{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}

module Prometheus.MonadMonitor (
    MonadMonitor (..)
,   Monitor
,   runMonitor
,   MonitorT
,   runMonitorT
) where

import Control.Applicative (Applicative)
import Control.Monad.Identity (Identity, runIdentity)
import Control.Monad.Trans.Class
import Control.Monad.Trans.Class (MonadTrans)
import Control.Monad.Trans.Error (ErrorT, Error)
import Control.Monad.Trans.Except (ExceptT)
import Control.Monad.Trans.Identity (IdentityT)
import Control.Monad.Trans.Maybe (MaybeT)
import qualified Control.Monad.Trans.RWS.Lazy as L
import qualified Control.Monad.Trans.RWS.Strict as S
import Control.Monad.Trans.Reader (ReaderT)
import qualified Control.Monad.Trans.State.Lazy as L
import qualified Control.Monad.Trans.State.Strict as S
import qualified Control.Monad.Trans.Writer.Lazy as L
import qualified Control.Monad.Trans.Writer.Strict as S
import Control.Monad.Writer.Strict (WriterT, runWriterT, tell)
import Data.Monoid (Monoid)


-- | MonadMonitor describes a class of Monads that are capable of performing
-- asynchronous IO operations.
class Monad m => MonadMonitor m where
    doIO :: IO () -> m ()
    default doIO :: (MonadTrans t, MonadMonitor n, m ~ t n) => IO () -> m ()
    doIO = n () -> t n ()
forall (t :: (* -> *) -> * -> *) (m :: * -> *) a.
(MonadTrans t, Monad m) =>
m a -> t m a
lift (n () -> t n ()) -> (IO () -> n ()) -> IO () -> t n ()
forall b c a. (b -> c) -> (a -> b) -> a -> c
. IO () -> n ()
forall (m :: * -> *). MonadMonitor m => IO () -> m ()
doIO

instance MonadMonitor IO where
    doIO :: IO () -> IO ()
doIO = IO () -> IO ()
forall a. a -> a
id

instance (Error e, MonadMonitor m) => MonadMonitor (ErrorT e m)
instance (MonadMonitor m) => MonadMonitor (ExceptT e m)
instance (MonadMonitor m) => MonadMonitor (IdentityT m)
instance (MonadMonitor m) => MonadMonitor (MaybeT m)
instance (MonadMonitor m, Monoid w) => MonadMonitor (L.RWST r w s m)
instance (MonadMonitor m, Monoid w) => MonadMonitor (S.RWST r w s m) 
instance (MonadMonitor m) => MonadMonitor (ReaderT r m)
instance (MonadMonitor m) => MonadMonitor (L.StateT s m)
instance (MonadMonitor m) => MonadMonitor (S.StateT s m) 
instance (MonadMonitor m, Monoid w) => MonadMonitor (L.WriterT w m)
instance (MonadMonitor m, Monoid w) => MonadMonitor (S.WriterT w m) 

-- | Monitor allows the use of Prometheus metrics in pure code. When using
-- Monitor, all of the metric operations will be collected and queued into
-- a single IO () value that can be run from impure code.
--
-- Because all of the operations are performed asynchronously use of this class
-- is not recommended for use with metrics that are time sensitive (e.g. for
-- measuring latency).
type Monitor a = MonitorT Identity a

