import Spa.Analysis.Forward
import Spa.Analysis.Utils
import Spa.Interp
import Spa.Showable

namespace Spa

inductive Sign where
  | plus
  | minus
  | zero
  deriving DecidableEq

instance : Showable Sign :=
  ⟨fun
    | .plus => "+"
    | .minus => "-"
    | .zero => "0"⟩

instance : Inhabited Sign := ⟨.zero⟩

abbrev SignLattice : Type := AboveBelow Sign

open AboveBelow in
def plus : SignLattice → SignLattice → SignLattice
  | bot, _ => bot
  | _, bot => bot
  | top, _ => top
  | _, top => top
  | mk .plus, mk .plus => mk .plus
  | mk .plus, mk .minus => top
  | mk .plus, mk .zero => mk .plus
  | mk .minus, mk .plus => top
  | mk .minus, mk .minus => mk .minus
  | mk .minus, mk .zero => mk .minus
  | mk .zero, mk .plus => mk .plus
  | mk .zero, mk .minus => mk .minus
  | mk .zero, mk .zero => mk .zero

open AboveBelow in
def minus : SignLattice → SignLattice → SignLattice
  | bot, _ => bot
  | _, bot => bot
  | top, _ => top
  | _, top => top
  | mk .plus, mk .plus => top
  | mk .plus, mk .minus => mk .plus
  | mk .plus, mk .zero => mk .plus
  | mk .minus, mk .plus => mk .minus
  | mk .minus, mk .minus => top
  | mk .minus, mk .zero => mk .minus
  | mk .zero, mk .plus => mk .minus
  | mk .zero, mk .minus => mk .plus
  | mk .zero, mk .zero => mk .zero

theorem plus_mono₂ : Monotone₂ plus :=
  AboveBelow.monotone₂_of_strict plus
    (fun y => by cases y <;> rfl)
    (fun x => by rcases x with _ | _ | s <;> first | rfl | (cases s <;> rfl))
    (fun y hy => by cases y <;> first | exact absurd rfl hy | rfl)
    (fun x hx => by
      rcases x with _ | _ | s <;>
        first | exact absurd rfl hx | rfl | (cases s <;> rfl))

theorem minus_mono₂ : Monotone₂ minus :=
  AboveBelow.monotone₂_of_strict minus
    (fun y => by cases y <;> rfl)
    (fun x => by rcases x with _ | _ | s <;> first | rfl | (cases s <;> rfl))
    (fun y hy => by cases y <;> first | exact absurd rfl hy | rfl)
    (fun x hx => by
      rcases x with _ | _ | s <;>
        first | exact absurd rfl hx | rfl | (cases s <;> rfl))

def interpSign : SignLattice → Value → Prop
  | .bot, _ => False
  | .top, _ => True
  | .mk .plus, v => ∃ n : ℕ, v = .int (n + 1)
  | .mk .zero, v => v = .int 0
  | .mk .minus, v => ∃ n : ℕ, v = .int (-(n + 1))

theorem interpSign_mk_disjoint {s₁ s₂ : Sign} (hne : s₁ ≠ s₂) {v : Value} :
    ¬(interpSign (.mk s₁) v ∧ interpSign (.mk s₂) v) := by
  rintro ⟨h₁, h₂⟩
  rcases s₁ <;> rcases s₂ <;> try exact hne rfl
  all_goals simp only [interpSign] at h₁ h₂
  · obtain ⟨n₁, rfl⟩ := h₁
    obtain ⟨n₂, hv⟩ := h₂
    injection hv with hz
    omega
  · obtain ⟨n₁, rfl⟩ := h₁
    injection h₂ with hz
    omega
  · obtain ⟨n₁, rfl⟩ := h₁
    obtain ⟨n₂, hv⟩ := h₂
    injection hv with hz
    omega
  · obtain ⟨n₁, rfl⟩ := h₁
    injection h₂ with hz
    omega
  · subst h₁
    obtain ⟨n₂, hv⟩ := h₂
    injection hv with hz
    omega
  · subst h₁
    obtain ⟨n₂, hv⟩ := h₂
    injection hv with hz
    omega

instance signInterpretation : LatticeInterpretation SignLattice where
  interp := interpSign
  interp_sup := fun v h => AboveBelow.interp_sup_of (fun _ h => h) (fun _ => trivial) v h
  interp_inf := fun v h => AboveBelow.interp_inf_of (fun hne _ => interpSign_mk_disjoint hne) v h

namespace SignAnalysis

variable (prog : Program)

def eval : Expr → VariableValues SignLattice prog → SignLattice
  | .add e₁ e₂, vs => plus (eval e₁ vs) (eval e₂ vs)
  | .sub e₁ e₂, vs => minus (eval e₁ vs) (eval e₂ vs)
  | .var k, vs =>
    if h : FiniteMap.MemKey k vs then (FiniteMap.locate h).1 else .top
  | .num 0, _ => .mk .zero
  | .num (_ + 1), _ => .mk .plus

