import OAI.Analysis.C0Absorption.Triangular

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

structure CylinderOperation (I : Finset ℕ) where
  scaleIndex : ℕ
  center : OperationGrid I scaleIndex
  isG : Bool

namespace CylinderOperation
variable {I : Finset ℕ}
def scale (r : CylinderOperation I) : ℝ := dyadic r.scaleIndex
def point (r : CylinderOperation I) : Cube I := operationGridPoint I r.scaleIndex r.center
def act (r : CylinderOperation I) : (Cube I → ℝ) →ₗ[ℝ] (Cube I → ℝ) :=
  localOp r.isG r.point r.scale

theorem scale_pos (r : CylinderOperation I) : 0 < r.scale := dyadic_pos r.scaleIndex

theorem act_lipschitz (r : CylinderOperation I) {K : ℝ≥0} {u : Cube I → ℝ}
    (hu : LipschitzWith K u) : LipschitzWith (4*K) (r.act u) := by
  cases hr : r.isG <;> simp only [act, localOp, hr, Bool.false_eq_true, ↓reduceIte]
  · exact (localR_lipschitz r.point r.scale_pos u hu).weaken (by nlinarith)
  · exact localG_lipschitz r.point r.scale_pos u hu

theorem act_sup (r : CylinderOperation I) {A : ℝ} (hA : 0 ≤ A)
    {u : Cube I → ℝ} (hu : ∀ x, |u x| ≤ A) : ∀ x, |r.act u x| ≤ 2*A := by
  intro x
  cases hr : r.isG <;> simp only [act, localOp, hr, Bool.false_eq_true, ↓reduceIte]
  · exact localR_sup r.point r.scale u A hu x
  · exact (localG_sup r.point r.scale u A hu x).trans (by linarith)

end CylinderOperation

def applyOperations {I : Finset ℕ} (ops : List (CylinderOperation I)) :
    (Cube I → ℝ) →ₗ[ℝ] (Cube I → ℝ) :=
  match ops with
  | [] => LinearMap.id
  | r :: rs => (applyOperations rs).comp r.act

@[simp] theorem applyOperations_nil {I : Finset ℕ} (u : Cube I → ℝ) : applyOperations [] u = u := rfl
@[simp] theorem applyOperations_cons {I : Finset ℕ} (r : CylinderOperation I)
    (rs : List (CylinderOperation I)) (u : Cube I → ℝ) :
    applyOperations (r::rs) u = applyOperations rs (r.act u) := rfl

theorem applyOperations_append {I : Finset ℕ} (rs ss : List (CylinderOperation I))
    (u : Cube I → ℝ) : applyOperations (rs++ss) u = applyOperations ss (applyOperations rs u) := by
  induction rs generalizing u with
  | nil => rfl
  | cons r rs ih => simpa using ih (r.act u)

theorem applyOperations_lipschitz {I : Finset ℕ} (ops : List (CylinderOperation I))
    {K : ℝ≥0} {u : Cube I → ℝ} (hu : LipschitzWith K u) :
    LipschitzWith (4^ops.length*K) (applyOperations ops u) := by
  induction ops generalizing K u with
  | nil => simpa using hu
  | cons r rs ih =>
    have hh := ih (r.act_lipschitz hu)
    simpa only [applyOperations_cons, List.length_cons, pow_succ, mul_assoc] using hh

theorem applyOperations_sup {I : Finset ℕ} (ops : List (CylinderOperation I))
    {A : ℝ} (hA : 0 ≤ A) {u : Cube I → ℝ} (hu : ∀ x, |u x| ≤ A) :
    ∀ x, |applyOperations ops u x| ≤ 2^ops.length*A := by
  induction ops generalizing A u with
  | nil => simpa using hu
  | cons r rs ih =>
    have hh := ih (by positivity : 0 ≤ 2*A) (r.act_sup hA hu)
    simpa only [applyOperations_cons, List.length_cons, pow_succ, mul_assoc] using hh

