lean/OAI/Computability/MaxCut/Machines/MachineExpanderTableRows.lean

import Mathlib
import OAI.Computability.MaxCut.Machines.MachineExpanderRowFrames
import OAI.Computability.MaxCut.PCP.ExpanderTableEnumeration

namespace OAI

/-!
# Actual execution of all expander-table positions for one vertex

The inner loop calls the complete row machine once per fixed cloud/port position.
The returned state and the successful machine execution are constructed together.
Neither a row execution nor an inner-loop execution is a caller premise.
-/

namespace MaxCutGames.Foundations.Complexity.MachineExpanderTable

open Turing
open PCP.ExpanderTables PCP.ExpanderRowControl PCP.ExpanderTableWords
open PCP.ExpanderTableEnumeration

private def singleStep_inline_MachineExpanderTableRows {α : Type*} (step : α → Option α) (a b : α)
    (h : step a = some b) : StateTransition.EvalsToInTime step a (some b) 1 where
  steps := 1
  evals_in_steps := by change step a = some b; exact h
  steps_le_m := Nat.le_refl _

private def sequence_inline_MachineExpanderTableRows {α : Type*} {step : α → Option α} {a b c : α} {m n : Nat}
    (first : StateTransition.EvalsToInTime step a (some b) m)
    (second : StateTransition.EvalsToInTime step b (some c) n) :
    StateTransition.EvalsToInTime step a (some c) (m + n) := by
  simpa only [Nat.add_comm n m] using
    StateTransition.EvalsToInTime.trans step m n a b (some c) first second

private def widen_inline_MachineExpanderTableRows {α : Type*} {step : α → Option α} {a : α} {b : Option α} {m n : Nat}
    (run : StateTransition.EvalsToInTime step a b m) (bound : m ≤ n) :
    StateTransition.EvalsToInTime step a b n where
  toEvalsTo := run.toEvalsTo
  steps_le_m := run.steps_le_m.trans bound

def tableRowData {v d : Nat} (G : Table v (degree d)) (H : Table (cloudSize d) d)
    (vertex : Fin v) (position : Position d) : MachineExpanderRow.RowData v d :=
  MachineExpanderRow.rowData G H vertex (positionPair position).1 (positionPair position).2

theorem tableRowData_finalValue {v d : Nat} (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (position : Position d) :
    (tableRowData G H vertex position).finalValue = rowValue G H vertex position := rfl

theorem tableRowData_frame0 {v d : Nat} (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (position : Position d) (output : List Bool) :
    MachineExpanderRow.frame0 (tableRowData G H vertex position) output =
      rowTapes vertex.val (encodeWords (rotationWords G)) output := by
  funext tape
  cases tape <;> rfl

theorem tableRowData_finalFrame {v d : Nat} (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (position : Position d) (output : List Bool) :
    MachineExpanderRow.emittedWord .output
      (MachineExpanderRow.frame0 (tableRowData G H vertex position) output)
      (tableRowData G H vertex position).finalValue =
      rowTapes vertex.val (encodeWords (rotationWords G))
        ((encodeWord (rowValue G H vertex position)).reverse ++ output) := by
  rw [tableRowData_frame0, tableRowData_finalValue]
  funext tape
  cases tape <;> simp [MachineExpanderRow.emittedWord, rowTapes]

variable {ρ : Type} [Fintype ρ] {v d : Nat}

def rowAfterState (positive : 0 < d) (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (state : State ρ d) : State ρ d :=
  (MachineExpanderRow.divisionState positive (caller state)
    (tableRowData G H vertex state.2).control2 none, state.2)

omit [Fintype ρ] in
@[simp] theorem rowAfterState_position (positive : 0 < d) (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (state : State ρ d) :
    (rowAfterState positive G H vertex state).2 = state.2 := rfl

omit [Fintype ρ] in
@[simp] theorem caller_rowAfterState (positive : 0 < d) (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (state : State ρ d) :
    caller (rowAfterState positive G H vertex state) = caller state := rfl

/-- Preparation and one actual embedded row call, with the two extra tapes
retained. The row value is computed from the actual old and small tables. -/
def preparedRowInTime (positive : 0 < d) (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (state : State ρ d)
    (remaining : Nat) (output countSuffix result : List Bool) :
    StateTransition.EvalsToInTime (TM2.step (program positive H))
      ⟨some (.inr .prepareRow), state,
        boundaryTapes vertex.val remaining (encodeWords (rotationWords G)) output countSuffix result⟩
      (some ⟨some (.inr .afterRow), rowAfterState positive G H vertex state,
        boundaryTapes vertex.val remaining (encodeWords (rotationWords G))
          ((encodeWord (rowValue G H vertex state.2)).reverse ++ output) countSuffix result⟩)
      (1 + 80 * ((encodeWords (rotationWords G)).length + 1)) := by
  have raw := rowExecution positive H state.2 (extraTapes remaining countSuffix result)
    (MachineExpanderRow.rowInTime positive (tableRowData G H vertex state.2) output (caller state))
  have run : StateTransition.EvalsToInTime (TM2.step (program positive H))
      ⟨some (.inl .initialize), prepareState positive H state,
        boundaryTapes vertex.val remaining (encodeWords (rotationWords G)) output countSuffix result⟩
      (some ⟨some (.inr .afterRow), rowAfterState positive G H vertex state,
        boundaryTapes vertex.val remaining (encodeWords (rotationWords G))
          ((encodeWord (rowValue G H vertex state.2)).reverse ++ output) countSuffix result⟩)
      (80 * ((encodeWords (rotationWords G)).length + 1)) := by
    rw [tableRowData_finalFrame, tableRowData_frame0] at raw
    simpa only [MachineEmbedding.configuration, MachineEmbedding.label, rowReturn,
      prepareState, boundaryState, rowAfterState, boundaryTapes,
      MachineExpanderRow.RowData.tableLength, MachineExpanderRow.RowData.control0,
      tableRowData, MachineExpanderRow.rowData] using raw
  exact sequence_inline_MachineExpanderTableRows
    (singleStep_inline_MachineExpanderTableRows _ _ _ (prepareRowStep positive H
      (boundaryTapes vertex.val remaining (encodeWords (rotationWords G)) output countSuffix result)
      state)) run

