function loadFuel(amount)
  local level = amount
  while (turtle.getFuelLevel() < level) do
    for i = 1,16 do
      turtle.select(i)
      while (turtle.refuel(1)) do
        if (turtle.getFuelLevel() > level) then
          return
        end
      end
    end
    print("More fuel required to continue.")
    print(tostring(turtle.getFuelLevel()) .. " / " ..tostring(level))
    os.sleep(0.5)
   end
end

function waitForward()
  loadFuel(1)
  while (not turtle.forward()) do
    print("Obstructed, Halting until clear.")
    os.sleep(0.5)
  end
end

function breakForward()
  loadFuel(1)
  while (not turtle.forward()) do
    turtle.dig()
  end
end

function turnAround()
  turtle.turnLeft()
  turtle.turnLeft()
end

function waitUp()
  loadFuel(1)
  while (not turtle.up()) do
    print("Obstructed, Halting until clear.")
    os.sleep(0.5)
  end
end

function breakUp()
  loadFuel(1)
  while (not turtle.up()) do
    turtle.digUp()
  end
end

function waitDown()
  loadFuel(1)
  while (not turtle.down()) do
    print("Obstructed, Halting until clear.")
    os.sleep(0.5)
  end
end

function breakDown()
  loadFuel(1)
  while (not turtle.down()) do
    turtle.digDown()
  end
end

function select()
  for i = 2, 16 do
    if (turtle.getItemCount(i) > 0) then
      turtle.select(i)
      return true
    end
  end
  return false
end

function waitMats()
  while (not select()) do
    print("Waiting for materials.")
    os.sleep(0.5)
  end
end

function turn(dir)
  if (dir == 0) then
    turtle.turnLeft()
  else
    turtle.turnRight()
  end
end

function line(dist)
  for i = 1,dist do
    waitMats()
    turtle.placeDown()
    if (i < dist) then
      waitForward()
    end
  end
end

function floor(length, width)
  local dir = 0
  for i = 1, width do
    line(length)
    if (i < width) then
      turn(dir)
      breakForward()
      turn(dir)
      dir = (dir + 1) % 2
    end
  end
end

function bridge(length,width)
  floor(length,width)
  if (width % 2 == 1) then
    turtle.turnLeft()
    waitForward()
    turtle.turnLeft()
    turtle.up()
    line(length)
    turtle.turnLeft()
    for i = 0, width do
      waitForward()
    end
    turtle.turnLeft()
    line(length)
  else
    turtle.turnRight()
    waitForward()
    turtle.turnRight()
    waitUp()
    line(length)
    turtle.turnRight()
    for i = 0, width do
      waitForward()
    end
    turtle.turnRight()
    line(length)
  end
end

function wall(length,height)
  turtle.up()
  for i = 1, height do
    line(length)
    if (i < height) then
      turtle.turnLeft()
      turtle.turnLeft()
      waitUp()
    end
  end
end