args = { ... }
-- size depth [startDepth]

direction = {}
direction.FORWARD = 0
direction.RIGHT = 1
direction.BACKWARD = 2
direction.LEFT = 3

task = {}
task.MINESHAFT = 0
task.MINEXZ = 1
task.MINEXZ_TURN = 2
task.NEXT_LEVEL = 3
task.NEXT_LEVEL_TURN = 4
task.FINISH = 5
task.UNLOAD = 6
task.DIG = 7

turnDirection = {
    LEFT = -1,
    RIGHT = 1
}

local size = 0
local depth = 0
local startDepth = 0

local facing = direction.FORWARD
local currTask = task.MINESHAFT
local xzTurnMoves = 0
local mineDirection = 0
local mineX = 1
local mineZ = 1
local nextLevel = 1 -- counter for digging down to the next mining level
local level = 1

local stepsForward = 0
local stepsRight = 0
local stepsDown = 0

local savedForward = 0
local savedRight = 0
local savedDown = 0
local savedFacing = 0

local isPaused = false

function save()

    local file = fs.open("snapshot", "w")
    file.writeLine(currTask)
    file.writeLine(size)
    file.writeLine(depth)
    file.writeLine(startDepth)
    file.writeLine(nextLevel)
    file.writeLine(mineDirection)
    file.writeLine(mineX)
    file.writeLine(mineZ)
    file.writeLine(xzTurnMoves)
    file.writeLine(level)
    file.writeLine(stepsForward)
    file.writeLine(stepsRight)
    file.writeLine(stepsDown)
    file.writeLine(savedForward)
    file.writeLine(savedRight)
    file.writeLine(savedDown)
    file.writeLine(facing)
    file.close()
end


function resume()
    local file = fs.open("snapshot", "r")

    if file == nil then
        print("Failed to open snapshot file. Cannot resume.")
        return
    end

    currTask = tonumber(file.readLine())
    size = tonumber(file.readLine())
    depth = tonumber(file.readLine())
    startDepth = tonumber(file.readLine())
    nextLevel = tonumber(file.readLine())
    mineDirection = tonumber(file.readLine())
    mineX = tonumber(file.readLine())
    mineZ = tonumber(file.readLine())
    xzTurnMoves = tonumber(file.readLine())
    level = tonumber(file.readLine())
    stepsForward = tonumber(file.readLine())
    stepsRight = tonumber(file.readLine())
    stepsDown = tonumber(file.readLine())
    savedForward = tonumber(file.readLine())
    savedRight = tonumber(file.readLine())
    savedDown = tonumber(file.readLine())
    facing = tonumber(file.readLine())

    file.close()
end


if args[1] == "resume" then
    resume()
elseif args[1] == nil or args[2] == nil then
    print("size depth [startDepth]")
    return
else

    size = tonumber(args[1])
    depth = tonumber(args[2])
    startDepth = 0

    if args[3] ~= nil then
        startDepth = tonumber(args[3])
    end
end


function updateFacing(turnDir)

    facing = facing + turnDir

    if facing > 3 then
        facing = 0
    elseif facing < 0 then
        facing = 3
    end

end


function forward()

    while not turtle.forward() do
        os.sleep(0)
        turtle.dig()
    end

    if facing == direction.FORWARD then
        stepsForward = stepsForward + 1
    elseif facing == direction.RIGHT then
        stepsRight = stepsRight + 1
    elseif facing == direction.BACKWARD then
        stepsForward = stepsForward - 1
    elseif facing == direction.LEFT then
        stepsRight = stepsRight - 1
    end

    save()

end

function down()
    count = 0
    while not turtle.down() do
        os.sleep(0)
        turtle.digDown()
        if not turtle.digDown() and turtle.detectDown() then
            currTask = task.FINISH
            stepsDown = stepsDown - 1
            print("Failed to dig down. Going home.")
            break
        end
        count = count + 1
    end
    stepsDown = stepsDown + 1

    save()
end


function up()
    while not turtle.up() do
        os.sleep(0)
        turtle.digUp()
    end
    stepsDown = stepsDown - 1

    save()
end

function turnLeft()
    turtle.turnLeft()
    updateFacing(turnDirection.LEFT)

    save()
end


function turnRight()
    turtle.turnRight()
    updateFacing(turnDirection.RIGHT)

    save()
end


function setFacing(faceDir)
    while facing ~= faceDir do
        turnRight();
    end
end

function savePosition()
    savedForward = stepsForward
    savedRight = stepsRight
    savedDown = stepsDown
    savedFacing = facing
end


function refuel()

    for turn=1, 4 do
        local hasInventory = false

        for slot=1, 16 do
            turtle.select(slot)
            turtle.refuel(slot)
            if turtle.suck() then
                hasInventory = true
            end
            while turtle.refuel(slot) do
            end
        end

        if hasInventory then
            for slot=1, 16 do
                turtle.select(slot)
                turtle.drop()
            end
        end

        turnLeft()
    end

    if checkNeedsFuel() then
        currTask = task.FINISH
    end

end

function returnToDig()
    while savedDown ~= stepsDown do
        if savedDown < stepsDown then
            up()
        elseif savedDown > stepsDown then
            down()
        end
    end

    if savedRight < stepsRight then
        setFacing(direction.LEFT)
    elseif savedRight > stepsRight then
        setFacing(direction.RIGHT)
    end