/-- A successful suffix of the finite position loop, returning actual finite
state together with the execution certificate and its preserved caller. -/
structure VertexSuffixRun (positive : 0 < d) (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (state : State ρ d)
    (remaining : Nat) (output countSuffix result : List Bool) where
  finalState : State ρ d
  caller_preserved : caller finalState = caller state
  position_zero : finalState.2 = zeroPosition positive
  execution : StateTransition.EvalsToInTime (TM2.step (program positive H))
    ⟨some (.inr .prepareRow), state,
      boundaryTapes vertex.val remaining (encodeWords (rotationWords G)) output countSuffix result⟩
    (some ⟨some (.inr .vertexGuard), finalState,
      boundaryTapes (vertex.val + 1) remaining (encodeWords (rotationWords G))
        (accumulate ((vertexWords G H vertex).drop state.2.val) output) countSuffix result⟩)
    ((rowFactor d - state.2.val) * (80 * ((encodeWords (rotationWords G)).length + 1) + 2))

private def suffixRun_aux_inline_MachineExpanderTableRows (positive : 0 < d) (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (remaining : Nat)
    (countSuffix result : List Bool) (n : Nat) :
    (state : State ρ d) → state.2.val + n = rowFactor d → (output : List Bool) →
      VertexSuffixRun positive G H vertex state remaining output countSuffix result := by
  induction n with
  | zero =>
      intro state count output
      have hp := state.2.isLt
      exact False.elim (by omega)
  | succ n ih =>
      intro state count output
      let after := rowAfterState positive G H vertex state
      let nextOutput := (encodeWord (rowValue G H vertex state.2)).reverse ++ output
      have row := preparedRowInTime positive G H vertex state remaining output countSuffix result
      by_cases last : n = 0
      · have hp : state.2.val + 1 = rowFactor d := by omega
        have finish := singleStep_inline_MachineExpanderTableRows _ _ _ (afterRow_last_boundaryStep positive H vertex.val remaining
          (encodeWords (rotationWords G)) nextOutput countSuffix result after (by
            change ¬ state.2.val + 1 < rowFactor d
            omega))
        refine ⟨resetPositionState positive after, ?_, rfl, ?_⟩
        · rfl
        · have all := sequence_inline_MachineExpanderTableRows row finish
          have words : accumulate ((vertexWords G H vertex).drop state.2.val) output =
              nextOutput := by
            rw [vertexWords_drop_last G H vertex state.2 hp]
            rfl
          have budget : rowFactor d - state.2.val = 1 := by omega
          rw [words, budget, Nat.one_mul]
          exact widen_inline_MachineExpanderTableRows all (by omega)
      · have more : state.2.val + 1 < rowFactor d := by omega
        let next := advancePositionState positive after
        have nextPositionValue : next.2.val = state.2.val + 1 :=
          nextPosition_val_of_lt positive state.2 more
        have nextCount : next.2.val + n = rowFactor d := by omega
        let tail := ih next nextCount nextOutput
        have advance := singleStep_inline_MachineExpanderTableRows _ _ _ (afterRow_moreStep positive H
          (boundaryTapes vertex.val remaining (encodeWords (rotationWords G))
            nextOutput countSuffix result) after more)
        have all := sequence_inline_MachineExpanderTableRows (sequence_inline_MachineExpanderTableRows row advance) tail.execution
        refine ⟨tail.finalState, ?_, tail.position_zero, ?_⟩
        · exact tail.caller_preserved
        · have words : accumulate ((vertexWords G H vertex).drop state.2.val) output =
              accumulate ((vertexWords G H vertex).drop next.2.val) nextOutput := by
            rw [vertexWords_drop_succ G H vertex state.2, nextPositionValue]
            rfl
          rw [words]
          apply widen_inline_MachineExpanderTableRows all
          have hcount : rowFactor d - state.2.val = n + 1 := by omega
          have hnext : rowFactor d - next.2.val = n := by omega
          rw [hcount, hnext, Nat.add_mul, Nat.one_mul]
          omega

def suffixInTime (positive : 0 < d) (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (state : State ρ d)
    (remaining : Nat) (output countSuffix result : List Bool) :
    VertexSuffixRun positive G H vertex state remaining output countSuffix result :=
  suffixRun_aux_inline_MachineExpanderTableRows positive G H vertex remaining countSuffix result
    (rowFactor d - state.2.val) state (by have h := state.2.isLt; omega) output

/-- The complete inner loop for one vertex, starting at position zero. -/
structure VertexRun (positive : 0 < d) (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (state : State ρ d)
    (remaining : Nat) (output countSuffix result : List Bool) where
  finalState : State ρ d
  caller_preserved : caller finalState = caller state
  position_zero : finalState.2 = zeroPosition positive
  execution : StateTransition.EvalsToInTime (TM2.step (program positive H))
    ⟨some (.inr .prepareRow), state,
      boundaryTapes vertex.val remaining (encodeWords (rotationWords G)) output countSuffix result⟩
    (some ⟨some (.inr .vertexGuard), finalState,
      boundaryTapes (vertex.val + 1) remaining (encodeWords (rotationWords G))
        (accumulate (vertexWords G H vertex) output) countSuffix result⟩)
    (rowFactor d * (80 * ((encodeWords (rotationWords G)).length + 1) + 2))

def vertexInTime (positive : 0 < d) (G : Table v (degree d))
    (H : Table (cloudSize d) d) (vertex : Fin v) (state : State ρ d)
    (position : state.2 = zeroPosition positive)
    (remaining : Nat) (output countSuffix result : List Bool) :
    VertexRun positive G H vertex state remaining output countSuffix result := by
  let run := suffixInTime positive G H vertex state remaining output countSuffix result
  refine ⟨run.finalState, run.caller_preserved, run.position_zero, ?_⟩
  have zero : state.2.val = 0 := congrArg Fin.val position
  simpa only [zero, List.drop_zero, Nat.sub_zero] using run.execution

end MaxCutGames.Foundations.Complexity.MachineExpanderTable

/-!
# Actual outer vertex iteration for expander tables

The invariant is the reversed unary encoding of all completed vertices. Each
positive unary guard invokes the proved complete fixed-position row loop;
the zero guard enters the actual output-reversal phase. No execution premise
is supplied by the caller.
-/

namespace MaxCutGames.Foundations.Complexity.MachineExpanderTable

open Turing MachineComposition
open PCP.ExpanderTables PCP.ExpanderRowControl PCP.ExpanderTableWords
open PCP.ExpanderTableEnumeration

def oldTableWord {v d : Nat} (G : Table v (degree d)) : List Bool :=
  encodeWords (rotationWords G)

def accumulatedVertices {v d : Nat} (G : Table v (degree d))
    (H : Table (cloudSize d) d) (current : Nat) : List Bool :=
  accumulate (priorVertices G H current) []

