local robot = require("robot")
local moving = true
local invPos = 1

function verifyInv()
   if(robot.count(invPos) == 0) then
      invPos = invPos + 1
      if(invPos > (robot.inventorySize()) or robot.count(invPos) == 0) then
         return false
      end
      robot.select(invPos)
   end

   return true
end

function placeDown()
   local check = verifyInv()

   if(check) then
      local d1,d2 = robot.detectDown()
      if(not (d2 == "passable")) then
         robot.placeDown()
      end
   end

   return check
end

function placeUp()
   local check = verifyInv()

   if(check) then
      robot.placeUp()
   end

   return check
end

function placeForward()
   local check = verifyInv()

   if(check) then
      robot.place()
   end

   return check
end

while moving do
   moving = placeUp()
   if(not moving) then
      break
   end

   moving = placeDown()
   if(not moving) then
      break
   end

   moving = robot.back()
   if(not moving) then
      break
   end

   moving = placeForward()
   if(not moving) then
      break
   end
end