{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE CPP #-}

module Debug.Hoed.Observe
{-
  (
   -- * The main Hood API
  
  , observe
  , Observer(..)   -- contains a 'forall' typed observe (if supported).
  , Observable(..) -- Class

   -- * For advanced users, that want to render their own datatypes.
  , (<<)           -- (Observable a) => ObserverM (a -> b) -> a -> ObserverM b
  , thunk          -- (Observable a) => a -> ObserverM a        
  , nothunk
  , send
  , observeBase
  , observeOpaque
  , observedTypes
  , Generic
  , Trace
  , Event(..)
  , Change(..)
  , Parent(..)
  , UID
  , ParentPosition
  , ThreadId(..)
  , isRootEvent
  , initUniq
  , startEventStream
  , endEventStream
  , ourCatchAllIO
  , peepUniq
  ) -} where

import Prelude hiding (Right)
import qualified Prelude
import Control.Monad
import Data.Array as Array
import Debug.Hoed.Fields

import GHC.Generics

import Data.IORef
import System.IO.Unsafe

import qualified Control.Exception as Exception
import Control.Exception (throw, SomeException(..))
{-
 ( catch
                , Exception(..)
                , throw
                ) as Exception
-}
import Data.Dynamic ( Dynamic )

infixl 9 <<

class Observable a where
        observer  :: a -> Parent -> a 
        default observer :: (Generic a, GObservable (Rep a)) => a -> Parent -> a
        observer x c = to (gdmobserver (from x) c)

        constrain :: a -> a -> a
        default constrain :: (Generic a, GConstrain (Rep a)) => a -> a -> a
        constrain x c = to (gconstrain (from x) (from c))

class GObservable f where
        gdmobserver :: f a -> Parent -> f a
        gdmObserveArgs :: f a -> ObserverM (f a)
        gdmShallowShow :: f a -> String

constrainBase :: (Show a, Eq a) => a -> a -> a
constrainBase x c | x == c = x
                  | otherwise = error $ show x ++ " constrained by " ++ show c

class GConstrain f where gconstrain :: f a -> f a -> f a
instance (GConstrain a, GConstrain b) => GConstrain (a :+: b) where
  gconstrain (L1 x) (L1 c) = L1 (gconstrain x c)
  gconstrain (R1 x) (R1 c) = R1 (gconstrain x c)
instance (GConstrain a, GConstrain b) => GConstrain (a :*: b) where
  gconstrain (x :*: y) (c :*: d) = (gconstrain x c) :*: (gconstrain y d)
instance GConstrain U1 where
  gconstrain x c = x
instance (Observable a) => GConstrain (K1 i a) where
  gconstrain (K1 x) (K1 c) = K1 (constrain x c)
instance (GConstrain a) => GConstrain (M1 D d a) where
  gconstrain (M1 x) (M1 c) = M1 (gconstrain x c)
instance (GConstrain a, Selector s) => GConstrain (M1 S s a) where
  gconstrain m@(M1 x) n@(M1 c) | selName m ==  selName n = M1 (gconstrain x c)
instance (GConstrain a, Constructor c) => GConstrain (M1 C c a) where
  gconstrain m@(M1 x) n@(M1 c) | conName m == conName n = M1 (gconstrain x c)

-- Meta: data types
-- FieldLimit requires undecidable instances
instance (FieldLimit ('S ('S ('S ('S ('S ('S 'Z)))))) a, GObservable a) => GObservable (M1 D d a) where
 gdmobserver m@(M1 x) cxt = M1 (gdmobserver x cxt)
 gdmObserveArgs = gthunk
 gdmShallowShow = error "gdmShallowShow not defined on the <<data meta type>>"

-- Meta: Selectors
instance (GObservable a, Selector s) => GObservable (M1 S s a) where
 gdmobserver (M1 x) cxt = M1 (gdmobserver x cxt)
 gdmObserveArgs = gthunk
 gdmShallowShow = error "gdmShallowShow not defined on the <<selector meta type>>"

-- Meta: Constructors
instance (GObservable a, Constructor c) => GObservable (M1 C c a) where
 gdmobserver m1 = send (gdmShallowShow m1) (gdmObserveArgs m1)
 gdmObserveArgs (M1 x) = do {x' <- gdmObserveArgs x; return (M1 x')}
 gdmShallowShow = conName

