module A201706.IS4NormalisationNoTerms where

open import A201706.IS4SemanticsNoTerms public


-- Absolute values.

infix  _⊨_
_⊨_ : Cx → Ty → Set₁
Δ ⁏ Γ ⊨ A = ∀ {{_ : Model}} {w : World} →
               (∀ {w′ : World} → w′ Я w → w′ ⟪⊢⟫⋆ Δ) →
               (∀ {w′ : World} → w′ Я w → w′ ⟪⊩⟫⋆ Δ) →
               w ⊩⋆ Γ →
               w ⊩ A


-- Soundness.

⟦_⟧ : ∀ {Δ Γ A} → Δ ⁏ Γ ⊢ A → Δ ⁏ Γ ⊨ A
⟦ var 𝒾 ⟧                 δ₁ δ₂ γ = lookup⊩ γ 𝒾
⟦ mvar 𝒾 ⟧                δ₁ δ₂ γ = mlookup⟪⊩⟫ (δ₂ reflЯ) 𝒾
⟦ lam {A = A} {B} 𝒟 ⟧     δ₁ δ₂ γ = return {A ⇒ B}
                                      λ θ a →
                                        ⟦ 𝒟 ⟧ (λ ζ → δ₁ (transЯ ζ (⊒→Я θ)))
                                              (λ ζ → δ₂ (transЯ ζ (⊒→Я θ)))
                                              (mono⊩⋆ θ γ , a)
⟦ app {A = A} {B} 𝒟 ℰ ⟧   δ₁ δ₂ γ = bind {A ⇒ B} {B} (⟦ 𝒟 ⟧ δ₁ δ₂ γ)
                                      λ θ f →
                                        f refl⊒ (mono⊩ {A} θ (⟦ ℰ ⟧ δ₁ δ₂ γ))
⟦ box {A = A} 𝒟 ⟧         δ₁ δ₂ γ = return {□ A}
                                      λ ζ →
                                        mgraft⟨⊢⟩ (δ₁ ζ) 𝒟 ,
                                        ⟦ 𝒟 ⟧ (λ ζ′ → δ₁ (transЯ ζ′ ζ))
                                              (λ ζ′ → δ₂ (transЯ ζ′ ζ))
                                              ∅
⟦ unbox {A = A} {C} 𝒟 ℰ ⟧ δ₁ δ₂ γ = bind {□ A} {C} (⟦ 𝒟 ⟧ δ₁ δ₂ γ)
                                      λ θ q →
                                        ⟦ ℰ ⟧ (λ ζ → δ₁ (transЯ ζ (⊒→Я θ)) , π₁ (q ζ))
                                              (λ ζ → δ₂ (transЯ ζ (⊒→Я θ)) , π₂ (q ζ))
                                              (mono⊩⋆ θ γ)


-- Canonical model.

instance
  canon : Model
  canon = record
    { World  = Cx
    ; _⊒_    = λ { (Δ′ ⁏ Γ′) (Δ ⁏ Γ) → Δ′ ⊇ Δ ∧ Γ′ ⊇ Γ }
    ; refl⊒  = refl⊇ , refl⊇
    ; trans⊒ = λ { (ζ′ , η′) (ζ , η) → trans⊇ ζ′ ζ , trans⊇ η′ η }
    ; _Я_    = λ { (Δ′ ⁏ Γ′) (Δ ⁏ Γ) → Δ′ ⊇ Δ }
    ; reflЯ  = refl⊇
    ; transЯ = trans⊇
    ; G      = _⊢ⁿᵉ •
    ; monoG  = λ { (ζ , η) 𝒟 → mono⊢ⁿᵉ ζ η 𝒟 }
    ; ⊒→Я   = π₁
    ; peek   = id
    }

mutual
  reifyᶜ : ∀ {A Δ Γ} → Δ ⁏ Γ ⊩ A → Δ ⁏ Γ ⊢ⁿᶠ A
  reifyᶜ {•}      κ = κ (refl⊇ , refl⊇)
                        λ θ a →
                          neⁿᶠ a
  reifyᶜ {A ⇒ B} κ = κ (refl⊇ , refl⊇)
                        λ θ f →
                          lamⁿᶠ (reifyᶜ (f (refl⊇ , weak refl⊇) ⟦ varⁿᵉ zero ⟧ᶜ))
  reifyᶜ {□ A}    κ = κ (refl⊇ , refl⊇)
                        λ {w″} θ q →
                          boxⁿᶠ (π₁ (q {w′ = w″} refl⊇))

  ⟦_⟧ᶜ : ∀ {A Δ Γ} → Δ ⁏ Γ ⊢ⁿᵉ A → Δ ⁏ Γ ⊩ A
  ⟦_⟧ᶜ {•}      𝒟 = return {•} 𝒟
  ⟦_⟧ᶜ {A ⇒ B} 𝒟 = return {A ⇒ B}
                      λ { (ζ , η) a →
                        ⟦ appⁿᵉ (mono⊢ⁿᵉ ζ η 𝒟) (reifyᶜ a) ⟧ᶜ }
  ⟦_⟧ᶜ {□ A}    𝒟 = λ { (ζ , η) κ →
                      neⁿᶠ (unboxⁿᵉ (mono⊢ⁿᵉ ζ η 𝒟)
                                    (κ (weak refl⊇ , refl⊇)
                                       λ ζ′ →
                                         mvar (mono∋ ζ′ zero) ,
                                         ⟦ mvarⁿᵉ (mono∋ ζ′ zero) ⟧ᶜ)) }


-- TODO: Needs a name.

refl⊩⋆ : ∀ {Γ : Ty⋆} {Δ : BoxTy⋆} → Δ ⁏ Γ ⊩⋆ Γ
refl⊩⋆ {∅}     = ∅
refl⊩⋆ {Γ , A} = mono⊩⋆ (refl⊇ , weak refl⊇) refl⊩⋆ , ⟦ varⁿᵉ zero ⟧ᶜ

mrefl⟪⊩⟫⋆ : ∀ {Δ : BoxTy⋆} {Γ : Ty⋆} → Δ ⁏ Γ ⟪⊩⟫⋆ Δ
mrefl⟪⊩⟫⋆ {∅}       = ∅
mrefl⟪⊩⟫⋆ {Δ , □ A} = mono⟪⊩⟫⋆ (weak refl⊇ , refl⊇) mrefl⟪⊩⟫⋆ , ⟦ mvarⁿᵉ zero ⟧ᶜ


-- Completeness.

reify : ∀ {Δ Γ A} → Δ ⁏ Γ ⊨ A → Δ ⁏ Γ ⊢ⁿᶠ A
reify 𝔞 = reifyᶜ (𝔞 (λ ζ → mono⟨⊢⟩⋆ ζ mrefl⟨⊢⟩⋆)
                    (λ ζ → mono⟪⊩⟫⋆ (ζ , refl⊇) mrefl⟪⊩⟫⋆)
                    refl⊩⋆)


-- Normalisation.

nbe : ∀ {Δ Γ A} → Δ ⁏ Γ ⊢ A → Δ ⁏ Γ ⊢ⁿᶠ A
nbe = reify ∘ ⟦_⟧