{-# LANGUAGE ConstraintKinds           #-}
{-# LANGUAGE DeriveDataTypeable        #-}
{-# LANGUAGE DeriveFoldable            #-}
{-# LANGUAGE DeriveFunctor             #-}
{-# LANGUAGE DeriveTraversable         #-}
{-# LANGUAGE FlexibleContexts          #-}
{-# LANGUAGE FlexibleInstances         #-}
{-# LANGUAGE MultiParamTypeClasses     #-}
{-# LANGUAGE NoMonomorphismRestriction #-}
{-# LANGUAGE RankNTypes                #-}
{-# LANGUAGE ScopedTypeVariables       #-}
{-# LANGUAGE StandaloneDeriving        #-}
{-# LANGUAGE TupleSections             #-}
{-# LANGUAGE TypeFamilies              #-}
{-# LANGUAGE UndecidableInstances      #-}
{-# 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.Internal.Transform (

        module Music.Time.Types,

        -- * The Transformable class
        Transformable(..),
        transformed,

        -- * Apply under a transformation
        whilst,
        whilstL,
        whilstL2,
        whilstLT,
        whilstLD,
        whilstStretch,
        whilstDelay,
        onSpan,
        conjugateS,

        -- * Specific transformations
        -- ** Transformations
        delaying,
        undelaying,
        stretching,
        compressing,

        -- ** Transforming values
        delay,
        undelay,
        stretch,
        compress,
        delayTime,

  ) where

import           Music.Time.Types

import           Data.Ratio

import           Control.Applicative
import           Control.Lens           hiding (Indexable, Level, above, below,
                                         index, inside, parts, reversed,
                                         transform, (<|), (|>))
import           Data.AffineSpace
import           Data.AffineSpace.Point
import           Data.Map               (Map)
import qualified Data.Map               as Map
import           Data.Semigroup
import           Data.Semigroup.Instances ()
import           Data.Sequence          (Seq)
import qualified Data.Sequence          as Seq
import           Data.Set               (Set)
import qualified Data.Set               as Set
import           Data.VectorSpace       hiding (Sum (..))

-- Transformable laws:
-- > transform mempty   = id
-- > transform (s <> t) = transform s . transform t
--
-- Duration law:
-- > _duration a = _duration (_era a)
--
-- Position law:
-- > _position p (transform s a) = transform s (_position p a)
--
-- Lemma:
-- > _duration (transform s a) = transform s (_duration a)

-- |
-- Class of values that can be transformed (i.e. scaled and moved) in time.
--
class Transformable a where
  transform :: Span -> a -> a

instance Transformable () where
  transform _ = id

instance Transformable Bool where
  transform _ = id

instance Transformable Ordering where
  transform _ = id

instance Transformable Char where
  transform _ = id

instance Transformable Int where
  transform _ = id

instance Transformable Integer where
  transform _ = id

instance Transformable a => Transformable (Ratio a) where
  transform _ = id

instance Transformable Float where
  transform _ = id

instance Transformable Double where
  transform _ = id

instance Transformable Duration where
  (view delta -> (_, d1)) `transform` d2 = d1 * d2

instance Transformable Time where
  (view delta -> (t1, d1)) `transform` t2 = t1 ^+^ d1 *^ t2

instance Transformable Span where
  transform = (<>)

instance Transformable a => Transformable (Option a) where
  transform s = fmap (transform s)

instance Transformable a => Transformable (Last a) where
  transform s = fmap (transform s)

instance Transformable a => Transformable (Sum a) where
  transform s = fmap (transform s)

instance Transformable a => Transformable (Product a) where
  transform s = fmap (transform s)

instance Transformable a => Transformable (b, a) where
  transform t = fmap (transform t)

instance Transformable a => Transformable [a] where
  transform t = fmap (transform t)

instance Transformable a => Transformable (Seq a) where
  transform t = fmap (transform t)

instance (Ord a, Transformable a) => Transformable (Set a) where
  transform t = Set.map (transform t)

instance (Ord k, Transformable a) => Transformable (Map k a) where
  transform t = Map.map (transform t)

-- Functions transform by conjugation, i.e. we reverse-transform the argument
-- and transform the result.
--
instance (Transformable a, Transformable b) => Transformable (a -> b) where
  transform t = (`whilst` negateV t)
    where
    f `whilst` t = over (transformed t) f

-- |
-- View the given value in the context of the given transformation.
--
transformed :: (Transformable a, Transformable b) => Span -> Iso a b a b
transformed s = iso (transform s) (transform $ negateV s)


-- |
-- Apply a function under transformation.
--
-- >>> stretch 2 `whilst` delaying 2 $ (1 <-> 2)
-- 4 <-> 6
--
whilst :: (Transformable a, Transformable b) => (a -> b) -> Span -> a -> b
-- f `whilst` t = transform (negateV t) . f . transform t
f `whilst` t = over (transformed t) f


delayed :: (Transformable a, Transformable b) => Time -> Iso a b a b
delayed = transformed . delayingTime

stretched :: (Transformable a, Transformable b) => Duration -> Iso a b a b
stretched = transformed . stretching

-- |
-- A transformation that moves a value forward in time.
--
delaying :: Duration -> Span
delaying x = (0 .+^ x) >-> 1
delayingTime x = x >-> 1

-- |
-- A transformation that stretches (augments) a value by the given factor.
--
stretching :: Duration -> Span
stretching x = 0 >-> x

-- |
-- A transformation that moves a value backward in time.
--
undelaying :: Duration -> Span
undelaying x = delaying (negate x)

-- |
-- A transformation that compresses (diminishes) a value by the given factor.
--
compressing :: Duration -> Span
compressing x = stretching (recip x)

