lean/OAI/Computability/UniqueGames/Machines/MachineBinaryTotalInputMachine.lean

import OAI.Computability.UniqueGames.Machines.MachineBinaryParsingLemmas
import OAI.Computability.UniqueGames.Machines.MachineBinaryValidatorMachine
import OAI.Computability.UniqueGames.Machines.MachineDrain
import OAI.Computability.UniqueGames.Machines.MachineFiniteAlphabet
import OAI.Computability.UniqueGames.Reduction.MachineSubstitution

namespace OAI

/-!
Total raw-input preprocessing for the ordinary binary formula codec. The
machine copies each input bit onto a reverse stack while running the finite
validator. Accepted words are restored verbatim; rejected words are drained
and replaced by the fixed contradictory formula. All three stack alphabets
and all control/register types are finite.
-/

namespace UniqueGamesTheorem.BinaryTotalInputMachine

open Turing
open UniqueGamesTheorem.Foundations.Complexity
open MachineComposition
open UniqueGamesTheorem.Reduction.MachineTransfer
open UniqueGamesTheorem.Reduction.MachineSubstitution
open BinaryValidatorMachine (Mode nextMode run)

inductive Label
  | scan
  | restore
  | drain
  | rejectOutput
  deriving DecidableEq

protected abbrev Label.enumList : List Label := [.scan, .restore, .drain, .rejectOutput]

protected theorem Label.enumList_getElem?_ctorIdx_eq (x : Label) :
    Label.enumList[x.ctorIdx]? = some x := by
  cases x <;> rfl

protected theorem Label.enumList_nodup : Label.enumList.Nodup := by decide

instance : Fintype Label where
  elems := ⟨Label.enumList, Label.enumList_nodup⟩
  complete x := by cases x <;> decide

abbrev Alphabet (_ : Fin 3) := Bool
abbrev State := Mode × Option Bool

def rejectedWord : List Bool := BinaryEncoding.formulaBits BinaryLanguage.rejectBinary

/-- Stack zero is the input, one the output, and two the reversed input.
Branches inspect only the finite validator state and the popped symbol. -/
def instruction : Label → TM2.Stmt Alphabet Label State
  | .scan =>
      .pop 0 (fun state head => (state.1, head))
        (.branch (fun state => state.2.isSome)
          (.push 2 (fun state => state.2.getD false)
            (.load (fun state => (nextMode state.1 (state.2.getD false), none))
              (.goto fun _ => .scan)))
          (.branch (fun state => decide (state.1 = .done))
            (.load (fun _ => (.clause, none)) (.goto fun _ => .restore))
            (.load (fun _ => (.clause, none)) (.goto fun _ => .drain))))
  | .restore => loopAt 2 1 id false .restore none
  | .drain => MachineDrain.drain 2 .drain (some .rejectOutput)
  | .rejectOutput => pushWord 1 rejectedWord.reverse .halt

abbrev machine : FinTM2 where
  K := Fin 3
  k₀ := 0
  k₁ := 1
  Γ := Alphabet
  Λ := Label
  main := .scan
  σ := State
  initialState := (.clause, none)
  m := instruction

def tapes (input output saved : List Bool) : Fin 3 → List Bool
  | 0 => input
  | 1 => output
  | _ => saved

def cfg (label : Option Label) (input output saved : List Bool) (mode : Mode := .clause)
    (register : Option Bool := none) : machine.Cfg :=
  ⟨label, (mode, register), tapes input output saved⟩

@[simp] private theorem tapes_input (input output saved : List Bool) :
    tapes input output saved 0 = input := rfl

@[simp] private theorem tapes_output (input output saved : List Bool) :
    tapes input output saved 1 = output := rfl

@[simp] private theorem tapes_saved (input output saved : List Bool) :
    tapes input output saved 2 = saved := rfl

private theorem update_input (input output saved replacement : List Bool) :
    Function.update (tapes input output saved) 0 replacement =
      tapes replacement output saved := by
  funext k
  fin_cases k <;> rfl

private theorem update_output (input output saved replacement : List Bool) :
    Function.update (tapes input output saved) 1 replacement =
      tapes input replacement saved := by
  funext k
  fin_cases k <;> rfl

private theorem update_saved (input output saved replacement : List Bool) :
    Function.update (tapes input output saved) 2 replacement =
      tapes input output replacement := by
  funext k
  fin_cases k <;> rfl