theorem applyOperations_support_bound {I : Finset ℕ} (ops : List (CylinderOperation I))
    (u : Cube I → ℝ) {φ : Cube I → ℝ} (hφ : LipschitzWith 1 φ) {b : ℝ}
    (hu : ∀ x ∈ tsupport u, φ x ≤ b) :
    ∀ x ∈ tsupport (applyOperations ops u), φ x ≤ b+(ops.map CylinderOperation.scale).sum := by
  induction ops generalizing u b with
  | nil => simpa using hu
  | cons r rs ih =>
    have hnew : ∀ x ∈ tsupport (r.act u), φ x ≤ b+r.scale := by
      simpa only [CylinderOperation.act, NNReal.coe_one, mul_one] using localOp_support_bound r.isG r.point r.scale_pos u φ hφ b hu
    have hh := ih (r.act u) hnew
    simpa only [List.map_cons, List.sum_cons, applyOperations_cons, add_assoc] using hh

structure CylinderBases (Γ : Type*) where
  coordinates : Γ → Finset ℕ
  coordinates_nonempty : ∀ γ, (coordinates γ).Nonempty
  band : Γ → ℕ
  ell : ℕ → ℝ
  ell_pos : ∀ j, 0 < ell j
  base : (γ : Γ) → Cube (coordinates γ) → ℝ
  A : ℝ≥0
  L0 : ℝ≥0
  base_sup : ∀ γ x, |base γ x| ≤ A
  base_lipschitz : ∀ γ, LipschitzWith L0 (base γ)

structure GeneratedRepresentation {Γ : Type*} (B : CylinderBases Γ) (γ : Γ) where
  operations : List (CylinderOperation (B.coordinates γ))
  ordered : operations.Pairwise (fun p q => q.scale ≤ p.scale)
  budget : (operations.map CylinderOperation.scale).sum < B.ell (B.band γ)/2

namespace GeneratedRepresentation
variable {Γ : Type*} {B : CylinderBases Γ} {γ : Γ}

def cubeValue (r : GeneratedRepresentation B γ) : Cube (B.coordinates γ) → ℝ :=
  applyOperations r.operations (B.base γ)

def value (r : GeneratedRepresentation B γ) : C0Ball → ℝ :=
  r.cubeValue ∘ cubeRestrict (B.coordinates γ)

def baseRepresentation (B : CylinderBases Γ) (γ : Γ) : GeneratedRepresentation B γ :=
  ⟨[], by simp, by simpa using half_pos (B.ell_pos (B.band γ))⟩

theorem cubeValue_lipschitz (r : GeneratedRepresentation B γ) :
    LipschitzWith (4^r.operations.length*B.L0) r.cubeValue :=
  applyOperations_lipschitz _ (B.base_lipschitz γ)

theorem value_lipschitz (r : GeneratedRepresentation B γ) :
    LipschitzWith (4^r.operations.length*B.L0) r.value := by
  simpa only [value, mul_one] using r.cubeValue_lipschitz.comp (cubeRestrict_lipschitz (B.coordinates γ))

theorem cubeValue_sup (r : GeneratedRepresentation B γ) :
    ∀ x, |r.cubeValue x| ≤ (2 : ℝ)^r.operations.length*B.A :=
  applyOperations_sup _ B.A.coe_nonneg (B.base_sup γ)

theorem value_sup (r : GeneratedRepresentation B γ) :
    ∀ x, |r.value x| ≤ (2 : ℝ)^r.operations.length*B.A :=
  fun point => r.cubeValue_sup (cubeRestrict (B.coordinates γ) point)

end GeneratedRepresentation

def TClass {Γ : Type*} (B : CylinderBases Γ) (h : ℕ) : Set (C0Ball → ℝ) :=
  {f | ∃ γ, ∃ r : GeneratedRepresentation B γ, r.operations.length ≤ h ∧ f = r.value}

structure TailOperation where
  scaleIndex : ℕ
  tailIndex : ℕ
  isBasic : Bool

namespace TailOperation

def factor (t : TailOperation) (s : C0Ball) : ℝ :=
  if t.isBasic then tailFactor (dyadic t.scaleIndex) (t.tailIndex+1) s.val
  else tailFactor (dyadic t.scaleIndex) (t.tailIndex+1) s.val-1

theorem factor_abs_le (t : TailOperation) (s : C0Ball) : |t.factor s| ≤ 1 := by
  have hl := tailFactor_nonneg (dyadic t.scaleIndex) (t.tailIndex+1) s.val
  have hu := tailFactor_le_one (dyadic t.scaleIndex) (t.tailIndex+1) s.val
  rw [abs_le]
  unfold factor
  split <;> constructor <;> linarith

