"""gen_vectors.py - Test vector generator for poly_mul module.

Generates random NTT-domain polynomial pairs and computes expected
pointwise base-case multiplication results using embedded Python reference.
"""

import os
import random
import sys

sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..', '..', 'lib'))
from vector_gen import VectorGenerator

Q = 3329
N = 256

# Bit-reversed zeta values (same as NTT zeta_bitRev)
zeta_bitRev = [1, 1729, 2580, 3289, 2642, 630, 1897, 848,
               1062, 1919, 193, 797, 2786, 3260, 569, 1746,
               296, 2447, 1339, 1476, 3046, 56, 2240, 1333,
               1426, 2094, 535, 2882, 2393, 2879, 1974, 821,
               289, 331, 3253, 1756, 1197, 2304, 2277, 2055,
               650, 1977, 2513, 632, 2865, 33, 1320, 1915,
               2319, 1435, 807, 452, 1438, 2868, 1534, 2402,
               2647, 2617, 1481, 648, 2474, 3110, 1227, 910,
               17, 2761, 583, 2649, 1637, 723, 2288, 1100,
               1409, 2662, 3281, 233, 756, 2156, 3015, 3050,
               1703, 1651, 2789, 1789, 1847, 952, 1461, 2687,
               939, 2308, 2437, 2388, 733, 2337, 268, 641,
               1584, 2298, 2037, 3220, 375, 2549, 2090, 1645,
               1063, 319, 2773, 757, 2099, 561, 2466, 2594,
               2804, 1092, 403, 1026, 1143, 2150, 2775, 886,
               1722, 1212, 1874, 1029, 2110, 2935, 885, 2154]

# Precomputed PolyMul zeta values: zeta_sq_mul[i] = (zeta_bitRev[i]^2 * 17) % Q
zeta_sq_mul = [((z * z) * 17) % Q for z in zeta_bitRev]


def basecase_multiply(a0, a1, b0, b1, zeta):
    """Degree-1 NTT-domain base-case multiply.

    Computes:
      c0 = (a0*b0 + a1*b1*zeta) mod Q
      c1 = (a0*b1 + a1*b0) mod Q

    Uses modular arithmetic to match Barrett reduction semantics.
    """
    c0 = ((a0 * b0) % Q + (((a1 * b1) % Q) * zeta) % Q) % Q
    c1 = ((a0 * b1) % Q + (a1 * b0) % Q) % Q
    return c0, c1


def poly_mul(f_hat, g_hat):
    """Full NTT-domain polynomial multiplication.

    Given two 256-coefficient NTT-domain polynomials f_hat and g_hat,
    compute pointwise product using 128 degree-1 base-case multiplies.

    Args:
        f_hat: list of 256 coefficients in [0, Q-1]
        g_hat: list of 256 coefficients in [0, Q-1]

    Returns:
        list of 256 result coefficients in [0, Q-1]
    """
    h_hat = []
    for i in range(128):
        zeta = zeta_sq_mul[i]
        h1, h2 = basecase_multiply(
            f_hat[2 * i], f_hat[2 * i + 1],
            g_hat[2 * i], g_hat[2 * i + 1],
            zeta
        )
        h_hat.append(h1)
        h_hat.append(h2)
    return h_hat


class PolyMulVectorGenerator(VectorGenerator):
    """Generates test vectors for the poly_mul_sync module."""

    def generate_one(self, params: dict) -> dict:
        """Generate a random polynomial pair with expected result.

        Args:
            params: Unused for basic case.

        Returns:
            dict with 'input' (A coeffs, B coeffs) and 'expected' (C coeffs).
        """
        # Generate random NTT-domain polynomials
        A = [random.randint(0, Q - 1) for _ in range(N)]
        B = [random.randint(0, Q - 1) for _ in range(N)]

        # Compute expected result via Python reference
        C = poly_mul(A, B)

        return {
            'input': {'A': A, 'B': B},
            'expected': {'C': C}
        }

    def _format_coeffs(self, coeffs: list[int]) -> str:
        """Format a coefficient list as space-separated 3-digit hex."""
        return ' '.join(f'{c:03X}' for c in coeffs)

    def write_hex_file(self, vectors: list[dict], filepath: str) -> None:
        """Write input vectors: one line per vector with 512 hex values.

        Format: A[0] A[1] ... A[255] B[0] B[1] ... B[255]
        """
        os.makedirs(os.path.dirname(filepath), exist_ok=True)
        with open(filepath, 'w') as f:
            for v in vectors:
                all_coeffs = v['input']['A'] + v['input']['B']
                hex_str = self._format_coeffs(all_coeffs)
                f.write(f'{hex_str}\n')

    def write_expected_file(self, vectors: list[dict], filepath: str) -> None:
        """Write expected output: one line per vector with 256 hex values.

        Format: C[0] C[1] ... C[255]
        """
        os.makedirs(os.path.dirname(filepath), exist_ok=True)
        with open(filepath, 'w') as f:
            for v in vectors:
                hex_str = self._format_coeffs(v['expected']['C'])
                f.write(f'{hex_str}\n')