-- Unit: used for constructors without arguments
instance GObservable U1 where
 gdmobserver x _ = x
 gdmObserveArgs = return
 gdmShallowShow = error "gdmShallowShow not defined on <<the unit type>>"

-- Sums: encode choice between constructors
instance (GObservable a, GObservable b) => GObservable (a :+: b) where
 gdmobserver (L1 x) = send (gdmShallowShow x) (gdmObserveArgs $ L1 x)
 gdmobserver (R1 x) = send (gdmShallowShow x) (gdmObserveArgs $ R1 x)
 gdmShallowShow (L1 x) = gdmShallowShow x
 gdmShallowShow (R1 x) = gdmShallowShow x
 gdmObserveArgs (L1 x) = do {x' <- gdmObserveArgs x; return (L1 x')}
 gdmObserveArgs (R1 x) = do {x' <- gdmObserveArgs x; return (R1 x')}

-- Products: encode multiple arguments to constructors
instance (GObservable a, GObservable b) => GObservable (a :*: b) where
 gdmobserver (a :*: b) cxt = (gdmobserver a cxt) :*: (gdmobserver b cxt)
 gdmObserveArgs (a :*: b) = do 
   a'  <- gdmObserveArgs a
   b'  <- gdmObserveArgs b
   return (a' :*: b')
 gdmShallowShow = error "gdmShallowShow not defined on <<the product type>>"

-- Constants: additional parameters and recursion of kind *
instance (Observable a) => GObservable (K1 i a) where
 gdmobserver (K1 x) cxt = K1 $ observer x cxt
 gdmObserveArgs = gthunk
 gdmShallowShow = error "gdmShallowShow not defined on <<the constant type>>"

instance (Observable a,Observable b) => Observable (a -> b) where
  observer fn cxt arg = gdmFunObserver cxt fn arg
  constrain = error "how to constrain the function type?"

gdmFunObserver :: (Observable a,Observable b) => Parent -> (a->b) -> (a->b)
gdmFunObserver cxt fn arg
        = sendObserveFnPacket
            (do arg' <- thunk observer arg
                thunk observer (fn arg')
            ) cxt

instance Observable Int     where observer  = observeBase 
                                  constrain = constrainBase
instance Observable Bool    where observer  = observeBase
                                  constrain = constrainBase
instance Observable Integer where observer  = observeBase
                                  constrain = constrainBase
instance Observable Float   where observer  = observeBase
                                  constrain = constrainBase
instance Observable Double  where observer  = observeBase
                                  constrain = constrainBase
instance Observable Char    where observer  = observeBase
                                  constrain = constrainBase
instance Observable ()      where observer  = observeOpaque "()"
                                  constrain = constrainBase

-- utilities for base types.
-- The strictness (by using seq) is the same 
-- as the pattern matching done on other constructors.
-- we evalute to WHNF, and not further.

observeBase :: (Show a) => a -> Parent -> a
observeBase lit cxt = seq lit $ send (show lit) (return lit) cxt

observeOpaque :: String -> a -> Parent -> a
observeOpaque str val cxt = seq val $ send str (return val) cxt

instance (Observable a,Observable b) => Observable (a,b) where
  observer (a,b) = send "," (return (,) << a << b)

instance (Observable a,Observable b,Observable c) => Observable (a,b,c) where
  observer (a,b,c) = send "," (return (,,) << a << b << c)

instance (Observable a,Observable b,Observable c,Observable d) 
          => Observable (a,b,c,d) where
  observer (a,b,c,d) = send "," (return (,,,) << a << b << c << d)

instance (Observable a,Observable b,Observable c,Observable d,Observable e) 
         => Observable (a,b,c,d,e) where
  observer (a,b,c,d,e) = send "," (return (,,,,) << a << b << c << d << e)

instance (Observable a) => Observable [a] where
  observer (a:as) = send ":"  (return (:) << a << as)
  observer []     = send "[]" (return [])

instance (Observable a) => Observable (Maybe a) where
  observer (Just a) = send "Just"    (return Just << a)
  observer Nothing  = send "Nothing" (return Nothing)

