------------------------------------------------------------------------
-- Extraction of WHNF from algorithmic equality of types in WHNF.
------------------------------------------------------------------------

open import Definition.Typed.Restrictions
open import Graded.Modality

module Definition.Conversion.Whnf
  {a} {M : Set a}
  {𝕄 : Modality M}
  (R : Type-restrictions 𝕄)
  where

open Type-restrictions R

open import Definition.Untyped M
open import Definition.Untyped.Neutral M type-variant
open import Definition.Untyped.Whnf M type-variant
open import Definition.Conversion R

open import Tools.Nat
open import Tools.Product as Σ
import Tools.PropositionalEquality as PE

private
  variable
    m n : Nat
    ∇ : DCon (Term ) m
    Γ : Con Term n
    t : Term _
    V : Set a

opaque

  ne↑ₗ :
    ⦃ not : No-equality-reflection ⦄ →
    Neutral V ∇ t → Neutral No-equality-reflection ∇ t
  ne↑ₗ ⦃ not ⦄ = ne→ (λ _ → not)

mutual
  -- Extraction of neutrality from algorithmic equality of neutrals.
  ne~↑ : ∀ {t u A}
       → ∇ » Γ ⊢ t ~ u ↑ A
       → Neutral⁺ ∇ t × Neutral⁺ ∇ u
  ne~↑ (var-refl x₁ x≡y) = var⁺ _ , var⁺ _
  ne~↑ (defn-refl ⊢α α↦⊘ α≡β) =
    defn α↦⊘ , defn (PE.subst (_↦⊘∷ _ ∈ _) α≡β α↦⊘)
  ne~↑ (app-cong x x₁) = let _ , q , w = ne~↓ x
                         in  ∘ₙ q , ∘ₙ w
  ne~↑ (fst-cong x) =
    let _ , pNe , rNe = ne~↓ x
    in  fstₙ pNe , fstₙ rNe
  ne~↑ (snd-cong x) =
    let _ , pNe , rNe = ne~↓ x
    in  sndₙ pNe , sndₙ rNe
  ne~↑ (natrec-cong x x₁ x₂ x₃) = let _ , q , w = ne~↓ x₃
                                  in  natrecₙ q , natrecₙ w
  ne~↑ (prodrec-cong _ g~h _) =
    let _ , gNe , hNe = ne~↓ g~h
    in  prodrecₙ gNe , prodrecₙ hNe
  ne~↑ (emptyrec-cong x x₁) = let _ , q , w = ne~↓ x₁
                              in emptyrecₙ q , emptyrecₙ w
  ne~↑ (unitrec-cong _ k~l _ no-η) =
    let _ , kNe , lNe = ne~↓ k~l
    in  unitrecₙ no-η kNe , unitrecₙ no-η lNe
  ne~↑ (J-cong _ _ _ _ _ w₁~w₂ _) =
    Σ.map Jₙ Jₙ (ne~↓ w₁~w₂ .proj₂)
  ne~↑ (K-cong _ _ _ _ v₁~v₂ _ _) =
    Σ.map Kₙ Kₙ (ne~↓ v₁~v₂ .proj₂)
  ne~↑ ([]-cong-cong _ _ _ v₁~v₂ _ _) =
    Σ.map []-congₙ []-congₙ (ne~↓ v₁~v₂ .proj₂)

  -- Extraction of neutrality and WHNF from algorithmic equality of neutrals
  -- with type in WHNF.
  ne~↓ : ∀ {t u A}
       → ∇ » Γ ⊢ t ~ u ↓ A
       → Whnf ∇ A × Neutral⁺ ∇ t × Neutral⁺ ∇ u
  ne~↓ ([~] _ (_ , whnfB) k~l) = whnfB , ne~↑ k~l

-- Extraction of WHNF from algorithmic equality of types in WHNF.
whnfConv↓ : ∀ {A B}
          → ∇ » Γ ⊢ A [conv↓] B
          → Whnf ∇ A × Whnf ∇ B
whnfConv↓ (U-refl x) = Uₙ , Uₙ
whnfConv↓ (ℕ-refl x) = ℕₙ , ℕₙ
whnfConv↓ (Empty-refl x) = Emptyₙ , Emptyₙ
whnfConv↓ (Unit-refl x _) = Unitₙ , Unitₙ
whnfConv↓ (ne x) = let _ , neA , neB = ne~↓ x
                   in  ne-whnf neA , ne-whnf neB
whnfConv↓ (ΠΣ-cong _ _ _) = ΠΣₙ , ΠΣₙ
whnfConv↓ (Id-cong _ _ _) = Idₙ , Idₙ

-- Extraction of WHNF from algorithmic equality of terms in WHNF.
whnfConv↓Term : ∀ {t u A}
              → ∇ » Γ ⊢ t [conv↓] u ∷ A
              → Whnf ∇ A × Whnf ∇ t × Whnf ∇ u
whnfConv↓Term (ℕ-ins x) = let _ , neT , neU = ne~↓ x
                           in ℕₙ , ne-whnf neT , ne-whnf neU
whnfConv↓Term (Empty-ins x) = let _ , neT , neU = ne~↓ x
                              in Emptyₙ , ne-whnf neT , ne-whnf neU
whnfConv↓Term (Unitʷ-ins _ t~u) =
  let _ , t-ne , u-ne = ne~↓ t~u in
  Unitₙ , ne-whnf t-ne , ne-whnf u-ne
whnfConv↓Term (Σʷ-ins x x₁ x₂) =
  let _ , neT , neU = ne~↓ x₂
  in  ΠΣₙ , ne-whnf neT , ne-whnf neU
whnfConv↓Term (ne-ins t u x x₁) =
  let _ , neT , neU = ne~↓ x₁
  in ne-whnf x , ne-whnf neT , ne-whnf neU
whnfConv↓Term (univ x x₁ x₂) = Uₙ , whnfConv↓ x₂
whnfConv↓Term (zero-refl x) = ℕₙ , zeroₙ , zeroₙ
whnfConv↓Term (starʷ-refl _ _ _) = Unitₙ , starₙ , starₙ
whnfConv↓Term (suc-cong x) = ℕₙ , sucₙ , sucₙ
whnfConv↓Term (prod-cong _ _ _ _) = ΠΣₙ , prodₙ , prodₙ
whnfConv↓Term (η-eq x₁ x₂ y y₁ x₃) = ΠΣₙ , functionWhnf y , functionWhnf y₁
whnfConv↓Term (Σ-η _ _ pProd rProd _ _) = ΠΣₙ , productWhnf pProd , productWhnf rProd
whnfConv↓Term (η-unit _ _ tWhnf uWhnf _) = Unitₙ , tWhnf , uWhnf
whnfConv↓Term (Id-ins _ v₁~v₂) =
  Idₙ , Σ.map ne-whnf ne-whnf (ne~↓ v₁~v₂ .proj₂)
whnfConv↓Term (rfl-refl _) =
  Idₙ , rflₙ , rflₙ