"""trim_clip.py — keep a frame window of a clip and re-base it to frame 0.

Samples every fcurve across [--start .. --end] (inclusive, source frames) and rewrites
the action to hold just that window at frames 0..(end-start). Use to lift a sub-beat out
of a longer take — e.g. keep only the dismount tail of a ladder clip so the descent loop
owns the vertical travel and the trimmed clip is purely the step-off.

Usage:
  blender --background --python tools/trim_clip.py -- \
    --src <in.glb> --out <out.glb> --name <NewClipName> --start <f> --end <f>
"""
import bpy, sys, argparse

def parse():
    argv = sys.argv[sys.argv.index("--")+1:] if "--" in sys.argv else []
    p = argparse.ArgumentParser()
    p.add_argument("--src", required=True)
    p.add_argument("--out", required=True)
    p.add_argument("--name", required=True, help="clip name baked into the output")
    p.add_argument("--start", type=int, required=True, help="first source frame to keep")
    p.add_argument("--end", type=int, required=True, help="last source frame to keep (inclusive)")
    return p.parse_args(argv)

def action_fcurves(a):
    """All fcurves across Blender 5 slotted-action layers/strips (legacy fallback)."""
    if hasattr(a, "fcurves") and getattr(a, "fcurves", None) is not None:
        return list(a.fcurves)
    fcs = []
    for layer in getattr(a, "layers", []):
        for strip in layer.strips:
            for bag in strip.channelbags:
                fcs.extend(bag.fcurves)
    return fcs

def main():
    a = parse()
    bpy.ops.wm.read_factory_settings(use_empty=True)
    bpy.context.scene.render.fps = 30           # pipeline is 30fps (see reverse_clip.py)
    bpy.ops.import_scene.gltf(filepath=a.src)
    arm = next(o for o in bpy.data.objects if o.type == 'ARMATURE')
    act = arm.animation_data.action
    if getattr(act, "slots", None) and arm.animation_data.action_slot is None:
        arm.animation_data.action_slot = act.slots[0]
    s, e = a.start, a.end
    n = e - s
    if n <= 0:
        raise SystemExit(f"[trim] bad window {s}..{e}")
    print(f"[trim] src '{act.name}' keep frames {s}..{e} -> 0..{n}")

    for fc in action_fcurves(act):
        vals = [fc.evaluate(s + k) for k in range(n + 1)]
        need = n + 1
        have = len(fc.keyframe_points)
        if have < need:
            fc.keyframe_points.add(need - have)
        elif have > need:
            for _ in range(have - need):
                fc.keyframe_points.remove(fc.keyframe_points[-1], fast=True)
        for k in range(need):
            kp = fc.keyframe_points[k]
            kp.co = (k, vals[k])
            kp.interpolation = 'LINEAR'
        fc.update()

    act.name = a.name

    for t in list(arm.animation_data.nla_tracks):
        arm.animation_data.nla_tracks.remove(t)
    track = arm.animation_data.nla_tracks.new()
    track.name = a.name
    strip = track.strips.new(a.name, 0, act)
    strip.name = a.name
    arm.animation_data.action = None

    for o in [o for o in bpy.data.objects if o.type == 'MESH']:
        bpy.data.objects.remove(o, do_unlink=True)

    bpy.context.scene.frame_start = 0
    bpy.context.scene.frame_end = n
    bpy.ops.export_scene.gltf(
        filepath=a.out,
        export_animation_mode="NLA_TRACKS",
        export_force_sampling=True,
        export_optimize_animation_size=False,
    )
    print(f"[trim] EXPORTED {a.out} clip '{a.name}' ({n+1} frames)")

if __name__ == "__main__":
    main()