local args = {...}
local maxDistance = args[1] or 100
local distance = 0
local blacklist = { 'minecraft:cobblestone', 'minecraft:dirt',
					'minecraft:gravel, 'minecraft:flint', 'minecraft:redstone'}

local function has_value (tab, val)
    for i, value in ipairs(tab) do
        if value == val then
            return true
        end
    end
    return false
end

function MoveFront()
	if turtle.detect() then
		turtle.dig()
		if turtle.forward() == false then
			MoveFront()
		end
	else
		turtle.forward()
	end
end

function PlaceTorch()
	turtle.select(3)
	turtle.placeDown()
end

function DigUp()
	if turtle.detectUp() then
		turtle.digUp()
	end
end

function DigDown()
	if turtle.detectDown() then
		turtle.digDown()
	end
end

-- Mines 3x3 infront of the turtle.
function Mine()
	MoveFront()
	DigUp()
	DigDown()
	turtle.turnLeft()
	MoveFront()
	DigUp()
	DigDown()
	turtle.turnRight()
	turtle.turnRight()
	MoveFront()
	MoveFront()
	DigUp()
	DigDown()
	turtle.back()
	turtle.turnLeft()
end

-- Checks if chests are present in slot 2, and if torches are present in slot 3.
function CheckForItem(n)
	--chest checking
	if n == 1 then
		if turtle.getItemDetail(2).name == "minecraft:chest" then
			return true
		else
			return false
		end
	end

	--torch checking
	if n == 2 then
		if turtle.getItemDetail(3).name == "minecraft:torch" then
			return true
		else
			return false
		end
	end
end

function CheckGround()
	turtle.down()
	if turtle.detectDown() then
		turtle.up()
		return true
	else
		--find cobble, then place
		for i = 4,16 do
			if turtle.getItemDetail(i).name == "minecraft:cobblestone" then
				turtle.select(i)
				turtle.placeDown()
				break
			else
				return false
			end
		end
		turtle.up()
		return true
	end
end


-- true if it can drop off items, false if it cant due to no chests
function Deposit()
	if CheckForItem(1) and CheckGround() then
		turtle.turnLeft()
		turtle.turnLeft()
		turtle.select(2)
		turtle.placeDown()
		turtle.select(1)
		for i = 4,16 do
			if turtle.getItemCount(i) > 0 then
				turtle.select(i)
				if has_value(blacklist, turtle.getItemDetail(i).name) then
					turtle.dropUp()
				else
					turtle.dropDown()
				end
			end
		end
		turtle.select(1)
		turtle.turnLeft()
		turtle.turnLeft()
		return true
	else
		return false
	end
end


function Refuel()
	for i = 1,16 do
        if turtle.getItemCount(i) > 0 then
            turtle.select(i)
            if turtle.refuel(2) then
                break
			end
		end
	end
    turtle.select(1)
end

-- deposit -> refuel -> mine
while true do
	if distance > maxDistance then
		Deposit()
		break
	end
	if turtle.getItemCount(16) > 0 and distance % 8 ~= 0 then
		if CheckForItem(1) then
			Deposit()
		else
			break --stop the turtle if it can't store items
		end
	elseif turtle.getFuelLevel() < 5 then
		Refuel()
	else
		Mine()
		distance = distance + 1 -- place torch every 8th block
		if distance % 8 == 0 then
			if CheckForItem(2) then
				PlaceTorch()
			end
		end
	end
end