------------------------------------------------------------------------
-- The Agda standard library
--
-- Properties of the setoid sublist relation
------------------------------------------------------------------------

{-# OPTIONS --cubical-compatible --safe #-}

open import Relation.Binary.Core using (Rel; _⇒_; _Preserves_⟶_)
open import Relation.Binary.Bundles using (Setoid)

module Data.List.Relation.Binary.Sublist.Setoid.Properties
  {c } (S : Setoid c ) where

open import Data.List.Base hiding (_∷ʳ_)
open import Data.List.Relation.Unary.Any using (Any)
import Data.Maybe.Relation.Unary.All as Maybe
open import Data.Nat.Base using (; _≤_; _≥_)
import Data.Nat.Properties as 
open import Data.Product.Base using (; _,_; proj₂)
open import Function.Base
open import Function.Bundles using (_⇔_; _⤖_)
open import Level
open import Relation.Binary.Definitions using () renaming (Decidable to Decidable₂)
open import Relation.Binary.PropositionalEquality.Core as  using (_≡_; refl; cong; cong₂)
open import Relation.Binary.Structures using (IsDecTotalOrder)
open import Relation.Unary using (Pred; Decidable; Irrelevant)
open import Relation.Nullary.Negation using (¬_)
open import Relation.Nullary.Decidable using (¬?; yes; no)

import Data.List.Relation.Binary.Equality.Setoid as SetoidEquality
import Data.List.Relation.Binary.Sublist.Setoid as SetoidSublist
import Data.List.Relation.Binary.Sublist.Heterogeneous.Properties
  as HeteroProperties
import Data.List.Membership.Setoid as SetoidMembership

open Setoid S using (_≈_; trans) renaming (Carrier to A; refl to ≈-refl)
open SetoidEquality S using (_≋_; ≋-refl)
open SetoidSublist S hiding (map)
open SetoidMembership S using (_∈_)

private
  variable
    p q r s t : Level
    a b x y : A
    as bs cs ds xs ys : List A
    P : Pred A p
    Q : Pred A q
    m n : 


------------------------------------------------------------------------
-- Injectivity of constructors
------------------------------------------------------------------------

module _ where

  ∷-injectiveˡ :  {px qx : x  y} {pxs qxs : xs  ys} 
                 ((x  xs)  (y  ys)  px  pxs)  (qx  qxs)  px  qx
  ∷-injectiveˡ refl = refl

  ∷-injectiveʳ :  {px qx : x  y} {pxs qxs : xs  ys} 
                 ((x  xs)  (y  ys)  px  pxs)  (qx  qxs)  pxs  qxs
  ∷-injectiveʳ refl = refl

  ∷ʳ-injective :  {pxs qxs : xs  ys}  y ∷ʳ pxs  y ∷ʳ qxs  pxs  qxs
  ∷ʳ-injective refl = refl

------------------------------------------------------------------------
-- Categorical properties
------------------------------------------------------------------------

module _ (trans-reflˡ :  {x y} (p : x  y)  trans ≈-refl p  p) where

  ⊆-trans-idˡ : (pxs : xs  ys)  ⊆-trans ⊆-refl pxs  pxs
  ⊆-trans-idˡ [] = refl
  ⊆-trans-idˡ (y ∷ʳ pxs) = cong (y ∷ʳ_) (⊆-trans-idˡ pxs)
  ⊆-trans-idˡ (x  pxs) = cong₂ _∷_ (trans-reflˡ x) (⊆-trans-idˡ pxs)

module _ (trans-reflʳ :  {x y} (p : x  y)  trans p ≈-refl  p) where

  ⊆-trans-idʳ : (pxs : xs  ys)  ⊆-trans pxs ⊆-refl  pxs
  ⊆-trans-idʳ [] = refl
  ⊆-trans-idʳ (y ∷ʳ pxs) = cong (y ∷ʳ_) (⊆-trans-idʳ pxs)
  ⊆-trans-idʳ (x  pxs) = cong₂ _∷_ (trans-reflʳ x) (⊆-trans-idʳ pxs)

module _ (≈-assoc :  {w x y z} (p : w  x) (q : x  y) (r : y  z) 
                    trans p (trans q r)  trans (trans p q) r) where

