supernova
=========
[](https://github.com/cr-org/supernova/actions)
⚠️ **it is still very much under development 🚧 so use it at your own risk** ⚠️
A *supernova* is a powerful and luminous stellar explosion. This transient astronomical event occurs during the last evolutionary stages of a massive star or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses to a [neutron](https://github.com/cr-org/neutron) star or black hole, or is completely destroyed. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months.
[](https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA22352)
### Quick Start
The example located in `test/Main.hs` showcases a simple consumer and producer running concurrently (needs the `async` library).
```haskell
main :: IO ()
main = runPulsar resources $ \(Consumer {..}, Producer {..}) ->
let c = forever $ fetch >>= \(Message i m) -> msgDecoder m >> ack i
p = forever $ sleep 5 >> traverse_ produce messages
in concurrently_ c p
resources :: Pulsar (Consumer IO, Producer IO)
resources = do
ctx <- connect defaultConnectData
consumer <- newConsumer ctx topic "test-sub"
producer <- newProducer ctx topic
return (consumer, producer)
```
A `Message` contains a `MessageID` you need for `ack`ing and a payload defined as a lazy `ByteString`.
Run it with the following command:
```shell
cabal new-run supernova-tests
```
By default, it logs to the standard output in DEBUG level. You can change it by suppling `LogOptions`.
```haskell
logOpts :: LogOptions
logOpts = LogOptions Info StdOut
runPulsar' logOpts resources
```
### Streaming
Since both consumers and producers operate on any `MonadIO m`, we could leverage some streaming libraries. Here's the same example using [streamly](https://hackage.haskell.org/package/streamly).
```haskell
import Streamly
import qualified Streamly.Prelude as S
main :: IO ()
main = runPulsar resources $ \(Consumer {..}, Producer {..}) ->
let c = forever $ fetch >>= \(Message i p) -> msgDecoder p >> ack i
p = forever $ sleep 5 >> traverse_ produce messages
in S.drain . asyncly . maxThreads 10 $ S.yieldM c <> S.yieldM p
```
### Development
It is recommended to use [Cachix](https://app.cachix.org/cache/hpulsar) to reduce the compilation time.
```shell
nix-build
```
Or within a Nix shell (run `nix-shell` at the project's root).
```shell
cabal new-build
```