feat: create `config` module

Add support for overriding plugin default options with
user preferences. Resolved user preferences are cached
between switching colorschemes.

lua/gruber-darker/config.lua

@@ -0,0 +1,40 @@
+---@class ConfigMgr
+---@field private resolved_opts Options|nil 
+
+---@class Options
+---@field message string
+
+---@type ConfigMgr
+local M = {
+  resolved_opts = nil
+}
+
+---Get default GruberDarker colorscheme options
+---@return Options
+---@nodiscard
+function M.get_default_opts()
+	return {
+		message = "Big Hello",
+	}
+end
+
+---Get GruberDarker user preferences
+---@return Options|nil
+---@nodiscard
+function M.get_resolved_opts()
+  return M.resolved_opts
+end
+
+---Set GruberDarker colorscheme options
+---@param opts Options
+function M.set(opts)
+  -- If user already called GruberDarker setup
+  -- either with/without default options
+  if M.resolved_opts ~= nil then
+    return
+  end
+
+	M.resolved_opts = vim.tbl_deep_extend("force", M.get_default_opts(), opts)
+end
+
+return M

lua/gruber-darker/init.lua

@@ -1,16 +1,17 @@
 local highlights = require("gruber-darker.hl")
+local config = require("gruber-darker.config")
 
 local M = {}
 
 ---Delete GruberDarker autocmds when the
 ---theme changes to something else
 ---@package
-function M.on_color_scheme()
+function M.on_colorscheme()
 	vim.cmd([[autocmd! GruberDarker]])
 	vim.cmd([[augroup! GruberDarker]])
 end
 
----Clear current highlights and set `g:colors_name`
+---Clear current highlights and set Neovim global `colors_name`
 local function prepare_env()
 	if vim.g.colors_name then
 		vim.cmd.hi("clear")
@@ -20,8 +21,19 @@ local function prepare_env()
 	vim.g.colors_name = "GruberDarker"
 end
 
-function M.setup()
-  prepare_env()
+---Change colorscheme to GruberDarker
+function M.colorsheme() end
+
+---GruberDarker configuration bootstrapper
+---@param opts Options
+function M.setup(opts)
+	config.set(opts or {})
+
+	opts = config.get_resolved_opts()
+
+	-- print("message: " .. opts.message)
+
+	prepare_env()
 	-- set highlights here...
 	for group, hl in pairs(highlights.groups) do
 		vim.api.nvim_set_hl(0, group, hl)
@@ -32,7 +44,7 @@ function M.setup()
 		group = gruber_darker_group,
 		pattern = "*",
 		callback = function()
-			require("gruber-darker").on_color_scheme()
+			require("gruber-darker").on_colorscheme()
 		end,
 	})
 	-- vim.api.nvim_create_autocmd("FileType", {
@@ -44,5 +56,9 @@ function M.setup()
 	-- })
 end
 
-return M
+M.setup({
+	message = "Test message ensuring when a user calls "
+    .. "`setup` with overrides, their preferences are kept.",
+})
 
+return M