theorem factor_lipschitz (t : TailOperation) : LipschitzWith (2^t.scaleIndex) t.factor := by
  apply LipschitzWith.of_dist_le_mul
  intro s u
  have hh := (tailFactor_lipschitz (dyadic_pos t.scaleIndex) (t.tailIndex+1)).dist_le_mul s.val u.val
  change dist (tailFactor (dyadic t.scaleIndex) (t.tailIndex+1) s.val)
      (tailFactor (dyadic t.scaleIndex) (t.tailIndex+1) u.val) ≤
      (dyadic t.scaleIndex)⁻¹ * dist s u at hh
  simp only [dyadic, inv_inv] at hh
  simp only [NNReal.coe_pow, NNReal.coe_ofNat]
  cases ht : t.isBasic
  · simpa only [factor, dyadic, ht, Bool.false_eq_true, ↓reduceIte, dist_sub_right] using hh
  · simpa only [factor, dyadic, ht, ↓reduceIte] using hh

end TailOperation

def tailProduct (ts : List TailOperation) (s : C0Ball) : ℝ := (ts.map (fun t => t.factor s)).prod

@[simp] theorem tailProduct_nil (s : C0Ball) : tailProduct [] s = 1 := rfl
@[simp] theorem tailProduct_cons (t : TailOperation) (ts : List TailOperation) (s : C0Ball) :
    tailProduct (t::ts) s = t.factor s * tailProduct ts s := rfl

theorem tailProduct_abs_le (ts : List TailOperation) (s : C0Ball) : |tailProduct ts s| ≤ 1 := by
  induction ts with
  | nil => simp
  | cons t ts ih =>
    rw [tailProduct_cons, abs_mul]
    exact (mul_le_mul (t.factor_abs_le s) ih (abs_nonneg _) zero_le_one).trans_eq (one_mul 1)

theorem bounded_product_lipschitz {X : Type*} [PseudoMetricSpace X]
    {f g : X → ℝ} {K L A B : ℝ≥0} (hf : LipschitzWith K f) (hg : LipschitzWith L g)
    (hfB : ∀ x, |f x| ≤ A) (hgB : ∀ x, |g x| ≤ B) :
    LipschitzWith (A*L+B*K) (fun x => f x*g x) := by
  apply LipschitzWith.of_dist_le_mul
  intro x y
  rw [Real.dist_eq]
  have he : f x*g x-f y*g y = f x*(g x-g y)+g y*(f x-f y) := by ring
  rw [he]
  calc
    _ ≤ |f x*(g x-g y)|+|g y*(f x-f y)| := abs_add_le _ _
    _ = |f x| * |g x-g y|+|g y| * |f x-f y| := by rw [abs_mul, abs_mul]
    _ ≤ A*(L*dist x y)+B*(K*dist x y) := add_le_add
      (mul_le_mul (hfB x) (hg.dist_le_mul x y) (abs_nonneg _) A.coe_nonneg)
      (mul_le_mul (hgB y) (hf.dist_le_mul x y) (abs_nonneg _) B.coe_nonneg)
    _ = _ := by push_cast; ring

theorem tailProduct_lipschitz (ts : List TailOperation) :
    LipschitzWith ((ts.map (fun t => (2 : ℝ≥0)^t.scaleIndex)).sum) (tailProduct ts) := by
  induction ts with
  | nil =>
    change LipschitzWith 0 (fun _ : C0Ball => (1 : ℝ))
    exact LipschitzWith.const 1
  | cons t ts ih =>
    have hh := bounded_product_lipschitz (A := 1) (B := 1) t.factor_lipschitz ih t.factor_abs_le (tailProduct_abs_le ts)
    convert hh using 1 <;> first | rfl | simp only [List.map_cons, List.sum_cons, one_mul, add_comm]

