local INVENTORY_SIZE = 16
local FUEL_SLOT = 1

local function getNumberFromUser(message)
    print(message)
    local raw = io.read()
    number = tonumber(raw)
    return number
end

local function getFirstSlotContainingBlocks()
    for slot = 1, INVENTORY_SIZE do
        local itemCount = turtle.getItemCount(slot)
        if slot ~= FUEL_SLOT and itemCount > 0 then
            return slot
        end
    end
    return -1
end

local function hasEnoughFuel()
    return turtle.getFuelLevel() > 16
end

local function checkFuel()
    if not hasEnoughFuel() then
        refuel()
    end
end

local function refuel()
    turtle.select(FUEL_SLOT)
    turtle.refuel(1)
end

local function build(x, y)
    for xProgress = 1, x do
        for yProgress = 1, y do
            checkFuel()
            turtle.forward()
            if (turtle.detectDown()) then
                -- clear the block so we can place a new one
                turtle.digDown()
            end
            local slot = getFirstSlotContainingBlocks()
            if (slot == -1) then
                print("No buildable blocks")
                return
            end
            turtle.select(slot)
            turtle.placeDown()
        end
        turtle.forward()
        turtle.turnRight()
        turtle.forward()
        turtle.turnRight()
    end
    print("Done!")
end

local function init()
    local x = getNumberFromUser("How far straight should I build?")
    local y = getNumberFromUser("How far right should I build?")
    build(x, y)
end

init()