal#locator#list(...) abort
+  return call(s:WindowLocator.list, a:000, s:WindowLocator)
 endfunction
 
-function! fern#internal#locator#find(origin) abort
-  let nwinnr = winnr('$')
-  if nwinnr == 1
-    return 1
-  endif
-  let origin = a:origin == 0 ? winnr() : a:origin
-  let former = range(origin, winnr('$'))
-  let latter = reverse(range(1, origin - 1))
-  let threshold = g:fern#internal#locator#THRESHOLD
-  while threshold > 0
-    for winnr in (former + latter)
-      if fern#internal#locator#score(winnr) >= threshold
-        return winnr
-      endif
-    endfor
-    let threshold -= 1
-  endwhile
-  return 0
+function! fern#internal#locator#focus(...) abort
+  return call(s:WindowLocator.focus, a:000, s:WindowLocator)
 endfunction
 
-function! fern#internal#locator#focus(origin) abort
-  let winnr = fern#internal#locator#find(a:origin)
-  if winnr == 0 || winnr == winnr()
-    return 1
-  endif
-  call win_gotoid(win_getid(winnr))
+function! fern#internal#locator#get_condition(...) abort
+  return call(s:WindowLocator.get_condition, a:000, s:WindowLocator)
 endfunction
 
-let g:fern#internal#locator#THRESHOLD = len(s:conditions) + 1
-lockvar g:fern#internal#locator#THRESHOLD
+function! fern#internal#locator#set_condition(...) abort
+  return call(s:WindowLocator.set_condition, a:000, s:WindowLocator)
+endfunction
+
+function! fern#internal#locator#get_threshold(...) abort
+  return call(s:WindowLocator.get_threshold, a:000, s:WindowLocator)
+endfunction
+
+function! fern#internal#locator#set_threshold(...) abort
+  return call(s:WindowLocator.set_threshold, a:000, s:WindowLocator)
+endfunction
diff --git a/autoload/fern/internal/viewer.vim b/autoload/fern/internal/viewer.vim
index 46280f12..497839c0 100644
--- a/autoload/fern/internal/viewer.vim
+++ b/autoload/fern/internal/viewer.vim
@@ -101,7 +101,7 @@ function! s:init() abort
     call helper.fern.renderer.syntax()
     call fern#hook#emit('viewer:syntax', helper)
     doautocmd <nomodeline> User FernSyntax
-    call fern#internal#action#init()
+    call fern#action#_init()
 
     let Profile = fern#profile#start('fern#internal#viewer:init')
     return s:Promise.resolve()
diff --git a/autoload/fern/internal/window.vim b/autoload/fern/internal/window.vim
index ca136e87..000c5777 100644
--- a/autoload/fern/internal/window.vim
+++ b/autoload/fern/internal/window.vim
@@ -1,4 +1,5 @@
 let s:Config = vital#fern#import('Config')
+let s:WindowSelector = vital#fern#import('App.WindowSelector')
 
 function! fern#internal#window#find(predicator, ...) abort
   let n = winnr('$')
@@ -20,102 +21,27 @@ function! fern#internal#window#find(predicator, ...) abort
 endfunction
 
 function! fern#internal#window#select() abort
-  let threshold = g:fern#internal#locator#THRESHOLD
-  while threshold > 0
-    let ws = filter(
-          \ range(1, winnr('$')),
-          \ { -> fern#internal#locator#score(v:val) >= threshold },
-          \)
-    if empty(ws)
-      let threshold -= 1
-    else
-      break
-    endif
-  endwhile
-  if empty(ws)
-    let ws = range(1, winnr('$'))
-  endif
-  return s:select(ws, {
+  let ws = fern#internal#locator#list()
+  let ws = empty(ws) ? range(1, winnr('$')) : ws
