import Mathlib
import OAI.Combinatorics.IndependentSets.Repetition.Basic
import OAI.Combinatorics.IndependentSets.Repetition.ProfileCorrection
import OAI.Combinatorics.IndependentSets.Repetition.Value

namespace OAI

namespace IndependentSetsGames.Foundations.Repetition

open scoped BigOperators
open Games
noncomputable section

variable {X Y : Type*} [Fintype X] [Fintype Y]

def normalizeOr (w : X → ℝ) (hw : ∀ x, 0 ≤ w x)
    (fallback : FiniteDistribution X) : FiniteDistribution X :=
  if h : 0 < ∑ x, w x then
    { weight := normalizedWeight w
      nonnegative := (normalizedWeight_isProbability w hw h).1
      normalized := (normalizedWeight_isProbability w hw h).2 }
  else fallback

theorem sum_mul_normalizeOr (w : X → ℝ) (hw : ∀ x, 0 ≤ w x)
    (fallback : FiniteDistribution X) (x : X) :
    (∑ z, w z) * (normalizeOr w hw fallback).weight x = w x := by
  classical
  have hs : 0 ≤ ∑ z, w z := Finset.sum_nonneg (fun z _ => hw z)
  by_cases h : 0 < ∑ z, w z
  · simp only [normalizeOr, dite_eq_left h, normalizedWeight]
    field_simp
  · have hz : ∑ z, w z = 0 := le_antisymm (le_of_not_gt h) hs
    have hx : w x = 0 := by
      apply le_antisymm _ (hw x)
      have hl := Finset.single_le_sum (fun z _ => hw z) (Finset.mem_univ x)
      simpa only [hz] using hl
    simp [normalizeOr, hz, hx]

theorem local_completion_recombination
    (left : X → ℝ) (right : Y → ℝ)
    (hl : ∀ x, 0 ≤ left x) (hr : ∀ y, 0 ≤ right y)
    (defaultLeft : FiniteDistribution X) (defaultRight : FiniteDistribution Y)
    (c : ℝ) (x : X) (y : Y) :
    (c * (∑ z, left z) * (∑ z, right z)) *
      ((normalizeOr left hl defaultLeft).weight x *
        (normalizeOr right hr defaultRight).weight y) = c * left x * right y := by
  calc
    _ = c * ((∑ z, left z) * (normalizeOr left hl defaultLeft).weight x) *
        ((∑ z, right z) * (normalizeOr right hr defaultRight).weight y) := by ring
    _ = _ := by rw [sum_mul_normalizeOr, sum_mul_normalizeOr]

theorem factorized_completion_row
    (left : X → ℝ) (right : Y → ℝ)
    (hl : ∀ x, 0 ≤ left x) (hr : ∀ y, 0 ≤ right y)
    (defaultLeft : FiniteDistribution X) (defaultRight : FiniteDistribution Y)
    (c : ℝ) (xy : X × Y) :
    (∑ z : X × Y, c * left z.1 * right z.2) *
      ((normalizeOr left hl defaultLeft).product
        (normalizeOr right hr defaultRight)).weight xy = c * left xy.1 * right xy.2 := by
  have hm : (∑ z : X × Y, c * left z.1 * right z.2) =
      c * (∑ z, left z) * (∑ z, right z) := by
    simp_rw [mul_assoc, ← Finset.mul_sum]
    rw [productWeight_mass]
  rw [hm]
  exact local_completion_recombination left right hl hr defaultLeft defaultRight c xy.1 xy.2

end
end IndependentSetsGames.Foundations.Repetition

end OAI