models/wagon.b3d

-- atomic.lua
-- Utilities for transaction-like handling of serialized state files
-- Also for multiple files that must be synchronous, as advtrains currently requires.


-- Managing files and backups
-- ==========================

--[[
The plain scheme just overwrites the file in place. This however poses problems when we are interrupted right within
the write, so we have incomplete data. So, the following scheme is applied:
Unix:
1. writes to <filename>.new
2. moves <filename>.new to <filename>, clobbering previous file
Windows:
1. writes to <filename>.new
2. delete <filename>
3. moves <filename>.new to <filename>

We count a new version of the state as "committed" after stage 2.

During loading, we apply the following order of precedence:
1. <filename>
2. <filename>.new (windows only, in case we were interrupted just before 3. when saving)


All of these functions return either true on success or nil, error on error.
]]--

local ser = serialize_lib.serialize

local windows_mode = false

-- == local functions ==

local function save_atomic_move_file(filename)
	--2. if windows mode, delete main file
	if windows_mode then
		local delsucc, err = os.remove(filename)
		if not delsucc then
			serialize_lib.log_warn("Unable to delete old savefile '"..filename.."':")
			serialize_lib.log_warn(err)
			serialize_lib.log_info("Trying to replace the save file anyway now...")
		end
	end
	
	--3. move file
	local mvsucc, err = os.rename(filename..".new", filename)
	if not mvsucc then
		if minetest.settings:get_bool("serialize_lib_no_auto_windows_mode") or windows_mode then
			serialize_lib.log_error("Unable to replace save file '"..filename.."':")
			serialize_lib.log_error(err)
			return nil, err
		else
			-- enable windows mode and try again
			serialize_lib.log_info("Unable to replace save file '"..filename.."' by direct renaming:")
			serialize_lib.log_info(err)
			serialize_lib.log_info("Enabling Windows mode for atomic saving...")