From 210de650077bbc00a714682894e49d2341e0c537 Mon Sep 17 00:00:00 2001
From: Derik Ramirez <rderik@gmail.com>
Date: Fri, 17 Jul 2020 13:53:01 -0600
Subject: [PATCH] Adds support for new option to create anchors on headings

Currently,  when the Table of Contents is created the links are built
in the table of contents but no anchor is created on the titles.

This pull requests contains an optional feature that allows us to
create an anchor with the following format:

```
<a name="SLUG-GENERATED-BY-THE-PLUGIN"></a>
```

The anchor is enclosed in the `fence-text` so it can be updated if
the `g:vmt_auto_update_on_save` option is enabled. So it can be
deleted and updated in the same manner as the Table of Contents.

To activate the new anchor creation options we do it by setting the
variable:

```
g:vmt_insert_anchors = 1
```

Developer notes:

To implement this new feature we modify the return value of the
folllowing function:

function! s:GetHeadingLines()

Now we return an array containing a touple(represented by an array)
with the following content:

["heading", lineNum]

The lineNum represents the position of this heading, so we can later
decide to insert the anchor before the title.

The anchor option supports auto update when enabled.
---
 ftplugin/markdown.vim | 50 +++++++++++++++++++++++++++++++++++++++----
 1 file changed, 46 insertions(+), 4 deletions(-)

diff --git a/ftplugin/markdown.vim b/ftplugin/markdown.vim
index de58409..dc03de2 100644
--- a/ftplugin/markdown.vim
+++ b/ftplugin/markdown.vim
@@ -42,6 +42,10 @@ if !exists("g:vmt_include_headings_before")
     let g:vmt_include_headings_before = 0
 endif
 
+if !exists("g:vmt_insert_anchors")
+    let g:vmt_insert_anchors = 0
+endif
+
 let g:GFMHeadingIds = {}
 
 let s:supportMarkdownStyles = ['GFM', 'Redcarpet', 'GitLab', 'Marked']
@@ -129,7 +133,7 @@ function! s:GetHeadingLines()
             endif
             " ===
 
-            call add(l:headingLines, l:line)
+            call add(l:headingLines, [l:line, l:lineNum])
         endif
         let l:flags = "W"
     endwhile
@@ -255,6 +259,20 @@ function! GetHeadingLinkTest(headingLine, markdownStyle)
     return <SID>GetHeadingLink(l:headingName, a:markdownStyle)
 endfunction
 
+function! s:GenerateAnchor(headingLine, line, markdownStyle, isModeline)
+    let l:anchorText = []
+    if g:vmt_dont_insert_fence == 0
+        call add(l:anchorText, <SID>GetBeginFence(a:markdownStyle, a:isModeline))
+        call add(l:anchorText, "") "Add newline
+    endif
+    call add(l:anchorText, "<a name='". <SID>GetHeadingLink(a:headingLine, a:markdownStyle) ."'></a>")
+    call add(l:anchorText, "") "Add newline
+    if g:vmt_dont_insert_fence == 0
+        call add(l:anchorText, <SID>GetEndFence())
+    endif
+    call append(a:line, l:anchorText)
+endfunction
+
 function! s:GenToc(markdownStyle)
     call <SID>GenTocInner(a:markdownStyle, 0)
 endfunction
@@ -265,12 +283,15 @@ function! s:GenTocInner(markdownStyle, isModeline)
         return
     endif
 
-    let l:headingLines = <SID>GetHeadingLines()
+    let l:fullHeadingLines = <SID>GetHeadingLines()
+    let l:headingLines = deepcopy(l:fullHeadingLines)
+    call map(l:headingLines, {_, val -> val[0]})
     let l:levels = []
     let l:listItemChars = [g:vmt_list_item_char]
+    let l:currentOffset = line('.')
 
     let g:GFMHeadingIds = {}
-    
+
     for headingLine in l:headingLines
         call add(l:levels, <SID>GetHeadingLevel(headingLine))
     endfor
@@ -312,6 +333,16 @@ function! s:GenTocInner(markdownStyle, isModeline)
     if g:vmt_dont_insert_fence == 0
         silent put =<SID>GetEndFence()
     endif
+
+    let l:currentOffset = line('.') - l:currentOffset - 1
+
+    if g:vmt_insert_anchors == 1
+        call reverse(l:fullHeadingLines)
+        for headingLine in l:fullHeadingLines
+            let l:offset = headingLine[1] + l:currentOffset
+            call <SID>GenerateAnchor(headingLine[0], l:offset, a:markdownStyle, a:isModeline)
+        endfor
+    endif
 endfunction
 
 function! s:GetIndentText()
@@ -406,7 +437,7 @@ function! s:DeleteExistingToc()
     keepjumps normal! gg0
 
     let l:markdownStyle = <SID>GetMarkdownStyleInModeline()
-    
+
     let l:isModeline = 0
 
     if index(s:supportMarkdownStyles, l:markdownStyle) != -1
@@ -454,6 +485,17 @@ function! s:DeleteExistingToc()
         echom "Cannot find toc begin fence"
     endif
 
+    "Delete anchors
+    while search(l:tocBeginPattern, "Wc") != 0
+        let l:anchorBeginLineNumber = line(".")
+        if search(l:tocEndPattern, "W") != 0
+            let l:anchorEndLineNumber = line(".")
+            silent execute l:anchorBeginLineNumber. "," . l:anchorEndLineNumber. "delete_"
+        else
+            echom "Cannot find toc end fence"
+        endif
+    endwhile
+
     call winrestview(l:winview)
 
     return [l:markdownStyle, l:beginLineNumber, l:endLineNumber, l:isModeline]