"""
blender_extract_armature.py
Usage: tooling/blender --background --python tooling/blender_extract_armature.py -- <input.gltf> <output.glb>

Loads a Quaternius GLTF file, strips all mesh objects and animation data,
and exports only the armature as a GLB skeleton file.

Requirements:
- 65-bone hierarchy preserved
- No mesh geometry
- No animation data
- Y-up, -Z forward (glTF default)
- 1 unit = 1 meter (Quaternius convention)
"""

import sys
import bpy


def extract_armature(input_path: str, output_path: str) -> None:
    # Clear the default scene
    bpy.ops.wm.read_factory_settings(use_empty=True)

    # Import the GLTF/GLB
    print(f"Loading: {input_path}")
    bpy.ops.import_scene.gltf(filepath=input_path)

    # Report what was imported
    all_objects = list(bpy.context.scene.objects)
    print(f"Imported {len(all_objects)} objects:")
    for obj in all_objects:
        print(f"  {obj.name} ({obj.type})")

    # Find armature objects
    armatures = [obj for obj in all_objects if obj.type == 'ARMATURE']
    if not armatures:
        print("ERROR: No armature found in the imported file.")
        sys.exit(1)

    armature = armatures[0]
    print(f"Armature: {armature.name} — {len(armature.data.bones)} bones")

    if len(armature.data.bones) < 60:
        print(f"WARNING: Expected ~65 bones, found {len(armature.data.bones)}. Check compatibility.")

    # Remove all non-armature objects (meshes, lights, cameras, empties)
    bpy.ops.object.select_all(action='DESELECT')
    for obj in all_objects:
        if obj.type != 'ARMATURE':
            obj.select_set(True)
    bpy.ops.object.delete()

    # Remove all animation data (skeleton only, no poses)
    if armature.animation_data:
        armature.animation_data_clear()
    for action in list(bpy.data.actions):
        bpy.data.actions.remove(action)

    # Select only the armature for export
    bpy.ops.object.select_all(action='DESELECT')
    armature.select_set(True)
    bpy.context.view_layer.objects.active = armature

    # Export as GLB — skeleton only, no animations, no meshes
    print(f"Exporting to: {output_path}")
    bpy.ops.export_scene.gltf(
        filepath=output_path,
        use_selection=True,
        export_format='GLB',
        export_animations=False,
        export_skins=True,
        export_yup=True,
    )

    # Verify: report bone count and names
    bones = sorted(armature.data.bones, key=lambda b: b.name)
    print(f"Export complete. {len(bones)} bones:")
    for bone in bones:
        print(f"  {bone.name}")


if __name__ == "__main__":
    argv = sys.argv
    if "--" not in argv:
        print("Usage: tooling/blender --background --python tooling/blender_extract_armature.py -- <input.gltf> <output.glb>")
        sys.exit(1)

    args = argv[argv.index("--") + 1:]
    if len(args) < 2:
        print("ERROR: Provide input GLTF/GLB path and output GLB path.")
        sys.exit(1)

    extract_armature(args[0], args[1])