Fix the bug that a redo reaching the latest change is taken as a new

change by modifying the criterion on undo and redo, causing another
problem that ongoing changes in Insert mode and Replace mode are not
taken as new changes. To avoid this, the 'b:AutoCenter_MaxChangeNr'
variable is introduced to record the current max change number for
current buffer, which is updated only when not in the modes said above.

autoload/AutoCenter.vim

@@ -20,7 +20,9 @@ function! AutoCenter#On() "{{{
     " text changes. So we don't center text in these cases.
     autocmd TextChanged,TextChangedI *
     \ if !s:isUndoRedo() | call s:center() | endif
+    autocmd BufEnter * call s:upMaxChangeNr()
   augroup END
+  call s:upMaxChangeNr()
   call s:saveMapping() " Save mappings for later restoring.
   call s:addMapping()
   call s:markState(1)
@@ -41,21 +43,22 @@ function! AutoCenter#Off() "{{{
   call s:markState(0)
 endfunction "}}}
 
+function! s:isUndoRedo() "{{{
+  return changenr() <= b:AutoCenter_MaxChangeNr
+endfunction "}}}
+
 function! s:center() "{{{
   " Remember the cursor position relative to current indent for restoring after
   " centering the line.
   let l:curpos = col('.') - indent('.')
   center
   " Put cursor back on the same char it is on before centering.
   call cursor('.', l:curpos + indent('.'))
-endfunction "}}}
-
-function! s:isUndoRedo() "{{{
-  let l:undolist = split(execute('undolist'), "\n")
-  let l:maxChangeNr = split(l:undolist[-1], ' \+')[0]
-  " known bug: a redo reaching the lastest change makes changenr() equal to
-  " l:maxChangeNr.
-  return changenr() < l:maxChangeNr
+  " A change in Insert mode or Replace mode is in progress.
+  " Only update the max change number when a change is done.
+  if mode() !~ '^[iR]'
+    call s:upMaxChangeNr()
+  endif
 endfunction "}}}
 
 function! s:opCenter(type) "{{{
@@ -101,6 +104,13 @@ function! s:markState(state) "{{{
   lockvar g:AutoCenter_On
 endfunction "}}}
 
+function! s:upMaxChangeNr() "{{{
+  unlockvar b:AutoCenter_MaxChangeNr
+  let l:undolist = split(execute('undolist'), "\n")
+  let b:AutoCenter_MaxChangeNr = split(l:undolist[-1], ' \+')[0]
+  lockvar b:AutoCenter_MaxChangeNr
+endfunction "}}}
+
 if !exists('g:AutoCenter_On') | call s:markState(0) | endif
 
 " Restore 'cpoptions' setting {{{