cm_bags/init.lua

local S = minetest.get_translator(minetest.get_current_modname())

local function getBagSize(stack)
	if not stack:get_definition().groups.bag_size then
		return 0
	end

	return stack:get_definition().groups.bag_size
end

local function openBag(
	player,
	player_name,
	bag_stack,
	context --[[opened equipped or inhand]]
)
	--minetest.chat_send_all("Enter")
	local inv_name = player_name .. "_bag_tmp"
	--Chaeck if something is broken. To prevent item voiding
	local inv = minetest.get_inventory({ type = "detached", name = inv_name })
	if inv ~= nil then
		minetest.chat_send_all("Bag is already open!")
		return false, "Bag is already open!"
	end

	minetest.create_detached_inventory(player_name .. "_bag_tmp", {
		--Forbids puting bags into bags
		allow_put = function(inv, listname, index, stack, player)
			if minetest.get_item_group(stack:get_name(), "bag_size") > 0 then
				return 0
			else
				return stack:get_stack_max()
			end
		end,
	}, player_name)
	inv = minetest.get_inventory({ type = "detached", name = inv_name })
	inv:set_size("main", getBagSize(bag_stack) * 9)

	local meta = bag_stack:get_meta()
	--minetest.chat_send_all(dump(meta:to_table()))
	local content = meta:get_string("bag:content")
	local list = content and minetest.deserialize(content) or {}

	for i, stack in ipairs(list) do
		inv:set_stack("main", i, stack)
		--[[if stack ~= nil then
			minetest.chat_send_all(dump(stack:to_string()))
		end]]
	end

	local form = "size[9,"
		.. (getBagSize(bag_stack) + 6)
		.. "]"
		.. mcl_formspec.get_itemslot_bg(0, 0, 9, getBagSize(bag_stack))
		.. "list[detached:"
		.. inv_name
		.. ";main;0,0;9,"
		.. getBagSize(bag_stack)
		.. ";]"
		.. mcl_formspec.get_itemslot_bg(0, getBagSize(bag_stack) + 1.5, 9, 3)
		.. "list[current_player;main;0,"
		.. (getBagSize(bag_stack) + 1.5)
		.. ";9,3;9]"
		.. mcl_formspec.get_itemslot_bg(0, getBagSize(bag_stack) + 5, 9, 1)
		.. "list[current_player;main;0,"
		.. (getBagSize(bag_stack) + 5)
		.. ";9,1;]"
		.. "listring[current_player;main]"
		.. "listring[detached:"
		.. inv_name
		.. ";main]"
		.. "listring[current_player;main]"
	minetest.show_formspec(player_name, "bag:" .. context, form)
end

minetest.register_on_player_receive_fields(function(player, formname, fields)
	--[[ Support for special "bag" slot at player gear.
    if formname == "bag:equipped" and fields.quit then
		--minetest.chat_send_all("Exit")
		local player_inv = player:get_inventory()
		local bag_stack = player_inv:get_stack("bag", 1)
		
	    local inv_name = player:get_player_name() .. "_bag_tmp"
        local inv = minetest.get_inventory({ type = "detached", name = inv_name })
		local stacks = {}
		for i = 0, inv:get_size("main"), 1 do
			stacks[i] = inv:get_stack("main", i):to_string()
		end
		
		bag_stack:get_meta():set_string("bag:content", minetest.serialize(stacks))
		player_inv:set_stack("backpack", 1, backapack_stack)
		--minetest.chat_send_all(dump(meta:to_table()))
		minetest.remove_detached_inventory(inv_name)
	else]]
	if formname == "bag:inhand" and fields.quit then
		local bag_stack = player:get_wielded_item()
		local inv_name = player:get_player_name() .. "_bag_tmp"
		local inv = minetest.get_inventory({ type = "detached", name = inv_name })

		local stacks = {}
		for i = 0, inv:get_size("main"), 1 do
			stacks[i] = inv:get_stack("main", i):to_string()
		end

		bag_stack:get_meta():set_string("bag:content", minetest.serialize(stacks))
		player:set_wielded_item(bag_stack)
		minetest.remove_detached_inventory(inv_name)
	end
end)

