If you want to get into the deepest detail there are several decentralised perpetual futures exchanges.

Here are some open source codebases on Github:

https://github.com/vegaprotocol/vega

https://github.com/dydxprotocol/v4-chain/

https://github.com/gmx-io/gmx-synthetics

https://github.com/0xOstium/smart-contracts-public/

Vega is a stalled project, but they have good documentation:

https://docs.vega.xyz/release/concepts/new-to-vega

you can go through the drift labs code to see implementation of perps