+  return s:WindowSelector.select(ws, {
         \ 'auto_select': g:fern#internal#window#auto_select,
+        \ 'select_chars': g:fern#internal#window#select_chars,
+        \ 'statusline_hl': 'FernWindowSelectStatusLine',
+        \ 'indicator_hl': 'FernWindowSelectIndicator',
         \})
 endfunction
 
-function! s:select(winnrs, ...) abort
-  let options = extend({
-        \ 'auto_select': 0,
-        \}, a:0 ? a:1 : {})
-  if options.auto_select && len(a:winnrs) <= 1
-    call win_gotoid(len(a:winnrs) ? win_getid(a:winnrs[0]) : win_getid())
-    return 0
-  endif
-  let length = len(a:winnrs)
-  let store = {}
-  for winnr in a:winnrs
-    let store[winnr] = getwinvar(winnr, '&statusline')
-  endfor
-  try
-    let chars = map(
-          \ range(length + 1),
-          \ { _, v -> get(g:fern#internal#window#select_chars, v, string(v)) },
-          \)
-    call map(keys(store), { k, v -> setwinvar(v, '&statusline', s:statusline(v, chars[k])) })
-    redrawstatus
-    call s:cnoremap_all(chars)
-    let n = input('choose window: ')
-    call s:cunmap_all()
-    redraw | echo
-    if n is# v:null
-      return 1
-    endif
-    let n = index(chars, n)
-    if n is# -1
-      return 1
-    endif
-    call win_gotoid(win_getid(a:winnrs[n]))
-  finally
-    call map(keys(store), { _, v -> setwinvar(v, '&statusline', store[v]) })
-    redrawstatus
-  endtry
-endfunction
-
-function! s:statusline(winnr, char) abort
-  let width = winwidth(a:winnr) - len(a:winnr . '') - 6
-  let leading = repeat(' ', width / 2)
-  return printf(
-        \ '%%#FernWindowSelectStatusLine#%s%%#FernWindowSelectIndicator#   %s   %%#FernWindowSelectStatusLine#',
-        \ leading,
-        \ a:char,
-        \)
-endfunction
-
-function! s:cnoremap_all(chars) abort
-  for nr in range(256)
-    silent! execute printf("cnoremap \<buffer>\<silent> \<Char-%d> \<Nop>", nr)
-  endfor
-  for char in a:chars
-    silent! execute printf("cnoremap \<buffer>\<silent> %s %s\<CR>", char, char)
-  endfor
-  silent! cunmap <buffer> <Return>
-  silent! cunmap <buffer> <Esc>
-endfunction
-
-function! s:cunmap_all() abort
-  for nr in range(256)
-    silent! execute printf("cunmap \<buffer> \<Char-%d>", nr)
-  endfor
-endfunction
-
-function! s:highlight() abort
-  highlight default link FernWindowSelectStatusLine StatusLineNC
-  highlight default link FernWindowSelectIndicator  DiffText
-endfunction
-
 call s:Config.config(expand('<sfile>:p'), {
       \ 'auto_select': 1,
       \ 'select_chars': split('abcdefghijklmnopqrstuvwxyz', '\zs'),
       \})
 
-augroup fern_internal_window_internal
+function! s:highlight() abort
+  highlight default link FernWindowSelectStatusLine VitalWindowSelectorStatusLine
+  highlight default link FernWindowSelectIndicator VitalWindowSelectorIndicator
+endfunction
+
+augroup fern_internal_window
   autocmd!
   autocmd ColorScheme * call s:highlight()
 augroup END
diff --git a/autoload/vital/_fern/App/Action.vim b/autoload/vital/_fern/App/Action.vim
new file mode 100644
index 00000000..fe362656
--- /dev/null
+++ b/autoload/vital/_fern/App/Action.vim
@@ -0,0 +1,242 @@
+" ___vital___
+" NOTE: lines between '" ___vital___' is generated by :Vitalize.
