turtle = {}
local matrix = {}

local x = { x=1, y=0, z=0 }
local y = { x=0, y=1, z=0 }
local z = { x=0, y=0, z=1 }

local is_num = function(c)
   return type(tonumber(c))=="number" or c=="-"
      and true or false 
end

local round = function(n)
   return math.floor(n+0.5)
end

turtle.spawn = function (pos, def)   
   local min = { x = pos.x, y = pos.y, z = pos.z }
   local max = { x = pos.x, y = pos.y, z = pos.z }
   
   local nodes = {}
   local materials = {}
   print("huh: "..dump(def))
   for _, mat in pairs(def.materials) do
      table.insert( materials, minetest.get_content_id(mat) )
   end
   
   local tmp = matrix.new()
   local rot = matrix.orient(tmp, math.pi/2, z )
   local pos = vector.new(pos)
   local stk = {}

   local axis = y
   local angle = 0

   local pen_down = true
   local mat = 1

   local arg = ""
   for c in def.prog:gmatch"." do 
      if is_num(c) then
	 arg = arg..c
      elseif c == "G" then
	 if pen_down then
	    if pos.x < min.x then min.x = pos.x end
	    if pos.y < min.y then min.y = pos.y end
	    if pos.z < min.z then min.z = pos.z end
	    if pos.x > max.x then max.x = pos.x end
	    if pos.y > max.y then max.y = pos.y end
	    if pos.z > max.z then max.z = pos.z end
	    local rpos = { x=round(pos.x), y=round(pos.y), z=round(pos.z)}
	    table.insert(nodes, { pos=rpos, mat=materials[mat] } )
	 end
	 pos = pos + matrix.transpose(rot, x)
      elseif c == "U" then
	 pen_down = false
      elseif c == "D" then
	 pen_down = true
      elseif c == "T" then
	 pen_down = not pen_down
      elseif c == "[" then
	 table.insert(stk, { rot=rot, pos=pos } )
      elseif c == "]" then
	 local s = table.remove(stk)
	 rot = s.rot
	 pos = s.pos
      elseif c == "X" then
	 axis = x
      elseif c == "Y" then
	 axis = y
      elseif c == "Z" then
	 axis = z
      elseif c == "A" then
	 angle = tonumber(arg) or 0
	 arg = ""
      elseif c == "M" then
	 mat = tonumber(arg) or 1
	 arg = ""
      elseif c == "R" then
	 tmp = matrix.id()
	 tmp = matrix.orient(tmp, angle*math.pi/180, axis)
	 rot = matrix.mul(tmp, rot)
      elseif c == "I" then
	 tmp = matrix.id()
	 tmp = matrix.orient(tmp, math.pi/2, axis)
	 rot = tmp
      end
   end
   
   local vm = VoxelManip()
   min, max = vm:read_from_map(min, max)
   local area = VoxelArea:new{ MinEdge = min, MaxEdge = max }
   local data = vm:get_data()

   for _, node in pairs(nodes) do
      local index = area:indexp(node.pos)
      data[index] = node.mat
   end
   
   vm:set_data(data)
   vm:write_to_map()
   vm:update_map()
end

matrix.new = function()
   local m = {}
   for i = 1,4 do m[i] = {}
   for j = 1,4 do m[i][j] = 0
   end
   end
   return m
end

matrix.id = function()
   local m = {}
   for i = 1, 4 do m[i] = {}
   for j = 1, 4 do
      if i == j then
	 m[i][j] = 1
      else
	 m[i][j] = 0
      end
   end
   end
   return m
end

matrix.mul = function(m1, m2)
   local m = {}
   for i = 1, 4 do m[i] = {}
   for j = 1, 4 do
      local num = 0
      for n = 1, 4 do
	 num = num + m1[i][n] * m2[n][j]
      end
      m[i][j] = num
   end
   end
   return m
end

matrix.orient = function(m, angle, axis)
   local c = math.cos(angle)
   local s = math.sin(angle)
   local t = 1.0 - c
   
   local tx  = t * axis.x
   local ty  = t * axis.y
   local tz  = t * axis.z
   local sx  = s * axis.x
   local sy  = s * axis.y
   local sz  = s * axis.z
   
   m[1][1] = tx * axis.x + c
   m[1][2] = tx * axis.y + sz
   m[1][3] = tx * axis.z - sy
   
   m[2][1] = ty * axis.x - sz
   m[2][2] = ty * axis.y + c
   m[2][3] = ty * axis.z + sx
   
   m[3][1] = tz * axis.x + sy
   m[3][2] = tz * axis.y - sx
   m[3][3] = tz * axis.z + c
   return m
end

matrix.transpose = function (m, v)
   local x = m[1][1] * v.x + m[2][1] * v.y + m[3][1] * v.z + m[4][1]
   local y = m[1][2] * v.x + m[2][2] * v.y + m[3][2] * v.z + m[4][2]
   local z = m[1][3] * v.x + m[2][3] * v.y + m[3][3] * v.z + m[4][3]
   return vector.new(x,y,z)
end