{- | An EDSL to make working with concurrent in-process code a bit easier
   to read.

This module is expected to be imported qualified as `Go`. Inspired by
Golang and Clojure's core.async.

$example
-}
{-# LANGUAGE NoImplicitPrelude #-}
module Com.Simatime.Go
  (
  -- * Running and forking
    Go
  , run
  , fork
  -- * Channels
  , Channel
  , chan
  , broadcast
  , tap
  , read
  , write
  )
where

import           Control.Concurrent             ( forkIO
                                                , ThreadId
                                                )
import qualified Control.Concurrent.STM.TChan  as TChan
import           GHC.Conc                       ( STM
                                                , atomically
                                                )
import           Protolude                      ( IO )

type Go = STM
type Channel = TChan.TChan

-- | Runs a Go command in IO.
run :: Go a -> IO a
run = atomically

-- | Starts a background process.
fork :: IO () -> IO ThreadId
fork = forkIO

-- | Make a new channel.
chan :: Go (Channel a)
chan = TChan.newTChan

-- | Make a read-only channel.
broadcast :: Go (Channel a)
broadcast = TChan.newBroadcastTChan

-- | Duplicates a channel, but then anything written to the source will
-- be available to both. This is like a combination of Clojure's
-- `core.async/mult` and `core.async/tap` but.
tap :: Channel a -> Go (Channel a)
tap = TChan.dupTChan

-- | Take from a channel. Blocks until a value is received.
read :: Channel a -> Go a
read = TChan.readTChan

-- | Write to a channel.
write :: Channel a -> a -> Go ()
write = TChan.writeTChan

{- $example

A simple example from ghci:

>>> import qualified Com.Simatime.Go as Go
>>> c <- Go.run Go.chan :: IO (Go.Channel Text)
>>> Go.run $ Go.write c "test"
>>> Go.run $ Go.read c
"test"
-}