-- |
-- Module      : Data.Manifold.FibreBundle
-- Copyright   : (c) Justus Sagemüller 2018
-- License     : GPL v3
-- 
-- Maintainer  : (@) sagemueller $ geo.uni-koeln.de
-- Stability   : experimental
-- Portability : portable
-- 

{-# LANGUAGE FlexibleInstances          #-}
{-# LANGUAGE FlexibleContexts           #-}
{-# LANGUAGE MultiParamTypeClasses      #-}
{-# LANGUAGE TypeFamilies               #-}
{-# LANGUAGE UndecidableInstances       #-}
{-# LANGUAGE ScopedTypeVariables        #-}
{-# LANGUAGE UnicodeSyntax              #-}
{-# LANGUAGE GADTs                      #-}
{-# LANGUAGE DefaultSignatures          #-}
{-# LANGUAGE CPP                        #-}
{-# LANGUAGE PatternSynonyms            #-}
#if __GLASGOW_HASKELL__ >= 800
{-# LANGUAGE UndecidableSuperClasses    #-}
#endif


module Data.Manifold.FibreBundle where


import Data.AdditiveGroup
import Data.VectorSpace
import Math.LinearMap.Category

import Data.Manifold.Types.Primitive
import Data.Manifold.PseudoAffine

import Math.Rotations.Class
    
import qualified Prelude as Hask

import Control.Category.Constrained.Prelude hiding ((^))
import Control.Category.Discrete
import Control.Arrow.Constrained

import Linear.V2 (V2(V2))
import Linear.V3 (V3(V3))

import Data.Tagged


pattern TangentBundle :: m -> Needle m -> FibreBundle m (Needle m)
pattern TangentBundle p v = FibreBundle p v

infixr 5 :@.
-- | Provided for convenience. Flipped synonym of 'FibreBundle', restricted to manifolds
--   without boundary (so the type of the whole can be inferred from its interior).
pattern (:@.) :: f -> m -> FibreBundle m f
pattern f :@. p = FibreBundle p f

-- | A zero vector in the fibre bundle at the given position. Intended to be used
--   with tangent-modifying lenses such as 'Math.Manifold.Real.Coordinates.delta'.
tangentAt :: (AdditiveGroup (Needle m), m ~ Interior m) => m -> TangentBundle m
tangentAt p = zeroV :@. p

data TransportOnNeedleWitness k m f where
  TransportOnNeedle :: (ParallelTransporting (LinearFunction (Scalar (Needle m)))
                                             (Needle m) (Needle f))
                     => TransportOnNeedleWitness k m f

data ForgetTransportProperties k m f where
  ForgetTransportProperties :: ParallelTransporting (->) m f
                     => ForgetTransportProperties k m f

class (PseudoAffine m, m ~ Interior m, Category k, Object k f)
           => ParallelTransporting k m f where
  transportOnNeedleWitness :: TransportOnNeedleWitness k m f
  default transportOnNeedleWitness
      :: ParallelTransporting (LinearFunction (Scalar (Needle m))) (Needle m) (Needle f)
           => TransportOnNeedleWitness k m f
  transportOnNeedleWitness = TransportOnNeedle
  forgetTransportProperties :: ForgetTransportProperties k m f
  default forgetTransportProperties :: ParallelTransporting (->) m f
           => ForgetTransportProperties k m f
  forgetTransportProperties = ForgetTransportProperties
  
  parallelTransport :: m -> Needle m -> k f f
  translateAndInvblyParTransport
        :: m -> Needle m -> (m, (k f f, k f f))
  translateAndInvblyParTransport p v
              = (q, ( parallelTransport p v
                    , parallelTransport q $ p.-~!q ))
   where q = p.+~^v

