From 8b9b713782c31dd8b5288fdbd3890dab91a8aca0 Mon Sep 17 00:00:00 2001
From: Fernando Schauenburg <dev@schauenburg.me>
Date: Fri, 16 Feb 2024 01:30:20 +0100
Subject: [PATCH] Initial commit

---
 config/nvim/lua/fschauen/labs/md.lua | 69 ++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 config/nvim/lua/fschauen/labs/md.lua

diff --git a/config/nvim/lua/fschauen/labs/md.lua b/config/nvim/lua/fschauen/labs/md.lua
new file mode 100644
index 0000000..fdb5e5a
--- /dev/null
+++ b/config/nvim/lua/fschauen/labs/md.lua
@@ -0,0 +1,69 @@
+local M = {}
+
+-- Features to implement:
+--  [ ] increase/decrease heading level
+--  [ ] change _current_ heading type (setex/atx)
+--  [ ] jump to previous/next header
+--  [ ] generate TOC
+--  [ ] go to file in link (with `gf`)
+--  [ ] open URLs with browser
+--  [ ] folding?
+
+local preserve_mark = function(buffer, name, fn)
+  local line, col = unpack(vim.api.nvim_buf_get_mark(buffer, name))
+  local result = fn()
+  vim.api.nvim_buf_set_mark(buffer, name, line, col, {})
+  return result
+end
+
+-- local preserve_cursor = function(fn)
+--   local mark = 'a'
+--   return preserve_mark(0, mark, function()
+--     vim.api.nvim_command('mark ' .. mark)
+--     local result = fn()
+--     vim.api.nvim_win_set_cursor(0, vim.api.nvim_buf_get_mark(0, mark))
+--     return result
+--   end)
+-- end
+
+local preserve_view = function(fn)
+  local mark = 'a'
+  return preserve_mark(0, mark, function()
+    local view = vim.fn.winsaveview()
+    vim.api.nvim_command('mark ' .. mark)
+
+    local result = fn()
+
+    local line, col = unpack(vim.api.nvim_buf_get_mark(0, mark))
+    view.topline = line - (view.lnum - view.topline)
+    view.lnum = line
+    view.col = col
+    vim.fn.winrestview(view)
+
+    return result
+  end)
+end
+
+M.heading_setex = function()
+-- TODO: add an option to extend the Setex underline until 'textwidth'
+-- TODO: make it possible to use a range instead of the whole file
+  preserve_view(function()
+    vim.api.nvim_command([[silent! %s/\v^#\s+(.*)$/\=submatch(1)."\r".repeat('=', len(submatch(1)))/]])
+    vim.api.nvim_command([[silent! %s/\v^##\s+(.*)$/\=submatch(1)."\r".repeat('-', len(submatch(1)))/]])
+  end)
+end
+
+M.heading_atx = function()
+  preserve_view(function()
+    vim.api.nvim_command([[silent! %s/\v(.*\S.*)\n\=+$/# \1]])
+    vim.api.nvim_command([[silent! %s/\v(.*\S.*)\n\-+$/## \1]])
+  end)
+end
+
+M.setup = function()
+  vim.keymap.set('n', '<localleader>hs', M.heading_setex, { buffer = 0 })
+  vim.keymap.set('n', '<localleader>ha', M.heading_atx, { buffer = 0 })
+end
+
+return M
+