-- | MonitorT is the monad transformer analog of Monitor and allows for
-- monitoring pure monad transformer stacks.
newtype MonitorT m a = MkMonitorT (WriterT [IO ()] m a)
    deriving (Functor (MonitorT m)
a -> MonitorT m a
Functor (MonitorT m)
-> (forall a. a -> MonitorT m a)
-> (forall a b.
    MonitorT m (a -> b) -> MonitorT m a -> MonitorT m b)
-> (forall a b c.
    (a -> b -> c) -> MonitorT m a -> MonitorT m b -> MonitorT m c)
-> (forall a b. MonitorT m a -> MonitorT m b -> MonitorT m b)
-> (forall a b. MonitorT m a -> MonitorT m b -> MonitorT m a)
-> Applicative (MonitorT m)
MonitorT m a -> MonitorT m b -> MonitorT m b
MonitorT m a -> MonitorT m b -> MonitorT m a
MonitorT m (a -> b) -> MonitorT m a -> MonitorT m b
(a -> b -> c) -> MonitorT m a -> MonitorT m b -> MonitorT m c
forall a. a -> MonitorT m a
forall a b. MonitorT m a -> MonitorT m b -> MonitorT m a
forall a b. MonitorT m a -> MonitorT m b -> MonitorT m b
forall a b. MonitorT m (a -> b) -> MonitorT m a -> MonitorT m b
forall a b c.
(a -> b -> c) -> MonitorT m a -> MonitorT m b -> MonitorT m c
forall (f :: * -> *).
Functor f
-> (forall a. a -> f a)
-> (forall a b. f (a -> b) -> f a -> f b)
-> (forall a b c. (a -> b -> c) -> f a -> f b -> f c)
-> (forall a b. f a -> f b -> f b)
-> (forall a b. f a -> f b -> f a)
-> Applicative f
forall (m :: * -> *). Applicative m => Functor (MonitorT m)
forall (m :: * -> *) a. Applicative m => a -> MonitorT m a
forall (m :: * -> *) a b.
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MonitorT m a -> MonitorT m b -> MonitorT m b
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$c<* :: forall (m :: * -> *) a b.
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$cliftA2 :: forall (m :: * -> *) a b c.
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    MonitorT m a -> (a -> MonitorT m b) -> MonitorT m b)
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forall a. a -> MonitorT m a
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$clift :: forall (m :: * -> *) a. Monad m => m a -> MonitorT m a
MonadTrans)

instance Monad m => MonadMonitor (MonitorT m) where
    doIO :: IO () -> MonitorT m ()
doIO IO ()
f = WriterT [IO ()] m () -> MonitorT m ()
forall (m :: * -> *) a. WriterT [IO ()] m a -> MonitorT m a
MkMonitorT (WriterT [IO ()] m () -> MonitorT m ())
-> WriterT [IO ()] m () -> MonitorT m ()
forall a b. (a -> b) -> a -> b
$ [IO ()] -> WriterT [IO ()] m ()
forall w (m :: * -> *). MonadWriter w m => w -> m ()
tell [IO ()
f]

-- | Extract a value and the corresponding monitor update value from the Monitor
-- monad. For an example use see 'Monitor'.
runMonitor :: Monitor a -> (a, IO ())
runMonitor :: Monitor a -> (a, IO ())
runMonitor Monitor a
a = Identity (a, IO ()) -> (a, IO ())
forall a. Identity a -> a
runIdentity (Identity (a, IO ()) -> (a, IO ()))
-> Identity (a, IO ()) -> (a, IO ())
forall a b. (a -> b) -> a -> b
$ Monitor a -> Identity (a, IO ())
forall (m :: * -> *) a. Monad m => MonitorT m a -> m (a, IO ())
runMonitorT Monitor a
a

-- | Extract a value and the corresponding monitor update value from the
-- MonitorT monad transformer.
runMonitorT :: Monad m => MonitorT m a -> m (a, IO ())
runMonitorT :: MonitorT m a -> m (a, IO ())
runMonitorT (MkMonitorT WriterT [IO ()] m a
writerT) = do
    (a
v, [IO ()]
operations) <- WriterT [IO ()] m a -> m (a, [IO ()])
forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
runWriterT WriterT [IO ()] m a
writerT
    (a, IO ()) -> m (a, IO ())
forall (m :: * -> *) a. Monad m => a -> m a
return (a
v, [IO ()] -> IO ()
forall (t :: * -> *) (m :: * -> *) a.
(Foldable t, Monad m) =>
t (m a) -> m ()
sequence_ [IO ()]
operations)