From d4d2e8822108943f1aadd876053c6d9e65ab1659 Mon Sep 17 00:00:00 2001
From: Tom Ryder <tom@sanctum.geek.nz>
Date: Mon, 4 Jun 2018 18:07:32 +1200
Subject: Use heuristics on Markdown to guess autoformat

---
 vim/after/ftplugin/markdown/autoformat.vim    |  4 ++++
 vim/autoload/ftplugin/markdown/autoformat.vim | 24 ++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

(limited to 'vim')

diff --git a/vim/after/ftplugin/markdown/autoformat.vim b/vim/after/ftplugin/markdown/autoformat.vim
index 9a963fbb..8e476158 100644
--- a/vim/after/ftplugin/markdown/autoformat.vim
+++ b/vim/after/ftplugin/markdown/autoformat.vim
@@ -13,6 +13,10 @@ if exists('b:undo_ftplugin')
         \ . '|unlet b:did_ftplugin_markdown_autoformat'
 endif
 
+" Turn on autoformatting if the buffer has no code-block lines with spaces
+" that is longer than 'textwidth'
+call ftplugin#markdown#autoformat#Load()
+
 " Suspend auto-formatting when in a code block (four-space indent)
 autocmd BufWinEnter,CursorMoved,CursorMovedI,WinEnter
       \ <buffer>
diff --git a/vim/autoload/ftplugin/markdown/autoformat.vim b/vim/autoload/ftplugin/markdown/autoformat.vim
index 1d01c58e..f416da77 100644
--- a/vim/autoload/ftplugin/markdown/autoformat.vim
+++ b/vim/autoload/ftplugin/markdown/autoformat.vim
@@ -13,6 +13,30 @@ function! ftplugin#markdown#autoformat#Line() abort
   endif
 endfunction
 
+" Turn on autoformatting if less than 5% of the buffer's lines meet all three
+" of these conditions:
+"   * Longer than 'textwidth'
+"   * Contains at least one space (not an unsplittable line)
+"   * Not a code block (indented with at least four spaces)
+function! ftplugin#markdown#autoformat#Load() abort
+  let l:width = &textwidth ? &textwidth : 79
+  let l:count = 0
+  let l:total = line('$')
+  for l:li in range(1, l:total)
+    let l:line = getline(l:li)
+    if strlen(l:line) > l:width
+          \ && stridx(l:line, ' ') > -1
+          \ && l:line !~# '\m^    '
+      let l:count = l:count + 1
+    endif
+  endfor
+  if l:count * 100 / l:total < 5
+    setlocal formatoptions+=a
+  else
+    setlocal formatoptions-=a
+  endif
+endfunction
+
 " Suspend auto-formatting when in a code block (four-space indent)
 function! ftplugin#markdown#autoformat#Put(above) abort
   let l:suspended = 0
-- 
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