+" Do not modify the code nor insert new lines before '" ___vital___'
+function! s:_SID() abort
+  return matchstr(expand('<sfile>'), '<SNR>\zs\d\+\ze__SID$')
+endfunction
+execute join(['function! vital#_fern#App#Action#import() abort', printf("return map({'list': '', 'get_prefix': '', 'init': '', 'call': '', 'set_prefix': ''}, \"vital#_fern#function('<SNR>%s_' . v:key)\")", s:_SID()), 'endfunction'], "\n")
+delfunction s:_SID
+" ___vital___
+let s:prefix = matchstr(
+      \ fnamemodify(expand('<sfile>'), ':p:h:h:t'),
+      \ '^\%(__\zs.*\ze__\|_\zs.*\)$',
+      \)
+
+function! s:get_prefix() abort
+  return s:prefix
+endfunction
+
+function! s:set_prefix(prefix) abort
+  let s:prefix = a:prefix
+endfunction
+
+function! s:init() abort
+  execute printf(
+        \ 'nnoremap <buffer><silent> <Plug>(%s-action-choice) :<C-u>call <SID>_map_choice()<CR>',
+        \ s:prefix,
+        \)
+  execute printf(
+        \ 'nnoremap <buffer><silent> <Plug>(%s-action-repeat) :<C-u>call <SID>_map_repeat()<CR>',
+        \ s:prefix,
+        \)
+  execute printf(
+        \ 'nnoremap <buffer><silent> <Plug>(%s-action-help) :<C-u>call <SID>_map_help(0)<CR>',
+        \ s:prefix,
+        \)
+  execute printf(
+        \ 'nnoremap <buffer><silent> <Plug>(%s-action-help:all) :<C-u>call <SID>_map_help(1)<CR>',
+        \ s:prefix,
+        \)
+
+  if !hasmapto(printf('<Plug>(%s-action-choice)', s:prefix), 'n')
+    execute printf(
+          \ 'nmap <buffer> a <Plug>(%s-action-choice)',
+          \ s:prefix,
+          \)
+  endif
+  if !hasmapto(printf('<Plug>(%s-action-repeat)', s:prefix), 'n')
+    execute printf(
+          \ 'nmap <buffer> . <Plug>(%s-action-repeat)',
+          \ s:prefix,
+          \)
+  endif
+  if !hasmapto(printf('<Plug>(%s-action-help)', s:prefix), 'n')
+    execute printf(
+          \ 'nmap <buffer> ? <Plug>(%s-action-help)',
+          \ s:prefix,
+          \)
+  endif
+
+  let b:{s:prefix}_action = {
+        \ 'actions': s:_build_actions(),
+        \ 'previous': '',
+        \}
+endfunction
+
+function! s:call(name, ...) abort
+  let options = extend({
+        \ 'capture': 0,
+        \ 'verbose': 0,
+        \}, a:0 ? a:1 : {},
+        \)
+  if !exists(printf('b:%s_action', s:prefix))
+    throw 'the buffer has not been initialized for actions'
+  endif
+  if index(b:{s:prefix}_action.actions, a:name) is# -1
+    throw printf('no action %s found in the buffer', a:name)
+  endif
+  let b:{s:prefix}_action.previous = a:name
+  let Fn = funcref('s:_call', [a:name])
+  if options.verbose
+    let Fn = funcref('s:_verbose', [Fn])
+  endif
+  if options.capture
+    let Fn = funcref('s:_capture', [Fn])
+  endif
+  call Fn()
+endfunction
+
+function! s:list(...) abort
+  let conceal = a:0 ? a:1 : v:true
+  let Sort = { a, b -> s:_compare(a[1], b[1]) }
+  let rs = split(execute('nmap'), '\n')
+  call map(rs, { _, v -> v[3:] })
+  call map(rs, { _, v -> matchlist(v, '^\([^ ]\+\)\s*\*\?@\?\(.*\)$')[1:2] })
+
+  " To action mapping
+  let pattern1 = printf('^<Plug>(%s-action-\zs.*\ze)$', s:prefix)
+  let pattern2 = printf('^<Plug>(%s-action-', s:prefix)
+  let rs1 = map(copy(rs), { _, v -> v + [matchstr(v[1], pattern1)] })
+  call filter(rs1, { _, v -> !empty(v[2]) })
+  call filter(rs1, { _, v -> v[0] !~# '^<Plug>' || v[0] =~# pattern2 })
+  call map(rs1, { _, v -> [v[0], v[2], v[1]] })
+
+  " From action mapping
+  let rs2 = map(copy(rs), { _, v -> v + [matchstr(v[0], pattern1)] })
+  call filter(rs2, { _, v -> !empty(v[2]) })
