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

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

local function arcRight()
    turtle.forward()
    turtle.turnRight()
    turtle.forward()
    turtle.turnRight()
end

local function arcLeft()
    turtle.forward()
    turtle.turnLeft()
    turtle.forward()
    turtle.turnLeft()
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
        if xProgress % 2 == 0 then
            arcLeft()
        else
            arcRight()
        end
    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()