theorem eval_mono (e : Expr) : Monotone (eval prog e) := by
  induction e with
  | add e₁ e₂ ih₁ ih₂ =>
    intro vs₁ vs₂ h
    exact eval_combine₂ plus_mono₂ (ih₁ h) (ih₂ h)
  | sub e₁ e₂ ih₁ ih₂ =>
    intro vs₁ vs₂ h
    exact eval_combine₂ minus_mono₂ (ih₁ h) (ih₂ h)
  | var k =>
    intro vs₁ vs₂ h
    simp only [eval]
    by_cases hk : k ∈ prog.vars
    · rw [dif_pos (FiniteMap.memKey_iff.mpr hk),
          dif_pos (FiniteMap.memKey_iff.mpr hk)]
      exact FiniteMap.le_of_mem_mem prog.vars_nodup h
        (FiniteMap.locate _).2 (FiniteMap.locate _).2
    · rw [dif_neg (fun hm => hk (FiniteMap.memKey_iff.mp hm)),
          dif_neg (fun hm => hk (FiniteMap.memKey_iff.mp hm))]
  | num n =>
    intro vs₁ vs₂ _
    cases n <;> exact le_refl _

instance exprEvaluator : ExprEvaluator SignLattice prog :=
  ⟨eval prog, eval_mono prog⟩

def output : String :=
  show' (result SignLattice prog)

/-- A nonneg-shifted interpretation `∃ n : ℕ, z = n + 1` just means `z` is positive. -/
private theorem int_pos_iff (z : ℤ) : (∃ n : ℕ, z = (n : ℤ) + 1) ↔ 0 < z := by
  constructor
  · rintro ⟨n, rfl⟩; omega
  · intro h; exact ⟨(z - 1).toNat, by omega⟩

/-- Dually, `∃ n : ℕ, z = -(n + 1)` just means `z` is negative. -/
private theorem int_neg_iff (z : ℤ) : (∃ n : ℕ, z = -((n : ℤ) + 1)) ↔ z < 0 := by
  constructor
  · rintro ⟨n, rfl⟩; omega
  · intro h; exact ⟨(-z - 1).toNat, by omega⟩

theorem plus_valid {g₁ g₂ : SignLattice} {z₁ z₂ : ℤ}
    (h₁ : ⟦g₁⟧ (.int z₁)) (h₂ : ⟦g₂⟧ (.int z₂)) :
    ⟦plus g₁ g₂⟧ (.int (z₁ + z₂)) := by
  rcases g₁ with _ | _ | s₁ <;> rcases g₂ with _ | _ | s₂ <;>
    (try rcases s₁) <;> (try rcases s₂) <;>
    simp only [plus, signInterpretation, interpSign, Value.int.injEq, int_pos_iff, int_neg_iff]
      at h₁ h₂ ⊢ <;>
    omega

theorem minus_valid {g₁ g₂ : SignLattice} {z₁ z₂ : ℤ}
    (h₁ : ⟦g₁⟧ (.int z₁)) (h₂ : ⟦g₂⟧ (.int z₂)) :
    ⟦minus g₁ g₂⟧ (.int (z₁ - z₂)) := by
  rcases g₁ with _ | _ | s₁ <;> rcases g₂ with _ | _ | s₂ <;>
    (try rcases s₁) <;> (try rcases s₂) <;>
    simp only [minus, signInterpretation, interpSign, Value.int.injEq, int_pos_iff, int_neg_iff]
      at h₁ h₂ ⊢ <;>
    omega

instance eval_valid : ValidExprEvaluator SignLattice prog := by
  constructor
  intro vs ρ e v hev
  induction hev with
  | num n =>
    intro _
    show ⟦eval prog (.num n) vs⟧ (.int n)
    cases n with
    | zero => rfl
    | succ n' => exact ⟨n', congrArg Value.int (by norm_cast)⟩
  | var x v hxv =>
    intro hvs
    show ⟦eval prog (.var x) vs⟧ v
    simp only [eval]
    by_cases hk : FiniteMap.MemKey x vs
    · rw [dif_pos hk]
      exact hvs _ _ (FiniteMap.locate hk).2 _ hxv
    · rw [dif_neg hk]
      exact trivial
  | add e₁ e₂ z₁ z₂ _ _ ih₁ ih₂ =>
    intro hvs
    have h₁ : ⟦eval prog e₁ vs⟧ (.int z₁) := ih₁ hvs
    have h₂ : ⟦eval prog e₂ vs⟧ (.int z₂) := ih₂ hvs
    show ⟦eval prog (.add e₁ e₂) vs⟧ (.int (z₁ + z₂))
    exact plus_valid h₁ h₂
  | sub e₁ e₂ z₁ z₂ _ _ ih₁ ih₂ =>
    intro hvs
    have h₁ : ⟦eval prog e₁ vs⟧ (.int z₁) := ih₁ hvs
    have h₂ : ⟦eval prog e₂ vs⟧ (.int z₂) := ih₂ hvs
    show ⟦eval prog (.sub e₁ e₂) vs⟧ (.int (z₁ - z₂))
    exact minus_valid h₁ h₂

theorem analyze_correct {ρ : Env} (hrun : EvalStmt [] prog.rootStmt ρ) :
    ⟦ variablesAt prog.finalState (result SignLattice prog) ⟧ ρ :=
  Spa.analyze_correct SignLattice prog hrun

end SignAnalysis

end Spa