module A201801.List where

open import A201801.Prelude
open import A201801.Category
open import A201801.Fin


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data List (X : Set) : Set
  where
    ∙   : List X
    _,_ : List X → X → List X


len : ∀ {X} → List X
            → Nat
len ∙       = zero
len (Ξ , A) = suc (len Ξ)


map : ∀ {X Y} → (X → Y) → List X
              → List Y
map f ∙       = ∙
map f (Ξ , A) = map f Ξ , f A


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inj,₁ : ∀ {X A₁ A₂} → {Ξ₁ Ξ₂ : List X}
                    → Ξ₁ List., A₁ ≡ Ξ₂ , A₂
                    → Ξ₁ ≡ Ξ₂
inj,₁ refl = refl


inj,₂ : ∀ {X A₁ A₂} → {Ξ₁ Ξ₂ : List X}
                    → Ξ₁ List., A₁ ≡ Ξ₂ , A₂
                    → A₁ ≡ A₂
inj,₂ refl = refl


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GET : ∀ {X n} → (Ξ : List X) {{_ : len Ξ ≡ n}} → Fin n
              → X
GET ∙       {{refl}} ()
GET (Ξ , A) {{refl}} zero    = A
GET (Ξ , B) {{refl}} (suc I) = GET Ξ I


GETS : ∀ {X n n′} → (Ξ : List X) {{_ : len Ξ ≡ n′}} → n′ ≥ n
                  → List X
GETS ∙       {{refl}} done     = ∙
GETS (Ξ , B) {{refl}} (drop e) = GETS Ξ e
GETS (Ξ , A) {{refl}} (keep e) = GETS Ξ e , A


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infix  _⊇_
data _⊇_ {X} : List X → List X → Set
  where
    done : ∙ ⊇ ∙

    drop : ∀ {A Ξ Ξ′} → Ξ′ ⊇ Ξ
                      → Ξ′ , A ⊇ Ξ

    keep : ∀ {A Ξ Ξ′} → Ξ′ ⊇ Ξ
                      → Ξ′ , A ⊇ Ξ , A


bot⊇ : ∀ {X} → {Ξ : List X}
             → Ξ ⊇ ∙
bot⊇ {Ξ = ∙}     = done
bot⊇ {Ξ = Ξ , A} = drop bot⊇


id⊇ : ∀ {X} → {Ξ : List X}
            → Ξ ⊇ Ξ
id⊇ {Ξ = ∙}     = done
id⊇ {Ξ = Ξ , A} = keep id⊇


_∘⊇_ : ∀ {X} → {Ξ Ξ′ Ξ″ : List X}
             → Ξ′ ⊇ Ξ → Ξ″ ⊇ Ξ′
             → Ξ″ ⊇ Ξ
η₁      ∘⊇ done    = η₁
η₁      ∘⊇ drop η₂ = drop (η₁ ∘⊇ η₂)
drop η₁ ∘⊇ keep η₂ = drop (η₁ ∘⊇ η₂)
keep η₁ ∘⊇ keep η₂ = keep (η₁ ∘⊇ η₂)


-- TODO: Remove this

-- map⊇ : ∀ {X Y} → {Ξ Ξ′ : List X} {f : X → Y}
--                → Ξ′ ⊇ Ξ
--                → map f Ξ′ ⊇ map f Ξ
-- map⊇ done     = done
-- map⊇ (drop η) = drop (map⊇ η)
-- map⊇ (keep η) = keep (map⊇ η)


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infix  _∋_
data _∋_ {X} : List X → X → Set
  where
    zero : ∀ {Ξ A} → Ξ , A ∋ A

    suc : ∀ {B Ξ A} → Ξ ∋ A
                    → Ξ , B ∋ A


ren∋ : ∀ {X A} → {Ξ Ξ′ : List X}
               → Ξ′ ⊇ Ξ → Ξ ∋ A
               → Ξ′ ∋ A
ren∋ done     i       = i
ren∋ (drop η) i       = suc (ren∋ η i)
ren∋ (keep η) zero    = zero
ren∋ (keep η) (suc i) = suc (ren∋ η i)


-- TODO: Remove this

-- map∋ : ∀ {X Y A} → {Ξ : List X} {f : X → Y}
--                  → Ξ ∋ A
--                  → map f Ξ ∋ f A
-- map∋ zero    = zero
-- map∋ (suc i) = suc (map∋ i)


--------------------------------------------------------------------------------


-- TODO: Remove this

module List²
  where
    List² : Set → Set → Set
    List² X Y = List X × List Y


    infix  _⨾_
    pattern _⨾_ Δ Γ = _,_ Δ Γ


    infix  _⊇²_
    _⊇²_ : ∀ {X Y} → List² X Y → List² X Y → Set
    Δ′ ⨾ Γ′ ⊇² Δ ⨾ Γ = Δ′ ⊇ Δ × Γ′ ⊇ Γ


    drop₁ : ∀ {X Y A} → {Δ Δ′ : List X} {Γ Γ′ : List Y}
                      → Δ′ ⨾ Γ′ ⊇² Δ ⨾ Γ
                      → Δ′ , A ⨾ Γ′ ⊇² Δ ⨾ Γ
    drop₁ (η₁ , η₂) = drop η₁ , η₂


    drop₂ : ∀ {X Y A} → {Δ Δ′ : List X} {Γ Γ′ : List Y}
                      → Δ′ ⨾ Γ′ ⊇² Δ ⨾ Γ
                      → Δ′ ⨾ Γ′ , A ⊇² Δ ⨾ Γ
    drop₂ (η₁ , η₂) = η₁ , drop η₂


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