instance ∀ m s . (PseudoAffine m, m ~ Interior m, s ~ (Scalar (Needle m)), Num' s)
      => ParallelTransporting Discrete m (ZeroDim s) where
  transportOnNeedleWitness = case (pseudoAffineWitness :: PseudoAffineWitness m) of
    (PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)) -> TransportOnNeedle
  forgetTransportProperties = case (pseudoAffineWitness :: PseudoAffineWitness m) of
    (PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness))
        -> ForgetTransportProperties
  parallelTransport _ _ = id
instance ∀ m s . (PseudoAffine m, m ~ Interior m, s ~ (Scalar (Needle m)), Num' s)
      => ParallelTransporting (LinearFunction s) m (ZeroDim s) where
  transportOnNeedleWitness = case (pseudoAffineWitness :: PseudoAffineWitness m) of
    (PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)) -> TransportOnNeedle
  forgetTransportProperties = case (pseudoAffineWitness :: PseudoAffineWitness m) of
    (PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness))
        -> ForgetTransportProperties
  parallelTransport _ _ = id
instance ∀ m s . (PseudoAffine m, m ~ Interior m, s ~ (Scalar (Needle m)), Num' s)
      => ParallelTransporting (->) m (ZeroDim s) where
  transportOnNeedleWitness = case (pseudoAffineWitness :: PseudoAffineWitness m) of
    (PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)) -> TransportOnNeedle
  forgetTransportProperties = case (pseudoAffineWitness :: PseudoAffineWitness m) of
    (PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness))
        -> ForgetTransportProperties
  parallelTransport _ _ = id

instance (Category k, Object k ℝ) => ParallelTransporting k ℝ ℝ where
  parallelTransport _ _ = id
instance (Category k, Object k ℝ²) => ParallelTransporting k ℝ² ℝ² where
  parallelTransport _ _ = id
instance (Category k, Object k ℝ³) => ParallelTransporting k ℝ³ ℝ³ where
  parallelTransport _ _ = id
instance (Category k, Object k ℝ⁴) => ParallelTransporting k ℝ⁴ ℝ⁴ where
  parallelTransport _ _ = id

instance (Category k, Object k ℝ) => ParallelTransporting k S¹ ℝ where
  parallelTransport _ _ = id

instance (EnhancedCat k (LinearMap ℝ), Object k ℝ²)
             => ParallelTransporting k S² ℝ² where
  parallelTransport p v = (fst . snd) (translateAndInvblyParTransport p v)
  translateAndInvblyParTransport (S²Polar θ₀ φ₀) 𝐯
     | d < pi     = (S²Polar θ₁ φ₁, (arr fwd, arr bwd))
     | d < 2*pi   = translateAndInvblyParTransport (S²Polar θ₀ φ₀)
                      $ 𝐯^*(-(2*pi-d)/d)
     | otherwise  = translateAndInvblyParTransport (S²Polar θ₀ φ₀)
                      $ let revolutions = floor $ d/(2*pi)
                        in 𝐯^*((d - 2*pi*fromIntegral revolutions)/d)
   where -- See images/constructions/sphericoords-needles.svg. Translation as in
         -- "Data.Manifold.PseudoAffine" instance.
         S¹Polar γc₀ = coEmbed 𝐯
         γ₀ | θ₀ < pi/2   = γc₀ - φ₀
            | otherwise   = γc₀ + φ₀
         d = magnitude 𝐯
         S¹Polar φ₁ = S¹Polar φ₀ .+~^ δφ
         
         -- Cartesian coordinates of p₁ in the system whose north pole is p₀
         -- with φ₀ as the zero meridian
         V3 bx by bz = embed $ S²Polar d γ₀
         
         sθ₀ = sin θ₀; cθ₀ = cos θ₀
         -- Cartesian coordinates of p₁ in the system with the standard north pole,
         -- but still φ₀ as the zero meridian
         (qx,qz) = ( cθ₀ * bx + sθ₀ * bz
                   ,-sθ₀ * bx + cθ₀ * bz )
         qy      = by
         
         S²Polar θ₁ δφ = coEmbed $ V3 qx qy qz
         
         sθ₁ = sin θ₁; cθ₁ = cos θ₁
         
         γ₁
          | sθ₀<=sθ₁  = let
              -- Cartesian coordinates of the standard north pole in the system whose north
              -- pole is p₀ with 𝐯 along the zero meridian
              V3 nbx nby nbz = embed $ S²Polar θ₀ (pi-γ₀)
              
              sd = sin d; cd = cos d
              -- Cartesian coordinates of the standard north pole in the system whose north
              -- pole is p₁ with 𝐯 along the zero meridian
              (ox,oz) = ( cd * nbx - sd * nbz
                        , sd * nbx + cd * nbz )
              oy      = nby

           in atan2 oy (-ox)

          | otherwise = let
              -- Cartesian coordinates of p₀ in the system with the standard north pole,
              -- with p₁ on the zero meridian
              V3 gx gy gz = embed $ S²Polar θ₀ (-δφ)
              
