------------------------------------------------------------------------
-- The Agda standard library
--
-- Sum combinators for propositional equality preserving functions
------------------------------------------------------------------------

{-# OPTIONS --without-K --safe #-}

module Data.Sum.Function.Propositional where

open import Data.Sum
open import Data.Sum.Function.Setoid
open import Data.Sum.Relation.Binary.Pointwise using (Pointwise-≡↔≡)
open import Function.Equivalence as Eq using (_⇔_; module Equivalence)
open import Function.Injection as Inj using (_↣_; module Injection)
open import Function.Inverse as Inv using (_↔_; module Inverse)
open import Function.LeftInverse as LeftInv
  using (_↞_; _LeftInverseOf_; module LeftInverse)
open import Function.Related
open import Function.Surjection as Surj using (_↠_; module Surjection)

------------------------------------------------------------------------
-- Combinators for various function types

module _ {a b c d} {A : Set a} {B : Set b} {C : Set c} {D : Set d} where

  _⊎-⇔_ : A ⇔ B → C ⇔ D → (A ⊎ C) ⇔ (B ⊎ D)
  _⊎-⇔_ A⇔B C⇔D =
    Inverse.equivalence (Pointwise-≡↔≡ B D) ⟨∘⟩
    (A⇔B ⊎-equivalence C⇔D) ⟨∘⟩
    Eq.sym (Inverse.equivalence (Pointwise-≡↔≡ A C))
    where open Eq using () renaming (_∘_ to _⟨∘⟩_)

  _⊎-↣_ : A ↣ B → C ↣ D → (A ⊎ C) ↣ (B ⊎ D)
  _⊎-↣_ A↣B C↣D =
    Inverse.injection (Pointwise-≡↔≡ B D) ⟨∘⟩
    (A↣B ⊎-injection C↣D) ⟨∘⟩
    Inverse.injection (Inv.sym (Pointwise-≡↔≡ A C))
    where open Inj using () renaming (_∘_ to _⟨∘⟩_)

  _⊎-↞_ : A ↞ B → C ↞ D → (A ⊎ C) ↞ (B ⊎ D)
  _⊎-↞_ A↞B C↞D =
    Inverse.left-inverse (Pointwise-≡↔≡ B D) ⟨∘⟩
    (A↞B ⊎-left-inverse C↞D) ⟨∘⟩
    Inverse.left-inverse (Inv.sym (Pointwise-≡↔≡ A C))
    where open LeftInv using () renaming (_∘_ to _⟨∘⟩_)

  _⊎-↠_ : A ↠ B → C ↠ D → (A ⊎ C) ↠ (B ⊎ D)
  _⊎-↠_ A↠B C↠D =
    Inverse.surjection (Pointwise-≡↔≡ B D) ⟨∘⟩
    (A↠B ⊎-surjection C↠D) ⟨∘⟩
    Inverse.surjection (Inv.sym (Pointwise-≡↔≡ A C))
    where open Surj using () renaming (_∘_ to _⟨∘⟩_)

  _⊎-↔_ : A ↔ B → C ↔ D → (A ⊎ C) ↔ (B ⊎ D)
  _⊎-↔_ A↔B C↔D =
    Pointwise-≡↔≡ B D ⟨∘⟩
    (A↔B ⊎-inverse C↔D) ⟨∘⟩
    Inv.sym (Pointwise-≡↔≡ A C)
    where open Inv using () renaming (_∘_ to _⟨∘⟩_)

module _ {a b c d} {A : Set a} {B : Set b} {C : Set c} {D : Set d} where

  _⊎-cong_ : ∀ {k} → A ∼[ k ] B → C ∼[ k ] D → (A ⊎ C) ∼[ k ] (B ⊎ D)
  _⊎-cong_ {implication}         = map
  _⊎-cong_ {reverse-implication} = λ f g → lam (map (app-← f) (app-← g))
  _⊎-cong_ {equivalence}         = _⊎-⇔_
  _⊎-cong_ {injection}           = _⊎-↣_
  _⊎-cong_ {reverse-injection}   = λ f g → lam (app-↢ f ⊎-↣ app-↢ g)
  _⊎-cong_ {left-inverse}        = _⊎-↞_
  _⊎-cong_ {surjection}          = _⊎-↠_
  _⊎-cong_ {bijection}           = _⊎-↔_