-- Forbid moving bag while it is open. To prevent item deletion on bag closure.
minetest.register_allow_player_inventory_action(function(player, action, inventory, inventory_info)
	if
		action == "move"
		and inventory_info.from_list == "main"
		and inventory_info.from_index == player:get_wield_index()
	then
		local bag_inv = minetest.get_inventory({ type = "detached", name = player:get_player_name() .. "_bag_tmp" })
		if bag_inv ~= nil then
			return 0
		end
	end

	if action == "take" and inventory_info.listname == "main" and inventory_info.index == player:get_wield_index() then
		local bag_inv = minetest.get_inventory({ type = "detached", name = player:get_player_name() .. "_bag_tmp" })
		if bag_inv ~= nil then
			return 0
		end
	end
end)

--[[
--A chat command for now. Wonna change to hot-key later.
minetest.register_chatcommand("bag", {
    func = function(player_name)
		local player = minetest.get_player_by_name(player_name)
		local player_inv = player:get_inventory()
		local backapack_stack = player_inv:get_stack("backpack", 1)
		if backapack_stack:is_empty() then
			return false, "No backpack equiped!"
		end
		
		openBackpack(player, player_name, backapack_stack, "equipped")
		return true, ""
    end,
})

minetest.register_allow_player_inventory_action(function(player, action, inventory, inventory_info)
	if action == "move" and inventory_info.to_list == "backpack" then
		local itemstack = inventory:get_stack(inventory_info.from_list, inventory_info.from_index)
		if not (minetest.get_item_group(itemstack:get_name(), "backpack_size") > 0)  then
			return 0
		else
			return itemstack:get_stack_max()
		end
	end
end)
]]

local function on_bag_place(itemstack, user, pointed_thing)
	openBag(user, user:get_player_name(), itemstack, "inhand")
	return nil
end

-- register backapack's
minetest.register_tool("cm_bags:leather", {
	description = S("Leather bag"),
	inventory_image = "bag_leather.png",
	groups = { bag_size = 1 },
	on_place = on_bag_place,
	on_secondary_use = on_bag_place,
})

minetest.register_craftitem("cm_bags:iron", {
	description = S("Iron bag"),
	inventory_image = "bag_iron.png",
	groups = { bag_size = 2 },
	on_place = on_bag_place,
	on_secondary_use = on_bag_place,
})

minetest.register_craftitem("cm_bags:gold", {
	description = S("Gold bag"),
	inventory_image = "bag_gold.png",
	groups = { bag_size = 3 },
	on_place = on_bag_place,
	on_secondary_use = on_bag_place,
})

minetest.register_craftitem("cm_bags:diamond", {
	description = S("Diamond bag"),
	inventory_image = "bag_diamond.png",
	groups = { bag_size = 4 },
	on_place = on_bag_place,
	on_secondary_use = on_bag_place,
})

-- register bag crafts
minetest.register_craft({
	output = "cm_bags:leather",
	recipe = {
		{ "mcl_mobitems:leather", "mcl_mobitems:leather", "mcl_mobitems:leather" },
		{ "mcl_mobitems:leather", "mcl_chests:chest", "mcl_mobitems:leather" },
		{ "mcl_mobitems:leather", "mcl_mobitems:leather", "mcl_mobitems:leather" },
	},
})

minetest.register_craft({
	output = "cm_bags:iron",
	recipe = {
		{ "mcl_core:iron_ingot", "mcl_core:iron_ingot", "mcl_core:iron_ingot" },
		{ "mcl_core:iron_ingot", "cm_bags:leather", "mcl_core:iron_ingot" },
		{ "mcl_core:iron_ingot", "mcl_core:iron_ingot", "mcl_core:iron_ingot" },
	},
})

minetest.register_craft({
	output = "cm_bags:gold",
	recipe = {
		{ "mcl_core:gold_ingot", "mcl_core:gold_ingot", "mcl_core:gold_ingot" },
		{ "mcl_core:gold_ingot", "cm_bags:iron", "mcl_core:gold_ingot" },
		{ "mcl_core:gold_ingot", "mcl_core:gold_ingot", "mcl_core:gold_ingot" },
	},
})

minetest.register_craft({
	output = "cm_bags:diamond",
	recipe = {
		{ "mcl_core:diamond", "mcl_core:diamond", "mcl_core:diamond" },
		{ "mcl_core:diamond", "cm_bags:gold", "mcl_core:diamond" },
		{ "mcl_core:diamond", "mcl_core:diamond", "mcl_core:diamond" },
	},
})

--transfer content of backpack on craft
minetest.register_on_craft(function(itemstack, player, old_craft_grid, craft_inv)
	if minetest.get_item_group(itemstack:get_name(), "bag_size") > 0 then
		local content = old_craft_grid[5]:get_meta():get_string("bag:content")
		itemstack:get_meta():set_string("bag:content", content)
		return itemstack
	end
end)