--Stairs Down Simple Script v1
--Turtle Program Computer Craft
--by SemlerPDX(July2016)

--COMMENT SYNTAX EXPLAINATION
--torches must be in slot 1 (one for every 3rd layer dug)
--stairs can be in slot 2 if desired, see below

--StairsDown 20 (number of stairs down) 1 (or blank -- 1 will add stairs from slot 2)
--example:  StairsDown 20 (makes stairs 20 deep with torches but no stair blocks)
--example2: StairsDown 20 1 (makes stairs 20 deep w/ torches and stair blocks)


-- Variables --
local args = {...}
local d = args[1] or 0
local s = args[2] or 0
local r = 0 + d
local t = turtle
local lit = 2

-- F-ACK --
if #args ~= 2 then
  print("<error420: syntax>")
  print("<ex: Stairs 20 1 (starts digging stairs 20 blocks deep with stair blocks in slot 2)>")
  return
end

if d == 0 then
  print("<error421: missing length>")
  print("<ex: Stairs 20 (starts digging stairs 20 blocks deep)>")
  return
end

-- Functions --
--force forward function by CCCode
local function forceForward()
  while not t.forward() do
    t.dig()
  end
end

--dig down, decrement lit variable
local function fDown()
  t.digDown()
  t.down()
  lit = lit - 1
end

--shave 4 blocks and place torch if needed
local function fShave()
  for v=1,4 do
   	if v == 3 then
 	    if lit == 0 then
	      	t.placeUp()
  	    	lit = lit + 2
	        forceForward()
	     else
       	    forceForward()
	     end
   	else
	     forceForward()
   	end
  end
end

--move to next shaving position
local function fReturn()
  for v=1,3 do
   	t.back()
  end
end

--place stairs while returning home
local function fHomeS()
  t.turnLeft()
  t.turnLeft()
  t.select(2)
  while r ~=0 do
   	t.place()
   	t.up()
   	t.forward()
   	r = r -1
  end
end

--return home
local function fHome()
  while r ~=0 do
 	t.up()
 	t.back()
 	r = r -1
  end
end

--clear display screen
local function fset()
  term.clear()
  term.setCursorPos(1,1)
end

-- Pre-fire scripts --
fset()
print("Building staircase "..tostring(d).." blocks down...")
t.digDown()
t.down()
sleep(2)

---- Main Loop ----
while d ~= 0 do

  local function fcancel()
    local event, key = os.pullEvent("key")
  end

  local function fmain()
    fShave()
   	fReturn()
   	fDown()
   	d = d - 1
  end

  FunctionEnabled = parallel.waitForAny(fcancel,fmain)

  if FunctionEnabled == 1 then
    textutils.slowPrint("Cancelling Build...", 15)
    sleep(1.65)
    break
  end

end

-- Evaluate Ending --
if FunctionEnabled == 1 then    --(1 = functions cancelled, 2 = standard function looped)
  fset()
  print("Build Cancelled by user")
  print("...returning to start in 5 seconds - move out of path")
  sleep(6)
  fHome()
  t.select(1)
else
  fset()
  print("Build Completed")
  if s == 1 then
    print("Building stairs and returning home...")
    fHomeS()
    t.select(1)
   	fset()
   	print("...program complete")
  else
    fset()
    fHome()
    t.select(1)
   	print("...program complete")
  end
end