import OAI.Analysis.C0Absorption.Blocks

namespace OAI

open Set Filter Topology
open scoped NNReal BigOperators ZeroAtInfty
open NormedSpace

namespace C0Absorption
noncomputable section
open Set Filter Topology
open scoped NNReal BigOperators ZeroAtInfty

def blockVector (lev : Level) (s : C0Ball) (b : Block lev) : ℝ :=
  theta (levelJ lev) (localRadius lev s.val) b.1 * bandVector b.1 b.2 (prefixRestrict b.1 s)

def blockRow (lev : Level) (s : C0Ball) (b : Block lev) : ℝ :=
  theta (levelJ lev) (localRadius lev s.val) b.1 * bandRow b.1 b.2 (prefixRestrict b.1 s)

theorem blockVector_nonneg (lev : Level) (s : C0Ball) (b : Block lev) :
    0≤blockVector lev s b := mul_nonneg (theta_nonneg _ _ _) (bandVector_nonneg _ _ _)

theorem blockVector_le_one (lev : Level) (s : C0Ball) (b : Block lev) :
    blockVector lev s b ≤ 1 := by
  calc
    _ ≤ 1*1 := mul_le_mul (theta_le_one _ _ _) (bandVector_le_one _ _ _) (bandVector_nonneg _ _ _) zero_le_one
    _ = 1 := one_mul _

theorem blockRow_nonneg (lev : Level) (s : C0Ball) (b : Block lev) :
    0≤blockRow lev s b := mul_nonneg (theta_nonneg _ _ _) (bandRow_nonneg _ _ _)

theorem blockRow_sum (lev : Level) (s : C0Ball) : ∑ b : Block lev,blockRow lev s b ≤ 2 := by
  change (∑ b : (j : Fin (levelJ lev+1)) × BandGrid j.val,
    theta (levelJ lev) (localRadius lev s.val) b.1 * bandRow b.1 b.2 (prefixRestrict b.1 s)) ≤ 2
  rw [Fintype.sum_sigma]
  simp only [← Finset.mul_sum,bandRow_sum,mul_one]
  exact theta_sum_le _ _

theorem blockRow_vector (lev : Level) (s : C0Ball) :
    ∑ b : Block lev, blockRow lev s b*blockVector lev s b=1 := by
  change (∑ b : (j : Fin (levelJ lev+1)) × BandGrid j.val,
    (theta (levelJ lev) (localRadius lev s.val) b.1 * bandRow b.1 b.2 (prefixRestrict b.1 s))*
    (theta (levelJ lev) (localRadius lev s.val) b.1 * bandVector b.1 b.2 (prefixRestrict b.1 s)))=1
  rw [Fintype.sum_sigma]
  have he (j : Fin (levelJ lev+1)) : (∑ ξ : BandGrid j,
    (theta (levelJ lev) (localRadius lev s.val) j*bandRow j ξ (prefixRestrict j s))*
    (theta (levelJ lev) (localRadius lev s.val) j*bandVector j ξ (prefixRestrict j s)))=
    theta (levelJ lev) (localRadius lev s.val) j^2 := by
    calc
      _ = ∑ ξ : BandGrid j, theta (levelJ lev) (localRadius lev s.val) j^2*
          (bandRow j ξ (prefixRestrict j s)*bandVector j ξ (prefixRestrict j s)) := by
        apply Finset.sum_congr rfl
        intro ξ _
        ring
      _ = _ := by rw [← Finset.mul_sum,bandRow_vector,mul_one]
  simp only [he]
  exact theta_squares _ _

theorem bandL_ge_dyadic_inv (j : ℕ) : (2 : ℝ)^j ≤ bandL j := by
  let : Nonempty (BandGrid j) := ⟨fun _ => ⟨0,by constructor; exact neg_nonpos.mpr (Int.natCast_nonneg _); exact Int.natCast_nonneg _⟩⟩
  have hc : (1 : ℝ) ≤ Fintype.card (BandGrid j) := by exact_mod_cast Fintype.card_pos
  simp only [bandL,NNReal.coe_mul,NNReal.coe_ofNat,NNReal.coe_natCast,NNReal.coe_pow]
  nlinarith [pow_pos (by norm_num : (0:ℝ)<2) j]

theorem bandVector_distance (j : ℕ) (ξ : BandGrid j) (s t : PrefixCube j) :
    |bandVector j ξ s-bandVector j ξ t| ≤ bandL j*dist s t := by
  exact ((bandVector_lipschitz j ξ).dist_le_mul s t).trans
    (mul_le_mul_of_nonneg_right (by exact_mod_cast bandL_ge_dyadic_inv j) dist_nonneg)