@[simp] theorem accumulatedVertices_zero {v d : Nat} (G : Table v (degree d))
    (H : Table (cloudSize d) d) : accumulatedVertices G H 0 = [] := by
  simp [accumulatedVertices, accumulate]

theorem accumulatedVertices_succ {v d : Nat} (G : Table v (degree d))
    (H : Table (cloudSize d) d) (current : Nat) (valid : current < v) :
    accumulatedVertices G H (current + 1) =
      accumulate (vertexWords G H ⟨current, valid⟩) (accumulatedVertices G H current) := by
  simp only [accumulatedVertices, priorVertices_succ G H current valid, accumulate_append]

theorem accumulatedVertices_full {v d : Nat} (G : Table v (degree d))
    (H : Table (cloudSize d) d) : accumulatedVertices G H v =
      (encodeWords (rotationWords (step G H))).reverse := by
  simp [accumulatedVertices, accumulate_generatedWords]

def vertexBodyBudget {v d : Nat} (G : Table v (degree d)) : Nat :=
  rowFactor d * (80 * ((oldTableWord G).length + 1) + 2)

def vertexLoopBudget {v d : Nat} (G : Table v (degree d)) (remaining : Nat) : Nat :=
  remaining * (vertexBodyBudget G + 1) + 1

def vertexLoopTapes {v d : Nat} (G : Table v (degree d)) (H : Table (cloudSize d) d)
    (current remaining : Nat) (suffix : List Bool) : ∀ tape, List (Alphabet tape) :=
  boundaryTapes current remaining (oldTableWord G) (accumulatedVertices G H current) suffix []

structure VertexLoopRun {v d : Nat} {ρ : Type} [Fintype ρ]
    (positive : 0 < d) (G : Table v (degree d)) (H : Table (cloudSize d) d)
    (current remaining : Nat) (state : State ρ d) (suffix : List Bool) where
  finalState : State ρ d
  caller_preserved : caller finalState = caller state
  position_zero : finalState.2 = zeroPosition positive
  execution : StateTransition.EvalsToInTime (TM2.step (program positive H))
    ⟨some (.inr .vertexGuard), state, vertexLoopTapes G H current remaining suffix⟩
    (some ⟨some (.inr .reverseOutput), finalState, vertexLoopTapes G H v 0 suffix⟩)
    (vertexLoopBudget G remaining)

private def boundarySingleStep_inline_MachineExpanderTableLoop {S : Type*} (f : S → Option S) (a b : S)
    (h : f a = some b) : StateTransition.EvalsToInTime f a (some b) 1 where
  steps := 1
  evals_in_steps := by change f a = some b; exact h
  steps_le_m := Nat.le_refl _

/-- Execute every remaining vertex in the common finite table program. -/
def vertexLoopInTime {v d : Nat} {ρ : Type} [Fintype ρ]
    (positive : 0 < d) (G : Table v (degree d)) (H : Table (cloudSize d) d)
    (current remaining : Nat) (state : State ρ d) (suffix : List Bool)
    (count : current + remaining = v) (position : state.2 = zeroPosition positive) :
    VertexLoopRun positive G H current remaining state suffix := by
  induction remaining generalizing current state with
  | zero =>
      have hc : current = v := by omega
      subst current
      refine ⟨clearRegister state, caller_clearRegister state, ?_, ?_⟩
      · simpa only [clearRegister] using position
      · simpa only [vertexLoopBudget, Nat.zero_mul, Nat.zero_add, vertexLoopTapes] using
          boundarySingleStep_inline_MachineExpanderTableLoop _ _ _ (vertexGuard_boundary_zeroStep positive H v (oldTableWord G)
            (accumulatedVertices G H v) suffix [] state)
  | succ remaining ih =>
      have valid : current < v := by omega
      let vertex : Fin v := ⟨current, valid⟩
      let body := vertexInTime positive G H vertex (clearRegister state)
        (by simpa only [clearRegister] using position) remaining
        (accumulatedVertices G H current) suffix []
      have nextCount : current + 1 + remaining = v := by omega
      let rest := ih (current + 1) body.finalState nextCount body.position_zero
      have output_eq : accumulate (vertexWords G H vertex)
          (accumulatedVertices G H current) = accumulatedVertices G H (current + 1) :=
        (accumulatedVertices_succ G H current valid).symm
      let guard := boundarySingleStep_inline_MachineExpanderTableLoop _ _ _
        (vertexGuard_boundary_succStep positive H current remaining (oldTableWord G)
          (accumulatedVertices G H current) suffix [] state)
      have bodyRun : StateTransition.EvalsToInTime (TM2.step (program positive H))
          ⟨some (.inr .prepareRow), clearRegister state,
            boundaryTapes current remaining (oldTableWord G)
              (accumulatedVertices G H current) suffix []⟩
          (some ⟨some (.inr .vertexGuard), body.finalState,
            vertexLoopTapes G H (current + 1) remaining suffix⟩)
          (vertexBodyBudget G) := by
        simpa only [vertexLoopTapes, vertexBodyBudget, oldTableWord, output_eq] using body.execution
      let first := StateTransition.EvalsToInTime.trans (TM2.step (program positive H))
        _ _ _ _ _ guard bodyRun
      let all := StateTransition.EvalsToInTime.trans (TM2.step (program positive H))
        _ _ _ _ _ first rest.execution
      refine ⟨rest.finalState, ?_, rest.position_zero, ?_⟩
      · exact rest.caller_preserved.trans
          (body.caller_preserved.trans (caller_clearRegister state))
      · refine { toEvalsTo := all.toEvalsTo, steps_le_m := ?_ }
        have bound := all.steps_le_m
        simp only [vertexLoopBudget, Nat.succ_mul] at bound ⊢
        omega

end MaxCutGames.Foundations.Complexity.MachineExpanderTable

namespace MaxCutGames.Foundations.Complexity.MachineExpanderTable

open Turing
open MachineComposition
open PCP.ExpanderTables PCP.ExpanderRowControl

variable {ρ : Type} {d : Nat}

@[simp] theorem clearRegister_position (state : State ρ d) :
    (clearRegister state).2 = state.2 := rfl

