Is it possible to write software to sell a stock once it goes below a certain price, and buy it once it goes above that price?

Let's sat there is a stock worth $100. I would like write a program that does the following:

• If the stock hit's $99, then sell immediately
• If the stock rises above $99, then buy the stock.

So let's say the stock goes from $100 -> $90 -> $105. You would sell the stock at $99 when it goes down to $90, and buy it back when it goes up to $105. Using this method I don't understand how you could lose anything besides $1. It seems like you get all the up side with none of the down side.

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Now let's kick it up a notch. Let's say now I'm selling covered calls on that stock for $2. That means for every covered call I sell, I make $2 and the max I can lose is $1. Let's say I buy the $100 stock and sell a covered call for $2. Here are the multiple options that can happen:

• If it goes below $99 then I sell and end up with a net gain of $1 ($2 for the covered call and $1 for the stock loss)
• If the stock goes up then I make a maximum of $2 (for selling the covered call since I have to give the stock to the buyer of that call)
• If the stock goes below $99 and then above it, remember I have the software that will sell at $99 and buy the stock back when it goes back above $99

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Can someone explain why this method would not work as an infinite money hack? I'm assuming that base on the ways markets are made, you can't buy EXACTLY at $99. I would have to sell at $98.97 and buy at $99.04 and if the stock hovers around that $99 price then those small price differences add up.

Is there any other reason I may be missing?