width = 5
length = 31
MinFuelLevel = 19500

y = 0


function layer()
    turnLeft = 1
    
    function turn()
        if turnLeft == 1 then
            turtle.turnLeft()
        else
            turtle.turnRight()
        end
    end
    function digStep() 
        turtle.dig()
        turtle.digUp()
        turtle.digDown()
        turtle.forward()
    end
    
    for row = 1, width do
        for i = 1,length do
            digStep()
        end
        turn()
        digStep()
        turn()
        turnLeft = -turnLeft
    end
    if turnLeft == 1 then
        turtle.turnRight()
        for i = 1, width do
            turtle.forward()
        end
        turtle.turnLeft()
    else
        turtle.turnLeft()
        turtle.forward()
        turtle.turnRight()
        for i = 1, length do 
            turtle.forward()
        end
        turtle.turnLeft()
        for i = 1, width do
            turtle.forward()
        end
        turtle.turnLeft()
    end
end

function unload()
    for i = 1, 16 do
        turtle.select(i)
        turtle.dropUp()
    end
    turtle.turnLeft()
    turtle.turnLeft()
    while turtle.getFuelLevel() < MinFuelLevel do
        turtle.suck()
        turtle.refuel()
    end
    turtle.drop()
    turtle.turnLeft()
    turtle.turnLeft()
    
end

while true do
    turtle.forward()
    for i = 1, y do
        turtle.digDown()
        turtle.down()
    end
    layer()
    for i = 1, y do
        turtle.up()
    end
    turtle.back()
    unload()
    y = y + 3
end