ComputerCraft Turtle Rectangle Dig

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-- Warning ! WORK IN PROGRESS ! --
-- Has not been fully tested !  --
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--
-- MigukNamja's 1st Rectangle Dig Program
-- Copyright 2013 MigukNamja
-- [email protected]
--

-- 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: rectangle <blocks_forward> <blocks_right>" )
  print( "Both values must be a least 1" )
end

function parseArgs(args)
  local validSyntax = false
  local bForward = 0
  local bRight = 0

  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
    bForward = tonumber( args[1] )
    bRight   = tonumber( args[2] )

    if bForward <= 0 or bRight <= 0 then
      validSyntax = false
    else
      validSyntax = true
    end
  end

  return validSyntax, bForward, bRight
end

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

print( "Digging ", bForward, " blocks forward and ", bRight, " blocks rightwards." )

local i = 0
while i < bRight do

  if i == 0 then -- The 1st row is different because turtle starts 1 block behind dig area
    -- Dig forward
    assert( moveForward( bForward ) == bForward )
  else -- All other rows
    -- Dig forward
    assert( moveForward( bForward-1 ) == bForward-1 )
  end

  -- Mark that row as done
  i = i + 1

  if i >= bRight then -- Done ?
     break
  else -- Turn and get ready for next row
    if i % 2 == 1 then -- Even rows, including the 0th row
      turtle.turnRight()
      assert( moveForward( 1 ) == 1 )
      turtle.turnRight()
    else -- Odd rows
      turtle.turnLeft()
      assert( moveForward( 1 ) == 1 )
      turtle.turnLeft()
    end
  end
end

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