{-----------------------------------------------------------------------------
    reactive-banana
------------------------------------------------------------------------------}
{-# LANGUAGE RecordWildCards, BangPatterns #-}
module Reactive.Banana.Prim.Evaluation (
    step
    ) where

import qualified Control.Exception                  as Strict (evaluate)
import           Control.Monad                                (foldM)
import           Control.Monad                                (join)
import           Control.Monad.IO.Class
import qualified Control.Monad.Trans.RWSIO          as RWS
import qualified Control.Monad.Trans.ReaderWriterIO as RW
import           Data.Functor
import           Data.Maybe
import qualified Data.PQueue.Prio.Min               as Q
import qualified Data.Vault.Lazy                    as Lazy
import           System.Mem.Weak

import qualified Reactive.Banana.Prim.OrderedBag as OB
import           Reactive.Banana.Prim.Plumbing
import           Reactive.Banana.Prim.Types
import           Reactive.Banana.Prim.Util

type Queue = Q.MinPQueue Level

{-----------------------------------------------------------------------------
    Evaluation step
------------------------------------------------------------------------------}
-- | Evaluate all the pulses in the graph,
-- Rebuild the graph as necessary and update the latch values.
step :: Inputs -> Step
step (inputs,pulses)
        Network{ nTime = time1
        , nOutputs = outputs1
        , nAlwaysP = Just alwaysP   -- we assume that this has been built already
        }
    = {-# SCC step #-} do

    -- evaluate pulses
    ((_, (latchUpdates, outputs)), topologyUpdates, os)
            <- runBuildIO (time1, alwaysP)
            $  runEvalP pulses
            $  evaluatePulses inputs

    doit latchUpdates                           -- update latch values from pulses
    doit topologyUpdates                        -- rearrange graph topology
    let actions = OB.inOrder outputs outputs1   -- EvalO actions in proper order
        state2  = Network
            { nTime    = next time1
            , nOutputs = OB.inserts outputs1 os
            , nAlwaysP = Just alwaysP
            }
    return (runEvalOs $ map snd actions, state2)

runEvalOs :: [EvalO] -> IO ()
runEvalOs = sequence_ . map join

{-----------------------------------------------------------------------------
    Traversal in dependency order
------------------------------------------------------------------------------}
-- | Update all pulses in the graph, starting from a given set of nodes
evaluatePulses :: [SomeNode] -> EvalP ()
evaluatePulses roots = wrapEvalP $ \r -> go r =<< insertNodes r roots Q.empty
    where
    -- go :: Queue SomeNode -> EvalP ()
    go r q = {-# SCC go #-}
        case ({-# SCC minView #-} Q.minView q) of
            Nothing         -> return ()
            Just (node, q)  -> do
                children <- unwrapEvalP r (evaluateNode node)
                q        <- insertNodes r children q
                go r q

-- | Recalculate a given node and return all children nodes
-- that need to evaluated subsequently.
evaluateNode :: SomeNode -> EvalP [SomeNode]
evaluateNode (P p) = {-# SCC evaluateNodeP #-} do
    Pulse{..} <- readRef p
    ma        <- _evalP
    writePulseP _keyP ma
    case ma of
        Nothing -> return []
        Just _  -> liftIO $ deRefWeaks _childrenP
evaluateNode (L lw) = {-# SCC evaluateNodeL #-} do
    time           <- askTime
    LatchWrite{..} <- readRef lw
    mlatch         <- liftIO $ deRefWeak _latchLW -- retrieve destination latch
    case mlatch of
        Nothing    -> return ()
        Just latch -> do
            a <- _evalLW                    -- calculate new latch value
            -- liftIO $ Strict.evaluate a      -- see Note [LatchStrictness]
            rememberLatchUpdate $           -- schedule value to be set later
                modify' latch $ \l ->
                    a `seq` l { _seenL = time, _valueL = a }
    return []
evaluateNode (O o) = {-# SCC evaluateNodeO #-} do
    debug "evaluateNode O"
    Output{..} <- readRef o
    m          <- _evalO                    -- calculate output action
    rememberOutput $ (o,m)
    return []

-- | Insert nodes into the queue
-- insertNode :: [SomeNode] -> Queue SomeNode -> EvalP (Queue SomeNode)
insertNodes (RWS.Tuple (time,_) _ _) = {-# SCC insertNodes #-} go
    where
    go []              q = return q
    go (node@(P p):xs) q = do
        Pulse{..} <- readRef p
        if time <= _seenP
            then go xs q        -- pulse has already been put into the queue once
            else do             -- pulse needs to be scheduled for evaluation
                put p $! (let p = Pulse{..} in p { _seenP = time })
                go xs (Q.insert _levelP node q)
    go (node:xs)      q = go xs (Q.insert ground node q)
            -- O and L nodes have only one parent, so
            -- we can insert them at an arbitrary level