+  call map(rs2, { _, v -> ['', v[2], v[0]] })
+
+  let rs = uniq(sort(rs1 + rs2, Sort), Sort)
+  if conceal
+    call filter(rs, { -> v:val[1] !~# ':' || !empty(v:val[0]) })
+  endif
+
+  return rs
+endfunction
+
+function! s:_map_choice() abort
+  if !exists(printf('b:%s_action', s:prefix))
+    throw 'the buffer has not been initialized for actions'
+  endif
+  call inputsave()
+  try
+    let fn = get(function('s:_complete_choice'), 'name')
+    let expr = input('action: ', '', printf('customlist,%s', fn))
+  finally
+    call inputrestore()
+  endtry
+  let r = s:_parse_expr(expr)
+  let ns = copy(b:{s:prefix}_action.actions)
+  let r.name = get(filter(ns, { -> v:val =~# '^' . r.name }), 0)
+  if empty(r.name)
+    return
+  endif
+  call s:call(r.name, {
+       \ 'capture': r.capture,
+       \ 'verbose': r.verbose,
+       \})
+endfunction
+
+function! s:_map_repeat() abort
+  if !exists(printf('b:%s_action', s:prefix))
+    throw 'the buffer has not been initialized for actions'
+  endif
+  if empty(b:{s:prefix}_action.previous)
+    return
+  endif
+  call s:call(b:{s:prefix}_action.previous)
+endfunction
+
+function! s:_map_help(all) abort
+  let rs = s:list(!a:all)
+
+  let len0 = max(map(copy(rs), { -> len(v:val[0]) }))
+  let len1 = max(map(copy(rs), { -> len(v:val[1]) }))
+  let len2 = max(map(copy(rs), { -> len(v:val[2]) }))
+  call map(rs, { _, v -> [
+       \   printf(printf('%%-%dS', len0), v[0]),
+       \   printf(printf('%%-%dS', len1), v[1]),
+       \   printf(printf('%%-%dS', len2), v[2]),
+       \ ]
+       \})
+
+  call map(rs, { -> join(v:val, '  ') })
+  if !a:all
+    echohl Title
+    echo "NOTE: Some actions are concealed. Use 'help:all' action to see all actions."
+    echohl None
+  endif
+  echo join(rs, "\n")
+endfunction
+
+function! s:_parse_expr(expr) abort
+  if empty(a:expr)
+    return {'name' : '', 'capture': 0, 'verbose': 0}
+  endif
+  let terms = split(a:expr)
+  let name = remove(terms, -1)
+  let Has = { ns, n -> len(filter(copy(ns), { -> v:val ==# n })) }
+  return {
+        \ 'name': name,
+        \ 'capture': Has(terms, 'capture'),
+        \ 'verbose': Has(terms, 'verbose'),
+        \}
+endfunction
+
+function! s:_build_actions() abort
+  let n = len(printf('%s-action-', s:prefix))
+  let ms = split(execute(printf('nmap <Plug>(%s-action-', s:prefix)), '\n')
+  call map(ms, { _, v -> split(v)[1] })
+  call map(ms, { _, v -> matchstr(v, '^<Plug>(\zs.*\ze)$') })
+  call filter(ms, { _, v -> !empty(v) })
+  call map(ms, { _, expr -> expr[n :] })
+  return sort(ms)
+endfunction
+
+function! s:_complete_choice(arglead, cmdline, cursorpos) abort
+  if !exists(printf('b:%s_action', s:prefix))
+    return []
+  endif
+  let names = copy(b:{s:prefix}_action.actions)
+  let names += ['capture', 'verbose']
+  if empty(a:arglead)
+    call filter(names, { -> v:val !~# ':' })
+  endif
+  return filter(names, { -> v:val =~# '^' . a:arglead })
+endfunction
+
+function! s:_compare(i1, i2) abort
+  return a:i1 == a:i2 ? 0 : a:i1 > a:i2 ? 1 : -1
+endfunction
+
+function! s:_call(name) abort
+  execute printf(
+        \ "normal \<Plug>(%s-action-%s)",
+        \ s:prefix,
+        \ a:name,
+        \)
+endfunction
+
+function! s:_capture(fn) abort
+  let output = execute('call a:fn()')
+  let rs = split(output, '\r\?\n')
+  execute printf('botright %dnew', len(rs))
+  call setline(1, rs)
+  setlocal buftype=nofile bufhidden=wipe
+  setlocal noswapfile nobuflisted
+  setlocal nomodifiable nomodified
