{-# LANGUAGE ConstraintKinds            #-}
{-# LANGUAGE DeriveDataTypeable         #-}
{-# LANGUAGE DeriveFunctor              #-}
{-# LANGUAGE DeriveFoldable             #-}
{-# LANGUAGE DeriveTraversable          #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses      #-}
{-# LANGUAGE StandaloneDeriving         #-}
{-# LANGUAGE TupleSections              #-}
{-# LANGUAGE TypeFamilies               #-}
{-# LANGUAGE ViewPatterns               #-}

-------------------------------------------------------------------------------------
-- |
-- Copyright   : (c) Hans Hoglund 2012-2014
--
-- License     : BSD-style
--
-- Maintainer  : hans@hanshoglund.se
-- Stability   : experimental
-- Portability : non-portable (TF,GNTD)
--
-------------------------------------------------------------------------------------

module Music.Time.Reactive (
        -- * Reactive type
        Reactive,

        -- * Query
        initial,
        final,
        intermediate,
        discrete,
        updates,
        occs,
        atTime,

        -- * Construction
      
        -- * Combine
        switchR,
        trimR,

        -- * Split
        splitReactive,

        -- * Sampling
        continous,
        continousWith,
        sample,
        -- TODO
        -- window,
        -- windowed,   

  ) where

-- Reactive values, or piecewise functions of time.
--
-- Similar to Conal's definition in <http://conal.net/blog/posts/reactive-normal-form>,
-- but defined in negative time as well. Its semantics function is either 'occs' @&&&@ '?'
-- /or/ 'initial' @&&&@ 'updates', where 'intial' is the value from negative infinity
-- to the first update.
--
-- TODO integrate better in the library
--

import           Music.Time.Behavior
import           Music.Time.Bound
import           Music.Time.Event
import           Music.Time.Reverse
import           Music.Time.Segment
import           Music.Time.Split

import           Music.Pitch.Alterable
import           Music.Pitch.Augmentable
import           Music.Pitch.Literal


import           Control.Applicative
import           Control.Lens            hiding (Indexable, Level, above, below,
                                          index, inside, parts, reversed,
                                          transform, (<|), (|>))
import           Control.Monad
import           Control.Monad.Plus
import           Data.Distributive
import           Data.Functor.Rep
import           Data.Functor.Rep.Lens
import qualified Data.List               as List
import           Data.Semigroup          hiding ()
import           Data.Typeable
import           Music.Dynamics.Literal
import           Music.Pitch.Literal

-- |
-- Forms an applicative as per 'Behavior', but only switches at discrete points.
--
newtype Reactive a = Reactive { getReactive :: ([Time], Behavior a) }
    deriving (Functor, Semigroup, Monoid, Typeable)

-- $semantics
--
-- type Reactive a = (a, Time, Voice a)
--

--
-- TODO Define a more compact representation and reimplement Behavior as (Reactive Segment).
--
-- Possible approach:
--
--  * Implement PosReactive (no negative values) and define Reactive = Delayed (PosReactive)
--
--  * Implement liftA2 for PosReactive (preferably with a single traversal)
--

instance Transformable (Reactive a) where
    transform s (Reactive (t,r)) = Reactive (transform s t, transform s r)

instance Reversible (Reactive a) where
  rev = stretch (-1)

instance Wrapped (Reactive a) where
    type Unwrapped (Reactive a) = ([Time], Behavior a)
    _Wrapped' = iso getReactive Reactive

instance Rewrapped (Reactive a) (Reactive b)
instance Applicative Reactive where
    pure  = pureDefault
      where
        pureDefault = view _Unwrapped . pure . pure
        
    (<*>) = apDefault
      where
        (view _Wrapped -> (tf, rf)) `apDefault` (view _Wrapped -> (tx, rx)) = view _Unwrapped (tf <> tx, rf <*> rx)

instance IsPitch a => IsPitch (Reactive a) where
  fromPitch = pure . fromPitch

instance IsInterval a => IsInterval (Reactive a) where
  fromInterval = pure . fromInterval

instance IsDynamics a => IsDynamics (Reactive a) where
  fromDynamics = pure . fromDynamics

instance Alterable a => Alterable (Reactive a) where
    sharpen = fmap sharpen
    flatten = fmap flatten

instance Augmentable a => Augmentable (Reactive a) where
    augment = fmap augment
    diminish = fmap diminish



-- |
-- Get the initial value.
--
initial :: Reactive a -> a
initial r = r `atTime` minB (occs r)
    where
        -- If there are no updates, just use value at time 0
        -- Otherwise pick an arbitrary time /before/ the first value
        -- It looks strange but it works
        minB []    = 0
        minB (x:_) = x - 1

