dofile("Gassy")

function PlaceBlockDownAndRefuel()
  while (true) do
    if (turtle.getItemCount() > 0) then
      turtle.placeDown()
      break
    end
    local curSlot = turtle.getSelectedSlot()
    if (curSlot == 16) then
      curSlot = 1 -- skip 1: fuel
    end
    turtle.select(curSlot + 1)
  end
  if (turtle.getFuelLevel() < 5) then
    local slot = turtle.getSelectedSlot()
    turtle.select(1)
    while (turtle.getItemCount() <= 0) do end
    turtle.refuel(1)
  end
end

local r1 = 20.5
local r2 = 37.5

local pn = math.floor(r2 * 2 + 4)
local pc = math.floor(pn / 2 + 0.5) -- (pc, pc) = center

local pat = {}
local cstart = {}
local cend = {}
local lc = 0
local rc = 0

for i = 1, pn do
  pat[i] = {}
  cstart[i] = 0
  cend[i] = 0
  local dx = i - pc
  for j = 1, pn do
    local dy = j - pc
    local d = math.sqrt(dx * dx + dy * dy)
    pat[i][j] = d > r1 and d < r2
    if (pat[i][j]) then
      rc = i -- trick: i increasing
      if (lc == 0) then
        lc = i
      end
      if (cstart[i] == 0) then
        cstart[i] = j
        cend[i] = j
      end
      if (cend[i] == j - 1) then
        cend[i] = j
      end
    end
  end
end

Gassy.x = pc
Gassy.y = pc
Gassy.z = 0
-- initially face South
Gassy.dump()

turtle.select(2)

local ns = 1
for i = rc, lc, -1 do
  if (ns == 1) then
    Gassy.go(i, cend[i], 0);
    Gassy.turn(0)
    PlaceBlockDownAndRefuel()
  else
    Gassy.go(i, cstart[i], 0);
    Gassy.turn(2)
    PlaceBlockDownAndRefuel()
  end
  for jj = 0, (cend[i] - cstart[i]) do
    Gassy.forward()
    PlaceBlockDownAndRefuel()
  end
end