instance (Observable a,Observable b) => Observable (Either a b) where
  observer (Left a)  = send "Left"  (return Left  << a)
  observer (Prelude.Right a) = send "Right" (return Prelude.Right << a)

instance (Ix a,Observable a,Observable b) => Observable (Array.Array a b) where
  observer arr = send "array" (return Array.array << Array.bounds arr 
                                                  << Array.assocs arr
                              )
  constrain = undefined

instance (Observable a) => Observable (IO a) where
  observer fn cxt = 
        do res <- fn
           send "<IO>" (return return << res) cxt
  constrain = undefined

instance Observable SomeException where
  observer e = send ("<Exception> " ++ show e) (return e)
  constrain = undefined

-- instance Observable ErrorCall where
--   observer (ErrorCall a)        = send "ErrorCall"   (return ErrorCall << a)


instance Observable Dynamic where
  observer = observeOpaque "<Dynamic>"
  constrain = undefined

type Observing a = a -> a

newtype Observer = O (forall a . (Observable a) => String -> a -> a)

newtype ObserverM a = ObserverM { runMO :: Int -> Int -> (a,Int) }

instance Functor ObserverM where
    fmap  = liftM

#if __GLASGOW_HASKELL__ >= 710
instance Applicative ObserverM where
    pure  = return
    (<*>) = ap
#endif

instance Monad ObserverM where
        return a = ObserverM (\ c i -> (a,i))
        fn >>= k = ObserverM (\ c i ->
                case runMO fn c i of
                  (r,i2) -> runMO (k r) c i2
                )

thunk :: (a -> Parent -> a) -> a -> ObserverM a
thunk f a = ObserverM $ \ parent port ->
                ( observer_ f a (Parent
                                { parentUID = parent
                                , parentPosition   = port
                                }) 
                , port+1 )

gthunk :: (GObservable f) => f a -> ObserverM (f a)
gthunk a = ObserverM $ \ parent port ->
                ( gdmobserver_ a (Parent
                                { parentUID = parent
                                , parentPosition   = port
                                }) 
                , port+1 )

(<<) :: (Observable a) => ObserverM (a -> b) -> a -> ObserverM b
-- fn << a = do { fn' <- fn ; a' <- thunk a ; return (fn' a') }
fn << a = gdMapM (thunk observer) fn a

gdMapM :: (Monad m)
        => (a -> m a)  -- f
        -> m (a -> b)  -- data constructor
        -> a           -- argument
        -> m b         -- data
gdMapM f c a = do { c' <- c ; a' <- f a ; return (c' a') }

-- | 'observe' observes data structures in flight.
--  
-- An example of use is 
--  @
--    map (+1) . observe \"intermeduate\" . map (+2)
--  @
--
-- In this example, we observe the value that flows from the producer
-- @map (+2)@ to the consumer @map (+1)@.
-- 
-- 'observe' can also observe functions as well a structural values.
-- 
{-# NOINLINE gobserve #-}
gobserve :: (a->Parent->a) -> String -> a -> (a,Int)
gobserve f name a = generateContext f name a

{- | 
Functions which you suspect of misbehaving are annotated with observe and
should have a cost centre set. The name of the function, the label of the cost
centre and the label given to observe need to be the same.

Consider the following function:

@triple x = x + x@

This function is annotated as follows:

> triple y = (observe "triple" (\x -> {# SCC "triple" #}  x + x)) y

To produce computation statements like:

@triple 3 = 6@

To observe a value its type needs to be of class Observable.
We provided instances for many types already.
If you have defined your own type, and want to observe a function
that takes a value of this type as argument or returns a value of this type,
an Observable instance can be derived as follows:

@  
  data MyType = MyNumber Int | MyName String deriving Generic

  instance Observable MyType
@
-}
{-# NOINLINE observe #-}
observe ::  (Observable a) => String -> a -> a
observe lbl = fst . (gobserve observer lbl)

{- This gets called before observer, allowing us to mark
 - we are entering a, before we do case analysis on
 - our object.
 -}

