1 files changed, 239 insertions, 0 deletions
diff --git a/scripts/text_utils.lua b/scripts/text_utils.lua
new file mode 100644
index 0000000000..5167ec42f2
--- /dev/null
+++ b/scripts/text_utils.lua
@@ -0,0 +1,239 @@
+local fmt = string.format
+
+--- @class nvim.text_utils.MDNode
+--- @field [integer] nvim.text_utils.MDNode
+--- @field type string
+--- @field text? string
+
+local INDENTATION = 4
+
+local M = {}
+
+local function contains(t, xs)
+  return vim.tbl_contains(xs, t)
+end
+
+--- @param text string
+--- @return nvim.text_utils.MDNode
+local function parse_md(text)
+  local parser = vim.treesitter.languagetree.new(text, 'markdown', {
+    injections = { markdown = '' },
+  })
+
+  local root = parser:parse(true)[1]:root()
+
+  local EXCLUDE_TEXT_TYPE = {
+    list = true,
+    list_item = true,
+    section = true,
+    document = true,
+    fenced_code_block = true,
+    fenced_code_block_delimiter = true,
+  }
+
+  --- @param node TSNode
+  --- @return nvim.text_utils.MDNode?
+  local function extract(node)
+    local ntype = node:type()
+
+    if ntype:match('^%p$') or contains(ntype, { 'block_continuation' }) then
+      return
+    end
+
+    --- @type table<any,any>
+    local ret = { type = ntype }
+
+    if not EXCLUDE_TEXT_TYPE[ntype] then
+      ret.text = vim.treesitter.get_node_text(node, text)
+    end
+
+    for child, child_field in node:iter_children() do
+      local e = extract(child)
+      if child_field then
+        ret[child_field] = e
+      else
+        table.insert(ret, e)
+      end
+    end
+
+    return ret
+  end
+
+  return extract(root) or {}
+end
+
+--- @param x string
+--- @param start_indent integer
+--- @param indent integer
+--- @param text_width integer
+--- @return string
+function M.wrap(x, start_indent, indent, text_width)
+  local words = vim.split(vim.trim(x), '%s+')
+  local parts = { string.rep(' ', start_indent) } --- @type string[]
+  local count = indent
+
+  for i, w in ipairs(words) do
+    if count > indent and count + #w > text_width - 1 then
+      parts[#parts + 1] = '\n'
+      parts[#parts + 1] = string.rep(' ', indent)
+      count = indent
+    elseif i ~= 1 then
+      parts[#parts + 1] = ' '
+      count = count + 1
+    end
+    count = count + #w
+    parts[#parts + 1] = w
+  end
+
+  return (table.concat(parts):gsub('%s+\n', '\n'):gsub('\n+$', ''))
+end
+
+--- @param node nvim.text_utils.MDNode
+--- @param start_indent integer
+--- @param indent integer
+--- @param text_width integer
+--- @param level integer
+--- @return string[]
+local function render_md(node, start_indent, indent, text_width, level, is_list)
+  local parts = {} --- @type string[]
+
+  -- For debugging
+  local add_tag = false
+  -- local add_tag = true
+
+  if add_tag then
+    parts[#parts + 1] = '<' .. node.type .. '>'
+  end
+
+  if node.type == 'paragraph' then
+    local text = assert(node.text)
+    text = text:gsub('(%s)%*(%w+)%*(%s)', '%1%2%3')
+    text = text:gsub('(%s)_(%w+)_(%s)', '%1%2%3')
+    text = text:gsub('\\|', '|')
+    text = text:gsub('\\%*', '*')
+    text = text:gsub('\\_', '_')
+    parts[#parts + 1] = M.wrap(text, start_indent, indent, text_width)
+    parts[#parts + 1] = '\n'
+  elseif node.type == 'code_fence_content' then
+    local lines = vim.split(node.text:gsub('\n%s*$', ''), '\n')
+
+    local cindent = indent + INDENTATION
+    if level > 3 then
+      -- The tree-sitter markdown parser doesn't parse the code blocks indents
+      -- correctly in lists. Fudge it!