@[simp] theorem clearRegister_register (state : State ρ d) :
    (clearRegister state).1.2 = none := rfl

@[simp] theorem clearRegister_idempotent (state : State ρ d) :
    clearRegister (clearRegister state) = clearRegister state := rfl

theorem boundaryTapes_reverse_update (vertex remaining : Nat)
    (oldTable output countSuffix result nextOutput nextResult : List Bool) :
    Function.update
      (Function.update (boundaryTapes vertex remaining oldTable output countSuffix result)
        (.inl .output) nextOutput)
      (.inr .result) nextResult =
      boundaryTapes vertex remaining oldTable nextOutput countSuffix nextResult := by
  funext tape
  rcases tape with row | extra
  · cases row <;>
      simp [boundaryTapes, rowTapes, MachineEmbedding.tapes, Function.update]
  · cases extra <;>
      simp [boundaryTapes, extraTapes, MachineEmbedding.tapes, Function.update]

variable [Fintype ρ]

/-- Exact execution of the entire final reverse loop, including its empty
test. No reversal-execution hypothesis is assumed. -/
theorem reverseOutputTrace (positive : 0 < d) (H : Table (cloudSize d) d)
    (vertex remaining : Nat) (oldTable output countSuffix result : List Bool)
    (state : State ρ d) :
    (advance (TM2.step (program positive H)))^[output.length + 1]
      (some ⟨some (.inr .reverseOutput), state,
        boundaryTapes vertex remaining oldTable output countSuffix result⟩) =
      some ⟨some (.inr .done), clearRegister state,
        boundaryTapes vertex remaining oldTable [] countSuffix (output.reverse ++ result)⟩ := by
  induction output generalizing result state with
  | nil =>
      simpa only [List.length_nil, Nat.zero_add, Function.iterate_one, advance_some,
        List.reverse_nil, List.nil_append] using
        reverseOutput_nilStep positive H
          (boundaryTapes vertex remaining oldTable [] countSuffix result) state rfl
  | cons symbol output ih =>
      rw [List.length_cons, Function.iterate_succ_apply]
      simp only [advance_some]
      rw [reverseOutput_consStep positive H
        (boundaryTapes vertex remaining oldTable (symbol :: output) countSuffix result)
        state symbol output rfl]
      change (advance (TM2.step (program positive H)))^[output.length + 1]
        (some ⟨some (.inr .reverseOutput), ((state.1.1, some symbol), state.2),
          Function.update
            (Function.update
              (boundaryTapes vertex remaining oldTable (symbol :: output) countSuffix result)
              (.inl .output) output)
            (.inr .result) (symbol :: result)⟩) = _
      rw [boundaryTapes_reverse_update]
      simpa only [clearRegister, List.reverse_cons, List.append_assoc,
        List.singleton_append] using
        ih (symbol :: result) ((state.1.1, some symbol), state.2)

/-- The actual `done` statement halts one transition after reversal completes. -/
theorem reverseOutputHaltTrace (positive : 0 < d) (H : Table (cloudSize d) d)
    (vertex remaining : Nat) (oldTable output countSuffix result : List Bool)
    (state : State ρ d) :
    (advance (TM2.step (program positive H)))^[output.length + 2]
      (some ⟨some (.inr .reverseOutput), state,
        boundaryTapes vertex remaining oldTable output countSuffix result⟩) =
      some ⟨none, clearRegister state,
        boundaryTapes vertex remaining oldTable [] countSuffix (output.reverse ++ result)⟩ := by
  rw [show output.length + 2 = (output.length + 1) + 1 by omega,
    Function.iterate_succ_apply',
    reverseOutputTrace positive H vertex remaining oldTable output countSuffix result state]
  exact doneStep positive H
    (boundaryTapes vertex remaining oldTable [] countSuffix (output.reverse ++ result))
    (clearRegister state)

def reverseOutputInTime (positive : 0 < d) (H : Table (cloudSize d) d)
    (vertex remaining : Nat) (oldTable output countSuffix result : List Bool)
    (state : State ρ d) :
    StateTransition.EvalsToInTime (TM2.step (program positive H))
      ⟨some (.inr .reverseOutput), state,
        boundaryTapes vertex remaining oldTable output countSuffix result⟩
      (some ⟨some (.inr .done), clearRegister state,
        boundaryTapes vertex remaining oldTable [] countSuffix (output.reverse ++ result)⟩)
      (output.length + 1) where
  steps := output.length + 1
  evals_in_steps := reverseOutputTrace positive H vertex remaining oldTable output countSuffix result state
  steps_le_m := Nat.le_refl _

def reverseOutputHaltInTime (positive : 0 < d) (H : Table (cloudSize d) d)
    (vertex remaining : Nat) (oldTable output countSuffix result : List Bool)
    (state : State ρ d) :
    StateTransition.EvalsToInTime (TM2.step (program positive H))
      ⟨some (.inr .reverseOutput), state,
        boundaryTapes vertex remaining oldTable output countSuffix result⟩
      (some ⟨none, clearRegister state,
        boundaryTapes vertex remaining oldTable [] countSuffix (output.reverse ++ result)⟩)
      (output.length + 2) where
  steps := output.length + 2
  evals_in_steps := reverseOutputHaltTrace positive H vertex remaining oldTable output countSuffix result state
  steps_le_m := Nat.le_refl _