theorem theta_band_budget (J : ℕ) (j : Fin (J+1)) {r s δ D : ℝ}
    (hr : 0≤r) (hs : 0 ≤ s) (hδ : 0≤δ) (hD : D≤bandL j*δ) (hD0 : j.val=0 → D=0) :
    min r s*(theta J r j*D) ≤ (eta/4)*theta J r j*δ := by
  by_cases hj : j.val=0
  · rw [hD0 hj,mul_zero,mul_zero]
    exact mul_nonneg (mul_nonneg (div_nonneg eta_pos.le (by norm_num)) (theta_nonneg _ _ _)) hδ
  by_cases ht : theta J r j=0
  · simp only [ht,zero_mul,mul_zero,le_refl]
  have hm : min r s≤rho j := (min_le_left _ _).trans (theta_upper_support (by omega) (by omega) hr ht)
  have hL : min r s*bandL j≤eta/4 := by
    calc
      _ ≤ rho j*bandL j := mul_le_mul_of_nonneg_right hm (bandL j).coe_nonneg
      _ = bandL j*rho j := mul_comm _ _
      _ ≤ eta/4 := rho_lip_budget (by omega)
  calc
    _ ≤ min r s*(theta J r j*(bandL j*δ)) :=
      mul_le_mul_of_nonneg_left (mul_le_mul_of_nonneg_left hD (theta_nonneg _ _ _)) (le_min hr hs)
    _ = (min r s*bandL j)*theta J r j*δ := by ring
    _ ≤ (eta/4)*theta J r j*δ := mul_le_mul_of_nonneg_right
      (mul_le_mul_of_nonneg_right hL (theta_nonneg _ _ _)) hδ

theorem bandRow_scaled_difference {j : ℕ} (a b : ℝ) (ha : 0≤a) (s t : PrefixCube j) :
    (∑ ξ : BandGrid j,|a*bandRow j ξ s-b*bandRow j ξ t|) ≤
      |a-b|+a*(∑ ξ : BandGrid j,|bandRow j ξ s-bandRow j ξ t|) := by
  calc
    _ ≤ ∑ ξ : BandGrid j,(|a-b| *bandRow j ξ t+a*|bandRow j ξ s-bandRow j ξ t|) := by
      apply Finset.sum_le_sum
      intro ξ _
      rw [show a*bandRow j ξ s-b*bandRow j ξ t=(a-b)*bandRow j ξ t+a*(bandRow j ξ s-bandRow j ξ t) by ring]
      refine (abs_add_le _ _).trans_eq ?_
      simp only [abs_mul,abs_of_nonneg ha,abs_of_nonneg (bandRow_nonneg j ξ t)]
    _ = _ := by rw [Finset.sum_add_distrib,← Finset.mul_sum,← Finset.mul_sum,bandRow_sum,mul_one]

theorem blockRow_distance_decompose (lev : Level) (s t : C0Ball) :
    (∑ b : Block lev,|blockRow lev s b-blockRow lev t b|) ≤
      ∑ j : Fin (levelJ lev+1), (|theta (levelJ lev) (localRadius lev s.val) j-
        theta (levelJ lev) (localRadius lev t.val) j|+
          theta (levelJ lev) (localRadius lev s.val) j*
            ∑ ξ : BandGrid j,|bandRow j ξ (prefixRestrict j s)-bandRow j ξ (prefixRestrict j t)|) := by
  unfold blockRow
  rw [Fintype.sum_sigma]
  apply Finset.sum_le_sum
  intro j _
  exact bandRow_scaled_difference (j := j.val)
    (theta (levelJ lev) (localRadius lev s.val) j.val)
    (theta (levelJ lev) (localRadius lev t.val) j.val)
    (theta_nonneg _ _ _) (prefixRestrict j.val s) (prefixRestrict j.val t)

