local set = require "util.set";

local known_options = {

	incremental = set.new { "mode", "threshold", "speed", "step_size" };

	generational = set.new { "mode", "minor_threshold", "major_threshold" };

};

if _VERSION ~= "5.4" then

	known_options.generational = nil;

	known_options.incremental:remove("step_size");

end

local function configure(user, defaults)

	local mode = user.mode or defaults.mode or "incremental";

	if not known_options[mode] then

		return nil, "GC mode not supported on ".._VERSION..": "..mode;

	end

	for k, v in pairs(user) do

		if not known_options[mode]:contains(k) then

			return nil, "Unknown GC parameter: "..k;

		elseif k ~= "mode" and type(v) ~= "number" then

			return nil, "parameter '"..k.."' should be a number";

		end

	end

	if mode == "incremental" then

		if _VERSION == "Lua 5.4" then

			collectgarbage(mode,

				user.threshold or defaults.threshold,

				user.speed or defaults.speed,

				user.step_size or defaults.step_size

			);

		else

			collectgarbage("setpause", user.threshold or defaults.threshold);

			collectgarbage("setstepmul", user.speed or defaults.speed);

		end

	elseif mode == "generational" then

		collectgarbage(mode,

			user.minor_threshold or defaults.minor_threshold,

			user.major_threshold or defaults.major_threshold

		);

	end

	return true;

end

return {

	configure = configure;

};