Platform

----------------------------------
-- Warning ! WORK IN PROGRESS ! --
-- Has not been fully tested !  --
----------------------------------
--
-- Copyright 2013 MigukNamja
-- [email protected]
--
-- MigukNamja's Platform Builder
--
--

-- Globals
gForward = 0 -- Set by program arg
gRight = 0   -- Set by program arg

--
-- Place a platform block
--
gSlot = 1
gTotalPlaced = 0
function place()
  while turtle.getItemCount(gSlot) == 0 do
    gSlot = gSlot + 1
  end

  turtle.select(gSlot)

  if not turtle.compareDown() then -- don't bother digging and placing if platform already there
    turtle.digDown()
    turtle.placeDown()
    gTotalPlaced = gTotalPlaced + 1
  end
end

--
-- Return to the starting position and orientation
--
function returnToStart()
  -- odd number of columns will have turtle at the far end (top) of the platform
  -- so, turtle should return to bottom row
  if gRight % 2 == 1 then
    local y = gForward - 1
    turtle.turnLeft()
    turtle.turnLeft()
    assert( moveForward( y ) == y )
  end

  local x = gRight - 1
  turtle.turnRight()
  assert( moveForward( x ) == x )
  turtle.turnRight()
end

-- Move forward 'blocks' number of blocks, digging when necessary
-- Hitting bedrock or something undiggable like an entity (creature) will
--   prevent forward movement
--
-- Return actual blocks moved forward
function moveForward(blocks)
  if blocks < 0 then return moveBack(0-blocks) end
  if blocks == 0 then return 0 end

  local moved = 0

  while moved < blocks do
    if turtle.forward() then -- air, nothing to dig, but go down
      moved = moved + 1
    elseif turtle.dig() then -- had to dig to go forwards
      if not turtle.forward() then
        local attempts = 0
        while turtle.dig() and attempts < 20 do
          attempts = attempts + 1 -- take care water won't cause infinite digging
          sleep(0.25) -- might have to chew through a stack of sand or gravel
        end

        if turtle.forward() then
          moved = moved + 1
        end
      else
        moved = moved + 1
      end
    else -- undiggable, give up (for now)
      return moved
    end

    sleep(0.25) -- sleep to avoid yielding error
  end

  return moved
end

-- Move backwards, digging when necessary
function moveBack(blocks)
  if blocks < 0 then return moveForward(0-blocks) end
  if blocks == 0 then return 0 end

  local moved = 0

  turtle.turnRight()
  turtle.turnRight()
  moved = moveForward(blocks)
  turtle.turnRight()
  turtle.turnRight()

  return moved
end

function usage()
  print( "Usage: platform <blocks_forward> <blocks_right>" )
  print( " Both values must be a least 1" )
end

function parseArgs(args)
  local validSyntax = false

  if #args ~= 2 then
    return false
  elseif args[1] == "help" then
    return false
  elseif args[1] == nil or args[2] == nil then
    return false
  else
    gForward = tonumber( args[1] )
    gRight   = tonumber( args[2] )

    if gForward <= 0 or gRight <= 0 then
      validSyntax = false
    else
      validSyntax = true
    end
  end

  return validSyntax
end

local tArgs = { ... }
validSyntax = parseArgs(tArgs)
if not validSyntax then
  usage()
  return
end

print( "Making platform ", gForward, " blocks forward and ", gRight, " blocks rightwards." )

local x = 1
local y = 1
turtle.select(1)
for x=1,gRight do
  for y=1,gForward do
    place()
    if y < gForward then
      assert( moveForward(1) == 1 )
    end
  end

  if x < gRight then
    if (x % 2) == 1 then -- odd numbered row, turn rightwards and get lined up for next row
      turtle.turnRight()
      assert( moveForward(1) == 1 )
      turtle.turnRight()
    else -- even numbered row, turn leftwards and get lined up for next row
      turtle.turnLeft()
      assert( moveForward(1) == 1 )
      turtle.turnLeft()
    end
  end
end

--returnToStart()

print( "I have finished the assigned task, my master !" )