import Mathlib
import OAI.Computability.VertexCover.Games.Value
import OAI.Computability.VertexCover.Games.TotalVariation
import OAI.Computability.VertexCover.Games.Mixture

namespace OAI

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namespace UniqueGames.Foundations.Games.Game

noncomputable section

variable {Q₁ Q₂ A₁ A₂ R₁ R₂ B₁ B₂ Seed : Type*}
  [Fintype Q₁] [Fintype Q₂] [Fintype A₁] [Fintype A₂]
  [Fintype R₁] [Fintype R₂] [Fintype B₁] [Fintype B₂] [Fintype Seed]
  [Nonempty A₁] [Nonempty A₂]

def localEmbeddingLaw (G : Game Q₁ Q₂ A₁ A₂)
    (seedLaw : FiniteDistribution Seed)
    (left : Seed → Q₁ → R₁) (right : Seed → Q₂ → R₂) :
    FiniteDistribution (R₁ × R₂) :=
  seedLaw.mixture fun seed =>
    G.questions.pushforward fun q => (left seed q.1, right seed q.2)

theorem success_le_value_add_embedding_distance
    (G : Game Q₁ Q₂ A₁ A₂) (H : Game R₁ R₂ B₁ B₂)
    (seedLaw : FiniteDistribution Seed)
    (left : Seed → Q₁ → R₁) (right : Seed → Q₂ → R₂)
    (answerLeft : Seed → Q₁ → B₁ → A₁)
    (answerRight : Seed → Q₂ → B₂ → A₂)
    (acceptance : ∀ seed x y a b,
      H.accepts (left seed x) (right seed y) a b = true →
      G.accepts x y (answerLeft seed x a) (answerRight seed y b) = true)
    (strategy : Strategy R₁ R₂ B₁ B₂) :
    H.success strategy ≤ G.value +
      H.questions.totalVariation (G.localEmbeddingLaw seedLaw left right) := by
  have localBound (seed : Seed) :
      (G.questions.pushforward (fun q => (left seed q.1, right seed q.2))).probability
        (H.wins strategy) ≤ G.value := by
    let embedded : Game R₁ R₂ B₁ B₂ :=
      { questions := G.questions.pushforward fun q => (left seed q.1, right seed q.2)
        accepts := H.accepts }
    change embedded.success strategy ≤ G.value
    exact (G.success_le_of_localSimulation embedded (left seed) (right seed)
      (answerLeft seed) (answerRight seed) rfl (acceptance seed) strategy).trans
      (G.success_le_value _)
  have mixtureBound :
      (G.localEmbeddingLaw seedLaw left right).probability (H.wins strategy) ≤ G.value :=
    seedLaw.probability_mixture_le _ _ _ localBound
  exact (H.questions.probability_le_add_totalVariation
    (G.localEmbeddingLaw seedLaw left right) (H.wins strategy)).trans
    (add_le_add mixtureBound (le_refl _))

def coordinateGame (G : Game Q₁ Q₂ A₁ A₂) {n : Nat} (coordinate : Fin n)
    (law : FiniteDistribution ((Fin n → Q₁) × (Fin n → Q₂))) :
    Game (Fin n → Q₁) (Fin n → Q₂) (Fin n → A₁) (Fin n → A₂) where
  questions := law
  accepts x y a b := G.accepts (x coordinate) (y coordinate) (a coordinate) (b coordinate)

theorem coordinate_probability_le_value_add_embedding_distance
    (G : Game Q₁ Q₂ A₁ A₂) {n : Nat} (coordinate : Fin n)
    (law : FiniteDistribution ((Fin n → Q₁) × (Fin n → Q₂)))
    (seedLaw : FiniteDistribution Seed)
    (left : Seed → Q₁ → Fin n → Q₁) (right : Seed → Q₂ → Fin n → Q₂)
    (left_preserves : ∀ seed x, left seed x coordinate = x)
    (right_preserves : ∀ seed y, right seed y coordinate = y)
    (strategy : Strategy (Fin n → Q₁) (Fin n → Q₂) (Fin n → A₁) (Fin n → A₂)) :
    law.probability (G.coordinateWin strategy coordinate) ≤ G.value +
      law.totalVariation (G.localEmbeddingLaw seedLaw left right) := by
  apply G.success_le_value_add_embedding_distance (G.coordinateGame coordinate law)
    seedLaw left right (fun _ _ a => a coordinate) (fun _ _ b => b coordinate)
  intro seed x y a b h
  simpa only [coordinateGame, left_preserves, right_preserves] using h

theorem coordinate_probability_le_value_of_approximate_embeddings
    {SeedFamily : Nat → Type*} [∀ t, Fintype (SeedFamily t)]
    (G : Game Q₁ Q₂ A₁ A₂) {n : Nat} (coordinate : Fin n)
    (law : FiniteDistribution ((Fin n → Q₁) × (Fin n → Q₂)))
    (seedLaw : (t : Nat) → FiniteDistribution (SeedFamily t))
    (left : (t : Nat) → SeedFamily t → Q₁ → Fin n → Q₁)
    (right : (t : Nat) → SeedFamily t → Q₂ → Fin n → Q₂)
    (left_preserves : ∀ t seed x, left t seed x coordinate = x)
    (right_preserves : ∀ t seed y, right t seed y coordinate = y)
    (strategy : Strategy (Fin n → Q₁) (Fin n → Q₂) (Fin n → A₁) (Fin n → A₂))
    (distance : ℝ)
    (close : ∀ η : ℝ, 0 < η → ∃ t,
      law.totalVariation (G.localEmbeddingLaw (seedLaw t) (left t) (right t)) ≤
        distance + η) :
    law.probability (G.coordinateWin strategy coordinate) ≤ G.value + distance := by
  by_contra h
  have gap : 0 < law.probability (G.coordinateWin strategy coordinate) -
      (G.value + distance) := sub_pos.mpr (lt_of_not_ge h)
  obtain ⟨t, ht⟩ := close
    ((law.probability (G.coordinateWin strategy coordinate) - (G.value + distance)) / 2)
    (by linarith)
  have bound := G.coordinate_probability_le_value_add_embedding_distance coordinate law
    (seedLaw t) (left t) (right t) (left_preserves t) (right_preserves t) strategy
  linarith

end
end UniqueGames.Foundations.Games.Game

end


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end OAI