md-tools.nvim/lua/md-tools/init.lua

local header_regex = "^(#+) (.+)"
local todo_symbols = { " ", "-", "X", "D" }

local table_lenght = function(T)
	local count = 0
	for _ in pairs(T) do
		count = count + 1
	end
	return count
end

local get_todo = function(line)
	local todo = nil
	local index = nil
	for n, v in ipairs(todo_symbols) do
		if v == "-" then
			v = "%-"
		end
		local ul = "^%s*[+*-]%s+%[" .. v .. "%]%s+"
		local ol = "^%s*%d+%.%s+%[" .. v .. "%]%s+"
		if line:match(ul, nil) or line:match(ol, nil) then
			todo = v
			index = n
		end
	end
	return todo, index
end

local M = {}

M.headerControl = function(action)
	local current_line = vim.api.nvim_get_current_line()
	local row = vim.api.nvim_win_get_cursor(0)[1]

	if current_line:match(header_regex) then
		if action == "promote" then
			if current_line:match("^# (.+)") then
				vim.notify("You can't promote this header anymore")
				return
			end
			vim.api.nvim_buf_set_text(0, row - 1, 0, row - 1, 1, { "" })
		elseif action == "demote" then
			if current_line:match("^###### (.+)") then
				vim.notify("You can't demote this header anymore")
				return
			end
			vim.api.nvim_buf_set_text(0, row - 1, 0, row - 1, 0, { "#" })
		end
	end
end

M.toggleTodo = function()
	local current_line = vim.api.nvim_get_current_line()
	local row = vim.api.nvim_win_get_cursor(0)[1]

	local todo, index = get_todo(current_line)
	if todo then
		local symbol = todo_symbols[index + 1]
		-- make sure symbol is set to first character if index is too big
		if index == table_lenght(todo_symbols) then
			symbol = todo_symbols[1]
		end
		local first, last = current_line:find("%[" .. todo .. "%]")
		vim.api.nvim_buf_set_text(0, row - 1, first, row - 1, last - 1, { symbol })
	end
end

return M