------------------------------------------------------------------------
-- The Agda standard library
--
-- The identity function
------------------------------------------------------------------------

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

module Function.Construct.Identity where

open import Data.Product using (_,_)
open import Function.Base using (id)
open import Function.Bundles
import Function.Definitions as Definitions
import Function.Structures as Structures
open import Level
open import Relation.Binary as B hiding (_⇔_; IsEquivalence)
open import Relation.Binary.PropositionalEquality using (_≡_; setoid)

private
  variable
    a ℓ : Level
    A : Set a

------------------------------------------------------------------------
-- Properties

module _ (_≈_ : Rel A ℓ) where

  open Definitions _≈_ _≈_

  congruent : Congruent id
  congruent = id

  injective : Injective id
  injective = id

  surjective : Reflexive _≈_ → Surjective id
  surjective refl x = x , refl

  bijective : Reflexive _≈_ → Bijective id
  bijective refl = injective , surjective refl

  inverseˡ : Reflexive _≈_ → Inverseˡ id id
  inverseˡ refl x = refl

  inverseʳ : Reflexive _≈_ → Inverseʳ id id
  inverseʳ refl x = refl

  inverseᵇ : Reflexive _≈_ → Inverseᵇ id id
  inverseᵇ refl = inverseˡ refl , inverseʳ refl

------------------------------------------------------------------------
-- Structures

module _ {_≈_ : Rel A ℓ} (isEq : B.IsEquivalence _≈_) where

  open Structures _≈_ _≈_
  open B.IsEquivalence isEq

  isCongruent : IsCongruent id
  isCongruent = record
    { cong           = id
    ; isEquivalence₁ = isEq
    ; isEquivalence₂ = isEq
    }

  isInjection : IsInjection id
  isInjection = record
    { isCongruent = isCongruent
    ; injective   = injective _≈_
    }

  isSurjection : IsSurjection id
  isSurjection = record
    { isCongruent = isCongruent
    ; surjective  = surjective _≈_ refl
    }

  isBijection : IsBijection id
  isBijection = record
    { isInjection = isInjection
    ; surjective  = surjective _≈_ refl
    }

  isLeftInverse : IsLeftInverse id id
  isLeftInverse = record
    { isCongruent = isCongruent
    ; cong₂       = id
    ; inverseˡ    = inverseˡ _≈_ refl
    }

  isRightInverse : IsRightInverse id id
  isRightInverse = record
    { isCongruent = isCongruent
    ; cong₂       = id
    ; inverseʳ    = inverseʳ _≈_ refl
    }

  isInverse : IsInverse id id
  isInverse = record
    { isLeftInverse = isLeftInverse
    ; inverseʳ      = inverseʳ _≈_ refl
    }

------------------------------------------------------------------------
-- Setoid bundles

module _ (S : Setoid a ℓ) where

  open Setoid S

  function : Func S S
  function = record
    { f    = id
    ; cong = id
    }

  injection : Injection S S
  injection = record
    { f         = id
    ; cong      = id
    ; injective = injective _≈_
    }

  surjection : Surjection S S
  surjection = record
    { f          = id
    ; cong       = id
    ; surjective = surjective _≈_ refl
    }

  bijection : Bijection S S
  bijection = record
    { f         = id
    ; cong      = id
    ; bijective = bijective _≈_ refl
    }

  equivalence : Equivalence S S
  equivalence = record
    { f     = id
    ; g     = id
    ; cong₁ = id
    ; cong₂ = id
    }

  leftInverse : LeftInverse S S
  leftInverse = record
    { f        = id
    ; g        = id
    ; cong₁    = id
    ; cong₂    = id
    ; inverseˡ = inverseˡ _≈_ refl
    }

  rightInverse : RightInverse S S
  rightInverse = record
    { f        = id
    ; g        = id
    ; cong₁    = id
    ; cong₂    = id
    ; inverseʳ = inverseʳ _≈_ refl
    }

  inverse : Inverse S S
  inverse = record
    { f       = id
    ; f⁻¹     = id
    ; cong₁   = id
    ; cong₂   = id
    ; inverse = inverseᵇ _≈_ refl
    }

------------------------------------------------------------------------
-- Propositional bundles

module _ (A : Set a) where

  ⟶-id : A ⟶ A
  ⟶-id = function (setoid A)

  ↣-id : A ↣ A
  ↣-id = injection (setoid A)

  ↠-id : A ↠ A
  ↠-id = surjection (setoid A)

  ⤖-id : A ⤖ A
  ⤖-id = bijection (setoid A)

  ⇔-id : A ⇔ A
  ⇔-id = equivalence (setoid A)

  ↩-id : A ↩ A
  ↩-id = leftInverse (setoid A)

  ↪-id : A ↪ A
  ↪-id = rightInverse (setoid A)

  ↔-id : A ↔ A
  ↔-id = inverse (setoid A)


------------------------------------------------------------------------
-- DEPRECATED NAMES
------------------------------------------------------------------------
-- Please use the new names as continuing support for the old names is
-- not guaranteed.

-- Version v2.0

id-⟶ = ⟶-id
{-# WARNING_ON_USAGE id-⟶
"Warning: id-⟶ was deprecated in v2.0.
Please use ⟶-id instead."
#-}

id-↣ = ↣-id
{-# WARNING_ON_USAGE id-↣
"Warning: id-↣ was deprecated in v2.0.
Please use ↣-id instead."
#-}

id-↠ = ↠-id
{-# WARNING_ON_USAGE id-↠
"Warning: id-↠ was deprecated in v2.0.
Please use ↠-id instead."
#-}

id-⤖ = ⤖-id
{-# WARNING_ON_USAGE id-⤖
"Warning: id-⤖ was deprecated in v2.0.
Please use ⤖-id instead."
#-}

id-⇔ = ⇔-id
{-# WARNING_ON_USAGE id-⇔
"Warning: id-⇔ was deprecated in v2.0.
Please use ⇔-id instead."
#-}

id-↩ = ↩-id
{-# WARNING_ON_USAGE id-↩
"Warning: id-↩ was deprecated in v2.0.
Please use ↩-id instead."
#-}

id-↪ = ↪-id
{-# WARNING_ON_USAGE id-↪
"Warning: id-↪ was deprecated in v2.0.
Please use ↪-id instead."
#-}

id-↔ = ↔-id
{-# WARNING_ON_USAGE id-↔
"Warning: id-↔ was deprecated in v2.0.
Please use ↔-id instead."
#-}