{-# LANGUAGE ConstraintKinds            #-}
{-# LANGUAGE DeriveDataTypeable         #-}
{-# LANGUAGE DeriveFoldable             #-}
{-# LANGUAGE DeriveFunctor              #-}
{-# LANGUAGE DeriveTraversable          #-}
{-# LANGUAGE FlexibleInstances          #-}
{-# LANGUAGE GADTs                      #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses      #-}
{-# LANGUAGE NoMonomorphismRestriction  #-}
{-# LANGUAGE ScopedTypeVariables        #-}
{-# LANGUAGE TemplateHaskell            #-}
{-# 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,
      
        -- * Construction
        initial,
        final,
        intermediate,
        discrete,
        updates,
        occs,
        atTime,
        splitReactive,
      
        -- * Combinators
        switchR,
        trimR,

        -- * Sampling and discretization
        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.Note
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.Arrow           (first, second, (&&&), (***))
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.
--
-- The semantics are given by
--
-- @
-- type Reactive a = (a, Time, Voice a)
-- @
--
newtype Reactive a = Reactive { getReactive :: ([Time], Behavior a) }
    deriving (Functor, Semigroup, Monoid, Typeable)
--
-- 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 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
    (<*>) = apDefault

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


(view _Wrapped -> (tf, rf)) `apDefault` (view _Wrapped -> (tx, rx)) = view _Unwrapped (tf <> tx, rf <*> rx)
pureDefault = view _Unwrapped . pure . pure

-- |
-- 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 = initial &&& updates

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

-- | Split a reactive into notes, as well as the values before and after the first/last update
splitReactive :: Reactive a -> Either a ((a, Time), [Note 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 mkNote $ mrights (res $ (t,x):xs), head $ mlefts (res $ (t,x):xs))

    where

        mkNote (t,u,x) = (t <-> u, x)^.note

        -- 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)

{-# DEPRECATED updates "" #-}
{-# DEPRECATED occs "" #-}
{-# DEPRECATED splitReactive "" #-}
{-# DEPRECATED atTime "" #-}

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 -> [Note a]
intermediate (updates -> []) = []
intermediate (updates -> xs) = fmap (\((t1, x), (t2, _)) -> (t1 <-> t2, x)^.note) $ 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.
--
-- See also 'concatSegment' and 'concatB'.
--
continous :: Reactive (Segment a) -> Behavior a

-- |
-- Realize a 'Reactive' value as an continous behavior.
--
-- See also 'concatSegment' and 'concatB'.
--
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 }
   -}