+      lines[1] = '    ' .. lines[1] -- ¯\_(ツ)_/¯
+      cindent = indent - level
+      local _, initial_indent = lines[1]:find('^%s*')
+      initial_indent = initial_indent + cindent
+      if initial_indent < indent then
+        cindent = indent - INDENTATION
+      end
+    end
+
+    for _, l in ipairs(lines) do
+      if #l > 0 then
+        parts[#parts + 1] = string.rep(' ', cindent)
+        parts[#parts + 1] = l
+      end
+      parts[#parts + 1] = '\n'
+    end
+  elseif node.type == 'fenced_code_block' then
+    parts[#parts + 1] = '>'
+    for _, child in ipairs(node) do
+      if child.type == 'info_string' then
+        parts[#parts + 1] = child.text
+        break
+      end
+    end
+    parts[#parts + 1] = '\n'
+    for _, child in ipairs(node) do
+      if child.type ~= 'info_string' then
+        vim.list_extend(parts, render_md(child, start_indent, indent, text_width, level + 1))
+      end
+    end
+    parts[#parts + 1] = '<\n'
+  elseif node.type == 'html_block' then
+    local text = node.text:gsub('^<pre>help', '')
+    text = text:gsub('</pre>%s*$', '')
+    parts[#parts + 1] = text
+  elseif node.type == 'list_marker_dot' then
+    parts[#parts + 1] = node.text
+  elseif contains(node.type, { 'list_marker_minus', 'list_marker_star' }) then
+    parts[#parts + 1] = '• '
+  elseif node.type == 'list_item' then
+    parts[#parts + 1] = string.rep(' ', indent)
+    local offset = node[1].type == 'list_marker_dot' and 3 or 2
+    for i, child in ipairs(node) do
+      local sindent = i <= 2 and 0 or (indent + offset)
+      vim.list_extend(
+        parts,
+        render_md(child, sindent, indent + offset, text_width, level + 1, true)
+      )
+    end
+  else
+    if node.text then
+      error(fmt('cannot render:\n%s', vim.inspect(node)))
+    end
+    for i, child in ipairs(node) do
+      vim.list_extend(parts, render_md(child, start_indent, indent, text_width, level + 1, is_list))
+      if node.type ~= 'list' and i ~= #node then
+        if (node[i + 1] or {}).type ~= 'list' then
+          parts[#parts + 1] = '\n'
+        end
+      end
+    end
+  end
+
+  if add_tag then
+    parts[#parts + 1] = '</' .. node.type .. '>'
+  end
+
+  return parts
+end
+
+--- @param text_width integer
+local function align_tags(text_width)
+  --- @param line string
+  --- @return string
+  return function(line)
+    local tag_pat = '%s+(%*[^ ]+%*)%s*$'
+    local tags = {}
+    for m in line:gmatch(tag_pat) do
+      table.insert(tags, m)
+    end
+
+    if #tags > 0 then
+      line = line:gsub(tag_pat, '')
+      local tags_str = ' ' .. table.concat(tags, ' ')
+      local pad = string.rep(' ', text_width - #line - #tags_str)
+      return line .. pad .. tags_str
+    end
+
+    return line
+  end
+end
+
+--- @param text string
+--- @param start_indent integer
+--- @param indent integer
+--- @param is_list? boolean
+--- @return string
+function M.md_to_vimdoc(text, start_indent, indent, text_width, is_list)
+  -- Add an extra newline so the parser can properly capture ending ```
+  local parsed = parse_md(text .. '\n')
+  local ret = render_md(parsed, start_indent, indent, text_width, 0, is_list)
+
+  local lines = vim.split(table.concat(ret), '\n')
+
+  lines = vim.tbl_map(align_tags(text_width), lines)
+
+  local s = table.concat(lines, '\n')
+
+  -- Reduce whitespace in code-blocks
+  s = s:gsub('\n+%s*>([a-z]+)\n?\n', ' >%1\n')
+  s = s:gsub('\n+%s*>\n?\n', ' >\n')
+
+  return s
+end
+
+return M