end MaxCutGames.Foundations.Complexity.MachineExpanderTable

/-!
# Complete finite machine execution for the next expander table

The initialized old table and unary vertex count are consumed by one actual
finite program. The machine writes precisely the complete square/zigzag
rotation table, preserving its old table and all promised framing. The bound
is quadratic in the unary old-table length for each fixed small graph.
-/

namespace MaxCutGames.Foundations.Complexity.MachineExpanderTable

open Turing MachineComposition
open PCP.ExpanderTables PCP.ExpanderRowControl PCP.ExpanderTableWords
open PCP.ExpanderTableEnumeration

def completeBudget {v d : Nat} (G : Table v (degree d)) (H : Table (cloudSize d) d) : Nat :=
  1 + vertexLoopBudget G v + ((encodeWords (rotationWords (step G H))).length + 2)

def timeCoefficient (d : Nat) : Nat :=
  rowFactor d * (rowFactor d + 1) + 82 * rowFactor d + 5

noncomputable def timePolynomial (d : Nat) : Polynomial Nat :=
  Polynomial.C (timeCoefficient d) * (Polynomial.X + 1) ^ 2

theorem vertices_le_word_length {v d : Nat} (positive : 0 < d)
    (G : Table v (degree d)) : v ≤ (oldTableWord G).length := by
  have hq : 1 ≤ degree d := Nat.mul_pos positive positive
  have hv : v ≤ v * degree d := by simpa using Nat.mul_le_mul_left v hq
  have hr : v * degree d ≤ (oldTableWord G).length := by
    simp only [oldTableWord, encodeWords_length, rotationWords_length]
    omega
  exact hv.trans hr

/-- All actual loop, row, and final reversal costs are bounded quadratically. -/
theorem completeBudget_le {v d : Nat} (positive : 0 < d)
    (G : Table v (degree d)) (H : Table (cloudSize d) d) :
    completeBudget G H ≤ (timePolynomial d).eval (oldTableWord G).length := by
  let L := (oldTableWord G).length
  let M := rowFactor d
  have vBound : v ≤ L + 1 := (vertices_le_word_length positive G).trans (Nat.le_succ L)
  have emitBound : 80 * (L + 1) + 2 ≤ 82 * (L + 1) := by omega
  have bodyBound : vertexBodyBudget G + 1 ≤ (82 * M + 1) * (L + 1) := by
    have mulBound := Nat.mul_le_mul_left M emitBound
    change M * (80 * (L + 1) + 2) + 1 ≤ _
    nlinarith
  have iterations := Nat.mul_le_mul vBound bodyBound
  have loopBound : v * (vertexBodyBudget G + 1) ≤ (82 * M + 1) * (L + 1)^2 := by
    calc
      _ ≤ (L + 1) * ((82 * M + 1) * (L + 1)) := iterations
      _ = _ := by ring
  have rowBound : v * M ≤ M * (L + 1) := by
    simpa only [Nat.mul_comm v M] using Nat.mul_le_mul_left M vBound
  have rowSuccBound : v * M + 1 ≤ (M + 1) * (L + 1) := by nlinarith
  have productBound := Nat.mul_le_mul rowBound rowSuccBound
  have lengthBound : (encodeWords (rotationWords (step G H))).length ≤
      M * (M + 1) * (L + 1)^2 := by
    calc
      _ ≤ (v * M) * (v * M + 1) := by
        simpa only [generatedWords_eq_rotationWords] using encode_generatedWords_length_le G H
      _ ≤ (M * (L + 1)) * ((M + 1) * (L + 1)) := productBound
      _ = _ := by ring
  have oneBound : 1 ≤ (L + 1)^2 := by nlinarith
  have combined := Nat.add_le_add loopBound lengthBound
  simp only [timePolynomial, Polynomial.eval_mul, Polynomial.eval_C, Polynomial.eval_pow,
    Polynomial.eval_add, Polynomial.eval_X, Polynomial.eval_one]
  change completeBudget G H ≤ (M * (M + 1) + 82 * M + 5) * (L + 1)^2
  unfold completeBudget vertexLoopBudget
  nlinarith

structure TableRun {v d : Nat} {ρ : Type} [Fintype ρ]
    (positive : 0 < d) (G : Table v (degree d)) (H : Table (cloudSize d) d)
    (state : State ρ d) (suffix : List Bool) where
  finalState : State ρ d
  caller_preserved : caller finalState = caller state
  position_zero : finalState.2 = zeroPosition positive
  execution : StateTransition.EvalsToInTime (TM2.step (program positive H))
    ⟨some (.inr .initialize), state, initialTapes v (oldTableWord G) suffix⟩
    (some ⟨none, finalState,
      finalTapes v (oldTableWord G) (encodeWords (rotationWords (step G H))) suffix⟩)
    ((timePolynomial d).eval (oldTableWord G).length)

private def initializeInTime_inline_MachineExpanderTable {v d : Nat} {ρ : Type} [Fintype ρ]
    (positive : 0 < d) (G : Table v (degree d)) (H : Table (cloudSize d) d)
    (state : State ρ d) (suffix : List Bool) :
    StateTransition.EvalsToInTime (TM2.step (program positive H))
      ⟨some (.inr .initialize), state, initialTapes v (oldTableWord G) suffix⟩
      (some ⟨some (.inr .vertexGuard), initialState positive H (caller state),
        vertexLoopTapes G H 0 v suffix⟩) 1 where
  steps := 1
  evals_in_steps := by
    change TM2.step (program (ρ := ρ) positive H)
      ⟨some (.inr .initialize), state, initialTapes v (oldTableWord G) suffix⟩ =
      some ⟨some (.inr .vertexGuard), initialState positive H (caller state),
        vertexLoopTapes G H 0 v suffix⟩
    simpa only [vertexLoopTapes, accumulatedVertices_zero] using
      initialize_boundaryStep positive H v (oldTableWord G) suffix state
  steps_le_m := Nat.le_refl _