theorem blockRow_weighted_distance (lev : Level) (s t : C0Ball) :
    min (localRadius lev s.val) (localRadius lev t.val)*
      (∑ b : Block lev,|blockRow lev s b-blockRow lev t b|) ≤ eta*dist s t := by
  let J := levelJ lev
  let r := localRadius lev s.val
  let r' := localRadius lev t.val
  let δ := dist s t
  let D (j : Fin (J+1)) := ∑ ξ : BandGrid j,|bandRow j ξ (prefixRestrict j s)-bandRow j ξ (prefixRestrict j t)|
  have hr : 0≤r := finiteRadius_nonneg _ _
  have hr' : 0≤r' := finiteRadius_nonneg _ _
  have hrad : |r-r'|≤δ := by
    change dist (finiteRadius (radiusCoordinates lev) s.val) (finiteRadius (radiusCoordinates lev) t.val) ≤ dist s.val t.val
    simpa only [NNReal.coe_one,one_mul] using (finiteRadius_lipschitz (radiusCoordinates lev)).dist_le_mul s.val t.val
  have hD (j : Fin (J+1)) : D j≤bandL j*δ := by
    exact (bandRow_distance j _ _).trans (mul_le_mul_of_nonneg_left
      (by simpa only [NNReal.coe_one,one_mul] using (prefixRestrict_lipschitz j).dist_le_mul s t) (bandL j).coe_nonneg)
  have hD0 (j : Fin (J+1)) (hj : j.val=0) : D j=0 := by
    dsimp [D]
    have he : prefixRestrict j s=prefixRestrict j t := by rw [hj]; exact Subsingleton.elim _ _
    simp only [he,sub_self,abs_zero,Finset.sum_const_zero]
  have hsum := blockRow_distance_decompose lev s t
  have hschedule : min r r'*(∑ j : Fin (J+1),|theta J r j-theta J r' j|) ≤ (eta/2)*δ := by
    calc
      _ ≤ (Real.pi/scheduleH)*|r-r'| := theta_weighted_distance J hr hr'
      _ ≤ (eta/2)*δ := mul_le_mul schedule_speed hrad (abs_nonneg _) (div_nonneg eta_pos.le (by norm_num))
  calc
    _ ≤ min r r'*(∑ j : Fin (J+1),(|theta J r j-theta J r' j|+theta J r j*D j)) :=
      mul_le_mul_of_nonneg_left hsum (le_min hr hr')
    _ = min r r'*(∑ j : Fin (J+1),|theta J r j-theta J r' j|)+
        ∑ j : Fin (J+1),min r r'*(theta J r j*D j) := by
      simp only [Finset.sum_add_distrib,mul_add,Finset.mul_sum]
    _ ≤ (eta/2)*δ+∑ j : Fin (J+1),(eta/4)*theta J r j*δ :=
      add_le_add hschedule (Finset.sum_le_sum (fun j _ => theta_band_budget J j hr hr' dist_nonneg (hD j) (hD0 j)))
    _ = (eta/2)*δ+(eta/4)*(∑ j : Fin (J+1),theta J r j)*δ := by
      rw [← Finset.sum_mul,← Finset.mul_sum]
    _ ≤ (eta/2)*δ+(eta/4)*2*δ := add_le_add le_rfl (mul_le_mul_of_nonneg_right
      (mul_le_mul_of_nonneg_left (theta_sum_le J r) (show 0 ≤ eta/4 from div_nonneg eta_pos.le (by norm_num))) (show 0 ≤ δ from dist_nonneg))
    _ = eta*dist s t := by dsimp [δ]; ring

end
end C0Absorption

namespace C0Absorption
noncomputable section
open Set Filter Topology
open scoped NNReal BigOperators ZeroAtInfty

theorem product_difference_bound {a b u v : ℝ} (ha : 0≤a) (hv : |v|≤1) :
    |a*u-b*v| ≤ |a-b|+a*|u-v| := by
  calc
    _ = |(a-b)*v+a*(u-v)| := by congr 1; ring
    _ ≤ |(a-b)*v|+|a*(u-v)| := abs_add_le _ _
    _ = |a-b| *|v|+a*|u-v| := by rw [abs_mul,abs_mul,abs_of_nonneg ha]
    _ ≤ |a-b| *1+a*|u-v| := add_le_add (mul_le_mul_of_nonneg_left hv (abs_nonneg _)) le_rfl
    _ = _ := by rw [mul_one]

theorem theta_weighted_coordinate (J : ℕ) (j : Fin (J+1)) {r s : ℝ} (hr : 0≤r) (hs : 0 ≤ s) :
    min r s*|theta J r j-theta J s j| ≤ (Real.pi/scheduleH)*|r-s| := by
  apply le_trans _ (theta_weighted_distance J hr hs)
  apply mul_le_mul_of_nonneg_left _ (le_min hr hs)
  exact Finset.single_le_sum (fun (i : Fin (J+1)) _ => abs_nonneg (theta J r i-theta J s i)) (Finset.mem_univ j)

