-- circle.lua — CC:Tweaked Turtle
-- Moves up 5, then draws a 2D circle outline on the floor below.
-- Default radius: 50

local radius = 50

-- ==== helpers ====
local function forward()
  while not turtle.forward() do
    if turtle.detect() then turtle.dig() end
  end
end

local function up()
  while not turtle.up() do
    if turtle.detectUp() then turtle.digUp() end
  end
end

local function placeDown()
  for s=1,16 do
    if turtle.getItemCount(s) > 0 then
      turtle.select(s)
      turtle.placeDown()
      return true
    end
  end
  return false
end

-- ==== movement tracking ====
local dir = 0 -- 0=north,1=east,2=south,3=west
local posX,posZ = 0,0

local function turnRight()
  turtle.turnRight()
  dir = (dir+1)%4
end

local function turnLeft()
  turtle.turnLeft()
  dir = (dir+3)%4
end

local function step()
  forward()
  if dir==0 then posZ=posZ-1
  elseif dir==1 then posX=posX+1
  elseif dir==2 then posZ=posZ+1
  elseif dir==3 then posX=posX-1 end
end

-- teleport-style move (grid walking)
local function goto(x,z)
  -- move in X
  if posX < x then
    while dir~=1 do turnRight() end
    for i=posX+1,x do step() end
  elseif posX > x then
    while dir~=3 do turnRight() end
    for i=x,posX-1 do step() end
  end
  -- move in Z
  if posZ < z then
    while dir~=2 do turnRight() end
    for i=posZ+1,z do step() end
  elseif posZ > z then
    while dir~=0 do turnRight() end
    for i=z,posZ-1 do step() end
  end
end

-- ==== main ====

-- go up 5
for i=1,5 do up() end

-- draw circle with midpoint algorithm
local function drawCircle(r)
  local x = r
  local z = 0
  local err = 1 - r

  while x >= z do
    local pts = {
      { x, z }, { z, x }, { -z, x }, { -x, z },
      { -x, -z }, { -z, -x }, { z, -x }, { x, -z }
    }
    for _,p in ipairs(pts) do
      goto(p[1],p[2])
      placeDown()
    end
    z = z + 1
    if err < 0 then
      err = err + 2*z + 1
    else
      x = x - 1
      err = err + 2*(z - x + 1)
    end
  end
end

drawCircle(radius)

print("Circle complete!")