-- The Agda standard library
-- Properties of operations on the Stream type

{-# OPTIONS --cubical-compatible --sized-types #-}

module Codata.Sized.Stream.Properties where

open import Level using (Level)
open import Size
open import Codata.Sized.Thunk as Thunk using (Thunk; force)
open import Codata.Sized.Stream
open import Codata.Sized.Stream.Bisimilarity

open import Data.Nat.Base
open import Data.Nat.GeneralisedArithmetic using (fold; fold-pull)

open import Data.List.Base as List using ([]; _∷_)
open import Data.List.NonEmpty as List⁺ using (List⁺; _∷_)
import Data.List.Relation.Binary.Equality.Propositional as Eq
open import Data.Product as Prod using (_,_)
open import Data.Vec.Base as Vec using (_∷_)

open import Function.Base using (id; _$_; _∘′_; const)
open import Relation.Binary.PropositionalEquality as P using (_≡_; _≢_)

    a b c : Level
    A : Set a
    B : Set b
    C : Set c
    i : Size

-- repeat

lookup-repeat-identity : (n : ) (a : A)  lookup (repeat a) n  a
lookup-repeat-identity zero    a = P.refl
lookup-repeat-identity (suc n) a = lookup-repeat-identity n a

take-repeat-identity : (n : ) (a : A)  take n (repeat a)  Vec.replicate a
take-repeat-identity zero    a = P.refl
take-repeat-identity (suc n) a = P.cong (a Vec.∷_) (take-repeat-identity n a)

splitAt-repeat-identity : (n : ) (a : A)  splitAt n (repeat a)  (Vec.replicate a , repeat a)
splitAt-repeat-identity zero    a = P.refl
splitAt-repeat-identity (suc n) a = P.cong (Prod.map₁ (a ∷_)) (splitAt-repeat-identity n a)

replicate-repeat :  {i} (n : ) (a : A)  i  List.replicate n a ++ repeat a  repeat a
replicate-repeat zero    a = refl
replicate-repeat (suc n) a = P.refl  λ where .force  replicate-repeat n a

cycle-replicate :  {i} (n : ) (n≢0 : n  0) (a : A)  i  cycle (List⁺.replicate n n≢0 a)  repeat a
cycle-replicate {i} n n≢0 a = let as = List⁺.replicate n n≢0 a in begin
  cycle as                           ≡⟨⟩
  as ⁺++ _                           ≈⟨ ⁺++⁺ Eq.≋-refl  where .force  cycle-replicate n n≢0 a) 
  as ⁺++  where .force  repeat a) ≈⟨ P.refl   where .force  replicate-repeat (pred n) a) 
  repeat a                            where open ≈-Reasoning

module _ {a b} {A : Set a} {B : Set b} where

  map-repeat :  (f : A  B) a {i}  i  map f (repeat a)  repeat (f a)
  map-repeat f a = P.refl  λ where .force  map-repeat f a

  ap-repeat :  (f : A  B) a {i}  i  ap (repeat f) (repeat a)  repeat (f a)
  ap-repeat f a = P.refl  λ where .force  ap-repeat f a

  ap-repeatˡ :  (f : A  B) as {i}  i  ap (repeat f) as  map f as
  ap-repeatˡ f (a  as) = P.refl  λ where .force  ap-repeatˡ f (as .force)

  ap-repeatʳ :  (fs : Stream (A  B) ) (a : A) {i}  i  ap fs (repeat a)  map (_$ a) fs
  ap-repeatʳ (f  fs) a = P.refl  λ where .force  ap-repeatʳ (fs .force) a

  map-++ :  {i} (f : A  B) as xs  i  map f (as ++ xs)  List.map f as ++ map f xs
  map-++ f []       xs = refl
  map-++ f (a  as) xs = P.refl  λ where .force  map-++ f as xs

  map-⁺++ :  {i} (f : A  B) as xs  i  map f (as ⁺++ xs)  List⁺.map f as ⁺++ Thunk.map (map f) xs
  map-⁺++ f (a  as) xs = P.refl   where .force  map-++ f as (xs .force))

  map-cycle :  {i} (f : A  B) as  i  map f (cycle as)  cycle (List⁺.map f as)
  map-cycle f as = begin
    map f (cycle as)       ≈⟨ map-⁺++ f as _ 
    List⁺.map f as ⁺++ _   ≈⟨ ⁺++⁺ Eq.≋-refl  where .force  map-cycle f as) 
    cycle (List⁺.map f as)  where open ≈-Reasoning

-- Functor laws

map-id :  (as : Stream A )  i  map id as  as
map-id (a  as) = P.refl  λ where .force  map-id (as .force)

map-∘ :  (f : A  B) (g : B  C) as  i  map g (map f as)  map (g ∘′ f) as
map-∘ f g (a  as) = P.refl  λ where .force  map-∘ f g (as .force)

-- splitAt

splitAt-map :  n (f : A  B) xs 
  splitAt n (map f xs)  Prod.map (Vec.map f) (map f) (splitAt n xs)
splitAt-map zero    f xs       = P.refl
splitAt-map (suc n) f (x  xs) =
  P.cong (Prod.map₁ (f x Vec.∷_)) (splitAt-map n f (xs .force))

-- iterate

lookup-iterate-identity :  n f (a : A)  lookup (iterate f a) n  fold a f n
lookup-iterate-identity zero     f a = P.refl
lookup-iterate-identity (suc n)  f a = begin
  lookup (iterate f a) (suc n) ≡⟨⟩
  lookup (iterate f (f a)) n   ≡⟨ lookup-iterate-identity n f (f a) 
  fold (f a) f n               ≡⟨ fold-pull a f (const ∘′ f) (f a) P.refl  _  P.refl) n 
  f (fold a f n)               ≡⟨⟩
  fold a f (suc n)              where open P.≡-Reasoning

-- Please use the new names as continuing support for the old names is
-- not guaranteed.

-- Version 2.0

map-identity = map-id
{-# WARNING_ON_USAGE map-identity
"Warning: map-identity was deprecated in v2.0.
Please use map-id instead."

map-map-fusion = map-∘
{-# WARNING_ON_USAGE map-map-fusion
"Warning: map-map-fusion was deprecated in v2.0.
Please use map-∘ instead."