              -- Cartesian coordinates of p₀ in the system whose north
              -- pole is p₁ and the standard north pole on the zero meridian
              (ux,uz) = ( cθ₁ * gx - sθ₁ * gz
                        , sθ₁ * gx + cθ₁ * gz )
              uy      = gy

           in atan2 (-uy) (-ux)

         γc₁ | θ₁ < pi/2  = γ₁ + φ₁
             | otherwise  = γ₁ - φ₁

         (sδγc, cδγc) = sin &&& cos $ γc₁ - γc₀

         fwd = LinearMap (V2 (V2   cδγc  sδγc)
                             (V2 (-sδγc) cδγc)) :: LinearMap ℝ ℝ² ℝ²
         bwd = LinearMap (V2 (V2 cδγc (-sδγc))
                             (V2 sδγc   cδγc )) :: LinearMap ℝ ℝ² ℝ²


instance {-# OVERLAPS #-} ∀ k a b fa fb s .
         ( ParallelTransporting k a fa, ParallelTransporting k b fb
         , PseudoAffine fa, PseudoAffine fb
         , Scalar (Needle a) ~ s, Scalar (Needle b) ~ s
         , Scalar (Needle fa) ~ s, Scalar (Needle fb) ~ s
         , Num' s
         , Morphism k, ObjectPair k fa fb )
              => ParallelTransporting k (a,b) (fa,fb) where
  transportOnNeedleWitness = case
         ( pseudoAffineWitness :: PseudoAffineWitness a
         , pseudoAffineWitness :: PseudoAffineWitness b
         , pseudoAffineWitness :: PseudoAffineWitness fa
         , pseudoAffineWitness :: PseudoAffineWitness fb
         , transportOnNeedleWitness :: TransportOnNeedleWitness k a fa
         , transportOnNeedleWitness :: TransportOnNeedleWitness k b fb ) of
     ( PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
      ,PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
      ,PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
      ,PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
      ,TransportOnNeedle, TransportOnNeedle)
         -> TransportOnNeedle
  forgetTransportProperties = case
    ( forgetTransportProperties :: ForgetTransportProperties k a fa
    , forgetTransportProperties :: ForgetTransportProperties k b fb ) of
     (ForgetTransportProperties, ForgetTransportProperties) -> ForgetTransportProperties
  parallelTransport (pa,pb) (va,vb)
       = parallelTransport pa va  *** parallelTransport pb vb

instance ∀ k a f g s .
         ( ParallelTransporting k a f, ParallelTransporting k a g
         , ParallelTransporting (LinearFunction s) (Needle a) (Needle f, Needle g)
         , PseudoAffine f, PseudoAffine g
         , Morphism k, ObjectPair k f g )
              => ParallelTransporting k a (f,g) where
  transportOnNeedleWitness = case
         ( pseudoAffineWitness :: PseudoAffineWitness a
         , pseudoAffineWitness :: PseudoAffineWitness f
         , pseudoAffineWitness :: PseudoAffineWitness g
         , transportOnNeedleWitness :: TransportOnNeedleWitness k a f
         , transportOnNeedleWitness :: TransportOnNeedleWitness k a g ) of
     ( PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
      ,PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
      ,PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
      ,TransportOnNeedle, TransportOnNeedle)
         -> TransportOnNeedle
  forgetTransportProperties = case
    ( forgetTransportProperties :: ForgetTransportProperties k a f
    , forgetTransportProperties :: ForgetTransportProperties k a g ) of
     (ForgetTransportProperties, ForgetTransportProperties) -> ForgetTransportProperties
  parallelTransport p v
       = parallelTransport p v *** parallelTransport p v


