How to create an OS with ComputerCraft?

buttons = {}

local function setBtn(x,y,xt)
--# x,y is the position
--# txt is the text 
table.insert(buttons,{x,y,txt}
--# We add a new table which the button informstions to the buttons table
end

local function drawBtn()
--# no need for arguments
term.setBackgroundColor(colors.white)
term.setTextColor(colors.black)
--# you can change to color if you want
for k,v in pairs(buttons) do
--# looping through the buttons table
term.setCursorPos(v.x,v.y)
--# going to the buttons position
term.write(v.txt)
--# draw the button's text
end
end

local function checkClick(x,y)
--# x,y the position where you click
for k,v in pairs(buttons) do
--# looping through the buttons
if x >= v.x and y == v.y and x <= v.x+v.txt.length() then
--# check if the poition fits to a button
return k
--# return the button id
break 
--# stop the loop
end
end

setBtn(3,4,"test") -- id is 1
while true do
local _,btn,x,y = os.pullEvent()
drawBtn()
if _ == "mouse_click" then
if checkClick(x,y) == 1 then
print("button 1 got clicked")
end
end
sleep(0)
end