-- |
-- Moves a value forward in time.
--
delay :: Transformable a => Duration -> a -> a
delay = transform . delaying

-- |
-- Moves a value backward in time. Equnitvalent to @'stretch' . 'negate'@.
--
undelay :: Transformable a => Duration -> a -> a
undelay = transform . undelaying

-- |
-- Stretches (augments) a value by the given factor.
--
stretch :: Transformable a => Duration -> a -> a
stretch = transform . stretching

-- |
-- Compresses (diminishes) a score. Equnitvalent to @'stretch' . 'recip'@.
--
compress :: Transformable a => Duration -> a -> a
compress = transform . compressing


-- |
-- Delay relative to 'origin'.
--
-- Provided for situations when we really want to use 'startAt', but the
-- type does not have an instance for 'HasPosition' and we can assume that
-- the value is starting at time zero.
--
delayTime :: Transformable a => Time -> a -> a
delayTime = transform . delayingTime


--
-- $musicTimeSpanConstruct
--
-- - To convert a span to a pair, use @s^.'delta'@.
-- - To construct a span from a pair, use @(t, d)^.'from' 'delta'@.
--

--
-- $musicTimeSpanLaws
--
-- > forall s . id `whilst` s = id
-- > forall s . return `whilstM` s = return
-- > forall s . extract `whilstW` s = extract


-- We really must flip all these functions. To do:
--
--    1) Come up with some other name for the infix version
--    2) Acknowledge that this is a valid Lens (when flipped)
--
-- Perhaps we should call the inline version `whilst`, as in @f `whilst` delaying 2@?

{-

-- flip whilstM is a lens
flip whilstM :: (Functor f, Transformable a, Transformable b) => (a -> f b) -> Span -> a -> f b
s `flip whilstM` f = fmap (transform (negateV t)) . f . transform t

-- is this the same as transformed?


From lens:
  iso sa bt = dimap sa (fmap bt)
From profunctor:
  dimap ab cd bc = cd . bc . ab
  dimap ab cd    = \f -> cd . f . ab
  

flip whilstM = transformed
flip whilstM = \s -> iso (transform s) (itransform s)
flip whilstM = \s -> dimap (transform s) (fmap $ itransform s)
flip whilstM = \s f -> (fmap $ itransform s) . f . transform s
flip (\f t -> fmap (transform (negateV t)) . f . transform t) = \s f -> (fmap $ itransform s) . f . transform s

\t f -> fmap (transform (negateV t)) . f . transform t 
=
\t f -> (fmap $ itransform t) . f . transform t

\t f -> fmap (itransform t) . f . transform t 
=
\t f -> fmap (itransform t) . f . transform t




Something similar to whilstL* is being used in Note/Delayed/Stretched
Are they the same?

whilstL l f (s,a)  = (s,) <$> (l $ transformed s f) a
whilstL id f (s,a) = (s,) <$> (transformed s f) a
whilstL id         = \f (s,a) -> (s,) <$> (transformed s f) a

whilstL id
  :: (Transformable a, Transformable b, Functor f) =>
     (a -> f b) -> (Span, a) -> f (Span, b)

-}

-- dofoo
  -- :: Functor f => (t -> t2) -> (a1 -> a) -> (t2 -> f a1) -> (t1, t) -> f (t1, a)
dofoo v w = \f (s,a) -> (s,) <$> w s <$> f ((v s) a)



dobar :: (Functor f) 

  => 
  (sp -> (s -> f t) -> (s -> f t)) 
  -> ((s -> f t) -> a -> f b)
  -> (s -> f t)  -> ((sp, a) -> f (sp, b))

dobar q l = \f (s,a) -> (s,) <$> (l (q s f)) a

-- whilstL2 :: (Transformable a, Transformable b) => Lens (Span, a) (Span, b) a b
whilstL2 = dofoo (transform) (transform . negateV)

whilstL :: (Functor f, Transformable a, Transformable b)
  => LensLike f s t a b
  -> LensLike f (Span,s) (Span,t) a b
  -- whilstL l = whilstL2 . l
whilstL l = dobar transformed l

{-
If we could rewrite (whilstL l) as (whilstLXX . l)

-}

whilstLT :: (Functor f, Transformable a, Transformable b)
  => LensLike f s t a b
  -> LensLike f (Time,s) (Time,t) a b
whilstLT = dobar delayed

whilstLD :: (Functor f, Transformable a, Transformable b)
  => LensLike f s t a b
  -> LensLike f (Duration,s) (Duration,t) a b
whilstLD = dobar stretched


-- |
-- Apply a function under transformation.
--
whilstDelay :: (Transformable a, Transformable b) => (a -> b) -> Time -> a -> b
whilstDelay     = flip (flip whilst . delaying . (.-. 0))

-- |
-- Apply a function under transformation.
--
whilstStretch :: (Transformable a, Transformable b) => (a -> b) -> Duration -> a -> b
whilstStretch = flip (flip whilst . stretching)

-- |
-- The conjugate of two spans.
--
conjugateS :: Span -> Span -> Span
conjugateS t1 t2  = negateV t1 <> t2 <> t1


-- |
-- Transforms a lens of to a 'Transformable' type to act inside a transformation.
--
-- Designed to be used infix, as in
--
-- @
-- l `onSpan` (2 \<-> 3)
-- @
--
onSpan :: (Transformable s, Transformable t, Functor f) 
  => LensLike f s t a b -> Span -> LensLike f s t a b
f `onSpan` s = transformed (negateV s) . f
-- TODO name

-- deriving instance Functor Sum
-- deriving instance Functor Product