local function update_formspec(pos)
    
end

local function on_input(pos, m, inv)
    
end

local function on_add_fuel(pos, m, inv)
    
end

local function destination_list(s)
    return minetest.get_item_group(s:get_name(), "furnace_fuel") > 0 and "fuel" or "input"
end

local function can_run(pos, m, inv)
    return false
end

rgt_machines.register_machine("fuel_furnace", {
    states = {
        idle = {
            tiles = {"rgt_stone.png"},
        },
        active = {
            tiles = {"rgt_stone.png"},
        }
    },
    on_construct = function(pos)
        local m = minetest.get_meta(pos)
        local inv = m:get_inventory()
        inv:set_size("input", 1)
        inv:set_size("output", 1)
        -- Dummy list handle Shift-adding properly.
        inv:set_size("sort", 1)
        inv:set_size("fuel", 1)
        
        
    end,
    get_gui = function(pos)
        local loc = "nodemeta:"..pos.x..","..pos.y..","..pos.z
        local fs = "\
            formspec_version[10]\
            size[12,12]\
            \
            image["..(2 -0.0625)..","..(2 -0.0625)..";1.14,1.14;rgt_other_button_bg.png;8,8]\
            list["..loc..";input;2,2;1,1;]\
            \
            image["..(5 -0.0625)..","..(3 -0.0625)..";1.14,1.14;rgt_other_button_bg.png;8,8]\
            list["..loc..";output;5,3;1,1;]\
            \
            image["..(2 -0.0625)..","..(4 -0.0625)..";1.14,1.14;rgt_other_button_bg.png;8,8]\
            list["..loc..";fuel;2,4;1,1;]\
        "
        for x = 0, 7 do
            for y = 0, 3 do
                fs = fs.."\
                image["..(x *1.25 +1.125 -0.0625)..","..(y *1.25 +6.5 -0.0625)..";1.14,1.14;rgt_other_button_bg.png;8,8]\
                "
            end
        end
        fs = fs.."\
            list[current_player;main;1.125,6.5;8,4;]\
            \
            listring["..loc..";output]\
            listring[current_player;main]\
            listring["..loc..";sort]\
            listring[current_player;main]\
            listring["..loc..";input]\
            listring[current_player;main]\
            listring["..loc..";fuel]\
            listring[current_player;main]\
        "
    end,
    allow_metadata_inventory_put = function(pos, list, idx, s, p)
        local inv = minetest.get_meta(pos):get_inventory()
        if list == "output" then
            return 0
        elseif list == "input" then
            return s:get_count()
        elseif list == "fuel" then
            return minetest.get_item_group(s:get_name(), "furnace_fuel") > 0 and s:get_count() or 0
        elseif list == "sort" then
            local dst = destination_list(s)
            if dst then
                -- Add everything if we can.
                if inv:room_for_item(dst, s) then
                    return s:get_count()
                -- If not, and the stacks are compatible, add as much as possible.
                elseif inv:room_for_item(dst, s:take_item()) then
                    return s:get_stack_max() -inv:get_stack(dst, 1):get_count()
                end
            end
            return 0
        end
        return 0
    end,
    on_metadata_inventory_put = function(pos, list, idx, s, p)
        if list == "sort" then
            local inv = minetest.get_meta(pos):get_inventory()
            local dst = destination_list(s)
            inv:add_item(dst, s)
            -- Ensure the sorter list never has anything in it.
            inv:set_stack("sort", 1, ItemStack(""))
        end
    end
})