    while savedRight ~= stepsRight do
        forward()
    end

    if savedForward < stepsForward then
        setFacing(direction.BACKWARD)
    elseif savedForward > stepsForward then
        setFacing(direction.FORWARD)
    end

    while savedForward ~= stepsForward do
        forward()
    end

    setFacing(savedFacing)

    currTask = task.MINEXZ
end


function returnHome()
    savePosition()

    if stepsForward > 0 then
        setFacing(direction.BACKWARD)
    elseif stepsForward < 0 then
        setFacing(direction.FORWARD)
    end

    while stepsForward ~= 0 do
        forward()
    end

    if stepsRight > 0 then
        setFacing(direction.LEFT)
    elseif stepsRight < 0 then
        setFacing(direction.RIGHT)
    end

    while stepsRight ~= 0 do
        forward()
    end

    while stepsDown ~= 0 do
        if stepsDown > 0 then
            up()
        elseif stepsDown < 0 then
            down()
        end
    end

    setFacing(direction.BACKWARD)

    for slot=1, 16 do
        turtle.select(slot)
        turtle.drop()
    end


    if currTask == task.FINISH then
        setFacing(direction.FORWARD)
        return
    end

    if currTask == task.UNLOAD then
        currTask = task.DIG
        refuel()
    end

end


function isInventoryFull()
    local used = 0

    for slot=1, 16 do
        used = used + turtle.getItemCount(slot)
    end

    if used > 400 then
        return true
    end

    return false
end

function estimateDistanceHome()
    return math.abs(stepsForward) + math.abs(stepsRight) + math.abs(stepsDown) + 16;
end

function checkNeedsFuel()
    local fuel = turtle.getFuelLevel()

    if fuel ~= nil and fuel <= estimateDistanceHome() + 10 then
        return true
    end

    return false
end

function mineXZ()

    local turnFlag = mineDirection % 2 == 1

    turtle.digUp()
    turtle.digDown()
    forward()
    turtle.digUp()
    turtle.digDown()

    if checkNeedsFuel() then
        currTask = task.UNLOAD
        return
    end

    if isInventoryFull() then
       currTask = task.UNLOAD
       return
    end

    mineZ = mineZ + 1

    if mineZ >= size then
       mineZ = 1
       mineX = mineX + 1
       mineDirection = mineDirection + 1

       if mineX > size then
            currTask = task.NEXT_LEVEL_TURN
       else
            currTask = task.MINEXZ_TURN
       end
       save()
       return
    end

    if mineX > size then
       mineX = 1
       mineZ = 1
       --mineDirection = 0
       currTask = task.NEXT_LEVEL
       save()
    end

end

function mineXZ_Turn(moveForward)

    local turnFlag = mineDirection % 2 == 1

    if xzTurnMoves > 4 then
        xzTurnMoves = 0
        currTask = task.MINEXZ
        return
    end

    if turnFlag then
        if xzTurnMoves == 0 then
           turnLeft()
        end

        if xzTurnMoves == 4 then
           turnLeft()
        end
    else
        if xzTurnMoves == 0 then
           turnRight()
        end

        if xzTurnMoves == 4 then
           turnRight()
        end
    end

    if xzTurnMoves == 1 and moveForward then
        forward()
    end

    if xzTurnMoves == 2 then
       turtle.digUp()
    end

    if xzTurnMoves == 3 then
       turtle.digDown()
    end

    xzTurnMoves = xzTurnMoves + 1
end


function digMineShaft()
    if stepsDown == startDepth then
        currTask = task.MINEXZ
        return
    end

    down()

end


function mineNextLevel()

    if level >= depth then
        currTask = task.FINISH
        return
    end

    if nextLevel > 3 then

        mineX = 1
        mineZ = 1
        mineDirection = mineDirection + 1

        level = level + 1
        currTask = task.MINEXZ
        nextLevel = 1
        turtle.digDown()
        return
    end

    nextLevel = nextLevel + 1
    down()
end

function processMessages()
    rednet.open("right")
    local senderId, message = rednet.receive(0.1)
    if message == nil then
        return
    end

    print("Received " .. message)

    if message == "finishMining" then
        isPaused = false
        currTask = task.FINISH
        print("Received command to finish.")
    end

    if message == "unloadMining" then
        isPaused = false
        currTask = task.UNLOAD
        print("Received command to unload inventory at home base.")
    end

    if message == "pauseMining" then
        isPaused = true
        save()
    end

    if message == "resumeMining" then
        isPaused = false
    end

    rednet.send(senderId, "acknowledged")

end

while true do

    if not isPaused then

        if currTask == task.MINESHAFT then
            digMineShaft()
        end

        if currTask == task.MINEXZ then
            mineXZ()
        end

        if currTask == task.MINEXZ_TURN then
            mineXZ_Turn(true)
        end

        if currTask == task.NEXT_LEVEL then
            mineNextLevel()
        end

        if currTask == task.NEXT_LEVEL_TURN then
            mineXZ_Turn(false)

            if currTask == task.MINEXZ then
                currTask = task.NEXT_LEVEL
            end
        end

        if currTask == task.UNLOAD then
            returnHome()
        end

        if currTask == task.DIG then
            returnToDig()
        end

        if currTask == task.FINISH then
            break
        end

    end

    processMessages()

    if not isPaused then
        save()
    end

end

returnHome()
setFacing(direction.FORWARD)
save()