def afterScan (mode : Mode) : Label := if mode = .done then .restore else .drain

theorem step_scan_empty (output saved : List Bool) (mode : Mode) (register : Option Bool) :
    machine.step (cfg (some .scan) [] output saved mode register) =
      some (cfg (some (afterScan mode)) [] output saved) := by
  change some (TM2.stepAux (instruction .scan) _ _) = _
  by_cases accepted : mode = .done <;>
    simp [instruction, cfg, TM2.stepAux, update_input, afterScan, accepted] <;> rfl

theorem step_scan_cons (bit : Bool) (input output saved : List Bool)
    (mode : Mode) (register : Option Bool) :
    machine.step (cfg (some .scan) (bit :: input) output saved mode register) =
      some (cfg (some .scan) input output (bit :: saved) (nextMode mode bit)) := by
  change some (TM2.stepAux (instruction .scan) _ _) = _
  simp [instruction, cfg, TM2.stepAux, update_input, update_saved]
  rfl

/-- The finite DFA reads every bit, including all bits in its rejection sink.
The trace also records the physical reversed copy needed by the second phase. -/
theorem scanTrace (input output saved : List Bool) (mode : Mode) (register : Option Bool) :
    (advance machine.step)^[input.length + 1]
      (some (cfg (some .scan) input output saved mode register)) =
      some (cfg (some (afterScan (run mode input))) [] output (input.reverse ++ saved)) := by
  induction input generalizing saved mode register with
  | nil =>
      simpa only [List.length_nil, Nat.zero_add, Function.iterate_one,
        advance_some, run, List.reverse_nil, List.nil_append] using
          step_scan_empty output saved mode register
  | cons bit input ih =>
      rw [List.length_cons, Function.iterate_succ_apply]
      simp only [advance_some]
      rw [step_scan_cons]
      simpa only [run, List.reverse_cons, List.append_assoc, List.singleton_append] using
        ih (bit :: saved) (nextMode mode bit) none

theorem restoreTrace (saved output : List Bool) (register : Option Bool) :
    (advance machine.step)^[saved.length + 1]
      (some (cfg (some .restore) [] output saved .clause register)) =
      some (cfg none [] (saved.reverse ++ output) []) := by
  change (nextAt (1 : Fin 3) instruction)^[saved.length + 1]
    (some ⟨some .restore, (Mode.clause, register), tapes [] output saved⟩) =
    some ⟨none, (Mode.clause, none), tapes [] (saved.reverse ++ output) []⟩
  have trace := transferAt_steps (2 : Fin 3) 1 (by decide) id false .restore none
    instruction rfl (tapes [] [] []) saved output Mode.clause register
  simpa only [tapesAt, update_saved, update_output,
    List.map_id_fun, id_eq] using trace

theorem drainTrace (saved output : List Bool) (register : Option Bool) :
    (advance machine.step)^[saved.length + 1]
      (some (cfg (some .drain) [] output saved .clause register)) =
      some (cfg (some .rejectOutput) [] output []) := by
  change (advance (TM2.step instruction))^[saved.length + 1]
    (some ⟨some .drain, (Mode.clause, register), tapes [] output saved⟩) =
    some ⟨some .rejectOutput, (Mode.clause, none), tapes [] output []⟩
  have trace := MachineDrain.drainTrace (2 : Fin 3) .drain (some .rejectOutput)
    instruction rfl (tapes [] output []) saved Mode.clause register
  simpa only [update_saved] using trace

theorem step_rejectOutput (output : List Bool) :
    machine.step (cfg (some .rejectOutput) [] output []) =
      some (cfg none [] (rejectedWord ++ output) []) := by
  change some (TM2.stepAux
    (pushWord (Γ := Alphabet) (Λ := Label) (σ := State)
      (1 : Fin 3) rejectedWord.reverse .halt) _ _) = _
  rw [stepAux_pushWord]
  simp only [cfg, List.reverse_reverse, tapes_output, update_output, TM2.stepAux]
  rfl

private theorem joinTrace {X : Type*} {f : X → X} {a b c : X} {n m : Nat}
    (first : f^[n] a = b) (second : f^[m] b = c) : f^[n + m] a = c := by
  rw [Nat.add_comm, Function.iterate_add_apply, first, second]

theorem acceptedTrace (input : List Bool) (accepted : run .clause input = .done) :
    (advance machine.step)^[2 * input.length + 2]
      (some (cfg (some .scan) input [] [])) = some (cfg none [] input []) := by
  have first := scanTrace input [] [] .clause none
  simp only [afterScan, accepted, ↓reduceIte, List.append_nil] at first
  have second := restoreTrace input.reverse [] none
  simp only [List.length_reverse, List.reverse_reverse, List.append_nil] at second
  have time : 2 * input.length + 2 = (input.length + 1) + (input.length + 1) := by omega
  rw [time]
  exact joinTrace first second

