a

c = peripheral.wrap("top")
m = peripheral.wrap("monitor_3")
os.loadAPI("buttons")
sStart = 1
yStart = 2

x,y = m.getSize()
x2 = x - 4
x1 = 5
sSize = (y-yStart)/2-2

function getSize()
  c.condenseItems()
  for i = 1,c.getInventorySize() do
    if c.getStackInSlot(i) == nil then
      return i
    end
  end
  return c.getInventorySize()+1
end

function centerM(message)
  m.clear()
  m.setCursorPos((x-string.len(message))/2,y/2)
  m.write(message)
end

function screen()
  local name
  if sStart+sSize>size then
    i2 = size
  else
    i2 = sStart+sSize
  end
  j = 0
  for i = sStart, i2 do
    j = j + 1
    if c.getStackInSlot(i) ~= nil then
      name = c.getStackInSlot(i).destination
      buttons.setTable(name,moveItem,i,x1,x2,j+1*j+yStart,j+1*j+yStart)
    end
  end
  scroll()
  m.clear()
  buttons.heading("Portal Hub")
  buttons.screen()
end

function scroll()
  if sStart > 1 then
    buttons.setTable("< Prev",prev,0,x1,(x/2)-1,y,y)
  end
  if sStart+sSize < size then
    buttons.setTable("Next >",next,0,(x/2)+1,x2,y,y)
  end
end

function prev(i)
  sStart = sStart-sSize-1
end

function next(i)
  sStart = sStart+sSize+1
end

function moveItem(slot)
  c.pullItem("west",1,1,1)
  c.pushItem("west",slot,1,1)
end

function starter()
  size = getSize()
  c.condenseItems()
  buttons.clearTable()
  screen()
end

while true do
  starter()
  event,p1,p2,p3 = os.pullEvent("monitor_touch")
  centerM("Loading...")
  buttons.checkxy(p2,p3)
end