/-- Construct the entire table execution from its actual initialized inputs.
No row trace, loop trace, or abstract computational witness is a hypothesis. -/
def tableInTime {v d : Nat} {ρ : Type} [Fintype ρ]
    (positive : 0 < d) (G : Table v (degree d)) (H : Table (cloudSize d) d)
    (state : State ρ d) (suffix : List Bool) : TableRun positive G H state suffix := by
  let loop := vertexLoopInTime positive G H 0 v
    (initialState positive H (caller state)) suffix (by omega) rfl
  let initialRun := initializeInTime_inline_MachineExpanderTable positive G H state suffix
  have finish : StateTransition.EvalsToInTime (TM2.step (program positive H))
      ⟨some (.inr .reverseOutput), loop.finalState, vertexLoopTapes G H v 0 suffix⟩
      (some ⟨none, clearRegister loop.finalState,
        finalTapes v (oldTableWord G) (encodeWords (rotationWords (step G H))) suffix⟩)
      ((encodeWords (rotationWords (step G H))).length + 2) := by
    simpa only [vertexLoopTapes, finalTapes, accumulatedVertices_full, List.reverse_reverse,
      List.append_nil, List.length_reverse] using
      reverseOutputHaltInTime positive H v 0 (oldTableWord G)
        (accumulatedVertices G H v) suffix [] loop.finalState
  let first := StateTransition.EvalsToInTime.trans (TM2.step (program positive H))
    _ _ _ _ _ initialRun loop.execution
  let all := StateTransition.EvalsToInTime.trans (TM2.step (program positive H))
    _ _ _ _ _ first finish
  refine ⟨clearRegister loop.finalState, ?_, ?_, ?_⟩
  · exact (caller_clearRegister loop.finalState).trans loop.caller_preserved
  · simpa only [clearRegister] using loop.position_zero
  · refine { toEvalsTo := all.toEvalsTo, steps_le_m := ?_ }
    have bound := all.steps_le_m
    have polynomialBound := completeBudget_le positive G H
    unfold completeBudget at polynomialBound
    omega

end MaxCutGames.Foundations.Complexity.MachineExpanderTable

namespace MaxCutGames.Foundations.Complexity.MachineExpanderFamily

open PCP.ExpanderTables PCP.ExpanderRowControl PCP.ExpanderTableWords

/-- The six nonempty tape roles that may occur between expansion phases. -/
def cycleWords (remaining : Nat) (word current vertex count result suffix : List Bool) :
    Tape → List Bool
  | .inl (.inl .table) => word
  | .inl (.inl .inputVertex) => vertex
  | .inl (.inr .vertexCount) => count
  | .inl (.inr .result) => result
  | .inr .remainingLevel => encodeWord remaining ++ suffix
  | .inr .currentSize => current
  | _ => []

def cycleTapes (remaining : Nat) (word current vertex count result suffix : List Bool) :
    (tape : Tape) → List (Alphabet tape) :=
  fromBoolTapes (cycleWords remaining word current vertex count result suffix)

@[simp] theorem toBool_cycleTapes (remaining : Nat)
    (word current vertex count result suffix : List Bool) :
    toBoolTapes (cycleTapes remaining word current vertex count result suffix) =
      cycleWords remaining word current vertex count result suffix := toBool_fromBool _

theorem boundaryTapes_eq_cycleTapes (remaining current : Nat) (word suffix : List Bool) :
    boundaryTapes remaining current word suffix =
      cycleTapes remaining word (encodeWord current) [] [] [] suffix := by
  funext tape
  rcases tape with tape | tape
  · rcases tape with row | extra
    · cases row <;> rfl
    · cases extra <;> rfl
  · cases tape <;> rfl

def copyFrame (remaining current : Nat) (word suffix : List Bool) :
    (tape : Tape) → List (Alphabet tape) :=
  MachineEmbedding.tapes (MachineExpanderTable.initialTapes current word [])
    (extraFrame remaining current suffix)

def returnFrame (remaining current : Nat) (oldWord newWord suffix : List Bool) :
    (tape : Tape) → List (Alphabet tape) :=
  MachineEmbedding.tapes (MachineExpanderTable.finalTapes current oldWord newWord [])
    (extraFrame remaining current suffix)

def installedFrame (remaining current : Nat) (newWord suffix : List Bool) :
    (tape : Tape) → List (Alphabet tape) :=
  cycleTapes remaining newWord [] (encodeWord current) (encodeWord 0) [] suffix

def multipliedFrame (d remaining current : Nat) (newWord suffix : List Bool) :
    (tape : Tape) → List (Alphabet tape) :=
  cycleTapes remaining newWord (encodeWord (cloudSize d * current))
    (encodeWord current) (encodeWord 0) [] suffix

theorem copyFrame_eq_cycleTapes (remaining current : Nat) (word suffix : List Bool) :
    copyFrame remaining current word suffix =
      cycleTapes remaining word (encodeWord current) [] (encodeWord current) [] suffix := by
  funext tape
  rcases tape with tape | tape
  · rcases tape with row | extra
    · cases row <;> rfl
    · cases extra <;> simp [copyFrame, MachineEmbedding.tapes,
        MachineExpanderTable.initialTapes, MachineExpanderTable.extraTapes,
        cycleTapes, fromBoolTapes, boolWord, cycleWords]
  · cases tape <;> rfl

theorem returnFrame_eq_cycleTapes (remaining current : Nat)
    (oldWord newWord suffix : List Bool) :
    returnFrame remaining current oldWord newWord suffix =
      cycleTapes remaining oldWord (encodeWord current) (encodeWord current)
        (encodeWord 0) newWord suffix := by
  funext tape
  rcases tape with tape | tape
  · rcases tape with row | extra
    · cases row <;> rfl
    · cases extra <;> simp [returnFrame, MachineEmbedding.tapes,
        MachineExpanderTable.finalTapes, MachineExpanderTable.boundaryTapes,
        MachineExpanderTable.extraTapes, cycleTapes, fromBoolTapes, boolWord, cycleWords]
  · cases tape <;> rfl

theorem copyFrame_eq_update (remaining current : Nat) (word suffix : List Bool) :
    Function.update (boundaryTapes remaining current word suffix)
      vertexCountTape (encodeWord current) = copyFrame remaining current word suffix := by
  rw [boundaryTapes_eq_cycleTapes, copyFrame_eq_cycleTapes]
  funext tape
  rcases tape with tape | tape
  · rcases tape with row | extra
    · cases row <;> rfl
    · cases extra <;> rfl
  · cases tape <;> rfl