theorem blockVector_weighted_distance (lev : Level) (s t : C0Ball) (b : Block lev) :
    min (localRadius lev s.val) (localRadius lev t.val)*
      |blockVector lev s b-blockVector lev t b| ≤ eta*dist s t := by
  let J := levelJ lev
  let r := localRadius lev s.val
  let r' := localRadius lev t.val
  let δ := dist s t
  let D := |bandVector b.1 b.2 (prefixRestrict b.1 s)-bandVector b.1 b.2 (prefixRestrict b.1 t)|
  have hr : 0≤r := finiteRadius_nonneg _ _
  have hr' : 0≤r' := finiteRadius_nonneg _ _
  have hrad : |r-r'|≤δ := by
    change dist (finiteRadius (radiusCoordinates lev) s.val) (finiteRadius (radiusCoordinates lev) t.val) ≤ dist s.val t.val
    simpa only [NNReal.coe_one,one_mul] using (finiteRadius_lipschitz (radiusCoordinates lev)).dist_le_mul s.val t.val
  have hD : D≤bandL b.1*δ := by
    exact (bandVector_distance b.1 b.2 _ _).trans (mul_le_mul_of_nonneg_left
      (by simpa only [NNReal.coe_one,one_mul] using (prefixRestrict_lipschitz b.1).dist_le_mul s t) (bandL b.1).coe_nonneg)
  have hD0 (hj : b.1.val=0) : D=0 := by
    dsimp [D]
    have he : prefixRestrict b.1 s=prefixRestrict b.1 t := by rw [hj]; exact Subsingleton.elim _ _
    simp only [he,sub_self,abs_zero]
  have hschedule : min r r'*|theta J r b.1-theta J r' b.1| ≤ (eta/2)*δ := by
    calc
      _ ≤ (Real.pi/scheduleH)*|r-r'| := theta_weighted_coordinate J b.1 hr hr'
      _ ≤ (eta/2)*δ := mul_le_mul schedule_speed hrad (abs_nonneg _) (div_nonneg eta_pos.le (by norm_num))
  have hprod : |blockVector lev s b-blockVector lev t b| ≤
      |theta J r b.1-theta J r' b.1|+theta J r b.1*D :=
    product_difference_bound (theta_nonneg _ _ _) (by rw [abs_of_nonneg (bandVector_nonneg _ _ _)]; exact bandVector_le_one _ _ _)
  calc
    _ ≤ min r r'*(|theta J r b.1-theta J r' b.1|+theta J r b.1*D) :=
      mul_le_mul_of_nonneg_left hprod (le_min hr hr')
    _ = min r r'*|theta J r b.1-theta J r' b.1|+min r r'*(theta J r b.1*D) := mul_add _ _ _
    _ ≤ (eta/2)*δ+(eta/4)*theta J r b.1*δ :=
      add_le_add hschedule (theta_band_budget J b.1 hr hr' dist_nonneg hD hD0)
    _ ≤ (eta/2)*δ+(eta/4)*1*δ := add_le_add le_rfl
      (mul_le_mul_of_nonneg_right (mul_le_mul_of_nonneg_left (theta_le_one _ _ _)
        (show 0≤eta/4 from div_nonneg eta_pos.le (by norm_num))) dist_nonneg)
    _ ≤ eta*dist s t := by dsimp [δ]; nlinarith [eta_pos,mul_nonneg eta_pos.le (dist_nonneg (x := s) (y := t))]

theorem bandRow_continuous (j : ℕ) (ξ : BandGrid j) : Continuous (bandRow j ξ) := by
  exact (bandBump_lipschitz j ξ).continuous.div
    (continuous_finsetSum _ (fun ζ _ => (bandBump_lipschitz j ζ).continuous)) (fun s => (bandDenominator_pos j s).ne')

theorem localRadius_continuous (lev : Level) : Continuous (localRadius lev) :=
  (finiteRadius_lipschitz _).continuous

theorem blockVector_continuous (lev : Level) (b : Block lev) : Continuous (fun s => blockVector lev s b) :=
  ((theta_continuous (levelJ lev) b.1).comp ((localRadius_continuous lev).comp continuous_subtype_val)).mul
    ((bandVector_lipschitz b.1 b.2).continuous.comp (prefixRestrict_lipschitz b.1).continuous)

theorem blockRow_continuous (lev : Level) (b : Block lev) : Continuous (fun s => blockRow lev s b) :=
  ((theta_continuous (levelJ lev) b.1).comp ((localRadius_continuous lev).comp continuous_subtype_val)).mul
    ((bandRow_continuous b.1 b.2).comp (prefixRestrict_lipschitz b.1).continuous)

end
end C0Absorption

end OAI