"""Blender headless script: export a STEP-derived scene as a production GLB.

Usage:
    blender --background --python export_gltf.py -- \\
        --stl_path /path/to/file.stl \\
        --output_path /path/to/output.glb \\
        [--asset_library_blend /path/to/library.blend] \\
        [--material_map '{"SrcMat": "LibMat"}']

The script:
1. Imports the STL file (with mm→m scale).
2. Optionally applies asset library materials from a .blend.
3. Exports as GLB (Draco-compressed if available, otherwise standard).
"""
from __future__ import annotations

import argparse
import json
import sys
import traceback


def parse_args() -> argparse.Namespace:
    argv = sys.argv
    if "--" not in argv:
        print("No arguments after --", file=sys.stderr)
        sys.exit(1)
    rest = argv[argv.index("--") + 1:]
    parser = argparse.ArgumentParser()
    parser.add_argument("--glb_path", required=True,
                        help="Geometry GLB from export_step_to_gltf.py (already in metres)")
    parser.add_argument("--output_path", required=True)
    parser.add_argument("--asset_library_blend", default=None)
    parser.add_argument("--material_map", default="{}")
    return parser.parse_args(rest)


def main() -> None:
    args = parse_args()
    material_map: dict = json.loads(args.material_map)

    import bpy  # type: ignore[import]
    import math as _math

    # Clean scene
    bpy.ops.wm.read_factory_settings(use_empty=True)

    # Import geometry GLB from export_step_to_gltf.py (already in metres, Y-up)
    bpy.ops.import_scene.gltf(filepath=args.glb_path)
    print(f"Imported geometry GLB: {args.glb_path} "
          f"({len([o for o in bpy.data.objects if o.type == 'MESH'])} mesh objects)")

    # Apply smooth shading with 30° angle threshold (Blender 4.1+ API)
    for obj in bpy.data.objects:
        if obj.type == "MESH":
            bpy.context.view_layer.objects.active = obj
            obj.select_set(True)
            try:
                bpy.ops.object.shade_smooth_by_angle(angle=_math.radians(30))
            except Exception:
                pass

    # Apply asset library materials if provided.
    # link=False (append) is required: the GLTF exporter can only traverse
    # local (appended) Principled BSDF node trees to extract PBR values.
    if args.asset_library_blend and material_map:
        import os
        sys.path.insert(0, os.path.dirname(__file__))
        from asset_library import apply_asset_library_materials
        apply_asset_library_materials(args.asset_library_blend, material_map, link=False)

    # Export production GLB with full PBR material data
    try:
        bpy.ops.export_scene.gltf(
            filepath=args.output_path,
            export_format="GLB",
            export_apply=True,
            use_selection=False,
            export_materials="EXPORT",
            export_image_format="AUTO",
        )
    except Exception as exc:
        print(f"GLB export failed: {exc}", file=sys.stderr)
        sys.exit(1)

    print(f"Production GLB exported to {args.output_path}")


try:
    main()
except SystemExit:
    raise
except Exception:
    traceback.print_exc()
    sys.exit(1)