From Undecidability.L Require Import L Tactics.LTactics LBool.

Class eqbClass X (eqb : X -> X -> bool): Type :=
  _eqb_spec : forall (x y:X), reflect (x=y) (eqb x y).

#[export] Hint Mode eqbClass + -: typeclass_instances.
Definition eqb X eqb `{H:eqbClass (X:=X) eqb} := eqb.

Arguments eqb {_ _ _}: simpl never.

Lemma eqb_spec {X} {f : X -> X -> bool} {_:eqbClass f}:
  forall (x y:X), reflect (x=y) (eqb x y).
Proof.
  intros. eapply _eqb_spec.
Qed.

#[global]
Instance eqbBool_inst : eqbClass Bool.eqb.
Proof.
  intros ? ?. eapply iff_reflect. rewrite eqb_true_iff. reflexivity.
Qed.

Lemma dec_reflect_remove {P Y} (d:dec P) b (H:reflect P b) (y y' : Y):
  (if d then y else y') = (if b then y else y').
Proof.
  destruct H,d;easy.
Qed.

Lemma eqDec_remove {X Y eqb} {H:eqbClass (X:=X) eqb} x x' (d:dec (x=x')) (a b : Y):
  (if d then a else b) = (if eqb x x' then a else b).
Proof.
  apply dec_reflect_remove. eapply eqb_spec.
Qed.

Class eqbCompT X {R:registered X} eqb {H:eqbClass (X:=X) eqb} :=
  { c__eqbComp :nat;
    eqbTime x y:= min x y* c__eqbComp;
    comp_eqb : computableTime' eqb (fun x _ =>(5,fun y _ => (eqbTime (size (enc x)) (size (enc y)),tt)))
  }.
Arguments eqbCompT _ {_ _ _}.
Arguments c__eqbComp _ {_ _ _ _}.

#[export] Hint Mode eqbCompT + - - -: typeclass_instances.

#[global]
Existing Instance comp_eqb.

#[global]
Instance eqbComp_bool : eqbCompT bool.
Proof.
  evar (c:nat). exists c. unfold Bool.eqb.
  unfold enc;cbn.
  extract.
  solverec.
  [c]:exact 3.
  all:unfold c;try lia.
Qed.

Lemma eqbTime_le_l X {R : registered X} (eqb : X -> X -> bool) {H : eqbClass eqb}
      {H' : eqbCompT X} x n':
  eqbTime (X:=X) x n' <= x * c__eqbComp X.
Proof.
  unfold eqbTime. rewrite Nat.le_min_l. easy.
Qed.

Lemma eqbTime_le_r X (R : registered X) (eqb : X -> X -> bool) (H : eqbClass eqb)
      (eqbCompT : eqbCompT X) x n':
  eqbTime (X:=X) n' x <= x * c__eqbComp X.
Proof.
  unfold eqbTime. rewrite Nat.le_min_r. easy.
Qed.