#!/usr/bin/env python3
"""
Create a compact animation-only GLB from selected actions in a source GLB.

Usage:
  blender --background --python tools/extract_animation_subset.py -- \
      <source.glb> <output.glb> <clip> [<clip> ...]

The source skeleton is retained, all meshes and unrelated actions are removed,
and each requested action is exported as its own NLA track. This keeps external
authored animation libraries small enough to ship as retargeting sources.
"""
import os
import sys

import bpy


argv = sys.argv
argv = argv[argv.index("--") + 1:] if "--" in argv else []
if len(argv) < 3:
    print(
        "Usage: blender --background --python "
        "tools/extract_animation_subset.py -- "
        "<source.glb> <output.glb> <clip> [<clip> ...]"
    )
    sys.exit(1)

SOURCE = argv[0]
OUTPUT = argv[1]
REQUESTED = argv[2:]


def main():
    bpy.ops.object.select_all(action="SELECT")
    bpy.ops.object.delete()
    bpy.ops.import_scene.gltf(filepath=SOURCE)

    armatures = [obj for obj in bpy.data.objects if obj.type == "ARMATURE"]
    if len(armatures) != 1:
        print(f"ERROR: expected one armature, found {len(armatures)}")
        sys.exit(1)
    armature = armatures[0]

    missing = [name for name in REQUESTED if bpy.data.actions.get(name) is None]
    if missing:
        print(f"ERROR: requested actions not found: {missing}")
        sys.exit(1)

    for obj in list(bpy.data.objects):
        if obj != armature:
            bpy.data.objects.remove(obj, do_unlink=True)

    if not armature.animation_data:
        armature.animation_data_create()
    for track in list(armature.animation_data.nla_tracks):
        armature.animation_data.nla_tracks.remove(track)
    armature.animation_data.action = None

    keep = set()
    for name in REQUESTED:
        action = bpy.data.actions[name]
        action.use_fake_user = True
        track = armature.animation_data.nla_tracks.new()
        track.name = name
        strip = track.strips.new(name, 0, action)
        strip.name = name
        track.mute = True
        keep.add(action)

    for action in list(bpy.data.actions):
        if action not in keep:
            bpy.data.actions.remove(action)

    os.makedirs(os.path.dirname(os.path.abspath(OUTPUT)), exist_ok=True)
    bpy.ops.export_scene.gltf(
        filepath=OUTPUT,
        export_format="GLB",
        export_yup=True,
        export_animations=True,
        export_animation_mode="NLA_TRACKS",
        export_skins=True,
        export_bake_animation=True,
    )
    print(f"Exported {len(keep)} clips to {OUTPUT}")


main()