instance ( ParallelTransporting (LinearFunction (Scalar f)) m f, AdditiveGroup m
         , VectorSpace f )
                => AdditiveGroup (FibreBundle m f) where
  zeroV = FibreBundle zeroV zeroV
  FibreBundle p v ^+^ FibreBundle q w = FibreBundle (p^+^q) (v^+^w)
  negateV (FibreBundle p v) = FibreBundle (negateV p) (negateV v)

instance ∀ m f s .
         ( ParallelTransporting (->) m (Interior f), Semimanifold f
         , ParallelTransporting (LinearFunction s) (Needle m) (Needle f)
         , s ~ Scalar (Needle m) )
                => Semimanifold (FibreBundle m f) where
  type Interior (FibreBundle m f) = FibreBundle m (Interior f)
  type Needle (FibreBundle m f) = FibreBundle (Needle m) (Needle f)
  toInterior (FibreBundle p f) = FibreBundle p <$> toInterior f
  translateP = Tagged $ case ( translateP :: Tagged m (Interior m -> Needle m -> Interior m)
                             , semimanifoldWitness :: SemimanifoldWitness f) of
      (Tagged tpm, SemimanifoldWitness BoundarylessWitness)
           -> \(FibreBundle p f) (FibreBundle v δf)
                   -> FibreBundle (tpm p v) (parallelTransport p v f.+~^δf)
  semimanifoldWitness = case ( semimanifoldWitness :: SemimanifoldWitness m
                             , semimanifoldWitness :: SemimanifoldWitness f
                             , forgetTransportProperties
                               :: ForgetTransportProperties (LinearFunction s) (Needle m) (Needle f)
                             ) of
         (SemimanifoldWitness BoundarylessWitness, SemimanifoldWitness BoundarylessWitness
          ,ForgetTransportProperties)
           -> SemimanifoldWitness BoundarylessWitness
  FibreBundle p f .+~^ FibreBundle v δf
      = FibreBundle (p.+~^v) (parallelTransport p v f.+~^δf)

instance ∀ m f s .
         ( ParallelTransporting (->) m f, ParallelTransporting (->) m (Interior f)
         , PseudoAffine f
         , ParallelTransporting (LinearFunction s) (Needle m) (Needle f)
         , s ~ Scalar (Needle m) )
                => PseudoAffine (FibreBundle m f) where
  pseudoAffineWitness = case ( pseudoAffineWitness :: PseudoAffineWitness m
                             , pseudoAffineWitness :: PseudoAffineWitness f
                             , forgetTransportProperties
                               :: ForgetTransportProperties (LinearFunction s) (Needle m) (Needle f)
                             ) of
     ( PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
      ,PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
      ,ForgetTransportProperties)
         -> PseudoAffineWitness (SemimanifoldWitness BoundarylessWitness)
  FibreBundle p f .-~. FibreBundle q g = case p.-~.q of
      Nothing -> Nothing
      Just v  -> FibreBundle v <$> f .-~. parallelTransport p v g


instance (AdditiveGroup f, x ~ Interior x) => NaturallyEmbedded x (FibreBundle x f) where
  embed x = FibreBundle x zeroV
  coEmbed (FibreBundle x _) = x

instance (NaturallyEmbedded m v, VectorSpace f)
    => NaturallyEmbedded (FibreBundle m ℝ⁰) (FibreBundle v f) where
  embed (FibreBundle x Origin) = FibreBundle (embed x) zeroV
  coEmbed (FibreBundle u _) = FibreBundle (coEmbed u) Origin

instance (AdditiveGroup y, AdditiveGroup g)
           => NaturallyEmbedded (FibreBundle x f) (FibreBundle (x,y) (f,g)) where
  embed (FibreBundle x δx) = FibreBundle (x,zeroV) (δx,zeroV)
  coEmbed (FibreBundle (x,_) (δx,_)) = FibreBundle x δx

