stress_operator/data/tensile2d.py

"""Tensile2d (PLAID-datasets/Tensile2d, HF, CC-BY-SA-4.0) adapter — SECOND benchmark.

Why: unlike Geo-FNO Elasticity (scalar von Mises target -> our tensor is latent), Tensile2d directly
supervises the full 2D Cauchy stress tensor (sig11, sig22, sig12) per node on an irregular mesh, so our
equilibrium regularizer acts on a SUPERVISED tensor and we can validate the predicted tensor itself.

VERIFIED facts (golden rule, by reading real samples):
  - Each sample is a pickled CGNS tree (no PLAID lib needed): GridCoordinates {CoordinateX, CoordinateY}
    and PointData {sig11, sig22, sig12, U1, U2, q}; plus input scalars {P, p1..p5} and output scalars.
  - 702 rows: samples 0-499 are the labeled `train_500` set (full stress); samples 500-701 (test 200 +
    OOD 2) have stress fields WITHHELD (competition) -> only coords + input scalars. So we use the 500
    labeled samples and hold out a local test split (no official test ground truth is public).
  - Node count varies per sample (6143-11801, mean ~9400). Static, plane-strain, quasistatic.

`build_cache()` writes data/tensile2d/samples/*.npz once. `build_tensile_splits()` loads them, fits
z-score normalizers on the train split, and returns per-sample lists (variable N -> no stacking).
"""
from __future__ import annotations

import glob
import os
from dataclasses import dataclass
from typing import List

import numpy as np
import torch

INPUT_SCALARS = ["P", "p1", "p2", "p3", "p4", "p5"]


def _field(tree, name):
    stack = [tree]
    while stack:
        n = stack.pop()
        if isinstance(n, list) and len(n) == 4:
            if n[0] == name and isinstance(n[1], np.ndarray):
                return n[1]
            stack.extend(n[2] or [])
    return None


def build_cache(out_dir: str = "data/tensile2d/samples") -> int:
    """Download Tensile2d parquet shards and cache the 500 labeled samples as .npz. Returns count."""
    from huggingface_hub import hf_hub_download
    import pyarrow.parquet as pq
    import pickle

    os.makedirs(out_dir, exist_ok=True)
    shards = [hf_hub_download("PLAID-datasets/Tensile2d",
                              f"data/all_samples-0000{i}-of-00002.parquet", repo_type="dataset")
              for i in (0, 1)]
    idx = 0
    saved = 0
    for sh in shards:
        col = pq.read_table(sh).column("sample")
        for i in range(len(col)):
            try:
                obj = pickle.loads(col[i].as_py())
                tree = list(obj["meshes"].values())[0]
                x, y = _field(tree, "CoordinateX"), _field(tree, "CoordinateY")
                s11, s22, s12 = _field(tree, "sig11"), _field(tree, "sig22"), _field(tree, "sig12")
                if any(v is None for v in (x, y, s11, s22, s12)):
                    idx += 1
                    continue  # withheld test/OOD sample
                coords = np.stack([x, y], 1).astype(np.float32)
                sigma = np.stack([s11, s22, s12], 1).astype(np.float32)
                vm = np.sqrt(s11 ** 2 - s11 * s22 + s22 ** 2 + 3 * s12 ** 2).astype(np.float32)
                sc = obj.get("scalars", {})
                scin = np.array([float(sc[k]) for k in INPUT_SCALARS], np.float32)
                np.savez(os.path.join(out_dir, f"{saved:04d}.npz"),
                         coords=coords, sigma=sigma, vm=vm, scalars_in=scin)
                saved += 1
            except Exception:
                pass
            idx += 1
    return saved


@dataclass
class TensileSplits:
    train_coords: List[torch.Tensor]
    train_sigma: List[torch.Tensor]     # scaled by 1/S (N,3)
    train_scalars: List[torch.Tensor]   # z-scored (6,)
    test_coords: List[torch.Tensor]
    test_sigma: List[torch.Tensor]
    test_scalars: List[torch.Tensor]
    scale_S: float                      # SINGLE global stress scale; de-normalize: sigma*S
    scalar_mean: torch.Tensor           # (6,)
    scalar_std: torch.Tensor


def build_tensile_splits(samples_dir: str = "data/tensile2d/samples",
                         ntrain: int = 400, ntest: int = 100, seed: int = 0) -> TensileSplits:
    """Load cached samples; deterministic train/test split; z-score normalizers fit on TRAIN only.

    Coords are kept RAW (physical units) so the MLS divergence operator measures true distances; the
    model conditions on raw coords + normalized input scalars (the encoder MLP handles the coord scale).
    Stress is z-scored per component; input scalars z-scored per dim.
    """
    files = sorted(glob.glob(os.path.join(samples_dir, "*.npz")))
    if not files:
        raise FileNotFoundError(f"no cached Tensile2d samples in {samples_dir} — run build_cache() first")
    rng = np.random.default_rng(seed)
    order = rng.permutation(len(files))
    tr_idx, te_idx = order[:ntrain], order[ntrain:ntrain + ntest]

    def load(i):
        d = np.load(files[i])
        return d["coords"], d["sigma"], d["scalars_in"]

    tr = [load(i) for i in tr_idx]
    te = [load(i) for i in te_idx]

    # SINGLE global stress scale S (RMS of all train stress components) so the divergence regularizer
    # de-normalizes with one scalar: sigma_phys = S * sigma_norm  =>  div(sigma_phys) = S * div(sigma_norm).
    # (Per-component z-score would scale each channel differently and corrupt the physical divergence.)
    sig_all = np.concatenate([s for _, s, _ in tr], 0)            # (sum N, 3)
    S = float(np.sqrt((sig_all ** 2).mean()))                    # global RMS scale
    sc_all = np.stack([sc for _, _, sc in tr], 0)                 # (ntrain, 6)
    sc_mean, sc_std = sc_all.mean(0), sc_all.std(0) + 1e-8

    def pack(rows):
        cs, ss, scs = [], [], []
        for c, s, sc in rows:
            cs.append(torch.tensor(c))
            ss.append(torch.tensor(s / S))
            scs.append(torch.tensor((sc - sc_mean) / sc_std))
        return cs, ss, scs

    trc, trs, trsc = pack(tr)
    tec, tes, tesc = pack(te)
    return TensileSplits(
        train_coords=trc, train_sigma=trs, train_scalars=trsc,
        test_coords=tec, test_sigma=tes, test_scalars=tesc,
        scale_S=S,
        scalar_mean=torch.tensor(sc_mean), scalar_std=torch.tensor(sc_std),
    )