+  setlocal nolist signcolumn=no
+  setlocal nonumber norelativenumber
+  setlocal cursorline
+  nnoremap <buffer><silent> q :<C-u>q<CR>
+endfunction
+
+function! s:_verbose(fn) abort
+  let verbose_saved = &verbose
+  try
+    set verbose
+    call a:fn()
+  finally
+    let &verbose = verbose_saved
+  endtry
+endfunction
diff --git a/autoload/vital/_fern/App/WindowLocator.vim b/autoload/vital/_fern/App/WindowLocator.vim
new file mode 100644
index 00000000..79cb98e8
--- /dev/null
+++ b/autoload/vital/_fern/App/WindowLocator.vim
@@ -0,0 +1,94 @@
+" ___vital___
+" NOTE: lines between '" ___vital___' is generated by :Vitalize.
+" Do not modify the code nor insert new lines before '" ___vital___'
+function! s:_SID() abort
+  return matchstr(expand('<sfile>'), '<SNR>\zs\d\+\ze__SID$')
+endfunction
+execute join(['function! vital#_fern#App#WindowLocator#import() abort', printf("return map({'focus': '', 'get_conditions': '', 'list': '', 'find': '', 'score': '', 'set_threshold': '', 'set_conditions': '', 'get_threshold': ''}, \"vital#_fern#function('<SNR>%s_' . v:key)\")", s:_SID()), 'endfunction'], "\n")
+delfunction s:_SID
+" ___vital___
+let s:threshold = 0
+let s:conditions = [
+      \ { wi -> !wi.loclist },
+      \ { wi -> !wi.quickfix },
+      \ { wi -> !getwinvar(wi.winid, '&winfixwidth', 0) },
+      \ { wi -> !getwinvar(wi.winid, '&winfixheight', 0) },
+      \ { wi -> !getbufvar(wi.bufnr, '&previewwindow', 0) },
+      \]
+
+function! s:score(winnr) abort
+  let winid = win_getid(a:winnr)
+  let wininfo = getwininfo(winid)
+  if empty(wininfo)
+    return 0
+  endif
+  let wi = wininfo[0]
+  let score = 1
+  for Condition in s:conditions
+    let score += Condition(wi)
+  endfor
+  return score
+endfunction
+
+function! s:list() abort
+  let nwinnr = winnr('$')
+  if nwinnr == 1
+    return 1
+  endif
+  let threshold = s:get_threshold()
+  while threshold > 0
+    let ws = filter(
+          \ range(1, winnr('$')),
+          \ { -> s:score(v:val) >= threshold }
+          \)
+    if !empty(ws)
+      break
+    endif
+    let threshold -= 1
+  endwhile
+  return ws
+endfunction
+
+function! s:find(origin) abort
+  let nwinnr = winnr('$')
+  if nwinnr == 1
+    return 1
+  endif
+  let origin = a:origin == 0 ? winnr() : a:origin
+  let former = range(origin, winnr('$'))
+  let latter = reverse(range(1, origin - 1))
+  let threshold = s:get_threshold()
+  while threshold > 0
+    for winnr in (former + latter)
+      if s:score(winnr) >= threshold
+        return winnr
+      endif
+    endfor
+    let threshold -= 1
+  endwhile
+  return 0
+endfunction
+
+function! s:focus(origin) abort
+  let winnr = s:find(a:origin)
+  if winnr == 0 || winnr == winnr()
+    return 1
+  endif
+  call win_gotoid(win_getid(winnr))
+endfunction
+
+function! s:get_conditions() abort
+  return copy(s:conditions)
+endfunction
+
+function! s:set_conditions(conditions) abort
+  let s:conditions = copy(a:conditions)
+endfunction
+
+function! s:get_threshold() abort
+  return s:threshold is# 0 ? len(s:conditions) + 1 : s:threshold
+endfunction
+
+function! s:set_threshold(threshold) abort
+  let s:threshold = a:threshold
+endfunction
diff --git a/autoload/vital/_fern/App/WindowSelector.vim b/autoload/vital/_fern/App/WindowSelector.vim
new file mode 100644
index 00000000..8f8fbad3
--- /dev/null
+++ b/autoload/vital/_fern/App/WindowSelector.vim
@@ -0,0 +1,97 @@
+" ___vital___
+" NOTE: lines between '" ___vital___' is generated by :Vitalize.
