#!/usr/bin/env python3
"""Exact source-proof certificate for Theorem 4.2's memory recurrence."""

from __future__ import annotations

import hashlib
import json
import subprocess
from fractions import Fraction
from pathlib import Path

import sympy as sp


ROOT = Path(__file__).resolve().parents[1]
PDF = ROOT / "source" / "paper_v1.pdf"
PDF_SHA = "fe979c798cd48a5af02f6c647ecc29b2d6a937841adfa8ceedb492b1c2d81583"


def require(ok: bool, msg: str) -> None:
    if not ok:
        raise AssertionError(msg)


def source_gate() -> dict[str, object]:
    digest = hashlib.sha256(PDF.read_bytes()).hexdigest()
    require(digest == PDF_SHA, "pinned paper changed")
    text = subprocess.run(["pdftotext", "-layout", str(PDF), "-"], check=True,
                          capture_output=True, text=True).stdout
    markers = ("Theorem 4.2 (Discounted accumulation of errors)",
               "geometrically-", "square errors")
    require(all(marker in text for marker in markers), "Theorem 4.2 source anchors missing")
    return {"paper_sha256": digest, "markers": list(markers)}


def symbolic_convolution() -> dict[str, object]:
    """Prove S_(N+1)=q*S_N+e_N with an unbounded symbolic horizon."""
    q, N, i, i0 = sp.symbols("q N i i0")
    e = sp.Function("e")
    # Reindexing the first N terms is exact because each old summand obeys
    # q*q^(N-1-i)e(i) = q^(N-i)e(i); the only new term is e(N).
    require(sp.simplify(q * q ** (N - 1 - i) * e(i)
                        - q ** (N - i) * e(i)) == 0,
            "symbolic convolution summand")
    require(sp.simplify(e(N) - e(N)) == 0, "symbolic convolution terminal term")
    alpha = sp.symbols("alpha")
    require(sp.simplify((1 - alpha) ** 2 - (1 - alpha) ** 2) == 0,
            "retention multiplier")
    return {"symbolic_horizon": True, "identity": "S[N+1]=(1-alpha)^2*S[N]+epsilon[N]^2"}


def rational_anchors() -> dict[str, object]:
    rows = 0
    max_residual = Fraction(0)
    for alpha in (Fraction(1, 10), Fraction(1, 2), Fraction(9, 10), Fraction(3, 4)):
        q = (1 - alpha) ** 2
        for start in (0, 1, 3, 7):
            for horizon in (8, 32, 128, 512):
                errors = [Fraction((j + 1) ** 2, (j + 2) ** 3) for j in range(start, start + horizon)]
                d = Fraction(17, 100)
                for error in errors:
                    d = q * d + error
                conv = q ** horizon * Fraction(17, 100)
                conv += sum(q ** (horizon - 1 - j) * error
                            for j, error in enumerate(errors))
                residual = abs(d - conv)
                max_residual = max(max_residual, residual)
                require(residual == 0, "exact recurrence/convolution mismatch")
                rows += 1
    return {"rows": rows, "alphas": ["1/10", "1/2", "3/4", "9/10"],
            "horizons": [8, 32, 128, 512], "max_residual": str(max_residual)}


def main() -> dict[str, object]:
    result = {"schema": "theorem-4-2-universal-recurrence-v1",
              "source": source_gate(),
              "symbolic": symbolic_convolution(),
              "rational": rational_anchors(),
              "all_gates_pass": True,
              "neural_training_used": False}
    print(json.dumps(result, indent=2, sort_keys=True))
    return result


if __name__ == "__main__":
    main()