-- mod_storage_multi

local storagemanager = require"core.storagemanager";

local backends = module:get_option_array(module.name); -- TODO better name?

-- TODO migrate data "upwards"

-- one → one successful write is success

-- all → all backends must report success

-- majority → majority of backends must report success

local policy = module:get_option_string(module.name.."_policy", "all");

local keyval_store = {};

keyval_store.__index = keyval_store;

function keyval_store:get(username)

	local backends = self.backends;

	local data, err;

	for i = 1, #backends do

		module:log("debug", "%s:%s:get(%q)", tostring(backends[i].get), backends[i]._store, username);

		data, err = backends[i]:get(username);

		if err then

			module:log("error", tostring(err));

		elseif not data then

			module:log("debug", "No data returned");

		else

			module:log("debug", "Data returned");

			return data, err;

		end

	end

end

-- This is where it gets complicated

function keyval_store:set(username, data)

	local backends = self.backends;

	local ok, err, backend;

	local all, one, oks = true, false, 0;

	for i = 1, #backends do

		backend = backends[i];

		module:log("debug", "%s:%s:set(%q)", tostring(backends[i].get), backends[i].store, username);

		ok, err = backend:set(username, data);

		if not ok then

			module:log("error", "Error in storage driver %s: %s", backend.name, tostring(err));

		else

			oks = oks + 1;

		end

		one = one or ok; -- At least one successful write

		all = all and ok; -- All successful

	end

	if policy == "all" then

		return all, err

	elseif policy == "majority" then

		return oks > (#backends/2), err;

	end

	-- elseif policy == "one" then

	return one, err;

end

local stores = {

	keyval = keyval_store;

}

local driver = {};

function driver:open(store, typ)

	local store_mt = stores[typ or "keyval"];

	if store_mt then

		local my_backends = {};

		local driver, opened

		for i = 1, #backends do

			 driver = storagemanager.load_driver(module.host, backends[i]);

			 opened = driver:open(store, typ);

			 my_backends[i] = assert(driver:open(store, typ));

			 my_backends[i]._store = store;

		end

		return setmetatable({ backends = my_backends }, store_mt);

	end

	return nil, "unsupported-store";

end

module:provides("storage", driver);