question about wash sales and partial sales

so i've always wondered. let's say you buy 1000 shares of X corp on January 1st. and you see the price going down so you decide to sell 500 shares. Now you have 500 shares short term remaining. Let's say you decided to buy back 500 shares in July and then sell the 500 shares again in September. So you are back to having just 500 shares and you hold them until the next year. Are those considered long term shares since i always kept 500 shares? Or are you always selling the longest held shares when you sell? i don't see a way to specify selling short term shares or long term..