+" Do not modify the code nor insert new lines before '" ___vital___'
+function! s:_SID() abort
+  return matchstr(expand('<sfile>'), '<SNR>\zs\d\+\ze__SID$')
+endfunction
+execute join(['function! vital#_fern#App#WindowSelector#import() abort', printf("return map({'select': ''}, \"vital#_fern#function('<SNR>%s_' . v:key)\")", s:_SID()), 'endfunction'], "\n")
+delfunction s:_SID
+" ___vital___
+function! s:select(winnrs, ...) abort
+  let options = extend({
+        \ 'auto_select': 0,
+        \ 'select_chars': split('abcdefghijklmnopqrstuvwxyz', '\zs'),
+        \ 'statusline_hl': 'VitalWindowSelectorStatusLine',
+        \ 'indicator_hl': 'VitalWindowSelectorIndicator',
+        \}, a:0 ? a:1 : {})
+  if options.auto_select && len(a:winnrs) <= 1
+    call win_gotoid(len(a:winnrs) ? win_getid(a:winnrs[0]) : win_getid())
+    return 0
+  endif
+  let length = len(a:winnrs)
+  let store = {}
+  for winnr in a:winnrs
+    let store[winnr] = getwinvar(winnr, '&statusline')
+  endfor
+  try
+    let scs = options.select_chars
+    let chars = map(
+          \ range(length + 1),
+          \ { _, v -> get(scs, v, string(v)) },
+          \)
+    let S = funcref('s:_statusline', [
+          \ options.statusline_hl,
+          \ options.indicator_hl,
+          \])
+    call map(keys(store), { k, v -> setwinvar(v, '&statusline', S(v, chars[k])) })
+    redrawstatus
+    call s:_cnoremap_all(chars)
+    let n = input('choose window: ')
+    call s:_cunmap_all()
+    redraw | echo
+    if n is# v:null
+      return 1
+    endif
+    let n = index(chars, n)
+    if n is# -1
+      return 1
+    endif
+    call win_gotoid(win_getid(a:winnrs[n]))
+  finally
+    call map(keys(store), { _, v -> setwinvar(v, '&statusline', store[v]) })
+    redrawstatus
+  endtry
+endfunction
+
+function! s:_statusline(statusline_hl, indicator_hl, winnr, char) abort
+  let width = winwidth(a:winnr) - len(a:winnr . '') - 6
+  let leading = repeat(' ', width / 2)
+  return printf(
+        \ '%%#%s#%s%%#%s#   %s   %%#%s#',
+        \ a:statusline_hl,
+        \ leading,
+        \ a:indicator_hl,
+        \ a:char,
+        \ a:statusline_hl,
+        \)
+endfunction
+
+function! s:_cnoremap_all(chars) abort
+  for nr in range(256)
+    silent! execute printf("cnoremap \<buffer>\<silent> \<Char-%d> \<Nop>", nr)
+  endfor
+  for char in a:chars
+    silent! execute printf("cnoremap \<buffer>\<silent> %s %s\<CR>", char, char)
+  endfor
+  silent! cunmap <buffer> <Return>
+  silent! cunmap <buffer> <Esc>
+endfunction
+
+function! s:_cunmap_all() abort
+  for nr in range(256)
+    silent! execute printf("cunmap \<buffer> \<Char-%d>", nr)
+  endfor
+endfunction
+
+
+function! s:_highlight() abort
+  highlight default link VitalWindowSelectorStatusLine StatusLineNC
+  highlight default link VitalWindowSelectorIndicator  DiffText
+endfunction
+
+augroup vital_app_window_selector_internal
+  autocmd!