theorem rejectedTrace (input : List Bool) (rejected : run .clause input ≠ .done) :
    (advance machine.step)^[2 * input.length + 3]
      (some (cfg (some .scan) input [] [])) = some (cfg none [] rejectedWord []) := by
  have first := scanTrace input [] [] .clause none
  simp only [afterScan, rejected, ↓reduceIte, List.append_nil] at first
  have second := drainTrace input.reverse [] none
  simp only [List.length_reverse] at second
  have third : (advance machine.step)^[1]
      (some (cfg (some .rejectOutput) [] [] [])) = some (cfg none [] rejectedWord []) := by
    simpa only [Function.iterate_one, advance_some, List.append_nil] using
      step_rejectOutput []
  have time : 2 * input.length + 3 = (input.length + 1) + (input.length + 1) + 1 := by omega
  rw [time]
  exact joinTrace (joinTrace first second) third

theorem initList_eq (input : List Bool) :
    initList machine input = cfg (some .scan) input [] [] := by
  unfold initList cfg
  congr 1
  funext k
  fin_cases k <;> rfl

theorem haltList_eq (output : List Bool) :
    haltList machine output = cfg none [] output [] := by
  unfold haltList cfg
  congr 1
  funext k
  fin_cases k <;> rfl

def steps (input : List Bool) : Nat :=
  if run .clause input = .done then 2 * input.length + 2 else 2 * input.length + 3

theorem steps_le (input : List Bool) : steps input ≤ 2 * input.length + 3 := by
  unfold steps
  split <;> omega

/-- Full correspondence on every raw word, with no validity premise. -/
theorem totalTrace (input : List Bool) :
    (advance machine.step)^[steps input] (some (initList machine input)) =
      some (haltList machine (BinaryEncoding.formulaBits (BinaryLanguage.totalParsed input))) := by
  rw [initList_eq, haltList_eq]
  cases parsed : BinaryEncoding.decodeFormula input with
  | none =>
      have rejected : run .clause input ≠ .done := by
        intro accepted
        obtain ⟨formula, encoded⟩ := (BinaryValidatorMachine.run_clause_iff input).mp accepted
        have roundtrip := BinaryEncoding.decodeFormula_encoded formula
        rw [← encoded, parsed] at roundtrip
        cases roundtrip
      simpa only [steps, rejected, ↓reduceIte, BinaryLanguage.totalParsed, parsed,
        Option.getD_none, rejectedWord] using rejectedTrace input rejected
  | some formula =>
      have encoded := BinaryParsing.decodeFormula_sound input formula parsed
      have accepted := (BinaryValidatorMachine.run_clause_iff input).mpr ⟨formula, encoded⟩
      simp only [steps, accepted, ↓reduceIte, BinaryLanguage.totalParsed, parsed,
        Option.getD_some]
      rw [← encoded]
      exact acceptedTrace input accepted

def outputsInTime (input : List Bool) :
    TM2OutputsInTime machine input
      (some (BinaryEncoding.formulaBits (BinaryLanguage.totalParsed input)))
      (2 * input.length + 3) where
  steps := steps input
  evals_in_steps := totalTrace input
  steps_le_m := steps_le input

/-- The certificate contains the displayed total machine and its linear trace;
it assumes no execution, parser-cost, or malformed-input premise. -/
noncomputable def computableInPolyTime :
    TM2ComputableInPolyTime (id : List Bool → List Bool) BinaryEncoding.formulaBits
      BinaryLanguage.totalParsed where
  tm := machine
  inputAlphabet := Equiv.refl Bool
  outputAlphabet := Equiv.refl Bool
  time := 2 * Polynomial.X + 3
  outputsFun input := by
    change TM2OutputsInTime machine (input.map id)
      (some ((BinaryEncoding.formulaBits (BinaryLanguage.totalParsed input)).map id))
      ((2 * Polynomial.X + 3 : Polynomial Nat).eval input.length)
    simpa only [List.map_id_fun, id_eq, Polynomial.eval_add, Polynomial.eval_mul,
      Polynomial.eval_X, Polynomial.eval_ofNat] using outputsInTime input

theorem machine_finiteAlphabet (k : machine.K) : Finite (machine.Γ k) := by
  change Finite Bool
  infer_instance

theorem computation_finiteAlphabet : MachineFiniteAlphabet.FiniteAlphabet computableInPolyTime.tm :=
  machine_finiteAlphabet

end UniqueGamesTheorem.BinaryTotalInputMachine

end OAI