#!/usr/bin/env python3
"""Stream an OBJ and report the numbers that decide how to tile it for SUM Parts.

Reads line by line so a multi-GB mesh does not have to fit in RAM. Reports
vertex/face counts, the bounding box, whether UVs and vertex colours are
present, and the material/texture references.

Usage:
    python inspect_obj.py path/to/Block.obj [more.obj ...]
"""
from __future__ import annotations

import sys
from pathlib import Path


def inspect(path: Path) -> dict:
    n_v = n_vt = n_vn = n_f = 0
    has_vertex_color = False
    mtllib: list[str] = []
    usemtl: set[str] = set()
    lo = [float("inf")] * 3
    hi = [float("-inf")] * 3

    with path.open("r", encoding="utf-8", errors="replace") as f:
        for line in f:
            if line.startswith("v "):
                n_v += 1
                parts = line.split()
                x, y, z = float(parts[1]), float(parts[2]), float(parts[3])
                if x < lo[0]: lo[0] = x
                if y < lo[1]: lo[1] = y
                if z < lo[2]: lo[2] = z
                if x > hi[0]: hi[0] = x
                if y > hi[1]: hi[1] = y
                if z > hi[2]: hi[2] = z
                # "v x y z r g b" is how some exporters carry per-vertex colour
                if len(parts) >= 7:
                    has_vertex_color = True
            elif line.startswith("vt "):
                n_vt += 1
            elif line.startswith("vn "):
                n_vn += 1
            elif line.startswith("f "):
                n_f += 1
            elif line.startswith("mtllib"):
                mtllib.append(line.split(maxsplit=1)[1].strip())
            elif line.startswith("usemtl"):
                usemtl.add(line.split(maxsplit=1)[1].strip())

    return {
        "path": path,
        "size_mb": path.stat().st_size / 1024 / 1024,
        "n_v": n_v, "n_vt": n_vt, "n_vn": n_vn, "n_f": n_f,
        "vertex_color": has_vertex_color,
        "mtllib": mtllib, "usemtl": sorted(usemtl),
        "lo": lo, "hi": hi,
    }


def main() -> None:
    if len(sys.argv) < 2:
        print(__doc__)
        raise SystemExit(2)

    for arg in sys.argv[1:]:
        p = Path(arg)
        if not p.exists():
            print(f"{arg}: not found")
            continue

        r = inspect(p)
        ext = [r["hi"][i] - r["lo"][i] for i in range(3)]
        area = ext[0] * ext[1]

        print(f"=== {p.name}  ({r['size_mb']:,.0f} MB) ===")
        print(f"  vertices  : {r['n_v']:>12,}")
        print(f"  faces     : {r['n_f']:>12,}")
        print(f"  texcoords : {r['n_vt']:>12,}   {'(UV present)' if r['n_vt'] else '(NO UV)'}")
        print(f"  normals   : {r['n_vn']:>12,}")
        print(f"  vtx color : {r['vertex_color']}")
        print(f"  mtllib    : {r['mtllib']}")
        print(f"  materials : {len(r['usemtl'])} -> {r['usemtl'][:5]}"
              f"{' ...' if len(r['usemtl']) > 5 else ''}")
        print(f"  bbox min  : {[round(v, 2) for v in r['lo']]}")
        print(f"  bbox max  : {[round(v, 2) for v in r['hi']]}")
        print(f"  extent    : {[round(v, 2) for v in ext]}  (metres, local)")
        print(f"  footprint : {area / 1e6:.3f} km^2")
        if area:
            print(f"  density   : {r['n_f'] / area:,.1f} faces/m^2")
        # SUM Parts tiles are ~252 m square; this is how many that footprint is
        print(f"  ~252m tiles: {max(1, round(ext[0] / 252)) * max(1, round(ext[1] / 252))}")
        print()


if __name__ == "__main__":
    main()