  ⊆-trans-assoc : (ps : as  bs) (qs : bs  cs) (rs : cs  ds) 
            ⊆-trans ps (⊆-trans qs rs)  ⊆-trans (⊆-trans ps qs) rs
  ⊆-trans-assoc ps qs (_ ∷ʳ rs) = cong (_ ∷ʳ_) (⊆-trans-assoc ps qs rs)
  ⊆-trans-assoc ps (_ ∷ʳ qs) (_  rs) = cong (_ ∷ʳ_) (⊆-trans-assoc ps qs rs)
  ⊆-trans-assoc (_ ∷ʳ ps) (_  qs) (_  rs) = cong (_ ∷ʳ_) (⊆-trans-assoc ps qs rs)
  ⊆-trans-assoc (p  ps) (q  qs) (r  rs) = cong₂ _∷_ (≈-assoc p q r) (⊆-trans-assoc ps qs rs)
  ⊆-trans-assoc [] [] [] = refl


------------------------------------------------------------------------
-- Various functions' outputs are sublists
------------------------------------------------------------------------

tail-⊆ :  xs  Maybe.All (_⊆ xs) (tail xs)
tail-⊆ xs = HeteroProperties.tail-Sublist ⊆-refl

take-⊆ :  n xs  take n xs  xs
take-⊆ n xs = HeteroProperties.take-Sublist n ⊆-refl

drop-⊆ :  n xs  drop n xs  xs
drop-⊆ n xs = HeteroProperties.drop-Sublist n ⊆-refl

module _ (P? : Decidable P) where

  takeWhile-⊆ :  xs  takeWhile P? xs  xs
  takeWhile-⊆ xs = HeteroProperties.takeWhile-Sublist P? ⊆-refl

  dropWhile-⊆ :  xs  dropWhile P? xs  xs
  dropWhile-⊆ xs = HeteroProperties.dropWhile-Sublist P? ⊆-refl

  filter-⊆ :  xs  filter P? xs  xs
  filter-⊆ xs = HeteroProperties.filter-Sublist P? ⊆-refl

module _ (P? : Decidable P) where

  takeWhile⊆filter :  xs  takeWhile P? xs  filter P? xs
  takeWhile⊆filter xs = HeteroProperties.takeWhile-filter P? {xs} ≋-refl

  filter⊆dropWhile :  xs  filter P? xs  dropWhile (¬?  P?) xs
  filter⊆dropWhile xs = HeteroProperties.filter-dropWhile P? {xs} ≋-refl

------------------------------------------------------------------------
-- Various list functions are increasing wrt _⊆_
------------------------------------------------------------------------
-- We write f⁺ for the proof that `xs ⊆ ys → f xs ⊆ f ys`
-- and f⁻ for the one that `f xs ⊆ f ys → xs ⊆ ys`.

module _ where

  ∷ˡ⁻ : a  as  bs  as  bs
  ∷ˡ⁻ = HeteroProperties.∷ˡ⁻

  ∷ʳ⁻ : ¬ (a  b)  a  as  b  bs  a  as  bs
  ∷ʳ⁻ = HeteroProperties.∷ʳ⁻

  ∷⁻ : a  as  b  bs  as  bs
  ∷⁻ = HeteroProperties.∷⁻

------------------------------------------------------------------------
-- map

module _ {b } (R : Setoid b ) where

  open Setoid R using () renaming (Carrier to B; _≈_ to _≈′_)
  open SetoidSublist R using () renaming (_⊆_ to _⊆′_)

  map⁺ :  {as bs} {f : A  B}  f Preserves _≈_  _≈′_ 
         as  bs  map f as ⊆′ map f bs
  map⁺ {f = f} f-resp as⊆bs =
    HeteroProperties.map⁺ f f (SetoidSublist.map S f-resp as⊆bs)

------------------------------------------------------------------------
-- _++_

module _ where

  ++⁺ˡ :  cs  as  bs  as  cs ++ bs
  ++⁺ˡ = HeteroProperties.++ˡ

  ++⁺ʳ :  cs  as  bs  as  bs ++ cs
  ++⁺ʳ = HeteroProperties.++ʳ

  ++⁺ : as  bs  cs  ds  as ++ cs  bs ++ ds
  ++⁺ = HeteroProperties.++⁺

  ++⁻ : length as  length bs  as ++ cs  bs ++ ds  cs  ds
  ++⁻ = HeteroProperties.++⁻

