main

local blockIdx = 1
local slabIdx = 5
local wallIdx = 9
local torchIdx = 13

function selectOrDie(idx)
  turtle.select(idx)
  if turtle.getItemCount() <= 0 then
    error("Out of items at idx: "..idx)
  end
end

function initial()
  turtle.up()
  selectOrDie(slabIdx)
  turtle.placeDown()
  turtle.turnRight()
  turtle.forward()
  turtle.turnLeft()
  turtle.placeDown()
end

function bridge()
  turtle.forward()
  selectOrDie(blockIdx)
  turtle.placeDown()
  turtle.turnRight()
  turtle.forward()
  selectOrDie(wallIdx)
  turtle.placeDown()
  turtle.up()
  turtle.placeDown()
  turtle.turnLeft()
  turtle.turnLeft()
  turtle.forward()
  turtle.down()
  turtle.forward()
  selectOrDie(blockIdx)
  turtle.placeDown()
  turtle.forward()
  selectOrDie(wallIdx)
  turtle.placeDown()
  turtle.up()
  turtle.placeDown()
  turtle.turnRight()
  turtle.turnRight()
  turtle.forward()
  turtle.down()
  turtle.forward()
  turtle.turnLeft()
end

function turnAround()
  turtle.turnRight()
  turtle.turnRight()
end

function torch()
  selectOrDie(torchIdx)
  turtle.up()
  turtle.turnRight()
  turtle.place()
  turnAround()
  turtle.forward()
  turtle.place()
  turnAround()
  turtle.forward()
  turtle.turnLeft()
  turtle.down()
end

local len = 1

-- Entrance
initial()
bridge()
torch()

for i=1,50 do
  bridge()
  if len % 15 == 0 then
    torch()
  end
  len = len + 1
end