-- | Get the time of all updates and the value switched to at this point.
updates :: Reactive a -> [(Time, a)]
updates r = (\t -> (t, r `atTime` t)) <$> (List.sort . List.nub) (occs r)

renderR :: Reactive a -> (a, [(Time, a)])
renderR x = (initial x, updates x)

occs :: Reactive a -> [Time]
occs = fst . (^. _Wrapped')

-- | Split a reactive into events, as well as the values before and after the first/last update
splitReactive :: Reactive a -> Either a ((a, Time), [Event a], (Time, a))
splitReactive r = case updates r of
    []          -> Left  (initial r)
    (t,x):[]    -> Right ((initial r, t), [], (t, x))
    (t,x):xs    -> Right ((initial r, t), fmap mkEvent $ mrights (res $ (t,x):xs), head $ mlefts (res $ (t,x):xs))

    where

        mkEvent (t,u,x) = (t <-> u, x)^.event

        -- Always returns a 0 or more Right followed by one left
        res :: [(Time, a)] -> [Either (Time, a) (Time, Time, a)]
        res rs = let (ts,xs) = unzip rs in
            flip fmap (withNext ts `zip` xs) $
                \ ((t, mu), x) -> case mu of
                    Nothing -> Left (t, x)
                    Just u  -> Right (t, u, x)

        -- lenght xs == length (withNext xs)
        withNext :: [a] -> [(a, Maybe a)]
        withNext = go
            where
                go []       = []
                go [x]      = [(x, Nothing)]
                go (x:y:rs) = (x, Just y) : withNext (y : rs)

atTime :: Reactive a -> Time -> a
atTime = (!) . snd . (^. _Wrapped')

-- |
-- Get the final value.
--
final :: Reactive a -> a
final (renderR -> (i,[])) = i
final (renderR -> (i,xs)) = snd $ last xs

-- | @switch t a b@ behaves as @a@ before time @t@, then as @b@.
switchR :: Time -> Reactive a -> Reactive a -> Reactive a
switchR t (Reactive (tx, bx)) (Reactive (ty, by)) = Reactive $ (,)
    (filter (< t) tx <> [t] <> filter (> t) ty) (switch t bx by)

trimR :: Monoid a => Span -> Reactive a -> Reactive a
trimR (view range -> (t, u)) x = switchR t mempty (switchR u x mempty)

-- |
-- Get all intermediate values.
--
intermediate :: Transformable a => Reactive a -> [Event a]
intermediate (updates -> []) = []
intermediate (updates -> xs) = fmap (\((t1, x), (t2, _)) -> (t1 <-> t2, x)^.event) $ withNext $ xs
  where
    withNext xs = zip xs (tail xs)

-- |
-- Realize a 'Reactive' value as a discretely changing behavior.
--
discrete :: Reactive a -> Behavior a
discrete = continous . fmap pure

-- | Realize a 'Reactive' value as an continous behavior.
continous :: Reactive (Segment a) -> Behavior a

-- | Realize a 'Reactive' value as an continous behavior.
continousWith :: Segment (a -> b) -> Reactive a -> Behavior b
continousWith f x = continous $ liftA2 (<*>) (pure f) (fmap pure x)

-- | Sample a 'Behavior' into a reactive.
sample   :: [Time] -> Behavior a -> Reactive a

-- TODO linear approximation
(continous, sample) = error "Not implemented: (continous, sample)"


window :: [Time] -> Behavior a -> Reactive (Segment a)
windowed :: Iso (Behavior a) (Behavior b) (Reactive (Segment a)) (Reactive (Segment b))
(window, windowed) = error "Not implemented: (window, windowed)"

{-

-- Fre monad of ?
{-
data Score s a
  = SOne a
  | SPlus s [Score a]
-}
newtype Trans s a = Trans (s, [a]) deriving (Functor)
instance Monoid s => Monad (Trans s) where
  return = Trans . return . return
  -- TODO the usual >>=

type Score s a = Free (Trans s) a

viewScore :: Monoid s => Score s a -> [(s, a)]
viewScore x = case retract x of
  Trans (s,as) -> zip (repeat s) as


-- Free monad of (a,a)
{-
data Tree a
  = One a
  | Plus (Tree a) (Tree a)
-}
data Pair a = Pair a a deriving (Functor)
newtype MaybePair a = MaybePair (Maybe (Pair a)) deriving (Functor) -- Use compose
type Tree a = Free MaybePair a

-- CPS-version of Tree
newtype Search a = Search { getSearch :: forall r . (a -> Tree r) -> Tree r }
   -}