theorem tailProduct_lipschitz_bound (ts : List TailOperation) (h : ℕ)
    (hlen : ts.length ≤ h) (hscale : ∀ t ∈ ts, t.scaleIndex ≤ h) :
    LipschitzWith ((h : ℝ≥0)*2^h) (tailProduct ts) := by
  apply (tailProduct_lipschitz ts).weaken
  calc
    (ts.map (fun t => (2 : ℝ≥0)^t.scaleIndex)).sum ≤
        (ts.map (fun _ => (2 : ℝ≥0)^h)).sum := List.sum_le_sum
          (fun t ht => pow_le_pow_right₀ (by norm_num) (hscale t ht))
    _ = (ts.length : ℝ≥0)*2^h := by simp
    _ ≤ (h : ℝ≥0)*2^h := mul_le_mul_of_nonneg_right (by exact_mod_cast hlen) (by positivity)

def VClass {Γ : Type*} (B : CylinderBases Γ) (h : ℕ) : Set (C0Ball → ℝ) :=
  {f | ∃ γ, ∃ r : GeneratedRepresentation B γ, ∃ ts : List TailOperation,
    r.operations.length ≤ h ∧ B.band γ ≤ h ∧ ts.length ≤ h ∧
      (∀ t ∈ ts, t.scaleIndex ≤ h) ∧ f = fun s => r.value s*tailProduct ts s}

theorem TClass_lipschitz {Γ : Type*} (B : CylinderBases Γ) (h : ℕ) {f : C0Ball → ℝ}
    (hf : f ∈ TClass B h) : LipschitzWith (4^h*B.L0) f := by
  obtain ⟨γ,r,hlen,rfl⟩ := hf
  apply r.value_lipschitz.weaken
  exact mul_le_mul_of_nonneg_right (pow_le_pow_right₀ (by norm_num) hlen) B.L0.coe_nonneg

theorem TClass_sup {Γ : Type*} (B : CylinderBases Γ) (h : ℕ) {f : C0Ball → ℝ}
    (hf : f ∈ TClass B h) : ∀ s, |f s| ≤ (2 : ℝ)^h*B.A := by
  obtain ⟨γ,r,hlen,rfl⟩ := hf
  intro s
  exact (r.value_sup s).trans (mul_le_mul_of_nonneg_right
    (pow_le_pow_right₀ (by norm_num) hlen) B.A.coe_nonneg)

theorem VClass_lipschitz {Γ : Type*} (B : CylinderBases Γ) (h : ℕ) {f : C0Ball → ℝ}
    (hf : f ∈ VClass B h) : LipschitzWith (4^h*B.L0+h*4^h*B.A) f := by
  obtain ⟨γ,r,ts,hren,hband,hlen,hscale,rfl⟩ := hf
  have hu : LipschitzWith (4^h*B.L0) r.value := TClass_lipschitz B h ⟨γ,r,hren,rfl⟩
  have hb := tailProduct_lipschitz_bound ts h hlen hscale
  have hsup : ∀ s, |r.value s| ≤ ((2 : ℝ≥0)^h*B.A : ℝ≥0) := by
    intro s
    simpa only [NNReal.coe_mul, NNReal.coe_pow, NNReal.coe_ofNat] using TClass_sup B h ⟨γ,r,hren,rfl⟩ s
  have hh := bounded_product_lipschitz (B := 1) hu hb hsup (tailProduct_abs_le ts)
  convert hh using 1 ; try rfl
  rw [one_mul]
  have hp : (4 : ℝ≥0)^h = 2^h*2^h := by rw [← mul_pow]; norm_num
  rw [hp]
  ring

theorem VClass_sup {Γ : Type*} (B : CylinderBases Γ) (h : ℕ) {f : C0Ball → ℝ}
    (hf : f ∈ VClass B h) : ∀ s, |f s| ≤ (2 : ℝ)^h*B.A := by
  obtain ⟨γ,r,ts,hren,hband,hlen,hscale,rfl⟩ := hf
  intro s
  rw [abs_mul]
  exact (mul_le_mul (TClass_sup B h ⟨γ,r,hren,rfl⟩ s) (tailProduct_abs_le ts s)
    (abs_nonneg _) (by positivity)).trans_eq (mul_one _)

def sourceClasses {Γ : Type*} (B : CylinderBases Γ) (n : ℕ) : Set (C0Ball → ℝ) :=
  if n % 2 = 0 then TClass B (n/2+1) else VClass B (n/2+1)

