function itemIs(name)
    if (turtle.getItemDetail() and turtle.getItemDetail().name == ("minecraft:" .. name)) then
        if (name == "cobblestone") then
            if (turtle.getItemCount() > 1) then
                return true
            else
                return false
            end
        else
            return true
        end
    else
        return false
    end
end

function blockIs(name)
    if (turtle.inspect() and turtle.inspect().name == ("minecraft:" .. name)) then
        return true
    else
        return false
    end
end

function blockDownIs(name)
    if (turtle.inspectDown() and turtle.inspectDown().name == ("minecraft:" .. name)) then
        return true
    else
        return false
    end
end

function blockUpIs(name)
    if (turtle.inspectUp() and turtle.inspectUp().name == ("minecraft:" .. name)) then
        return true
    else
        return false
    end
end

function dig()
    block = turtle.inspect()
    if (blockIs("chest") or blockIs("hopper")) then
        os.pullEvent("key")
    end
    turtle.dig()
end

function fill()
    turtle.select(2)
    if (itemIs("cobblestone")) then
        turtle.place()
    end
end

function fillDown()
    turtle.select(2)
    if (itemIs("cobblestone")) then
        turtle.placeDown()
    end
end

function fillUp()
    turtle.select(2)
    if (itemIs("cobblestone")) then
        turtle.placeUp()
    end
end

function forward()
    refuel()
    if (blockIs("lava") or blockIs("water")) then
        fill()
        turtle.dig()
        turtle.forward()
        if (blockUpIs("lava") or blockUpIs("water")) then
            fillUp()
        end
        turtle.turnLeft()
        if (blockIs("lava") or blockIs("water")) then
            fill()
        end
        turtle.turnRight()
        turtle.turnRight()
        if (blockIs("lava") or blockIs("water")) then
            fill()
        end
        turtle.turnLeft()
    elseif (not turtle.foward()) then
        if (blockIs("gravel") or blockIs("sand")) then
            dig()
            while (not turtle.forward()) do
                dig()
            end
        end
    end
    if (blockDownIs("lava") or blockDownIs("water")) then
        turtle.select(2)
        if (itemIs("cobblestone")) then
            placeDown()
        end
    end
end

function digShaft()
    for i=1, shaftLength do
        dig()
        forward()
        digUp()
    end
end

function digShaftWidth(n)
    for j = 1, n do
        for i = 1,4 do
            dig()
            forward()
            digUp()
        end
    end
end

function refuel()
    if (turtle.getFuelLevel() < minimumFuel) then
        for i=1,16 do
            turtle.select(i)
            if (itemIs("coal")) then
                while(turtle.getFuelLevel() < minimumFuel and turtle.getItemCount() > 0) do
                    turtle.refuel(1)
                end
            end
        end
    end
end

function dropOff()
    refuel()
    for i=2,16 do
        turtle.select(i)
        if (i == 2) then
            turtle.drop(turtle.getItemCount() - 1)
        else
            if (itemIs("coal")) then
                turtle.drop(32)
            else
                turtle.drop()
            end
        end
    end
end

function stripMine(alreadyDone)
    for i = 1+start, 6 do
        if (i > 1) then
            turtle.turnRight()
            digShaftWidth(2*(i-1))
            turtle.turnLeft()
        end
        digShaft()
        turtle.turnRight()
        digShaftWidth(1)
        turtle.turnRight()
        digShaft()
        turtle.turnRight()
        digShaftWidth(2*i - 1)
        turtle.turnLeft()
        dropOff()
        turtle.turnLeft()
        turtle.turnLeft()
    end
end

shaftLength = 200
minimumFuel = 500
stripMine(2)