theorem multipliedFrame_eq_update (d remaining current : Nat) (word suffix : List Bool) :
    Function.update (installedFrame remaining current word suffix)
      (.inr .currentSize) (encodeWord (cloudSize d * current)) =
      multipliedFrame d remaining current word suffix := by
  funext tape
  rcases tape with tape | tape
  · rcases tape with row | extra
    · cases row <;> rfl
    · cases extra <;> rfl
  · cases tape <;> rfl

end MaxCutGames.Foundations.Complexity.MachineExpanderFamily

/-!
# Bounds for materializing the actual expander family

The costs use the encoded old and new rotation tables, and the already checked
table-machine polynomial. The finite sum follows the actual recursive table
family. These arithmetic lemmas introduce no execution assumptions and make no
claim that the output is polynomial in an isolated binary level parameter.
-/

namespace MaxCutGames.Foundations.Complexity.MachineExpanderFamilyBounds

open PCP.ExpanderTables PCP.ExpanderRowControl PCP.ExpanderTableWords

noncomputable def resizeCost {v d : Nat} (G : Table v (degree d))
    (H : Table (cloudSize d) d) : Nat :=
  (MachineExpanderTable.timePolynomial d).eval (MachineExpanderTable.oldTableWord G).length +
    6 * v + (MachineExpanderTable.oldTableWord G).length +
    2 * (encodeWords (rotationWords (step G H))).length + 15

def resizeCoefficient (d : Nat) : Nat :=
  MachineExpanderTable.timeCoefficient d * (degree d + 1) ^ 4 +
    3 * (degree d + 1) ^ 2 + 21

/-- The complete unary encoding, including every word delimiter, is counted. -/
theorem wordLength_add_one_le {v q N : Nat} (G : Table v q) (hv : v ≤ N) :
    (encodeWords (rotationWords G)).length + 1 ≤ (q + 1)^2 * (N + 1)^2 := by
  have hlength := encode_rotationWords_length_le G
  have hrow : v * q + 1 ≤ (q + 1) * (N + 1) := by
    have h := Nat.mul_le_mul_right q hv
    nlinarith
  calc
    _ ≤ (v * q + 1)^2 := by nlinarith
    _ ≤ ((q + 1) * (N + 1))^2 := Nat.pow_le_pow_left hrow 2
    _ = _ := by ring

theorem resizeCost_le {v d : Nat} (G : Table v (degree d))
    (H : Table (cloudSize d) d) (N : Nat) (hv : v ≤ N)
    (hnext : v * cloudSize d ≤ N) :
    resizeCost G H ≤ resizeCoefficient d * (N + 1)^4 := by
  let oldL := (MachineExpanderTable.oldTableWord G).length
  let newL := (encodeWords (rotationWords (step G H))).length
  have oldBound : oldL + 1 ≤ (degree d + 1)^2 * (N + 1)^2 :=
    wordLength_add_one_le G hv
  have newBound : newL + 1 ≤ (degree d + 1)^2 * (N + 1)^2 :=
    wordLength_add_one_le (step G H) hnext
  have timeBound : (MachineExpanderTable.timePolynomial d).eval oldL ≤
      MachineExpanderTable.timeCoefficient d * (degree d + 1)^4 * (N + 1)^4 := by
    simp only [MachineExpanderTable.timePolynomial, Polynomial.eval_mul,
      Polynomial.eval_C, Polynomial.eval_pow, Polynomial.eval_add,
      Polynomial.eval_X, Polynomial.eval_one]
    calc
      _ ≤ MachineExpanderTable.timeCoefficient d *
          ((degree d + 1)^2 * (N + 1)^2)^2 :=
        Nat.mul_le_mul_left _ (Nat.pow_le_pow_left oldBound 2)
      _ = _ := by ring
  have pow24 : (N + 1)^2 ≤ (N + 1)^4 :=
    Nat.pow_le_pow_right (Nat.succ_pos N) (by decide)
  have overheadBound : oldL + 2 * newL ≤
      3 * (degree d + 1)^2 * (N + 1)^4 := by
    have h := Nat.mul_le_mul_left ((degree d + 1)^2) pow24
    calc
      _ ≤ 3 * ((degree d + 1)^2 * (N + 1)^2) := by omega
      _ ≤ 3 * ((degree d + 1)^2 * (N + 1)^4) := Nat.mul_le_mul_left 3 h
      _ = _ := by ring
  have npow : N + 1 ≤ (N + 1)^4 := by
    simpa only [pow_one] using
      Nat.pow_le_pow_right (Nat.succ_pos N) (show 1 ≤ 4 by decide)
  have linearBound : 6 * v + 15 ≤ 21 * (N + 1)^4 := by omega
  change (MachineExpanderTable.timePolynomial d).eval oldL + 6 * v + oldL +
    2 * newL + 15 ≤ _
  unfold resizeCoefficient
  nlinarith only [timeBound, overheadBound, linearBound]

theorem vertexCount_monotone {q : Nat} (positive : 0 < q) :
    Monotone (vertexCount q) := by
  intro m n hmn
  rw [vertexCount_eq, vertexCount_eq]
  exact Nat.pow_le_pow_right (Nat.mul_pos positive positive) hmn

theorem level_le_vertexCount {q : Nat} (growth : 1 < q * q) (level : Nat) :
    level ≤ vertexCount q level := by
  have positive : 0 < q := by nlinarith
  induction level with
  | zero => exact Nat.zero_le _
  | succ level ih =>
    have hpos := vertexCount_positive positive level
    have hmul := Nat.mul_le_mul_left (vertexCount q level)
      (show 2 ≤ q * q by omega)
    change level + 1 ≤ vertexCount q level * (q * q)
    nlinarith

noncomputable def resizeSum {d : Nat} (H : Table (cloudSize d) d) (level : Nat) : Nat :=
  ∑ i ∈ Finset.range level, resizeCost (family H i) H