instance NaturallyEmbedded v w
      => NaturallyEmbedded (FibreBundle ℝ v) (FibreBundle ℝ w) where
  embed (FibreBundle p v) = FibreBundle p $ embed v
  coEmbed (FibreBundle p w) = FibreBundle p $ coEmbed w
instance NaturallyEmbedded v w
      => NaturallyEmbedded (FibreBundle ℝ² v) (FibreBundle ℝ² w) where
  embed (FibreBundle p v) = FibreBundle p $ embed v
  coEmbed (FibreBundle p w) = FibreBundle p $ coEmbed w
instance NaturallyEmbedded v w
      => NaturallyEmbedded (FibreBundle ℝ³ v) (FibreBundle ℝ³ w) where
  embed (FibreBundle p v) = FibreBundle p $ embed v
  coEmbed (FibreBundle p w) = FibreBundle p $ coEmbed w
instance NaturallyEmbedded v w
      => NaturallyEmbedded (FibreBundle ℝ⁴ v) (FibreBundle ℝ⁴ w) where
  embed (FibreBundle p v) = FibreBundle p $ embed v
  coEmbed (FibreBundle p w) = FibreBundle p $ coEmbed w

instance NaturallyEmbedded (FibreBundle S¹ ℝ) (FibreBundle ℝ² ℝ²) where
  embed (FibreBundle (S¹Polar φ) l) = FibreBundle (V2 cφ sφ) $ l*^(V2 (-sφ) cφ)
   where (cφ, sφ) = (cos &&& sin) φ
  coEmbed (FibreBundle (V2 0 0) (V2 _ δy)) = FibreBundle (S¹Polar 0) δy
  coEmbed (FibreBundle p (V2 δx δy)) = FibreBundle (S¹Polar $ atan2 sφ cφ) $ cφ*δy - sφ*δx
   where V2 cφ sφ = p^/r
         r = magnitude p

instance NaturallyEmbedded (FibreBundle S² ℝ²) (FibreBundle ℝ³ ℝ³) where
  embed (FibreBundle (S²Polar θ φ) 𝐯@(V2 δξ δυ))
       = FibreBundle (V3 (sθ*cφ) (sθ*sφ) cθ) 𝐯r
   where [V2 cθ sθ, V2 cφ sφ] = embed . S¹Polar <$> [θ,φ]
         S¹Polar γc = coEmbed 𝐯
         γ | θ < pi/2   = γc - φ
           | otherwise  = γc + φ
         d = magnitude 𝐯

         V2 δθ δφ = d *^ embed (S¹Polar γ)
         
         𝐞φ = V3 (-sφ) cφ 0
         𝐞θ = V3 (cθ*cφ) (cθ*sφ) (-sθ)
         𝐯r = δθ*^𝐞θ ^+^ δφ*^𝐞φ
  
  coEmbed (FibreBundle (V3 x y z) 𝐯r)
           = FibreBundle (S²Polar θ φ) (magnitude (δθ,δφ) *^ embed (S¹Polar γc))
   where r = sqrt $ x^2 + y^2 + z^2
         rxy = sqrt $ x^2 + y^2
         θ = atan2 rxy z
         φ = atan2 y x
         cθ = z / r
         sθ = rxy / r
         (cφ,sφ) | rxy>0      = (x,y)^/rxy
                 | otherwise  = (1,0)
         𝐞φ = V3 (-sφ) cφ 0
         𝐞θ = V3 (cθ*cφ) (cθ*sφ) (-sθ)
         δθ = 𝐞θ <.> 𝐯r
         δφ = 𝐞φ <.> 𝐯r
         γ = atan2 δφ δθ
         γc | θ < pi/2   = γ + φ
            | otherwise  = γ - φ


-- | @ex -> ey@, @ey -> ez@, @ez -> ex@
transformEmbeddedTangents
    :: ∀ x f v . ( NaturallyEmbedded (FibreBundle x f) (FibreBundle v v)
                               , v ~ Interior v )
           => (v -> v) -> FibreBundle x f -> FibreBundle x f
transformEmbeddedTangents f p = case embed p :: FibreBundle v v of
    FibreBundle v δv -> coEmbed (FibreBundle (f v) (f δv) :: FibreBundle v v)


instance Rotatable (FibreBundle S² ℝ²) where
  type AxisSpace (FibreBundle S² ℝ²) = ℝP²
  rotateAbout axis angle = transformEmbeddedTangents $ rotateℝ³AboutCenteredAxis axis angle