function line()
    for i=1, 200 do
        turtle.dig()
        turtle.forward()
        turtle.digUp()
    end
end

function goShaftWidth(n)
    for j = 1, n do
        for i = 1,4 do
            turtle.forward()
        end
    end
end

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

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

function refuel()
    if (turtle.getFuelLevel() < 500) then
        for i=1,16 do
            turtle.select(i)
            if (itemIs("coal")) then
                turtle.refuel()
            end
        end
    end
end

function dropOff()
    if (turtle.getFuelLevel() < 500) then
        for i=1,16 do
            turtle.select(i)
            if (itemIs("coal")) then
                turtle.refuel()
            else
                turtle.drop()
            end
        end
    else
        for i=1,16 do
            turtle.select(i)
            if (itemIs("coal")) then
                turtle.drop(32)
            else
                turtle.drop()
            end
        end
    end
end

function stripMine()
    for i=1,10 do
        if (i == 1) then
            refuel()
        elseif (i > 1) then
            turtle.turnRight()
            digShaftWidth(2*(i-1))
            turtle.turnLeft()
        end
        line()
        turtle.turnRight()
        digShaftWidth(1)
        turtle.turnRight()
        line()
        turtle.turnRight()
        digShaftWidth(2*i - 1)
        turtle.turnLeft()
        dropOff()
        turtle.turnLeft()
        turtle.turnLeft()
    end
end

stripMine()