------------------------------------------------------------------------
-- take

module _ where

  take⁺ : m  n  take m xs  take n xs
  take⁺ m≤n = HeteroProperties.take⁺ m≤n ≋-refl

------------------------------------------------------------------------
-- drop

module _ where

  drop⁺ : m  n  xs  ys  drop m xs  drop n ys
  drop⁺ = HeteroProperties.drop⁺

module _ where

  drop⁺-≥ : m  n  drop m xs  drop n xs
  drop⁺-≥ m≥n = drop⁺ m≥n ⊆-refl

module _ where

  drop⁺-⊆ :  n  xs  ys  drop n xs  drop n ys
  drop⁺-⊆ n xs⊆ys = drop⁺ {n} ℕ.≤-refl xs⊆ys

------------------------------------------------------------------------
-- takeWhile / dropWhile

module _ (P? : Decidable P) (Q? : Decidable Q) where

  takeWhile⁺ :  {xs}  (∀ {a b}  a  b  P a  Q b) 
               takeWhile P? xs  takeWhile Q? xs
  takeWhile⁺ {xs} P⇒Q = HeteroProperties.⊆-takeWhile-Sublist P? Q? {xs} P⇒Q ≋-refl

  dropWhile⁺ :  {xs}  (∀ {a b}  a  b  Q b  P a) 
               dropWhile P? xs  dropWhile Q? xs
  dropWhile⁺ {xs} P⇒Q = HeteroProperties.⊇-dropWhile-Sublist P? Q? {xs} P⇒Q ≋-refl

------------------------------------------------------------------------
-- filter

module _ (P? : Decidable P) (Q? : Decidable Q) where

  filter⁺ : (∀ {a b}  a  b  P a  Q b) 
            as  bs  filter P? as  filter Q? bs
  filter⁺ = HeteroProperties.⊆-filter-Sublist P? Q?

------------------------------------------------------------------------
-- reverse

module _ where

  reverseAcc⁺ : as  bs  cs  ds 
                reverseAcc cs as  reverseAcc ds bs
  reverseAcc⁺ = HeteroProperties.reverseAcc⁺

  ʳ++⁺ : as  bs  cs  ds 
         as ʳ++ cs  bs ʳ++ ds
  ʳ++⁺ = reverseAcc⁺

  reverse⁺ : as  bs  reverse as  reverse bs
  reverse⁺ = HeteroProperties.reverse⁺

  reverse⁻ : reverse as  reverse bs  as  bs
  reverse⁻ = HeteroProperties.reverse⁻

------------------------------------------------------------------------
-- merge

module _ {ℓ′} {_≤_ : Rel A ℓ′} (_≤?_ : Decidable₂ _≤_) where

  ⊆-mergeˡ :  xs ys  xs  merge _≤?_ xs ys
  ⊆-mergeˡ []       ys = minimum ys
  ⊆-mergeˡ (x  xs) [] = ⊆-refl
  ⊆-mergeˡ (x  xs) (y  ys)
   with x ≤? y  | ⊆-mergeˡ xs (y  ys)
                      | ⊆-mergeˡ (x  xs) ys
  ... | yes x≤y | rec | _   = ≈-refl  rec
  ... | no  x≰y | _   | rec = y ∷ʳ rec

  ⊆-mergeʳ :  xs ys  ys  merge _≤?_ xs ys
  ⊆-mergeʳ [] ys =  ⊆-refl
  ⊆-mergeʳ (x  xs) [] = minimum (merge _≤?_ (x  xs) [])
  ⊆-mergeʳ (x  xs) (y  ys)
   with x ≤? y  | ⊆-mergeʳ xs (y  ys)
                      | ⊆-mergeʳ (x  xs) ys
  ... | yes x≤y | rec | _   = x ∷ʳ rec
  ... | no  x≰y | _   | rec = ≈-refl  rec

