Auto Item Smelter (Basic, UNDER 50 LINES)

local efficiency = 8 --the amount of items each fuel item can smelt
local furnaces = 6 --the amount of furnaces the chef has (MAX 8)
local amounts = {}
function selectNext() --selects the next non-empty slot in the turtle and returns true, else returns false
    for i = 1, 16 do
        if turtle.getItemCount(i) ~= 0 then
            turtle.select(i)
            return true
        end
    end
    return false
end
while turtle.suck() do
    for i = 2, furnaces do --get's the ores out of the chest, until chest is empty or has [furnaces] stacks
        table.insert(amounts, 0)
        if not turtle.suck() then break end
    end
    for k, v in pairs(amounts) do --puts the ores it has collected into the furnaces
        turtle.back()
        selectNext()
        amounts[k] = turtle.getItemCount()
        turtle.dropDown()
    end
    while turtle.forward() do end --resets to the chest location
    turtle.select(1)
    turtle.down()
    for k, v in pairs(amounts) do
        turtle.suck(math.ceil(v/efficiency)) --sucks out of the coal chest how much fuel it needs
    end
    turtle.down()
    local biggestStack = 0
    for k, v in pairs(amounts) do
        if v > biggestStack then --calculates the size of the biggest stack
            biggestStack = v
        end
        turtle.back()
        selectNext()
        turtle.dropUp(math.ceil(v/efficiency)) --puts the correct amount of fuel into each furnace
    end
    sleep(biggestStack*10) --waits for the biggest stack to be done
    for k, v in pairs(amounts) do --collects all the items
        turtle.suckUp()
        turtle.forward()
    end
    while selectNext() do turtle.drop() end
    turtle.up()
    turtle.up()
    turtle.select(1)
end