Calculating bitcoin gains for taxation... Is every sell event taxed?

This year I'll have to declare my bitcoin gains to the IRS of a European country (Poland), and multiple questions come to my mind.

I've made in the course of many months many small bitcoin purchases (sometimes worth 50€, 80€), and have recently sold BTC for EURO in 3 sell events. The amount of euros I now have in COINBASE is €1500, waiting to be transferred to my regular bank account.

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SCENARIO 1:

Let's consider this scenario, all within Coinbase and the same tax year:

• I buy 1 bitcoin at $8000
• I sell 1 bitcoin at $9000 -- gain of $1000, never leaves Coinbase
• I buy 1 bitcoin at $9000
• I sell 1 bitcoin at $8000 -- loss of $1000

What are my gains after the year is finished? $0 or $1000?

SCENARIO 2:

Now let's look at this scenario:

• I buy 1 bitcoin at $8000
• I sell 1 bitcoin at $9000 -- gain of $1000, which never leaves Coinbase
• 10 minutes later, I re-buy 1 bitcoin at $9000

Do I need to pay taxes on the $1000 gain, even though it was reinvested in bitcoin right away?

SCENARIO 3:

• I buy 1 bitcoin at multiple rates in 10 different purchase events over the course of 6 months
• I sell .5 BTC in 3 sell events at multiple rates (higher than the purchase rates)

Here, how the hell is the gain calculated? Are there calculators for this?

Thanks!