{-# NOINLINE observer_ #-}
observer_ :: (a -> Parent -> a) -> a -> Parent -> a 
observer_ f a context = sendEnterPacket f a context

gdmobserver_ :: (GObservable f) => f a -> Parent -> f a
gdmobserver_ a context = gsendEnterPacket a context

unsafeWithUniq :: (Int -> IO a) -> a
unsafeWithUniq fn 
  = unsafePerformIO $ do { node <- getUniq
                         ; fn node
                         }

generateContext :: (a->Parent->a) -> String -> a -> (a,Int)
generateContext f {- tti -} label orig = unsafeWithUniq $ \node ->
     do sendEvent node (Parent 0 0) (Observe label)
        return (observer_ f orig (Parent
                      { parentUID      = node
                      , parentPosition = 0
                      })
               , node)

send :: String -> ObserverM a -> Parent -> a
send consLabel fn context = unsafeWithUniq $ \ node ->
     do { let (r,portCount) = runMO fn node 0
        ; sendEvent node context (Cons portCount consLabel)
        ; return r
        }

sendEnterPacket :: (a -> Parent -> a) -> a -> Parent -> a
sendEnterPacket f r context = unsafeWithUniq $ \ node ->
     do { sendEvent node context Enter
        ; ourCatchAllIO (evaluate (f r context))
                        (handleExc context)
        }

gsendEnterPacket :: (GObservable f) => f a -> Parent -> f a
gsendEnterPacket r context = unsafeWithUniq $ \ node ->
     do { sendEvent node context Enter
        ; ourCatchAllIO (evaluate (gdmobserver r context))
                        (handleExc context)
        }

evaluate :: a -> IO a
evaluate a = a `seq` return a

sendObserveFnPacket :: ObserverM a -> Parent -> a
sendObserveFnPacket fn context
  = unsafeWithUniq $ \ node ->
     do { let (r,_) = runMO fn node 0
        ; sendEvent node context Fun
        ; return r
        }

type Trace = [Event]

data Event = Event
                { eventUID     :: !UID      -- my UID
                , eventParent  :: !Parent
                , change       :: !Change
                }
        deriving (Eq,Generic)

data Change
        = Observe       !String
        | Cons    !Int  !String
        | Enter
        | Fun
        deriving (Eq, Show,Generic)

type ParentPosition = Int

data Parent = Parent
        { parentUID      :: !UID            -- my parents UID
        , parentPosition :: !ParentPosition -- my branch number (e.g. the field of a data constructor)
        } deriving (Eq,Generic)

instance Show Event where
  show e = (show . eventUID $ e) ++ ": " ++ (show . change $ e) ++ " (" ++ (show . eventParent $ e) ++ ")"

instance Show Parent where
  show p = "P " ++ (show . parentUID $ p) ++ " " ++ (show . parentPosition $ p)

root = Parent 0 0

isRootEvent :: Event -> Bool
isRootEvent e = case change e of Observe{} -> True; _ -> False

startEventStream :: IO ()
startEventStream = writeIORef events []

endEventStream :: IO Trace
endEventStream =
        do { es <- readIORef events
           ; writeIORef events badEvents 
           ; return es
           }

sendEvent :: Int -> Parent -> Change -> IO ()
sendEvent nodeId parent change =
        do { let !event = Event nodeId parent change
           ; atomicModifyIORef' events (\es -> (event : es, ()))
           }

-- local
events :: IORef Trace
events = unsafePerformIO $ newIORef badEvents

badEvents :: Trace
badEvents = error "Bad Event Stream"

type UID = Int

initUniq :: IO ()
initUniq = writeIORef uniq 1

getUniq :: IO UID
getUniq = atomicModifyIORef' uniq (\n -> (n+1,n))

peepUniq :: IO UID
peepUniq = readIORef uniq

-- locals
{-# NOINLINE uniq #-}
uniq :: IORef UID
uniq = unsafePerformIO $ newIORef 1

ourCatchAllIO :: IO a -> (SomeException -> IO a) -> IO a
ourCatchAllIO = Exception.catch

handleExc :: Parent -> SomeException -> IO a
-- handleExc context exc = return (send "throw" (return throw << exc) context)
handleExc context exc = return (send (show exc) (return (throw exc)) context)