@[simp] theorem resizeSum_zero {d : Nat} (H : Table (cloudSize d) d) :
    resizeSum H 0 = 0 := by simp [resizeSum]

theorem resizeSum_succ {d : Nat} (H : Table (cloudSize d) d) (level : Nat) :
    resizeSum H (level + 1) = resizeSum H level + resizeCost (family H level) H := by
  simp only [resizeSum, Finset.sum_range_succ]

theorem resizeSum_add {d : Nat} (H : Table (cloudSize d) d) (start count : Nat) :
    resizeSum H (start + count) = resizeSum H start +
      ∑ i ∈ Finset.range count, resizeCost (family H (start + i)) H :=
  Finset.sum_range_add (fun i => resizeCost (family H i) H) start count

noncomputable def familyBudget {d : Nat} (H : Table (cloudSize d) d) (level : Nat) : Nat :=
  resizeSum H level + level + 3

@[simp] theorem familyBudget_zero {d : Nat} (H : Table (cloudSize d) d) :
    familyBudget H 0 = 3 := by simp [familyBudget]

theorem familyBudget_succ {d : Nat} (H : Table (cloudSize d) d) (level : Nat) :
    familyBudget H (level + 1) =
      familyBudget H level + resizeCost (family H level) H + 1 := by
  simp only [familyBudget, resizeSum_succ]
  omega

theorem resizeSum_le {d : Nat} (H : Table (cloudSize d) d)
    (growth : 1 < cloudSize d) (level : Nat) :
    resizeSum H level ≤ resizeCoefficient d * (vertexCount (degree d) level + 1)^5 := by
  let N := vertexCount (degree d) level
  have positive : 0 < degree d := by
    have h : 1 < degree d * degree d := growth
    nlinarith
  have hmono := vertexCount_monotone positive
  have hlevel : level ≤ N := level_le_vertexCount growth level
  have eachBound : ∀ i ∈ Finset.range level,
      resizeCost (family H i) H ≤ resizeCoefficient d * (N + 1)^4 := by
    intro i hi
    have hi' : i < level := Finset.mem_range.mp hi
    apply resizeCost_le (family H i) H N
    · exact hmono (by omega)
    · exact hmono (show i + 1 ≤ level by omega)
  have sumBound : resizeSum H level ≤ level * (resizeCoefficient d * (N + 1)^4) := by
    calc
      _ ≤ ∑ _i ∈ Finset.range level, resizeCoefficient d * (N + 1)^4 :=
        Finset.sum_le_sum eachBound
      _ = _ := by simp
  calc
    _ ≤ level * (resizeCoefficient d * (N + 1)^4) := sumBound
    _ ≤ (N + 1) * (resizeCoefficient d * (N + 1)^4) :=
      Nat.mul_le_mul_right _ (hlevel.trans (Nat.le_succ N))
    _ = _ := by ring

/-- All actual resize costs plus the counted-loop overhead. -/
theorem familyBudget_le {d : Nat} (H : Table (cloudSize d) d)
    (growth : 1 < cloudSize d) (level : Nat) :
    familyBudget H level ≤
      (resizeCoefficient d + 4) * (vertexCount (degree d) level + 1)^5 := by
  have hsum := resizeSum_le H growth level
  have hlevel := level_le_vertexCount growth level
  have hpow : vertexCount (degree d) level + 1 ≤
      (vertexCount (degree d) level + 1)^5 := by
    simpa only [pow_one] using Nat.pow_le_pow_right
      (Nat.succ_pos (vertexCount (degree d) level)) (show 1 ≤ 5 by decide)
  have overhead : level + 3 ≤ 4 * (vertexCount (degree d) level + 1)^5 := by omega
  unfold familyBudget
  nlinarith only [hsum, overhead]

theorem paddedSize_le_succ_input (k : Nat) :
    PCP.PreprocessingLevels.paddedSize k ≤ PCP.ExpanderFamily.growth * (k + 1) := by
  by_cases hk : k = 0
  · subst k
    have h := PCP.ExpanderFamily.growth_gt_one
    simp only [PCP.PreprocessingLevels.paddedSize_zero, Nat.zero_add, Nat.mul_one]
    omega
  · exact (PCP.PreprocessingLevels.paddedSize_bounds (Nat.pos_of_ne_zero hk)).2.trans
      (Nat.mul_le_mul_left _ (Nat.le_succ k))

def inputCoefficient : Nat :=
  (resizeCoefficient PCP.Expanders.baseDegree + 4) * (PCP.ExpanderFamily.growth + 1)^5

/-- For the fixed base graph, the bounded padding level has a polynomial cost
in the requested unary size, including size zero. -/
theorem familyBudget_at_boundedLevel_le
    (H : Table (cloudSize PCP.Expanders.baseDegree) PCP.Expanders.baseDegree) (k : Nat) :
    familyBudget H (PCP.PreprocessingLevels.boundedLevel k) ≤ inputCoefficient * (k + 1)^5 := by
  have hg : cloudSize PCP.Expanders.baseDegree = PCP.ExpanderFamily.growth := by
    unfold cloudSize degree PCP.ExpanderFamily.growth
    ring
  have growth : 1 < cloudSize PCP.Expanders.baseDegree := by
    rw [hg]
    exact PCP.ExpanderFamily.growth_gt_one
  have bound := familyBudget_le H growth (PCP.PreprocessingLevels.boundedLevel k)
  rw [PCP.PreprocessingLevels.table_vertexCount_eq_paddedSize] at bound
  have sizeBound : PCP.PreprocessingLevels.paddedSize k + 1 ≤
      (PCP.ExpanderFamily.growth + 1) * (k + 1) := by
    have h := paddedSize_le_succ_input k
    nlinarith
  calc
    _ ≤ (resizeCoefficient PCP.Expanders.baseDegree + 4) *
        (PCP.PreprocessingLevels.paddedSize k + 1)^5 := bound
    _ ≤ (resizeCoefficient PCP.Expanders.baseDegree + 4) *
        ((PCP.ExpanderFamily.growth + 1) * (k + 1))^5 :=
      Nat.mul_le_mul_left _ (Nat.pow_le_pow_left sizeBound 5)
    _ = _ := by unfold inputCoefficient; ring

end MaxCutGames.Foundations.Complexity.MachineExpanderFamilyBounds

end OAI