@[simp] theorem sourceClasses_even {Γ : Type*} (B : CylinderBases Γ) (h : ℕ) :
    sourceClasses B (2*h) = TClass B (h+1) := by simp [sourceClasses]

@[simp] theorem sourceClasses_odd {Γ : Type*} (B : CylinderBases Γ) (h : ℕ) :
    sourceClasses B (2*h+1) = VClass B (h+1) := by
  have hh : (2*h+1)/2 = h := by omega
  simp [sourceClasses, hh]

theorem tsupport_comp_subset {X Y : Type*} [TopologicalSpace X] [TopologicalSpace Y]
    (f : Y → ℝ) {π : X → Y} (hπ : Continuous π) :
    tsupport (f ∘ π) ⊆ π ⁻¹' tsupport f := by
  apply closure_minimal
  · intro x hx; exact subset_tsupport f hx
  · exact (isClosed_tsupport f).preimage hπ

theorem tsupport_product_subset_left {X : Type*} [TopologicalSpace X] (f g : X → ℝ) :
    tsupport (fun x => f x*g x) ⊆ tsupport f := by
  apply closure_minimal _ (isClosed_tsupport f)
  intro x hx
  exact subset_tsupport f (left_ne_zero_of_mul (show f x*g x ≠ 0 from hx))

namespace GeneratedRepresentation
variable {Γ : Type*} {B : CylinderBases Γ} {γ : Γ}

theorem support_bound (r : GeneratedRepresentation B γ) {φ : Cube (B.coordinates γ) → ℝ}
    (hφ : LipschitzWith 1 φ) {b : ℝ} (hu : ∀ x ∈ tsupport (B.base γ), φ x ≤ b) :
    ∀ s ∈ tsupport r.value,
      φ (cubeRestrict (B.coordinates γ) s) ≤ b+(r.operations.map CylinderOperation.scale).sum := by
  intro s hs
  have hm := tsupport_comp_subset r.cubeValue (cubeRestrict_lipschitz (B.coordinates γ)).continuous hs
  exact applyOperations_support_bound r.operations (B.base γ) hφ hu _ hm

def append (r : GeneratedRepresentation B γ) (op : CylinderOperation (B.coordinates γ))
    (hord : ∀ p ∈ r.operations, op.scale ≤ p.scale)
    (hbudget : (r.operations.map CylinderOperation.scale).sum+op.scale < B.ell (B.band γ)/2) :
    GeneratedRepresentation B γ where
  operations := r.operations++[op]
  ordered := List.pairwise_append.mpr ⟨r.ordered, by simp, by
    intro p hp q hq; have hq' : q=op := by simpa using hq
    subst q; exact hord p hp⟩
  budget := by simpa using hbudget

@[simp] theorem append_cubeValue (r : GeneratedRepresentation B γ) (op : CylinderOperation (B.coordinates γ))
    (hord : ∀ p ∈ r.operations, op.scale ≤ p.scale)
    (hbudget : (r.operations.map CylinderOperation.scale).sum+op.scale < B.ell (B.band γ)/2) :
    (r.append op hord hbudget).cubeValue = op.act r.cubeValue := by
  exact applyOperations_append r.operations [op] (B.base γ)

theorem eventually_append_allowed (r : GeneratedRepresentation B γ) :
    ∀ᶠ a in atTop, (∀ p ∈ r.operations, dyadic a ≤ p.scale) ∧
      (r.operations.map CylinderOperation.scale).sum+dyadic a < B.ell (B.band γ)/2 := by
  have h1 : ∀ᶠ a in atTop, ∀ p ∈ r.operations, dyadic a ≤ p.scale := by
    apply r.operations.finite_toSet.eventually_all.mpr
    intro p hp
    exact dyadic_tendsto.eventually (eventually_le_nhds p.scale_pos)
  have h2 : ∀ᶠ a in atTop, dyadic a < B.ell (B.band γ)/2-(r.operations.map CylinderOperation.scale).sum :=
    dyadic_tendsto.eventually (eventually_lt_nhds (sub_pos.mpr r.budget))
  filter_upwards [h1,h2] with a ha hb
  exact ⟨ha, by linarith⟩

end GeneratedRepresentation

end
end C0Absorption

end OAI