local tArgs = {...}

local LEFT = 0
local FORWARD = 1
local RIGHT = 2

local nCurrentDir = FORWARD

local nCurrentX = 0
local nCurrentY = 0

--(( Functions ))--

local function look(nDir)
    while nDir < nCurrentDir do
        turtle.turnLeft()
        nCurrentDir = nCurrentDir - 1
    end
    while nDir > nCurrentDir do
        turtle.turnRight()
        nCurrentDir = nCurrentDir + 1
    end
end

local function _go(move, suffix)
    while not turtle[move]() do
        if not turtle["dig"..suffix]() then
            if turtle["detect"..suffix]() then
                error("Bedrock while trying to move " .. move, 0)
            end
            turtle["attack"..suffix]()
        end
    end
end

local function goForward()
    _go("forward", "")
    if nCurrentDir == RIGHT then
        nCurrentX = nCurrentX + 1
    elseif nCurrentDir == LEFT then
        nCurrentX = nCurrentX - 1
    end
end

local function goUp()
    _go("up", "Up")
    nCurrentY = nCurrentY + 1
end

local function goDown()
    _go("down", "Down")
    nCurrentY = nCurrentY - 1
end

local function _digTilTop(nHeight)
    -- dig til top-1
    while nCurrentY < nHeight - 2 do
        goUp()
    end
    if nCurrentY <= nHeight - 2 then
        repeat until not turtle.digUp()
    end
end

local function _digTilBottom(nHeight)
    -- dig til bottom+1
    while nCurrentY > 1 do
        goDown()
    end
    if nCurrentY >= 1 then
        repeat until not turtle.digDown()
    end
end

local function digColumn(nHeight)
    if nCurrentY < nHeight / 2 then
        -- bot to top
        _digTilBottom(nHeight)
        _digTilTop(nHeight)
    else
        -- top to bot
        _digTilTop(nHeight)
        _digTilBottom(nHeight)
    end
end

local function digFrame(nHeight, nWidth)
    digColumn(nHeight)

    if nWidth == 1 then
        return
    end

    if nCurrentX > nWidth / 2 then
        look(LEFT)
    else
        look(RIGHT)
    end

    for i = 1,nWidth-1 do
        goForward()
        digColumn(nHeight)
    end
end

local function tunnel(nLength, nHeight, nWidth)
    for i=1,nLength do
        look(FORWARD)
        goForward()
        digFrame(nHeight, nWidth)
    end

    if nCurrentX > 0 then
        look(LEFT)
        repeat
            goForward()
        until nCurrentX <= 0
    end

    look(FORWARD)
    while nCurrentY > 0 do
        goDown()
    end
end

--(( Error checking ))--

local nArgLength = tonumber(tArgs[1])
local nArgHeight = tonumber(tArgs[2] or 2)
local nArgWidth = tonumber(tArgs[3] or 1)

local function usage(sMsg)
    sMsg = sMsg and (sMsg .. "\n") or ""
    error(sMsg .. "Usage: tunnel <length> [height=2] [width=1]", 0)
end

if #tArgs==0 then usage("Missing length.") end
if not nArgLength then usage("Invalid length, expected number.") end
if not nArgHeight then usage("Invalid height, expected number.") end
if not nArgWidth then usage("Invalid width, expected number.") end

if nArgLength <= 0 then usage("Invalid length, negative not supported.") end
if nArgHeight <= 0 then usage("Invalid height, negative not supported.") end
if nArgWidth <= 0 then usage("Invalid width, negative not supported.") end

if nArgLength % 1 ~= 0 then usage("Invalid length, fractions not supported.") end
if nArgHeight % 1 ~= 0 then usage("Invalid height, fractions not supported.") end
if nArgWidth % 1 ~= 0 then usage("Invalid width, fractions not supported.") end

--(( Main program ))--

tunnel(nArgLength, nArgHeight, nArgWidth)

--(( EOF ))---