wordcount: Optimise formatter calls, cleanup code

- Formatter is now only called when the wordcount changes
- ...#apply() now only compares against the filetype list when necessary
- Old format() function is no longer called for (unsupported) counting
  of visual words
- Misc code quality improvements

autoload/airline/extensions/wordcount.vim

@@ -5,14 +5,15 @@ scriptencoding utf-8
 
 " get wordcount {{{1
 if exists('*wordcount')
-  function! s:get_wordcount(type)
-    return string(wordcount()[a:type])
+  function! s:get_wordcount(visual_mode_active)
+    let query = a:visual_mode_active ? 'visual_words' : 'words'
+    return string(wordcount()[query])
   endfunction
 else
-  function! s:get_wordcount(type)
+  function! s:get_wordcount(visual_mode_active)
     " index to retrieve from whitespace-separated output of g_CTRL-G
     " 11 : words, 5 : visual words (in visual mode)
-    let idx = (a:type == 'words') ? 11 : 5
+    let idx = a:visual_mode_active ? 5 : 11
 
     let save_status = v:statusmsg
     execute "silent normal! g\<cn-g>"
@@ -30,12 +31,11 @@ endif
 let s:formatter = get(g:, 'airline#extensions#wordcount#formatter', 'default')
 
 " wrapper function for compatibility; redefined below for old-style formatters
-function! s:format_wordcount(type)
-  return airline#extensions#wordcount#formatters#{s:formatter}#to_string(
-        \ s:get_wordcount(a:type))
+function! s:format_wordcount(wordcount)
+  return airline#extensions#wordcount#formatters#{s:formatter}#to_string(a:wordcount)
 endfunction
 
-" check user-defined formatter exists and has appropriate functions, otherwise
+" check user-defined formatter exists with appropriate functions, otherwise
 " fall back to default
 if s:formatter !=# 'default'
   execute 'runtime! autoload/airline/extensions/wordcount/formatters/'.s:formatter
@@ -44,8 +44,10 @@ if s:formatter !=# 'default'
       let s:formatter = 'default'
     else
       " redefine for backwords compatibility
-      function! s:format_wordcount(type)
-        if a:type !=# 'visual_words'
+      function! s:format_wordcount(_)
+        if mode() ==? 'v'
+          return b:airline_wordcount
+        else
           return airline#extensions#wordcount#formatters#{s:formatter}#format()
         endif
       endfunction
@@ -54,65 +56,65 @@ if s:formatter !=# 'default'
 endif
 
 " update {{{1
+let s:wordcount_cache = 0  " cache wordcount for performance when force_update=0
+function! s:update_wordcount(force_update)
+  let wordcount = s:get_wordcount(0)
+  if wordcount != s:wordcount_cache || a:force_update
+    let s:wordcount_cache = wordcount
+    let b:airline_wordcount =  s:format_wordcount(wordcount)
+  endif
+endfunction
+
 if exists('##TextChanged')
   let s:supported_autocmds = 'TextChanged,TextChangedI'
 
-  function! s:update_wordcount()
-    let b:airline_wordcount = s:format_wordcount('words')
+  function! s:on_check()
+    call s:update_wordcount(0)
   endfunction
 else
   let s:supported_autocmds = 'CursorMoved,CursorMovedI'
 
-  " without TextChanged a check is performed on every cursor movement, so
-  " cache for performance
-  function! s:update_wordcount()
-    if get(b:, 'airline_wordcount_cache', '') is# '' ||
-          \ get(b:, 'airline_change_tick', 0) != b:changedtick ||
-          \ get(b:, 'airline_winwidth', 0) != winwidth(0)
-      let b:airline_wordcount = s:format_wordcount('words')
-      let b:airline_wordcount_cache = b:airline_wordcount
+  " without TextChanged, use "b:changedtick" to track changes
+  function! s:on_check()
+    if get(b:, 'airline_change_tick', -1) != b:changedtick
       let b:airline_change_tick = b:changedtick
-      let b:airline_winwidth = winwidth(0)
+      call s:update_wordcount(0)
     endif
   endfunction
 endif
 
 " public {{{1
-" s:visual tracks visual mode
+let s:visual_active = 0  " Boolean: for when to get visual wordcount
 function airline#extensions#wordcount#get()
-  return s:visual
-        \ ? s:format_wordcount('visual_words')
-        \ : get(b:, 'airline_wordcount', '')
+  return s:visual_active
+        \ ? s:format_wordcount(s:get_wordcount(1))
+        \ : b:airline_wordcount
 endfunction
 
 " autocmds & airline functions {{{1
-function s:modify_autocmds()
-    if !exists('#airline_wordcount#BufEnter#')
-      execute 'autocmd! airline_wordcount BufEnter,'.s:supported_autocmds
-            \  .' <buffer> nested call s:update_wordcount()'
-      " ensure we have a starting wordcount
-      call s:update_wordcount()
-    else
-     execute 'autocmd! airline_wordcount BufEnter,'.'s:supported_autocmds'
-    endif
-endfunction
-
-" default filetypes
+" default filetypes:
 let s:filetypes = ['help', 'markdown', 'rst', 'org', 'text', 'asciidoc', 'tex', 'mail']
-
 function! airline#extensions#wordcount#apply(...)
   let filetypes = get(g:, 'airline#extensions#wordcount#filetypes', s:filetypes)
 
-  " filetypes used to be a regex-matching string, so check both
-  if type(filetypes) == v:t_list
-        \    && (index(filetypes, &filetype) > -1 || empty(filetypes))
-        \ || type(filetypes) == v:t_string && match(&ft, filetypes) > -1
-    " redo autocommands if filetype has changed
-    if filetypes isnot s:filetypes || did_filetype()
-      call s:modify_autocmds()
+  " check if autocmd updates are neccessary
+  if did_filetype() || filetypes isnot s:filetypes
     let s:filetypes = filetypes
+
+    " Select test based on type of "filetypes": new=list, old=string
+    if type(filetypes) == v:t_list
+          \ ? index(filetypes, &filetype) > -1 || index(filetypes, 'all') > -1
+          \ : match(&ft, filetypes) > -1
+      execute 'autocmd! airline_wordcount BufEnter,'.s:supported_autocmds
+            \  .' <buffer> nested call s:on_check()'
+      call s:update_wordcount(1) " force update ensures initial worcount exists
+    elseif exists('b:airline_wordcount') " cleanup
+      autocmd! airline_wordcount * <buffer>
+      unlet b:airline_wordcount
+    endif
   endif
 
+  if exists('b:airline_wordcount')
     call airline#extensions#prepend_to_section(
           \ 'z', '%{airline#extensions#wordcount#get()}')
   endif
@@ -121,7 +123,7 @@ endfunction
 function! airline#extensions#wordcount#init(ext)
   augroup airline_wordcount
     autocmd! User AirlineModeChanged nested
-          \ let s:visual = (mode() ==? 'v' || mode() ==? 's')
+          \ let s:visual_active = (mode() ==? 'v' || mode() ==? 's')
   augroup END
   call a:ext.add_statusline_func('airline#extensions#wordcount#apply')
 endfunction