Flatten Terrain for the road (4x3)

-- Safe forward movement: if blocked by an entity or obstacle,
-- try to dig if it's a block, or wait if it's an entity.
function safeForward()
  while not turtle.forward() do
    local success, data = turtle.inspect()
    if success then
      turtle.dig()
    else
      -- Likely an entity in the way; wait for it to clear.
      os.sleep(0.5)
    end
  end
end

-- Functions for lateral movement (keeping original direction)
function moveLeft(n)
  turtle.turnLeft()
  for i = 1, n do
    safeForward()
  end
  turtle.turnRight()
end

function moveRight(n)
  turtle.turnRight()
  for i = 1, n do
    safeForward()
  end
  turtle.turnLeft()
end

-- Function to "flatten" a column:
-- Assumes the turtle is at ground level.
-- It first moves up 2 blocks (ensuring a 3-block high space: floor + 2 air blocks),
-- then moves back down. If there is no block underfoot, it places one from the inventory.
function flattenColumn()
  -- Clear the vertical space (upper 2 blocks)
  for i = 1, 2 do
    if turtle.detectUp() then
      turtle.digUp()
    end
    turtle.up()
  end

  -- Move back down to ground level
  turtle.down()
  turtle.down()

  -- If no block is detected below, place a block from the inventory.
  if not turtle.detectDown() then
    for slot = 1, 16 do
      turtle.select(slot)
      if turtle.getItemCount() > 0 then
        turtle.placeDown()
        break
      end
    end
  end
end

-- Function to check for a deep drop (more than 5 blocks)
-- The turtle temporarily moves forward, then descends counting missing blocks.
-- Afterwards, it returns to the original position.
function isDeepDropAhead()
  if not turtle.forward() then
    -- Movement blocked, so assume no drop.
    return false
  end

  local depth = 0
  while depth <= 5 and not turtle.detectDown() do
    depth = depth + 1
    turtle.down()
  end

  -- Return to the original level.
  for i = 1, depth do
    turtle.up()
  end
  turtle.back()

  return depth > 5
end

-- Function for one step: flatten the corridor section and then move forward.
-- The corridor is considered 4 blocks wide (current block plus 3 blocks to the right).
function flattenStep()
  if isDeepDropAhead() then
    print("Deep drop ahead - stopping.")
    return false
  end

  local corridorWidth = 4
  for offset = 0, corridorWidth - 1 do
    if offset > 0 then
      moveRight(offset)
    end

    flattenColumn()

    if offset > 0 then
      moveLeft(offset)
    end
  end

  safeForward()
  return true
end

-- Main function: while fuel is available, perform the flattening step by step.
function flattenTerrain()
  while turtle.getFuelLevel() > 0 do
    if not flattenStep() then
      break
    end
  end
end

flattenTerrain()