local facing = true

function is_at_bedrock()
    local block_exists, block_data = turtle.inspectDown()
    if block_exists and block_data.name == 'minecraft:bedrock' then
        return true
    else
        return false
    end
end

function is_facing_bedrock()
    local block_exists, block_data = turtle.inspect()
    if block_exists and block_data.name == 'minecraft:bedrock' then
        return true
    else
        return false
    end
end

function refuel_and_move()
    if turtle.getFuelLevel() <= 0 and not turtle.refuel() then
        print('Out of fuel! :(')
        return false
    else
        return turtle.forward()
    end
end

while true do
    for i=0,15 do
        for j=0,15 do
            if is_at_bedrock() then
                return
            end
            turtle.digDown()

            if is_facing_bedrock() then
                return
            end
            turtle.dig()

            if not refuel_and_move() then
                return
            end
        end

        if i==15 and j==15 then
            turtle.turnRight()
            turtle.turnRight()
            facing = false
        elseif facing then
            turtle.turnRight()
            if is_facing_bedrock() then
                return
            else
                turtle.dig()
            end
            if not refuel_and_move() then
                return
            end
            turtle.turnRight()
        else
            turtle.turnLeft()
            if is_facing_bedrock() then
                return
            else
                turtle.dig()
            end
            if not refuel_and_move() then
                return
            end
            turtle.turnLeft()
        end
        facing = not facing
    end

    turtle.down()
end