"""Unit tests for stl_sampler."""
from __future__ import annotations

import io
import struct

import numpy as np
import pytest

from presa_mano.perception.stl_sampler import parse_stl_bytes, sample_surface


def _make_cube_stl_bytes(side_mm: float = 10.0) -> bytes:
    """Synthesize a binary STL of an axis-aligned cube centered at origin,
    from -side/2 to +side/2 on each axis. 12 triangles, no normals needed."""
    s = side_mm / 2.0
    v = [
        (-s, -s, -s), ( s, -s, -s), ( s,  s, -s), (-s,  s, -s),
        (-s, -s,  s), ( s, -s,  s), ( s,  s,  s), (-s,  s,  s),
    ]
    # 6 faces x 2 tris (vertex order: any orientation works for our use)
    tris = [
        (0, 1, 2), (0, 2, 3),  # z=-s
        (4, 6, 5), (4, 7, 6),  # z=+s
        (0, 4, 5), (0, 5, 1),  # y=-s
        (3, 2, 6), (3, 6, 7),  # y=+s
        (0, 3, 7), (0, 7, 4),  # x=-s
        (1, 5, 6), (1, 6, 2),  # x=+s
    ]
    buf = io.BytesIO()
    buf.write(b"\x00" * 80)                 # header
    buf.write(struct.pack("<I", len(tris))) # n_triangles
    for (i, j, k) in tris:
        buf.write(struct.pack("<fff", 0.0, 0.0, 0.0))  # normal (unused)
        for idx in (i, j, k):
            buf.write(struct.pack("<fff", *v[idx]))
        buf.write(struct.pack("<H", 0))                 # attribute byte count
    return buf.getvalue()


def test_parse_stl_cube_bbox():
    stl_bytes = _make_cube_stl_bytes(side_mm=10.0)
    verts, tris = parse_stl_bytes(stl_bytes)
    assert verts.ndim == 2 and verts.shape[1] == 3
    assert tris.ndim == 2 and tris.shape[1] == 3
    assert tris.dtype.kind == "i"
    # BB del cubo: [-5, +5] su ogni asse
    np.testing.assert_allclose(verts.min(axis=0), [-5.0, -5.0, -5.0], atol=1e-6)
    np.testing.assert_allclose(verts.max(axis=0), [ 5.0,  5.0,  5.0], atol=1e-6)


def test_sample_surface_in_bbox():
    stl_bytes = _make_cube_stl_bytes(side_mm=10.0)
    verts, tris = parse_stl_bytes(stl_bytes)
    pts = sample_surface(verts, tris, n=1000, seed=0)
    assert pts.shape == (1000, 3)
    # tutti i punti devono cadere dentro la BB del cubo (più epsilon
    # per il rumore di floating point bary)
    np.testing.assert_array_less(pts.max(axis=0), 5.0 + 1e-4)
    np.testing.assert_array_less(-pts.min(axis=0), 5.0 + 1e-4)


def test_sample_surface_distribution_uniform():
    """8 octanti del cubo, ognuno >= 8% dei punti (perfetto = 100/6 ~= 16.7%
    per faccia, distribuita su 4 octanti adiacenti)."""
    stl_bytes = _make_cube_stl_bytes(side_mm=10.0)
    verts, tris = parse_stl_bytes(stl_bytes)
    pts = sample_surface(verts, tris, n=2000, seed=1)
    counts = np.zeros(8, dtype=np.int64)
    for p in pts:
        # bin (x>0, y>0, z>0) -> 0..7
        idx = (int(p[0] > 0) << 2) | (int(p[1] > 0) << 1) | int(p[2] > 0)
        counts[idx] += 1
    frac = counts / pts.shape[0]
    assert (frac > 0.08).all(), f"octant fractions too uneven: {frac}"


def test_sample_surface_seed_deterministic():
    stl_bytes = _make_cube_stl_bytes(side_mm=10.0)
    verts, tris = parse_stl_bytes(stl_bytes)
    a = sample_surface(verts, tris, n=100, seed=42)
    b = sample_surface(verts, tris, n=100, seed=42)
    np.testing.assert_array_equal(a, b)


def test_parse_stl_bad_payload_raises():
    with pytest.raises(Exception):  # numpy-stl raises various; we just want it to not silently pass
        parse_stl_bytes(b"not a real STL")