+  autocmd ColorScheme * call s:_highlight()
+augroup END
+
+call s:_highlight()
diff --git a/autoload/vital/fern.vital b/autoload/vital/fern.vital
index abb8166f..8d914592 100644
--- a/autoload/vital/fern.vital
+++ b/autoload/vital/fern.vital
@@ -1,5 +1,5 @@
 fern
-ffd4400d5a19716716e8f803dc5084db74033ffc
+08087a6270f290e8d1974885f6705131b95691d9
 
 App.Spinner
 Async.CancellationTokenSource
@@ -13,3 +13,6 @@ Lambda
 System.Filepath
 Vim.Window.Cursor
 Prompt
+App.Action
+App.WindowSelector
+App.WindowLocator
diff --git a/doc/fern-develop.txt b/doc/fern-develop.txt
index 81227fd1..0121cdf8 100644
--- a/doc/fern-develop.txt
+++ b/doc/fern-develop.txt
@@ -625,6 +625,31 @@ fern#logger#error({object}...)
 =============================================================================
 UTILITY						*fern-develop-utility*
 
+						*fern#action#call()*
+fern#action#call({name}[, {options}])
+	Call an action {name} of the current buffer.
+	The following attributes are available in {options}
+
+	"capture"	1 to enable capture mode which write output messages
+			into a new empty buffer instead
+	"verbose"	1 to execute action with 'verbose' (1) mode.
+
+						*fern#action#list()*
+fern#action#list([{conceal}])
+	Return a |List| of available actions. Each item of the list is tuple
+	like [{lhs}, {name}, {rhs}] where {lhs} is an actual mapping, {name}
+	is an action name, and {rhs} is a <Plug> mapping like:
+>
+	assert_equal(fern#action#list(), [
+	      \ ['a', 'choice', '<Plug>(fern-action-choice)'],
+	      \ ['.', 'repeat', '<Plug>(fern-action-repeat)'],
+	      \ ['?', 'help', '<Plug>(fern-action-help)'],
+	      \ ['', 'help:all', '<Plug>(fern-action-help:all)'],
+	      \])
+<
+	When {conceal} is truthy value, it remove items which contains ":" in
+	it's name and no actual mapping (like "help:all" in above example.)
+
 						*fern#hook#add()*
 fern#hook#add({name}, {callback}[, {options}])
 	Add the {callback} to the {name} hook.
diff --git a/test/fern/internal/action.vimspec b/test/fern/internal/action.vimspec
deleted file mode 100644
index 049d78ff..00000000
--- a/test/fern/internal/action.vimspec
+++ /dev/null
@@ -1,44 +0,0 @@
-Describe fern#internal#action
-  After all
-    %bwipeout!
-  End
-
-  Before
-    %bwipeout!
-  End
-
-  Describe #init()
-    It defines <Plug> mappings for actions
-      call fern#internal#action#init()
-      let rs = map(
-            \ split(execute('nmap <Plug>(fern-action'), '\n'),
-            \ { -> split(v:val)[1] },
-            \)
-      Assert Equals(sort(rs), sort([
-            \ '<Plug>(fern-action-choice)',
-            \ '<Plug>(fern-action-repeat)',
-            \ '<Plug>(fern-action-help)',
-            \ '<Plug>(fern-action-help:all)',
-            \]))
-    End
-  End
-
-  Describe #call()
-    It invoke a corresponding mapping of a given name
-      function! s:map_test() abort
-        let b:called = 1
-      endfunction
-
-      nnoremap <buffer><silent> <Plug>(fern-action-test) :<C-u>call <SID>map_test()<CR>
-
-      call fern#internal#action#init()
-      call fern#internal#action#call('test')
-      Assert Equals(b:called, 1)
-    End
-
-    It throws exception when no corresponding mapping exists
-      call fern#internal#action#init()
-      Throws /no action test found in the buffer/ fern#internal#action#call('test')
-    End
-  End
-End