serialize_mapblock.lua

-- collect nodes with on_timer attributes
local node_names_with_timer = {}
minetest.register_on_mods_loaded(function()
	for _,node in pairs(minetest.registered_nodes) do
		if node.on_timer then
			table.insert(node_names_with_timer, node.name)
		end
	end
	minetest.log("action", "[mapsync] collected " .. #node_names_with_timer .. " items with node timers")
end)

local air_content_id = minetest.get_content_id("air")
local ignore_content_id = minetest.get_content_id("ignore")

-- map of ignored node_ids (node_id => true)
local ignore_node_ids = {
	[ignore_content_id] = true
}

-- search for other ignored node_ids
minetest.register_on_mods_loaded(function()
	for name, node_def in pairs(minetest.registered_nodes) do
		if node_def.groups and node_def.groups.mapsync_ignore then
			local node_id = minetest.get_content_id(name)
			ignore_node_ids[node_id] = true
		end
	end
end)

-- local vars for faster access
local insert = table.insert

--- Serializes the mapblock at the given position
-- @param mapblock_pos the mapblock-position
-- @return @{mapblock_data}
function mapsync.serialize_mapblock(mapblock_pos, node_mapping)
	node_mapping = node_mapping or {}

	local pos1, pos2 = mapsync.get_node_bounds_from_mapblock(mapblock_pos)
	assert((pos2.x - pos1.x) == 15)
	assert((pos2.y - pos1.y) == 15)
	assert((pos2.z - pos1.z) == 15)

	minetest.fix_light(pos1, pos2)

	local manip = minetest.get_voxel_manip()
	local e1, e2 = manip:read_from_map(pos1, pos2)
	local area = VoxelArea:new({MinEdge=e1, MaxEdge=e2})

	local node_data = manip:get_data()
	local param1 = manip:get_light_data()
	local param2 = manip:get_param2_data()

	assert(#node_data == 4096)
	assert(#param1 == 4096)
	assert(#param2 == 4096)

	-- serialized block
	local blockdata = {
		empty = true,
		has_metadata = false,
		metadata = {},
		node_ids = {},
		param1 = {},
		param2 = {}
	}

	-- id -> true
	local mapped_node_ids = {}
	-- collect mapped node ids
	for _, node_id in pairs(node_mapping) do
		mapped_node_ids[node_id] = true
	end

	-- loop over all blocks and fill cid,param1 and param2
	for z=pos1.z,pos2.z do
	for x=pos1.x,pos2.x do
	for y=pos1.y,pos2.y do
		local i = area:index(x,y,z)

		local node_id = node_data[i]
		if ignore_node_ids[node_id] then
			-- replace ignored blocks with air
			node_id = air_content_id
		end

		if node_id ~= air_content_id or param1[i] ~= 15 then
			-- there is a non-air node here or the light is set to a non-default value
			blockdata.empty = false
		end

		-- map node_id if not already mapped
		if not mapped_node_ids[node_id] then
			local nodename = minetest.get_name_from_content_id(node_id)
			mapped_node_ids[node_id] = nodename
			node_mapping[nodename] = node_id
		end

		insert(blockdata.node_ids, node_id)
		insert(blockdata.param1, param1[i])
		insert(blockdata.param2, param2[i])
	end
	end
	end

	-- serialize metadata
	local pos_with_meta = minetest.find_nodes_with_meta(pos1, pos2)
	for _, meta_pos in ipairs(pos_with_meta) do
		local relative_pos = vector.subtract(meta_pos, pos1)
		local meta = minetest.get_meta(meta_pos):to_table()

		-- Convert metadata item stacks to item strings
		for _, invlist in pairs(meta.inventory) do
			for index = 1, #invlist do
				local itemstack = invlist[index]
				if itemstack.to_string then
					invlist[index] = itemstack:to_string()
					blockdata.has_metadata = true
				end
			end
		end

		-- dirty workaround for https://github.com/minetest/minetest/issues/8943
		if next(meta) and (next(meta.fields) or next(meta.inventory)) then
			blockdata.has_metadata = true
			blockdata.metadata.meta = blockdata.metadata.meta or {}
			blockdata.metadata.meta[minetest.pos_to_string(relative_pos)] = meta
		end

	end

	-- serialize node timers
	if #node_names_with_timer > 0 then
		blockdata.metadata.timers = {}
		local list = minetest.find_nodes_in_area(pos1, pos2, node_names_with_timer)
		for _, timer_pos in pairs(list) do
			local timer = minetest.get_node_timer(timer_pos)
			local relative_pos = vector.subtract(timer_pos, pos1)
			if timer:is_started() then
				blockdata.has_metadata = true
				local timeout = timer:get_timeout()
				local elapsed = timer:get_elapsed()
				blockdata.metadata.timers[minetest.pos_to_string(relative_pos)] = {
					timeout = timeout,
					-- round down elapsed timer
					elapsed = math.min(math.floor(elapsed/10)*10, timeout)
				}
			end
		end

	end

	return blockdata
end