------------------------------------------------------------------------
-- Inversion lemmas
------------------------------------------------------------------------

module _ where

  ∷⁻¹ : a  b  as  bs  a  as  b  bs
  ∷⁻¹ = HeteroProperties.∷⁻¹

  ∷ʳ⁻¹ : ¬ (a  b)  a  as  bs  a  as  b  bs
  ∷ʳ⁻¹ = HeteroProperties.∷ʳ⁻¹

------------------------------------------------------------------------
-- Other
------------------------------------------------------------------------

module _ where

  length-mono-≤ : as  bs  length as  length bs
  length-mono-≤ = HeteroProperties.length-mono-≤

------------------------------------------------------------------------
-- Conversion to and from list equality

  to-≋ : length as  length bs  as  bs  as  bs
  to-≋ = HeteroProperties.toPointwise

------------------------------------------------------------------------
-- Irrelevant special case

  []⊆-irrelevant : Irrelevant ([] ⊆_)
  []⊆-irrelevant = HeteroProperties.Sublist-[]-irrelevant

------------------------------------------------------------------------
-- (to/from)∈ is a bijection

module _ where

  to∈-injective :  {p q : [ x ]  xs}  to∈ p  to∈ q  p  q
  to∈-injective = HeteroProperties.toAny-injective

  from∈-injective :  {p q : x  xs}  from∈ p  from∈ q  p  q
  from∈-injective = HeteroProperties.fromAny-injective

  to∈∘from∈≗id :  (p : x  xs)  to∈ (from∈ p)  p
  to∈∘from∈≗id = HeteroProperties.toAny∘fromAny≗id

  [x]⊆xs⤖x∈xs : ([ x ]  xs)  (x  xs)
  [x]⊆xs⤖x∈xs = HeteroProperties.Sublist-[x]-bijection

------------------------------------------------------------------------
-- Properties of Disjoint(ness) and DisjointUnion

open HeteroProperties.Disjointness {R = _≈_} public
open HeteroProperties.DisjointnessMonotonicity {R = _≈_} {S = _≈_} {T = _≈_} trans public

-- Shrinking one of two disjoint lists preserves disjointness.

-- We would have liked to define  shrinkDisjointˡ σ = shrinkDisjoint σ ⊆-refl
-- but alas, this is only possible for groupoids, not setoids in general.

shrinkDisjointˡ :  {xs ys zs us} {τ₁ : xs  zs} {τ₂ : ys  zs} (σ : us  xs) 
    Disjoint τ₁ τ₂ 
    Disjoint (⊆-trans σ τ₁) τ₂
-- Not affected by σ:
shrinkDisjointˡ σ          (y   ∷ₙ d) = y             ∷ₙ shrinkDisjointˡ σ d
shrinkDisjointˡ σ          (y≈z ∷ᵣ d) = y≈z           ∷ᵣ shrinkDisjointˡ σ d
-- In σ: keep x.
shrinkDisjointˡ (u≈x  σ)  (x≈z ∷ₗ d) = trans u≈x x≈z ∷ₗ shrinkDisjointˡ σ d
-- Not in σ: drop x.
shrinkDisjointˡ (x  ∷ʳ σ)  (x≈z ∷ₗ d) = _             ∷ₙ shrinkDisjointˡ σ d
shrinkDisjointˡ []         []         = []

shrinkDisjointʳ :  {xs ys zs vs} {τ₁ : xs  zs} {τ₂ : ys  zs} (σ : vs  ys) 
  Disjoint τ₁ τ₂ 
  Disjoint τ₁ (⊆-trans σ τ₂)
-- Not affected by σ:
shrinkDisjointʳ σ          (y   ∷ₙ d) = y             ∷ₙ shrinkDisjointʳ σ d
shrinkDisjointʳ σ          (x≈z ∷ₗ d) = x≈z           ∷ₗ shrinkDisjointʳ σ d
-- In σ: keep y.
shrinkDisjointʳ (v≈y  σ)  (y≈z ∷ᵣ d) = trans v≈y y≈z ∷ᵣ shrinkDisjointʳ σ d
-- Not in σ: drop y.
shrinkDisjointʳ (y  ∷ʳ σ)  (y≈z ∷ᵣ d) = _             ∷ₙ shrinkDisjointʳ σ d
shrinkDisjointʳ []         []         = []